Kidney International, Vol. 18 (1980), pp. 623-635

Aldosterone and dopamine receptors in the kidney: Sites forpharmacologic manipulation of renal function

WILLIAM R. ADAMwith the technical assistance of JANINE A. DANKS and GARY GOLAND

Renal Unit, Repatriation General Hospital, West Heidelberg, Victoria, Australia

The development of radio-ligands with a high spe-cific activity has greatly facilitated the study of hor-monal receptor systems. These receptor studieshave given us insight into the actions of drugs al-ready available and should be helpful in assessingpotential drugs, both for their desired and undesiredeffects.

The kidney is the most physiologically importantend organ for some hormones (for example, al-dosterone, antidiuretic hormone). In addition, somehormones with multiple actions have unique actionswithin the kidney (for example, parathyroid hor-mone and phosphate excretion). The kidney may al-so act as an end organ in a relatively subordinaterole compared with a hormone's action elsewherein the body (for example, glucocorticoids). Demon-stration of a hormone receptor system within thekidney, as elsewhere, does not, by itself, imply anyphysiologic action of the ligand. Before allowing re-ceptor studies to influence assessments of drugs, weneed to evaluate carefully the receptor for the ef-fector systems and their physiologic importance.

By intentionally manipulating the hormone recep-tor systems, we can seek the desired effects andevaluate them. Problems arise in the kidney in dis-cerning unintentional manipulation of receptor sys-tems, otherwise known as side effects. This prob-lem arises because of the kidneys' remarkable capa-bility to adapt to a functional impairment with aminimal change in the internal environment [I]. Thekidneys' ability to adapt to functional impairment ismost easily demonstrated with progressive loss ofrenal function, where many aspects of homeostasisare achieved until late in the disease [1]. A similaradaptation in function can be seen with drug-medi-ated manipulation of a specific kidney function. Forinstance, in healthy people, the administration of di-uretics of any type is hard to discern except in theearly diuretic phase, for sodium and potassium bal-

623

ance are achieved rapidly with a minimal observ-able change in sodium or potassium homeostasis.Evaluation of drugs by receptor studies may guidein predicting likely undesired effects.

In this paper, two topics will be discussed that, atfirst, may seem quite distinct but for which theredoes seem to be evidence for their interrelationshipin both renal and extrarenal sites. The first is druginteraction with the aldosterone receptor, as an ex-ample of a hormone receptor system in which thekidney is the end organ of major physiologic impor-tance. The second is the dopamine receptor in thekidney, studies of which might provide some futureinsight into possible problems with dopaminergicdrugs. The discussion of renal dopamine receptorswill include previously unreported studies on renaldopamine binding.

Aldosterone

Action of aldosterone. The major action of al-dosterone is on sodium and potassium transportacross epithelial tissues [2, 3]. In mammals, themost biologically significant end organ affected byaldosterone is the kidney. Aldosterone does exertsimilar effects on sodium and potassium transport inother secretory organs (for example, bowel, sali-vary and sweat glands), but under normal circum-stances these organs add little to the homeostaticcontrol of sodium and potassium. Aldosterone alsohas an effect on hydrogen ion transport, which attimes may become quite significant [4]. In amphibi-ans, however, the action of aldosterone on the blad-der and the skin may contribute to control of so-dium and potassium balance.

Received for publication May 29, 1980

0085—2538180/0018-0623 $02.60© 1980 by the International Society of Nephrology

624 Adam

Na-K-ATPase

Fig. 1. Cellular mechanism of action of aldosterone and its inhi-bition by spironolactone. The aldosterone binds to a cytoplasmicreceptor, which then attaches to the DNA in the nucleus induc-ing RNA-controlled protein production of "aldosterone-inducedprotein" (AlP). AlP is more than one protein (see text), and theexact roles are uncertain. Postulated roles include induction ofNa-K-ATPase, induction of a cell membrane permease, and en-hanced energy production. Spironolactone inhibits aldosteroneaction by binding to an allosteric form of the aldosterone recep-tor and inhibiting its uptake into the nucleus.

The action of aldosterone in the kidney is thoughtto be through a cytoplasmic receptor followed bynuclear uptake of the hormone receptor complexand genomic control of production of aldosterone-induced protein" [5]. This euphemism covers ourignorance of the actual mechanism of the action ofaldosterone on sodium and potassium transport.Postulates for this action include a cell membranepermease for ionic movement, enhanced energyproduction leading to increased ion transport, andeither direct or indirect effects of Na-K-ATPase,the enzymatic equivalent of the sodium transporter(Fig. 1). Intuitively it seems likely that Na-K-ATPase would be this final mediator of aldosteroneaction on sodium and potassium transport, althoughthere is little evidence to support this [3]. Studies onthe aldosterone-induced protein in toad urinarybladder suggest both a membrane and a solublecomponent, which might suggest at least two dis-tinct actions of aldosterone [6]. In toad bladder, an-other necessary component induced by aldosteroneis fatty acid synthesis, which is important for incor-poration of the protein into the membrane [7]. Al-dosterone also induces various biochemicalchanges that can precede any ionic effects. The sig-nificance of these in relation to homeostasis is un-certain. (For review, see Refs. 3, 8, and 9.)

Reports of actions of aldosterone by nonclassicalsteroid receptor systems (for example, RBC ghosts[10] and renal Na-K-ATPase [11]), although of greatinterest, are so far of doubtful significance be-cause of the lack of adequate control studies in rela-tion to dosage or crossreactivity by other steroids.These effects of aldosterone on membrane-basedsystems such as red cell ghosts may relate to thebinding of aldosterone to membrane preparations[12], although this finding has not been pursued.

There is evidence to suggest that the mechanismof action of aldosterone on different ions is, at leastin part, by different mechanisms. The sodium butnot the potassium effect is inhibited by prior treat-ment with inhibitors of ribonucleic-acid-inducedprotein synthesis [13, 14]. In turtle bladder, spi-ronolactone acts as an inhibitor of aldosterone ef-fect on sodium transport but as an agonist on al-dosterone effect on hydrogen ion transport [15]. Inview of our lack of knowledge of the precise ef-fector mechanism of aldosterone action, however,these apparent differences are hard to interpret.

The renal responsiveness to aldosterone may beunder genetic control, at least in mice [16]. The evi-dence for this involves separating the sodium andthe potassium responses. When the sodium and thepotassium responses were factored together as KJNa, however, there was no difference between thetwo species of mice [16]. In all our studies on al-dosterone in rats, the effect measured as K/Na isreasonably constant even though the separate so-dium and potassium effects vary widely from exper-iment to experiment. This makes me query the sig-nificance of observations separating the potassiumand the sodium effects.

In rats, there is some evidence of sex dependenceof the renal response to aldosterone based on dif-fering metabolic rates [17, 18]. Again in our labora-tory these differences were not marked.

Certainly physiologic and pharmacologic factorscan modify the renal response to aldosterone. It ishard to demonstrate an effect of aldosterone in theadrenalectomized rat unless it has been deprived ofpotassium overnight [8]. The significance of this isuncertain. Other factors include vena cava obstruc-tion in the dog [19], sodium restriction in the sheep[20], 5 days of postassium loading [21], and treat-ment with L-dopa [22] and 5 a-dihydrocortisol [23]in the rat. Variability in the renal response to al-dosterone in humans may be of importance in somecases of hypertension [24] and in the natriuresis offasting [25]. None of these known modifiers of therenal response to aldosterone do so by interference

Aldosterone

Aldosterone and dopamine receptors 625

with the aldosterone receptor, when measured invitro [21, 23] (Funder and Adam, unpublished).

Although there is still debate as to whether a!-dosterone has any action in the proximal con-voluted tubule, it seems certain that the major renalsite of action of aldosterone is the distal tubule andthe collecting ducts [8]. The action in the collectingduct might be by direct sodium and potassium ex-change by a luminal transporter but its action in thedistal convoluted tubule is less clear, there beinglittle evidence for direct sodium, potassium ex-change [8].

The major homeostatic effect of aldosterone onthe sodium and potassium balance by the kidneymakes the renal aldosterone receptor a suitable sitefor manipulation by drugs.

Aldosterone antagonists. Antagonists of aldos-terone would be expected to promote sodium excre-tion and potassium retention—the latter being a de-sirable effect in view of problems of potassium losswith most other diuretics. Aldosterone antagonistsas diuretics would be of theoretical importance inprimary or secondary hyperaldosteronism—thesecondary hyperaldosteronism either being relatedto the disease state or to the reduction of extra-cellular volume by other diuretic therapy.

(1) Spironolactone. The finding that progesteronewas natriuretic in aldosterone-treated, but not un-treated, patients with Addison's disease [26] led tothe search for steroidal antagonists of aldosterone.Once the antimineralocorticoid activity of spirono-lactones was demonstrated [27], a commercial spi-ronolactone was developed which is an effectivediuretic in primary and secondary hyperaldos-teronism, but not in those conditions where thereare low plasma aldosterone levels [28, 29]. Under-standing the mechanism of the action and side ef-fects of spironolactone has been complicated by thefinding that its major metabolite, canrenone [30](the side chain on 7 removed) (Fig. 2), has less affin-ity for the mineralocorticoid receptor but similar af-finity for the testosterone receptor when comparedwith spironolactone [31, 32].

So specific does the diuretic action of spironolac-tone seem that it has been postulated as a bettermarker of mineralocorticoid activity than the mea-surement of hormone levels [33]. That is, the re-sponse to spironolactone could be used to define in-creased mineralocorticoid activity occurring in theabsence of raised aldosterone levels. Increasedmineralocorticoid activity with normal or low al-dosterone levels could arise with an increased end-organ sensitivity to aldosterone [24], or by the ac-

Aldosterorie Spironolactorie

Fig. 2. Two-dimensional representation of the structure of al-dosterone and inhibitor spironolactone.

tion of unknown and thus unmeasurable steroidswith mineralocorticoid activity. The search for oth-er nonclassical mineralocorticoids in an effort to ex-plain some cases of hypertension has been and isthe subject of extensive investigations [33, 34]. Caremust be taken, however, in using spironolactone re-sponsiveness as a measure of increased mineral-ocorticoid activity. Hypertension due to any causemight well respond to interruption of any aspect ofthe homeostatic control of blood pressure, includ-ing salt depletion caused by any mechanism.

The spironolactones have also proven useful indefining the subcellular mechanism of action of al-dosterone—particularly in demonstrating the al-dosterone receptor. On the basis of these studies,spironolactone is thought to act by competing forthe aldosterone receptor, which exists in two allo-steric forms (active and inactive) and which arereadily interchangeable by the presence of agonistsor antagonists. Once bound to the receptor, the spi-ronolactone receptor complex, unlike the aldoster-one receptor complex, does not enter the nucleiand thus can exert no mineralocorticoid effect[35] (Fig. 1). Interestingly, progesterone, the sub-stance that led to the search for spironolactone, hasalso been shown to exert its antimineralocorticoidaction by a similar mechanism involving binding tothe aldosterone receptor [36].

Like many drugs, spironolactone has unwantedside effects, including gynecomastia and impotencein males and menstrual disturbances in females [28,29]. The side effects are dose dependent and readilyreversible. The antiandrogenic effect involves, inthe main, both spironolactone and its metabolite,canrenone, acting as an inhibitor of the testosteronereceptor [29, 31]. With spironolactone there is alsoenhanced peripheral metabolism of androgens to es-trogens, and inhibition of testicular biosynthesis of

CH2OH

c=o

5-CCH30

626 Adam

testosterone, These effects are, in retrospect, pre-dictable in view of the high doses of spironolactoneand its known affinity for the testosterone receptor[32]. Spironolactones also have other effects possi-bly not mediated by classical steroid receptors andof doubtful significance, for example, an inotropiceffect in the heart, proliferation of endoplasmic re-ticulation in hepatocytes, and stimulation of hepaticoxidizing enzyme [29].

In an attempt to avoid the unwanted side effectsof spironolactone, other drugs with similar actions(sodium losing, potassium retaining) have been de-veloped (for example, triamterene [28] and amilo-ride [37]). These do not appear to act as direct al-dosterone antagonists, however. More recently,spironolactone analogues have been studied to seeif the affinity for the mineralocorticoid receptor canbe maintained when the affinity for the testosteronereceptor is lost. SC 25152 has CO2 CH3 substitutedfor SCOCH3 in the 7 position (Fig. 2). Comparedwith spironolactone, it has equivalent affinities forthe mineralocorticoid receptor but reduced affini-ties (20%) for the testosterone receptor [38]. Recep-tor binding, however, does not predict either ago-nist or antagonist activity, and the electrolyte activi-ty of SC 25152 was not studied [38]. On otherevidence, it seems likely that the 7 substitutioncould induce changes in agonist to antagonist activi-ty [31], and this drug, SC 25152, needs to be eval-uated in this regard.

(2) /8-Deoxyaldosterone. Another, and intu-itively more specific, approach to develop an al-dosterone antagonist would be to modify the al-dosterone molecule. One of the problems is that thestructural basis of mineralocorticoid activity is notwell understood. Aldosterone, 1 1-deoxycorticoster-one, and 9-a-fluorocortisol all exhibit high bindingaffinity to the mineralocorticoid receptor and areexclusively agonist, yet their three-dimensionalstructures, as determined by x-ray crystallography,do not reveal common features to explain their spe-cific interaction with the receptor binding site [39].Similarly, affinity can be altered significantly bywhat appear to be minor structural modificationsthat are away from the apparent reactive sites (11and 18 positions). To give some examples: (a) Add-ing fluorine in the 9 a position to prednisolone leadsto mineralocorticoid activity, whereas adding fluo-rine in the 6 a position does not [40]. (b) Removingthe methyl group from the 19 position enhances theaffinity of DOC for the aldosterone receptor, but thesame manipulation has variable effects on spirono-

lactone affinity for the receptor [41, 42]. All thisserves to emphasize our lack of knowledge of ste-roidal structure-function relationships.

Notwithstanding, the above modifications of al-dosterone have been made, and the substanceshave been tested for aldosterone receptor affinity.Any substances having receptor affinity were thentested for agonist or antagonist activity in an al-dosterone bioassay system. One antagonist is 18-deoxyaldosterone, an analogue of aldosterone inwhich the hemiacetal structure is replaced by astable 1IB, 18 oxide ring. It binds to the mineral-ocorticoid receptor and has partial agonist (1/3) andantagonist (2/3) activity in rat kidney bioassay andtoad bladder bioassay [43]. 18-Deoxyaldosteronehas two desirable characteristics that make side ef-fects less likely. The first is a high affinity for thealdosterone receptor leading to low blood level re-quirements; the second is a negligible affinity forandrogen receptors. 18-Deoxyaldosterone may bethe basis for developing a more specific aldosteroneantagonist for clinical use.

Aldosterone agonists. Aldosterone is expensiveand needs to be given parenterally, thus limiting itsuse in the treatment of hypoaldosteronism. In mostsituations, hypoaldosteronism is associated withhypoglucocorticoidism, and the administered glucu-corticoid is selected to have some mineralocorticoideffect (for example, cortisone acetate) that is oftenadequate for sodium and potassium homeostasis.In isolated instances of hypoaldosteronism andin some patients with Addison's disease, anoral analogue of aldosterone, however, would bepreferable. For this purpose, 9-a-fluorohydrocorti-sone, a synthetic analogue of hydrocortisone, hasbeen proposed [44].

(1) 9- a-Fluorohydrocortisone. 9-a-Fluorohydro-cortisone binds to both glucocorticoid and mineral-ocorticoid receptors with high affinity [45], and as amineralocorticoid, it is as active on a mole-for-molebasis as is aldosterone in the rat (Adam, unpub-lished results) (Fig. 3). Although 9-a-fluorohydro-cortisone appears to act as a mineralocorticoid inman, some of its action (like hypertension in the rat[45]) appears to be due to its glucocorticoid action.It has been used with good effect in potassium-re-taining or sodium-losing states and hypotension dueto hypoaldosteronism, and it may have some effectin other potassium-retaining or sodium-losing states(for example, renal). It is also used to produce ex-pansion of extracellular fluid and suppression of re-nm in diagnostic tests in patients with hypertension

Aldosterone and dopamine receptors 627

[47]. It is not certain, however, that all its effects areproduced by either a glucocorticoid or mineral-ocorticoid mechanism.

Experimentally in sheep, 9-a-fluorohydrocorti-sone can produce hypertension that does not de-pend on a classical mineral or glucocorticoid mech-anism and is also not dependent on the kidneys [48].The site of action is unknown, but it may relate toanother experimentally induced type of hyperten-sion—that induced by ACTH in the sheep [49]. In-fusion of appropriate amounts of known adrenalglucocorticoids and mineralocorticoids cannot re-produce ACTH-induced hypertension without theaddition of either 17-OH-progesterone and/or 17-a,20-a,di-OH progesterone [50-52]. The mecha-nism of ACTH and 9-a-fluorohydrocortisone hyper-tension is unknown but is of interest in regard todrug-induced minera1ocorticoid" hypertension inman (see below).

(2) 9-a-Fluoroprednisolone. An outbreak of hy-pertension in Italy has been traced to nasal sprays,taken for rhinitis [53]. These nasal sprays contain 9-a-fluoroprednisolone, presumably included for itsglucocorticoid effects, although it is not clearwhether the manufacturer knew whether the spraycontained 9-a-fluoroprednisolone or 6-a-fluoro-prednisolone. 9-a-Fluoroprednisolone has an affini-ty for aldosterone receptors and an in vivo aldoster-one-like activity equivalent to 9-a-fluorohydrocorti-

sone and aldosterone [40] (Fig. 3). There is no doubtthe nasal spray produced increased mineral-ocorticoid activity (hypokalemic alkalosis, lowplasma renin activity, and hypertension), but thehypertension may also have been related to somenonmineralo, nonglucocorticoid effect similar tothat seen in the sheep with 9-a-fluorohydrocorti-sone. In this regard, it is interesting to note that theblood pressure returned to normal more slowly thanthe hypokalemia. The extra actions of 9-a-fluoro-hydrocortisone and 9-a-fluoroprednisolone mightexplain why these substances appear to be muchbetter than aldosterone is in producing hyperten-sion in sheep and man [40, 48, 54]. It should benoted, however, that although administration of a!-dosterone to man in the short term may produce on-ly mild or no elevation of blood pressure [55], moreprolonged administration is far more effective [56].

(3) Liquorice extracts. Aldosterone agonist activ-ity may also arise as an unwanted side effect of adrug directed elsewhere. Liquorice derivatives (gly-cyrrhetinic acid, glycyrrhizic acid, and carbenoxo-lone as the active components) used in treatment ofpeptic ulcers lead to sodium retention, hypoka-lemia, and hypertension, all reversible by spirono-lactone [57]. Glycyrrhetinic acid has a low but defi-nite affinity for aldosterone receptors, which, giventhe doses used, may explain its apparent mineral-ocorticoid action [57]. Studies on the effect of car-benoxolone on aldosterone receptors have not beenperformed. The characteristics of its action and thereversibility by spironolactone all suggest, how-ever, that these are receptor mediated [58]. Themode of action of glycyrrhetinic acid and carbe-noxolone on gastric acid excretion is unknown butmay involve histamine receptor (H2) blockade. It isof interest to note that cimetidine, a fairly specificH2 receptor antagonist, also binds to testosteronereceptors and produces antiandrogen effects—remi-niscent of the spironolactones [59]. Furthermore,spironolactone inhibits the effect of carbenoxoloneon gastric acid secretion, possibly acting as anagonist [60]. It may be there are some structuralsimilarities between the H2, androgen, and aldoste-rone receptors. There is pharmacologic evidence ofHi and H2 receptors in the kidney, but these seemmainly vascular and no evidence has been present-ed to show any other effect on renal function [61].

Dopamine

Dopamine is used therapeutically as an inotropicagent and as a relatively specific renal vasodilator[62]. Dopamine analogues are being developed, pre-

3

z+

zCO

0+C —

9oFF-. ,—AIdo

14

0 , —-0 3 10 30

Steroid, /.Lg/kg

Fig. 3. Renal response to aldosrerone (A/do) compared to 9-a-fluorohydrocortisone (9aFF) and 9-a-fluoroprednisolone (9aFP).The responses were not significantly different. Each point repre-sent the mean and SEM of at least eight rats (for methods, seeRef. 22).

628 Adam

sumably in the hope of obtaining an orally activeinotropic agent or an agent to enhance renal bloodflow or GFR [63].

Therapeutic manipulation of dopaminergic sys-tems occurs with the use of other agents with do-paminergic activities, precursors of dopamine, do-paminergic antagonists, and inhibitors of dopaminesynthesis (Table 1). All of these may interact withdopaminergic systems within the kidney.

The dopaminergic renal systems may respond toeither dopamine arriving in the arterial blood or tolocally produced dopamine. It is only recently that aradioenzymatic assay has been developed that isspecific and sensitive enough to measure plasmadopamine levels (approximately 0.5 nmoles/liter)[64]. The endogenous plasma levels of dopamineare much lower than those achieved therapeutical-ly. There is, however, some evidence for renalbinding studies (see below) that the endogenous lev-els are appropriate for physiologic action. Addition-al evidence that plasma dopamine may exert somephysiologic role is that the levels are modified bysodium intake. A low sodium diet increases plasmadopamine twofold, and there is a better correlationbetween sodium intake and plasma dopamine thanthere is with sodium intake and either epinephrineor norepinephrine [65].

Dopamine is produced within the kidney as wellas elsewhere. Dopamine has been demonstrated inrenal vascular tissue by fluorescent techniques [66].Further evidence for intrarenal production is thatthe amount of dopamine excreted in the urine ex-ceeds that which could be extracted from theplasma [67] (Table 2). Additional evidence is thepresence of enzymes necessary for dopamine syn-thesis—tyrosine hydroxylase and dopa decarboxy-lase. The tyrosine hydroxylase level is dependenton sympathetic nerve supply and is probably intra-neuronal [68]. The dopa decarboxylase is a relative-ly nonspecific aromatic acid decarboxylase and isextraneuronal [68]. Dopamine production mighttherefore be under neuronal or extraneuronal con-trol, or both. The concept of tissue catecholaminesoutside neuronal control is not unique, as epineph-rifle seems to be present outside neurons in heart[69].

The sympathetic supply to the kidney is abundantand is directly to the tubules as well as vascular tis-sue [68]. The actions of the sympathetic nerve sup-ply to the kidney include, at least, direct vascularactions and enhancement of sodium reabsorption[70]. Other actions, however, have not been ex-cluded and seem likely. If the dopamine productionis under neuronal control, this would enable intra-renal release to be anatomically discrete and thus

Table 1. Drugs that may interact with dopaminergic-mediated function in the kidney

Agonists DopamineL-DopaBromocryptine

Antagonists ChiorpromazineButyrophenones

(e.g. haloperidol)MetoclopramideOpiates

Inhibitors ofdopamine productionoutside the CNS

CarbidopaBenzeraside

Table 2. Plasma dopamine, urinary dopamine, dopamineclearance, and creatinine clearance in 6 normal malesa

Plasma Dopamine Dopamine Creatininedopamine excretion clearance clearance

nmoles/liter nmoles/hr mi/mm mi/mm

0.43 0.06 44.8 7.1 1996 453 112 7

a Values are the means SEM. The dopamine clearance ex-ceeds creatinine clearance and estimated renal blood flow (as-suming renal blood flow is approximately 5 times GFR) [67].

possibly have more than one action in the kidney.This would help provide a basis for the many dif-ferent renal actions of dopamine postulated below.

Renal actions of dopamine. The postulated renalaction of dopamine includes (1) vascular action(dilatation; stimulation of renin release) and (2) di-rect tubular action (sodium excretion, either in-crease or decrease; phosphate excretion; enhance-ment of the renal action of aldosterone).

There is ample evidence that vascular infusion ofdopamine produces renal vasodilatation [62] and anatriuresis [62, 72, 73]. Neurogenic control of dopa-mine-mediated renal vascular dilatation is likely tobe a physiologic control system based on the fol-lowing evidence. Electrical stimulation of specificareas in the midbrain and hypothalamus lead to anincrease in renal blood flow, which is blocked byhaloperidol, a dopamine receptor blocker [74].These changes in renal blood flow can not be ex-plained by changes in flow in other vascular beds.More recently, there has been histofluorescentdemonstration of dopamine-containing neuronalelements at the glomerular vascular poles [66].These dopamine-containing structures may repre-sent the prejunctional counterpart to the pharma-cologically identified dopamine receptors in the re-nal vasculature. There is also some evidence thatthe rise in renin secondary to stimulation of the re-nal sympathetic nerves is, at least in part, mediatedby dopamine [75].

The natriuresis induced by dopamine can be ex-plained to a large extent by the renal vasodilatation.

Aldosterone and dopainine receptors 629

The question is whether a direct effect of dopamineon the renal tubule also contributes to this natriure-sis. The commonly cited evidence that dopaminedoes have a direct tubular natriuretic effect is notcompletely satisfactory. In an abstract, McGiff andBurns [72] described a natriuretic effect of dopa-mine even when the renal blood flow and GFR hadbeen reduced to below control levels by aortic con-striction. The natriuresis, but not renal vasodilata-tion, was blocked by phentolamine, suggesting apossible a mediation of the sodium loss. Unfortu-nately, complete details are not available. In dogs,the i.v. infusion of dopamine produced a natriuresisthat occurred without any change in GFR. On thebasis of micropuncture, including tubular fluid-to-plasma inulin ratios, the natriuresis did not occur inthe proximal tubule and, by exclusion, was attrib-uted to the distal tubule. Renal blood flow, how-ever, was not measured in this study [73]. More re-cently, some preliminary evidence has been pre-sented that shows a natriuretic effect of dopamine inthe isolated perfused rat kidney. This natriuretic ef-fect was independent of changes of perfusion flowrate and GFR and, by exclusion, was attributed to atubular effect of the dopamine [75]. There is alsoindirect evidence of a natriuretic role for dopamine.Carbidopa, an inhibitor of dopa decarboxylase andthus dopamine production, has antinatriuretic ef-fects, and from this a natriuretic role for dopaminewas extrapolated [77]. Further evidence that dopa-mine may be an important natriuretic agent is basedon correlations between urine sodium and dopa-mine excretion under varying conditions [78]. It isimportant to note that in one study in rats the dopa-mine excretion correlated with chloride intake andnot sodium intake [67], raising the possibility thatthe natriuretic activity is secondary to chlorureticactivity. This needs further study.

It seems likely that the natriuretic effect is due todopamine produced intrarenally rather than to thatproduced elsewhere. Plasma dopamine levels corre-late inversely with sodium excretion [65], whereasurinary dopamine excretion (presumably reflectingintrarenal production) correlates directly with so-dium excretion [78].

An action of dopamine to enhance sodium reab-sorption is at variance with its proposed natriureticproperties, but these are not mutually exclusive ifactivated by anatomically discrete dopamine re-lease, as can occur with neuronal control. Such anantinatriuretic activity has been demonstrated fordopamine as part of a postulated action to enhancethe renal response to aldosterone [22]. The evi-dence for an action of dopamine on the renal actionof aldosterone has problems of interpretation. Pre-

treatment of rats with L-dopa leads to a natriuresis.The addition of aldosterone reduces the natriuresisand enhances potassium excretion leading to great-er increment of K/Na than with aldosterone alone.Other factors producing a natriuresis (sodium chlo-ride, furosemide, theophylline) do not modify theresponse to aldosterone. The enhanced responsecan be blocked by haloperidol (a dopamine receptorblocker) and carbidopa (a peripheral dopa decarbox-ylase inhibitor). The results with carbidopa suggeststhat the action of L-dopa is mediated through dopa-mine acting outside the central nervous system [22].The problem in interpreting these results led us tolook for a role for dopamine in aldosterone sensitiv-ity in a more physiologic situation. Chronic potas-sium loading produces enhanced end-organ respon-siveness to aldosterone [21], which appears to bemediated by dopamine as it is inhibited by both car-bidopa and haloperidol [79].

Dopaminergic potentiation of hormonally mediatedion transport may not be unique to the kidney. Bro-mergocryptine, a drug with dopaminergic agonistactivity, has been demonstrated to potentiate gastrin-mediated acid excretion in the stomach of the cat [80].There is other indirect evidence of a role for dopa-mine in sodium reabsorption by the kidney in thatplasma levels of dopamine rise with sodium restric-tion [65]. These results are difficult to interpret in thatplasma levels of both norepinephrine and epinephrinealso rise. Of all these catecholamines, however, plas-ma dopamine levels gave the best correlation withsodium excretion [65]. Additional, very indirect,evidence that dopamine may play a role in sodiumreabsorption is that interruption of the renal sympa-thetic fibers leads to natriuresis and stimulation tosodium retention [70, 81, 82]. This theory impliesthat the dopaminergic control of sodium reabsorp-tion is under neuronal control. One problem withthis interpretation is that sodium reabsorption canalso be enhanced with norepinephrine and epineph-rine [83]. The studies done on catecholamines andsodium reabsorption were done in the isolated per-fused rat kidney. They did not include the infusionof dopamine and used very high levels of proprano-lol (10 M) as evidence of /3-receptor involvement.They are thus incomplete and can not be interpretedconclusively [83].

Proof of an interaction between dopamine and so-dium reabsorption, particularly if it involves the re-sponsiveness to aldosterone, may come with stud-ies at a subcellular level. There is preliminary evi-dence that dopamine interacts with Na-K-ATPase,the enzyme equivalent of the sodium pump, andone of the possible effector mechanisms for aldo-sterone action [84].

630 Adam

Evidence has been presented that dopamine ex-erts some control over phosphate excretion. Bothdopamine and L-dopa, but not L-dopa with carbi-dopa (the dopa decarboxylase inhibitor), enhancedphosphate excretion by a mechanism independentof parathyroid hormone or sodium excretion [85].Whether this has a physiologic role in the control ofphosphate is not known.

Biochemical evidence suggestive of a metabolicrole for dopamine in the kidney is the enhancementof that part of the renal metabolic rate not associat-ed with sodium reabsorption [86] and the presenceof a dopamine-sensitive adenylate cyclase [87].How these fit in with the physiologic roles postulat-ed above is unclear.

The postulated actions may not be mutually ex-clusive or antagonistic if they are anatomically dis-crete and dopamine production is similarly discreteand controlled by neural regulation. Circulating lev-els of dopamine might be expected to intefere, how-ever, with local actions unless the required concen-trations for activation of those effector systems un-der control from local production were higher thanthose under control of plasma dopamine. Theplasma level of dopamine at renal sites of actionmay be further reduced by its active clearance fromthe plasma by tubular secretion [88], reducing back-ground levels and thus facilitating discrimination oflocally released dopamine.

Dopaminergic binding studies. One way of help-ing to define the intrarenal roles for dopamineshould be by studying the characteristics of renaldopamine receptors. To the present, receptors havebeen demonstrated pharmacologically and almostexclusively in relation to dopaminergic control ofblood flow. In unpublished studies, we have demon-strated binding of tritiated dopamine to homoge-nates of kidney.

The binding characteristics of both dopamine andhaloperidol in the kidney differ markedly from thoseobserved in the central nervous system [91, 92].Major differences include the lack of displacement(and of binding itself) by apomorphine and the lackof displacement of dopamine by d-butaclamol. Thedisplacement of dopamine by l-methorphan is anal-ogous to opiate inhibition of the dopamine receptorin the pituitary [93]. The relatively low affinity ofdopamine and haloperidol for each other's bindingsites is also of interest and suggests that each ligandbinds to a different site. In contrast to the binding ofhaloperidol, dopamine binding could be inhibited byomission of ATP or sodium, or by the addition ofpotassium (20 mM) or ouabain (10-6 M) (Fig. 4).There is growing evidence for multiple classes of

"dopamine" receptors in the central nervous sys-tem, and the binding sites demonstrated here mightextend the number of different types [94].

Is the binding of either dopamine or haloperidolof any physiologic significance? The opiates d- and 1-methorphan inhibit the enhanced renal response toaldosterone, induced by L-dopa, (Fig. 5), quite con-sistent with their displacement of dopamine bindingin kidney homogenates. No such function for thehaloperidol sites has been defined. The effect ofopiates on dopamine binding and on the renal re-sponse to aldosterone suggests the dopamine bind-ing is at least pharmacologically important. (The in-triguing possibility that this is a manifestation of anendogenous opiate mechanism has yet to be ex-plored. Recently, a structural similarity betweendopamine and enkephalin has been described [95].)In addition, the effect of removing sodium or ATPand adding potassium to the medium on dopaminebinding, but not haloperidol binding, suggests somesignificance of the dopamine binding site. In thiscontext it is of interest to note that the binding ofcatecholamines, including dopamine and /3 adre-noreceptor agonists, but not of antagonists, ismodulated by other nucleotides, in particular GTP,which can differentiate between agonist and antago-nist states [96—98].

The dopamine binding requirements for sodiumor ATP and inhibition by high potassium concentra-

I100-

4_6 75-0

000

a'50-

Co0 C

25=

Fig. 4. Effecton 3H—dopa mine— and 3H—haloperidol-bindingof ad-dition ofouabain (I tIM) or withdran'al of ATP (3 mM) from themediu,n. Both the addition of ouabain and the removal of ATPreduce dopamine binding significantly (paired I test, P < 0.02),but have no effect on haloperidol binding. The mean SEM ofmore than five determinations are plotted.

—ATP + Ouabain

Aldosterone and dopamine receptors 631

, ,

tion are similar to those for the enzyme Na-K-ATPase [89]. The possible relationship between thedopamine receptor and Na-K-ATPase is furthersupported by the finding that ouabain, a specific in-hibitor of Na-K-ATPase, inhibits dopamine bind-ing. Such an interaction between the dopamine re-ceptor and Na-K-ATPase may possibly explain theobserved effects of dopamine on this enzyme [84].A similar coupling (between a receptor and an iontransport system) has recently been proposed forthe benzodiazepine receptor and a chloride anionchannel [99].

Renal effects of dopaminergic drugs. Apart fromthe difficulties in detecting renal effects of dopami-nergic drugs owing to the kidneys ability to adapt tospecific functional loss (see introduction of sectionon dopamine), any observed effects may relate toextrarenal actions of dopamine. For instance, an ef-fect of dopamine on sodium could be to promoteeither its excretion or retention and may be mediat-ed in the kidney directly or secondary to interactionwith aldosterone, or by an action on renin release.Further complicating factors are that dopamine ap-pears to inhibit angiotensin-mediated aldosteronesecretion [100, 101]. All these factors combine to

make an action of dopaminergic agents unpredict-able, as indeed they are.

Certainly dopamine infusion is associated with anatriuresis, largely due to its vascular effects [62].Similarly, L-dopa, the precursor of dopamine, leadsto a natriuresis of variable extent [102]. L-Dopa mayalso lead to hypotension, although this is morelikely due to a central mechanism rather than so-dium loss [103]. Although carbidopa (the inhibitorof dopa carboxylase) is rarely used alone, it is asso-ciated with modest sodium retention [76]. Carbi-dopa reduces the incidence of hypotension seenwith L-dopa treatment [104] and can be shown ex-perimentally to block the natriuretic effect of L-dopa [85].

Another drug with dopaminergic agonist activity,bromocryptine, can lead to a small natriuresis,which is unlikely to cause its hypotensive effect[106]. The natriuresis may be directly mediated bythe kidney or be the result of the dopaminergic inhi-bition of aldosterone release mediated by bromo-cryptine [101, 107].

The psychotropic drug chlorpromazine is consid-ered a classical dopaminergic receptor blocker[108]. It acts as a diuretic, but its mechanism of ac-tion is uncertain. Possibilities include inhibition ofADH and inhibition of tubular reabsorption of so-dium (possibly acting as a dopaminergic receptorblocker). It also has nonspecific adrenergic receptorblocking activities [109]. Haloperidol, a butyrophe-none, is another psychotropic drug that is also usedas a dopamine receptor blocker [91]. Knowledge ofits renal action is poorly described.

Although there has been a general impressionthat dopaminergic antagonists have little gross ef-fect on renal function and that any effect might bemediated by an extrarenal mechanism rather thandirectly in the kidney, this should not stop us fromlooking for small manipulations of renal function, aseven minor changes may assume importance overthe longer term. Receptor studies may help defineareas of renal function that require careful observa-tion.

Summary

Therapeutic manipulation of renal hormone re-ceptors is appropriate for hormone functions inwhich the kidney is the most biologically significantend organ. Renal hormone receptors may also beaffected by drugs directed elsewhere. Two kidneyhormone receptor systems have been discussed—those for aldosterone and for dopamine.

Aldosterone agonists (9-cE-fluorohydrocortisone)and antagonists (spironolactone) are used to manip-

+

o• —

+

+

6

4SC0C-

C0

2

0C Ldopa L-dopa L-dopa

+ +1-meth. d-meth.

Fig. 5. Effect of L-dopa and d- and 1-methorphan on the renalresponse to aldosterone. The renal response is defined as (K2![K1+ K2]) ÷ (Na2/[Na1 + Na2]), and each point represents the meanand 5EM of at least eight rats (for methods, see Ref. 22). Pre-treatment by L-dopa (100 mg/kg) leads to an enhanced responseto aldosterone mediated by dopaminergic mechanisms [22] (seetext). Both I, and to a lesser extent d-methorphan (1 mg/kg), giv-en prior to the basal urine, inhibited the dopaminergic enhance-ment of the renal response to aldosterone (10 pg/kg). This inhibi-tion was significant (P <0.02) with l-methorphan.

632 Adam

ulate sodium and potassium balance. Unintentionalmanipulation of the aldosterone receptor causingsodium retention and hypertension can occur withputative glucocorticoids (9-a-fluoroprednisolone)administered in nasal sprays as well as with liquo-rice extracts used to treat peptic ulcers.

Dopamine agonists can increase renal blood flowbut may also interact (as may antagonists) with non-vascular renal dopamine receptors. In studies onpig kidney, microsomal fractions 3H-dopamine and8H-haloperidol can be demonstrated to bind specifi-cally, probably to two distinct sites. Both 3H-dopa-mine binding and dopamine-mediated enhancementof the renal response to aldosterone were inhibitedby opiates (methorphan). This suggests a directtubular action of dopamine on aldosterone-mediatedpotassium and sodium transport.

Other postulated nonvascular dopaminergic ef-fects include inhibition of proximal tubular sodiumreabsorption and enhancement of phosphate excre-tion.

Acknowledgments

This work was supported by grants from the De-partment of Veterans' Affairs (Commonwealth ofAustralia) and the National Health and Medical Re-search Council. Mrs. P. Marston typed the manu-script.

Reprint requests to Dr. W. R. Adam, Renal Unit, RepatriationGeneral Hospital, West Heidelberg, 3081, Victoria, Australia

References

I. HAYSLETT JP: Functional adaptation to reduction in renalmass. Physiol Rev 59:137—164, 1979

2. SHARP WG, LEAF A: Effect of aldosterone: Its mechanismof action on sodium transport, chapter 25 in Renal Physiol-ogy, edited by ORLOFF J, BERLINER RW, Washington,American Physiological Society, 1973, p. 818

3. EDELMAN IS: Mechanism of action of aldosterone: Ener-getic and permeability factors. J Endocrinol 81:49P—53P,1979

4. SEBASTIAN A, HULTER HN, SCHAMBELAN M: Renal hy-perchloremic acidosis with hyperkalemia type 4 renal tubu-lar acidosis (RTA), in Proc VIIth Intern Congr Nephrol,edited by BARCELO R, BERGERON M, CARRIERE S, DIRKSJH, DRUMMOND K, GUTTMANN RD, LEMIEUX G, M0N-GEAU G, SEELY JF, Basel, Karger, 1978, p. 351

5. ANDERSON NS, FANESTIL DD: Biology of mineral-ocorticoid receptors, chapter 12 inReceptors and HormoneAction, edited by O'MALLEY BW, BIRNBAUMER L, NewYork, Academic Press, 1978, vol. 2, p. 323

6. SCOTT WN, REICH TM, BROWN JA, YOUNG C-PH: Com-parison of toad bladder aldosterone induced proteins andprotein synthesis in vitro using aldosterone induced mes-senger RNA as template. J Memb Biol 40:213—220, 1978

7. SCOTT WN, REICH IM, GOODMAN DBP: Inhibition of fatty

acid synthesis prevents the incorporation of aldosterone-induced proteins into membranes. J Biol Chem 254:4957-4959, 1979

8. HIERHOLZER K, LANGE S: The effects of adrenal steroidson renal function, in MTP International Review of Science,Kidney and Urinary Tract Physiology, edited by THURAUK, London, Butterworths, 1974, vol. 6, pp. 273-334

9. SNART RS, TAYLOR E: Aldosterone effects on renal metab-olism. J Physiol 274:447—454, 1978

10. HAMLYN JM, DUFFY T: Direct stimulation of humanerythrocyte membrane (Nat + K)-Mg ATPase activity invitro by physiological concentrations of d-aldosterone. Bio-chem Biophys Res Comm 84:458-464, 1978

11. GILBERTJC, LAMBIE AT, OSORE H: Effects of aldosteroneand spironolactone on renal ATPase activities. Br J Phar-macol 64:408P, 1978

12. FORTE LR: Effect of mineralocorticoid agonists and antago-nists on binding of 3H-aldosterone to adrenalectomized ratkidney plasma membranes. Life Sci 11:461—473, 1972

13. FIMOGNARI GM, FANESTIL DD, EDELMAN IS: Induction ofRNA and protein synthesis in the action of aldosterone inthe rat. Am J Physiol 213:954—962, 1967

14. LIFSCWTZ MD, SCHRIER RW, EDELMAN IS: Effect of acti-nomycin D on aldosterone-mediated changes in electrolyteexcretion. Am J Physiol 224:376—380, 1973

15. MUELLER A, STEINMETZ PR: Spironolactone. An aldoste-rone agonist in the stimulation of W secretion by turtle uri-nary bladder. J Clin Invest 61:1666—1670, 1978

16. STEWART J: Genetic studies on the mechanism of action ofaldosterone in mice. Endocrinology 96:711—717, 1975

17. MORRIS DJ, DAVIS RP: Aldosterone: Current concepts.Metabolism 23:473—494, 1974

18. MoRRIs DJ, HANTOOT MS, DECONTIE GA: The enterohe-patic circulation of aldosterone metabolites and its sex-de-pendence in rats. Endocrinology 101:1776—1783, 1977

19. DAVIS JD, HOLMAN JE, CARPENTER CCJ, URQUHART J,HIGGINS JT: An extra adrenal factor essential for chronicrenal sodium retention in the presence of increased sodiumretaining hormones. Circ Res 15:16-3 1, 1964

20. BLAIR-WEST JR, COGHLAN JP, DENTON DA, SCOTT D,WRIGHT RD: The role of aldosterone in renal sodium con-servation during sodium depletion. Aust J Exp Biol Med Sci46:525—539, 1968

21. ADAM WR, FUNDER JW: Increased renal sensitivity to al-dosterone in the potassium loaded rat: Induction by a highpotassium diet. Clin Exp Pharmacol Physiol 4:283-293,1977

22. ADAM WR: Enhancement by i-dopa of the renal action ofaldosterone in the rat. Clin Exp Pharmacol Physiol 6:87—96,1979

23. ADAM WR, FUNDER JW, MERCER J, ULICK S: Amplifica-tion of the action of aldosterone by Sn dihydrocortisol. En-docrinology 103:465—471, 1978

24. ADAM WR, MENDELSOHN FAO: Measurement of the end-organ responses to aldosterone in man: Diversity of re-sponse and its possible biological significance. Aust NZ JMed 9:278-283, 1979

25. KOLANOWSKI J, DESMECHT P, CRABBE J: Sodium balanceand renal tubular sensitivity to aldosterone during total fastand carbohydrate refeeding in the obese. Eur J Clin Invest6:75—83, 1976

26. LANDAU RL, BERGENSTAL DM, LUGIBIHL K, KASCHTME: The metabolic effect of progesterone in man. J ClinEndocrinol 15:1194—1215, 1955

Aldosterone and dopamine receptors 633

27. KAGAWA CM, STURTEVANT FM, VAN ARMAN CG: Phar-macology of a new steroid that blocks salt activity of al-dosterone and desoxycorticosterone. J Pharmacol ExpTher 126:123—130, 1959

28. Ross EJ: Aldosterone and Aldosteronism. London, Lloyd-Luke (Medical Books), 1975, pp. 308—329

29. CORVOL P, CLAIRE M, RAFESTIN-OBLIN ME, MICHAUD A,ROTH-MEYER C, MENARD J: Spirolactones: Clinical andpharmacologic studies. Adv Nephrol 7: 199—215, 1977

30. SADEE W, DAGGIOGLU M, SCHRODER R: Pharmocokineticsof spironolactone, canrenone and canrenoate K in humans.J Pharmacol Exp Ther 185:686—695, 1973

31. SAKAUYE C, FELDMAN D: Agonist and anti-mineralocorticoid activities of spirolactones. Am J Physiol231:93—97, 1976

32. FUNDER JW, MERCER J, HOOD J: SC 23992: Radioreceptorassays for therapeutic and side effects. C/in Sci Mo! Med51:333S—334S, 1975

33. CAREY RM, DOUGLAS JG, SCHWEIKERT JR, LIDDLE GW:The syndrome of essential hypertension and suppressedplasma renin activity. Arch Intern Med 130:849—854, 1972

34. SEKIHARA H, HOLLIFIELD JW, ISLAND DP, SLATON PE,LIDDLE GW: Evidence for heterogeneity of mineral-ocorticoids in urine of patients with low renin essential hy-pertension. J C/in Endocrinol Metab 48:143-147, 1979

35. MARVER D, STEWART J, FUNDER JW, FELDMAN D, EDEL-MAN IS: Renal aldosterone receptors: Studies with (3H) al-dosterone and the anti-mineralocorticoid (3H) spirolactone(SC-26304). Proc Nat! Acad Sci USA 71:1431—1435, 1974

36. WAMBACH G, HIGGINS JR: Antimineralocorticoid action ofprogesterone in the rat: Correlation of the effect on elec-trolyte excretion and interaction with renal mineral-ocorticoid receptors. Endocrinology 102:1686—1693, 1978

37. CUTHBERT AW, FANELLI GM JR, SCRIABINE A (editors):Amiloride and Epithelial Sodium Transport. Baltimore, Ur-ban Schwartzenberg, 1979

38. CUTLER GB, PITA JC, RIEKA SM, MENARD RH, SAUERMA, LORIAUX DL: SC 25152: A potent mineralocorticoidantagonist with reduced affinity for the 5a-dihydrotestoste-rone receptor of human and rat prostate. J C/in EndocrinolMetab 47:171-175, 1978

39. DUAX WL, WEEKS CM, ROHRER DL: Crystal structure ofsteroids: Molecular conformation and biological function.Recent Prog Horm Res 32:81—109, 1976

40. FUNDERJW, ADAM WR, MANTERO F, KRAFT N, ULICK 5:The etiology of a syndrome of factitious mineralocorticoidexcess: A steroid-containing nasal spray. J C/in EndocrinolMetab 49:842-846, 1979

41. FUNDERJW, MERCERJ, INGRAM B, FELDMAN D, WYNNEK, ADAM WR: 19-Nor deoxycorticosterone (19-nor DOC):Mineralocorticoid receptor affinity higher than aldosterone:Electrolyte activity lower. Endocrinology 103:1514—1517,1978

42. FUNDER JW, FELDMAN D, HIGHLAND E, EDELMAN IS:Molecular modifications of anti-aldosterone compounds:Effects on affinity of spirolactones for renal aldosterone re-ceptors. Biochem Pharmacol 23:1493—1501, 1974

43. ULICK S, MARVER D, ADAM WR, FUNDER JW: The miner-alocorticoid antagonist activity of an 1 1B,18-oxidopreg-nane. Endocrinology 104:1352-1356, 1979

44. GOLDFIEN A, LAIDLAW JC, HAYDAR NA, RENOLD AE,THORN GW: Fluorohydrocortisone and chlorohydrocorti-sone, highly potent derivatives of compound F. N Engi JMed 252:415—421, 1955

45. LAN N, MATULICH DT, GRAHAM B, BAXTER JD: Relativeactivities of steroids for binding to glucocorticoid and mm-eralocorticoid receptors: Possible implications for anti-mineralocorticoid like actions of the glucocorticoids. Proc60th Annual Meeting Endocrine Soc 1978, p. 216

46. HEPP R, GARBADE K, OSTER P, GROSS F: Arterial hyper-tension induced by 9a fluorocortisol in the rat during vari-ous sodium intakes, in Research on Steroids, edited byBREUER H, North Hallam Publishing Co, Amsterdam,1975, p. 377

47. GORDON RD, JACKSON RV, STRAKOSCH CR, TUNNY TJ,RUTHERFORD JC, MCCOSKER J, MORIARTY W: Primary al-dosteronism: Fludrocortisone suppression and left adrenalvein catheterisation in diagnosis and management. Aust NZJ Med 9:676-682, 1980

48. COGI-ILAN JP, BUTKUS A, DENTON DA, MCDOUGALL JG,SCOGGINS BA, WHITWORTH JA: Blood pressure and meta-bolic effects of 9-aipha-fluoro-hydrocortisone in sheep. ClinExp Hypertension 1:629-648, 1979

49. SCOGGINS BA, BUTKUS A, COGHLAN JP, DENTON DA,FAN JSK, HUMPHREY TJ, WHITWORTH JA: Adrenocorti-cotropic hormone-induced hypertension in sheep: A modelfor the study of the effect of steroid hormones on bloodpressure. Circ Res 43(suppl. 1):76—81, 1978

50. COGHLAN JP, DENTON DA, FAN JSK, MCDOUGALL JG,SCOGGINS BA: Hypertensive effect of 17a, 2Ocs-dihydroxy-progesterone and 17a-hydroxyprogesterone in the sheep.Nature 263:608—609, 1976

51. WHITWORTH JA, DENTON DA, HUMPHREY Ti, COGHLANJP, GRAHAM WF, SC000INS BA: Comparison of the effectsof 'glucocorticoid' and 'mineralocorticoid' infusions onblood pressure in sheep. C/in Exp Hypertension 1:649-664,1979

52. COGHLAN JP, BUTKUS A, DENTON DA, GRAHAM WF,HUMPHREY Ti, SCOGGINS BA, WHITWORTH JA Steroidreceptors and hypertension. Circ Res, 1980, in press

53. MANTERO F, ARMANINI D, OPOCHER G, FALLO F, SAM-PIERI L, CUSPIDI C, AMBROSI B, SECCHI F, FAGLIA G:Pseudo-iperaldosteronismo primitivo da istillazione ando-sanale di fluoro-prednisone, in Atti del 17 Congresso na-zionale del/ar Societa Italiana de Endocrinologia, SeronoSymposia (in Italian), Torino-Saint Vincent- 17-20 Maggio,1978

54. NICHOLLS MG, RAMSAY LE, BODDY K, FRASER R, MOR-TON ii, ROBERTSON JIS: Mineralocorticoid-induced bloodpressure, electrolyte, and hormone changes, and reversalwith spironolactone, in healthy men. Metabolism 28:584-593, 1979

55. VAGNUCCI AH, SHAPIRO AP: Perspectives on the reninangiotensin aldosterone system. Metabolism 23:273—302,1974

56. KASSIRER JP, LONDON AM, GOLDMAN DM, SCHWARTZWB: On the pathogenesis of metabolic alkalosis in hyper-aldosteronism. Am J Med 49:306—315, 1970

57. ULMANN A, MENARD i, CORVOL P: Binding of glycyrrhe-tinic acid to kidney mineralocorticoid and glucocorticoidreceptors. Endocrinology 97:46—51, 1975

58. TOMKIN5 M, EDM0NDS Ci: Rectal potential difference, so-dium absorption and potassium secretion by the human rec-tum during carbenoxolone therapy. Gut 16:277-284, 1975

59. FUNDER JW, MERCER JE: Cimetidine, a histamine, H2, re-ceptor blocker occupies androgen receptors. J C/in Endo-cr/no! Metab 48:189—191, 1979

60. DOLL R, LANGMAN MJS, SHAWDON HH: Treatment of

634 Adam

gastric ulcer with carbenoxolone; antagonistic effect of spi-ronolactone. Gut 9:42-45, 1968

61. BANKS RO, FONDACARO JD, SCHWAIGER MM, JACOBSONED: Renal histamine H1 and H2 receptors; characterizationand functional significance. Am J Physiol 235(6):F570—

F575, 197862. GOLDBERG LI: The pharmacologic basis of the clinical use

of dopamine. Proc Roy Soc Med 70 (suppl 2):7-13, 197763. BIEL JH, S0MANI P, JONES PH, MINARD FN, GOLDBERG

LI: Aminoacyl derivatives of dopamine as orally effectiverenal vasodilators. Biochern Pharmacol Suppl (part 2) 748-750, 1974

64. DA PRADA M, ZURCHER G: Simultaneous radioenzymaticdetermination of plasma tissue adrenaline, noradrenalineand dopamine within the fentomole range. Life Sd 19:1161-1174, 1976

65. ROMOFF MS, KEUSCH G, CAMPESE VM, WANG MS,FRIEDLER RM, WEIDMANN P, MASSRY SG: Effect of so-dium intake on plasma catecholamines in normal subjects.J Clin Endocrinol Metab 48:26—31, 1979

66. DINERSTEIN RJ, VANNICE J, HENDERSON RC, ROTH U,GOLDBERG LI, H0FFMANN PC: Histofluorescence tech-niques provide evidence for dopamine-containing neuronalelements in canine kidney. Science 205:497—499, 1979

67. BALL SG, OATS NS, LEE MR: Urinary dopamine in manand rat: effects of inorganic salts on dopamine excretion.C/in Sci Mol Med 55:167—173, 1978

68. NAGATSU T, RUST LA, DEQUATTRO V: The activity oftyrosine hydroxylase and related enzymes of cate-cholamine biosynthesis and metabolism in dog kidney. Bio-chem Pharmacol 18:1441—1446, 1969

69. SPURGEON HA, PRIOLA DV, MONTOYA P, WEISS GK, AL-TER WA: Catecholamines associated with conductile andcontractile myocardium of normal and denervated doghearts.JPharmacolExp Ther 190:466—471, 1974

70. GOTTSCHALK CW, COLINDRES RE, SPIELMAN WS: Neuralinvolvement in renal function, in Proc VIIth mt CongNephrol, edited by BARCELO R, BERGERON M, CARRIERES, DIRKS JH, DRUMMOND K, GUTTMANN RD, LEMIEUXG, MONGEAU JG, SEELY JF, Basel, S, Karger, 1978, p. 545

71. GOLDBERG LI, VOLKMAN PH, KOHLI JD: A comparison ofthe vascular dopamine receptor with other dopamine recep-tors. Ann Rev Pharmacol Toxicol 18:57—79, 1978

72. MCGIFF JC, BURNS CR: Separation of dopamine natriur-esis from vasodilation: Evidence for dopamine receptors(abst). J Lab Clin Med 70:892, 1967

73. DAVIS BB, WALTER MJ, MURDAUGH HV: The mechanismof the increase in sodium excretion following dopamine in-fusion. Proc Soc Exp Bin! Med 129:210-213, 1968

74. BELL C, LANG WJ: Neural dopaminergic vasodilator con-trol in the kidney. Nature New Biology 246:27-29, 1973

75. BELL C, LANG WJ: Effects of renal dopamine receptor and/3-adrenoreceptor blockade on rises in blood angiotensin af-ter haemorrhage, renal ischaemia and frusemide diuresis inthe dog. C/in Sci Mol Med 54:17—23, 1978

76. MCGRATH BP, LEVERSHA L, JABLONSKI P, MATHEWS PG,HOWDEN B, MARSHALL VC: Natriuretic and diuretic ef-fects of dopamine in the isolated perfused rat kidney (abst).Aust NZJ Mcd, 1980, in press

77. BALL SG, LEE MR: The effect of carbidopa administrationon urinary sodium excretion in man: Is dopamine an intra-renal natriuretic hormone? BrJ C/in Pharmacol 4:115—119,1977

KEISER HR: Effect of dietary sodium and of acute salineinfusion on the interrelationship between dopamine excre-tion and adrenergic activity in man. J C/in Invest 54:194—200, 1974

79. ADAMWR, GOLAND G: Dopamine and the enhanced renalresponse to aldosterone in the rat on a high potassium diet.C/in Exp Pharmacol Physiol 6:631-655, 1979

80. HIRST BH, REED JD, GOMEZ-PAN A, LABIB LA: Bromo-criptine potentiation of gastric acid secretion in cats. C/inEndocrinol 5:723—729, 1976

81. BENCSATH P, ASZTALOS B, SZALAY L, TAKACS L: Renalhandling of sodium after chronic renal sympathectorny inthe anesthetized rat. Am J Physiol 236(6):F5 l3—F518, 1979

82. PROSNITZ EH, DIBONA GF: Effect of decreased renal sym-pathetic nerve activity on renal tubular sodium reabsorp-tion. Am J Physiol 235(6):F557—F563, 1978

83. BESARAB A, SILVA P, LANDSBERG L, EPSTEIN FH: Effectof catecholamines on tubular function in the isolated per-fused rat kidney. Am J Physiol 233(l):F39-F45, 1977

84. ADAM WR: The effect of dopamine on pig kidney medullaryNa/K ATPase as measured by 3H ouabain binding (abst).Proc Aust Soc Med Res 10:36, 1977

85. CUCHE JL, MARCHAND GR, GREGER RF, LANG FC, KNOXFG: Phosphaturic effect of dopamine in dogs: Possible roleon intrarenally produced dopamine in phosphate regula-tion. J C/in Invest 58:71—76, 1976

86. JOHANNESEN J, LIE M, MATHISEN 0, Kiii F: Dopamine-induced dissociation between renal metabolic rate and so-dium reabsorption. Am J Physiol 230:1126—1131, 1976

87. NAKAJIMA T, NAITOH F, KURUMA I: Dopamine-sensitiveadenylate cyclase in the rat kidney particulate preparation.Eur J Pharmacol 41:163—169, 1977

88. RENNICK BR: Proximal tubular transport and renal metabo-lism of organic cations and catechol, in chapter 11, Meth-ods in Pharmacology, edited by MARTINEZ-MALDONADO

M, New York, Plenum, 1976, vol 4A, pp. 33589. JORGENSEN PL, SKOU JC: Purification and characterisation

of (Na + K)-ATPase: I. The influence of detergents onthe activity of (Na + K) ATPase in preparations from theouter medulla of rabbit kidney. Biochem Biophys Acta233:366—380, 1971

90. LOWRY OH, ROSEBROUGH NJ, FARR AL, RANDALL RJ:Protein measurement with the folin phenol reagent. J Bio/Chem 193:265—275, 1951

91. CREESE I, BURT DR, SNYDER SH: Dopamine receptorbinding: Differentiation of agonist and antagonist stateswith 3H dopamine and 3H haloperidol. Life Sci 17:993-

1002, 1976

92. THAL L, CREESE I, SNYDER SH: 3H-apomorphine inter-

actions with dopamine receptors in calf brain. Eur J Phar-maco! 49:295—299, 1978

93. Tois G, DENT R, GUYDA H: Opiates, prolactin, and the

dopamine receptor. J C/in Endocrinol Metab 47:200—203,1978

94. KEBABIAN JW, CALNE DB: Multiple receptors for dopa-mine. Nature 277:93-96, 1979

95. TREGEAR GW, COGHLAN JP: Enkephalin, endorphin andthe opiate receptor. Circ Res 46:1-142—1-148, 1980

96. MAGUIRE ME, VAN ARSDALE PM, GILMAN AG: An ago-

nist-specific effect of guanine nucleotides on binding to the/3 adrenergic receptor. Mo! Pharmaco/ 12:335—339, 1976

97. ZAI-INISER NR, MOLINOFF PB: Effect of guanine nude-otides on striatal dopamine receptors. Nature 275:453—455,

78. ALEXANDER RW, GILL JR, YAMABE H, LOVENBERG W, 1978

Aldosterone and dopamine receptors 635

98. CREESE I, USDIN T, SNYDER SH: Guanine nucleotides dis-tinguish between two dopamine receptors. Nature 278:577—

578, 1979

99. COSTA T, RODBARD D, PERT CB: Is the benzodiazepine re-ceptor coupled to a chloride ion channel? Nature 277:315—317, 1979

100. MCKENNA TJ, ISLAND DP, NicHoLsoN WE, LIDDLE GW:Dopamine inhibits angiotensin-stimulated aldosterone bio-synthesis in bovine adrenal cells. J C/in Invest 64:287—291,1979

101. CAREY RM, THORNER MO, ORrr EM: Effects of meto-clopramide and bromocriptine on the renin angiotensin al-dosterone system in man. J C/in Invest 63:727—735, 1979

102. FINLAY GD, WHITSETT TL, CUCINELL EA, GOLDBERG LI:Augmentation of sodium and potassium excretion, gb-merular filtration rate and renal plasma flow by levodopa. NEngi J Med 284:865—870, 1971

103. TJANDRAMAGA TB, ANTON AH, GOLDBERG LI: Prelim-inary investigation of levodopa as adjunctive therapy forhypertension, in Hypertension: Mechanism and Manage-

ment, edited by ONESTI G, KIM KE, MEYER JH, NewYork, Grune on Stratton, 1973, p. 421

104. WATANABE AM, CHASE TN, CARDEN PV: Effect of L-dopaalone and in combination with an extracerebral decarboxy-lase inhibition on blood pressure and some cardiovascularreflexes. C/in Pharmacol Ther 11:740—746, 1970

105. BELL C, CONWAY El, LANG WJ: Ergometrine and apomor-phine as selective antagonists of dopamine in the renal vas-culature. Br J Pharmacol 52:591—595, 1974

106. STUMPE KO, KOLLOCH R, HioucHi M, KRUCK F, VETTERH: Hyperprolactinaemia and antihypertensive effect ofbromocriptine in essential hypertension. Lancet 2: 211—214, 1977

107. BIRKHAUSER M, RIONDEL A, VALLOTON MB: Bromocrip-tine-induced modulation of plasma aldosterone response toacute stimulation, Acta Endocrinol 91:294—302, 1979

108. GAUNT R, CHART JT, RENZI A: Interaction of drugs withendocrines. Ann Rev Pharmacol 3:109-128, l%3

109. BROTZU G: Inhibition by chlorpromazine of the effects ofdopamine on the dog kidney. J Pharm Pharmacol 22:664-667, 1970