blood flow to the avian kidney: the use of transit-time ultrasonic flow probes

JOURNAL OF EXPERIMENTAL ZOOLOGY 284:15–22 (1999)

© 1999 WILEY-LISS, INC.

Blood Flow to the Avian Kidney: The Use of Transit-Time Ultrasonic Flow Probes

J.R. ROBERTS,1* B.C. FORD,2 AND R.F. WIDEMAN, JR.31Department of Physiology, University of New England, Armidale, NSW2351, Australia

2Department of Poultry Science, The Pennsylvania State University,University Park, Pennsylvania 16802

3Department of Poultry Science, University of Arkansas, Fayetteville,Arkansas 72701

ABSTRACT A simplified model was used to assess blood flow to the kidney of the anaesthetiseddomestic fowl. The left kidney was intact and the right kidney consisted of the caudal divisionwith associated vasculature. Transonic perivascular flow probes were placed around the right proxi-mal ischiadic artery and renal vein. Snares around the caudal renal portal vein, common iliac veinand proximal ischiadic artery of the right kidney allowed manipulation of arterial and portalblood flow. Reduction of the pressure in the right renal artery to 50 mm Hg decreased right kidneyarterial plasma flow and glomerular filtration rate (GFR). The plasma flow in the right renal veinand the clearance of para-aminohippuric acid by the right kidney remained unchanged. The truefiltration fraction of the right kidney, determined from the ratio of GFR to the arterial flow in-creased slightly. Portal plasma flow and arterial plasma flow contributed 57% and 43%, respec-tively, to total renal plasma flow during normal arterial and portal flow. J. Exp. Zool. 284:15–22,1999. © 1999 Wiley-Liss, Inc.

The first studies which were undertaken to as-sess the patterns of blood flow in the renal portalsystem of the avian kidney involved the use ofradiographic techniques (Akester, ’64, ’67), theSperber technique (Shideman et al., ’81), ormicrospheres (Odlind, ’78). More direct studies ofthe blood flow to and from the avian kidney havebeen made possible by the development of the“simplified kidney model” by Wideman and co-workers (Wideman and Gregg, ’88; Gregg andWideman, ’90). The development of this model fol-lowed the observation that obstruction of the ure-ter either by kidney stones (Wideman et al., ’83)or by experimental occlusion (Wideman andLaverty, ’86) caused the kidney tissue “upstream”from the occlusion to degenerate. The major ves-sels to and from the kidney remained intact. As-sociated with the atrophy of the tissue upstreamfrom the point of ureteral obstruction was hyper-trophy of the downstream tissue as well as alldivisions of the contralateral kidney. If the occlu-sion is made at the junction between the medialand caudal divisions, the modified kidney (basi-cally the caudal division only) is supplied by asingle renal artery arising from the ischiadic ar-tery, around which flow probes and snares (forchanging the blood pressure in the artery) may

be placed. The renal vein draining the kidney andboth the caudal renal portal vein and the com-mon iliac vein (both part of the renal portal sys-tem) also become accessible to experimentalmanipulation. In the intact avian kidney, the pres-ence of the kidney tissue makes the placing of flowprobes around the renal portal vessels impossible.Hypertrophied kidneys were found to function likenormal kidneys except during a brisk osmotic di-uresis (Gregg and Wideman, ’90). In addition,Wideman and coworkers (Wideman et al., ’92a)found that in both male and female fowl with in-tact kidneys, glomerular size and volume distribu-tions for the cranial, medial, and caudal divisionsof the kidney were structurally homologous on aper gram kidney weight basis.

The simplified kidney model has been used todemonstrate autoregulation in the avian kidney(Wideman and Gregg, ’88; Wideman, ’91; Glahnet al., ’93; Wideman et al., ’93). However, these

Grant sponsors: University of New England and Pennsylvania StateUniversity.

*Correspondence to: Juliet R. Roberts, Department of Physiology,University of New England, Armidale, NSW 2351, Australia.

Received 26 August 1998; Accepted 14 September 1998.

16 J.R. ROBERTS ET AL.

studies did not measure blood flow in the renalvessels directly. Wideman, Glahn, and coworkers(Wideman et al., ’92b; Glahn et al., ’93) used ther-mal pulse decay (TPD) probes to measure localtissue perfusion.

In the present study, the use of Transonic tran-sit-time perivascular blood flow probes was as-sessed in a study of the perfusion of the aviankidney by the renal portal system. These probesare placed directly around the blood vessels of in-terest and, if correctly calibrated, provide a di-rect indicator of blood flow. In particular, the studyinvestigated the effect on renal function of eitherthe presence of the blood flow probes or of theprocedure involved in clearing along the vesselsprior to the placement of the flow probes. The aimof the study was to determine the suitability ofthe Transonic perivascular blood flow probes forstudies of avian renal function, including the con-struction of renal blood flow autoregulation curves.

MATERIALS AND METHODSInitial surgical preparation of

modified kidneysModified right kidneys were produced in roost-

ers as described by Wideman and Gregg (’88).Briefly, male 2- to 3-week-old single-comb WhiteLeghorn chicks were anaesthetized with DIAL (al-lobarbital (25 mg/ml) with urethane: 1.5 ml/kgbody weight). Local anaesthetic (Lignocaine) wasused at the surgical incision site. An approxi-mately 1-cm incision was made in the right flankof the bird, the right kidney was exposed, and theureter of the right kidney was severed at the levelof the ischiadic artery (at the junction betweenthe caudal and medial divisions of the kidney).The abdominal wound was closed with woundclips, furazolidone aerosol powder (VeterinaryProducts Industries, Phoenix, AZ) was applied,and the chicks were placed under a heat lamp for2–4 hr to recover from anaesthesia. The animalswere then returned to the animal care facility andallowed to reach adult size. Experiments were con-ducted when birds were 50–60 weeks of age.

Preparation of animals for renalfunction studies

A total of 15 roosters, 5 per experimental proto-col, was used. The body mass was not differentamong protocols at 2083 ± 68 g, 2301 ± 114 g, and2209 ± 71 g for protocols 1, 2, and 3, respectively.Birds were anaesthetized with DIAL (allobarbitalwith urethane: 3 ml/kg body weight) and cannu-

lae (Clay Adams: O.D. 1.5 mm, I.D. 1.0 mm) placedin the left cutaneous ulnar vein (for infusion ofrenal function markers, inulin and para-amino-hippuric [PAH]), one carotid artery (for collectionof blood samples) and the right ischiadic artery.The abdomen of the birds was opened and the can-nula in the right ischiadic artery was advancedto the level of the right caudal renal artery. Snareswere placed loosely around the proximal and dis-tal regions of the right ischiadic artery, the rightcaudal renal portal vein, and the right commoniliac vein (Fig. 1). The snare around the distal is-chiadic artery was tightened around the cannulato ensure that all blood flowing through the rightischiadic artery was going to the right kidney. Avascular clip was placed on the caudal renal por-tal vein adjacent to the interiliac anastomoses toprevent the exchange of portal blood between theright and left kidneys.

Transonic perivascular blood flow probes wereplaced around the proximal ischiadic artery (2Rprobe) and the renal vein (3R probe) and con-nected to a Transonics Model T201D blood flowmeter. The difference between the two flows wasassumed to represent renal portal flow. The bloodflow probes had been calibrated in vivo and invitro prior to the experiments. Blood pressure wasmonitored constantly in both the carotid and is-chiadic arteries. The pressure in the ischiadic ar-tery cannula was assumed to be the renal arterialperfusion pressure (RAPP) of the right renal ar-tery while the systemic blood pressure recordedfrom the carotid artery was taken as the RAPPfor the left kidney. The ureters were cannulatedaccording to the method of Wideman and Braun(’82) to allow the collection of urine from each kid-ney separately. The final surgical set-up is illus-trated in Figure 1. The proximal snare is shownon the ischiadic artery. The distal snare on theischiadic artery, positioned distal to the caudal re-nal artery, is not shown for the purpose of clarity.

Renal function studiesPrior to intravenous infusion, a 1.5-ml blood

sample was collected from the carotid artery toact as a “blank” for the measurements of renalfunction markers. A solution containing 2.5 gmannitol, 150 mg inulin, and 150 mg PAH per100 ml was infused into the cutaneous ulnar veinat a rate of 0.25 ml (min · kg)–1. At least 60 minwas allowed for the equilibration of the renalfunction markers within the birds. Urine sampleswere collected at 10-min intervals. For each stageof each protocol, three 10-min urine collections

BLOOD FLOW TO AVIAN KIDNEY 17

were made. Once a new set of conditions had beenestablished, a period of 10 min was allowed be-fore urine sampling commenced. Arterial bloodsamples, each of 1.5 ml, were collected from thecarotid cannula during the second of the tripli-cate urine samples. Urine samples were collectedin preweighed tubes and urine samples were al-

lowed to stand for 20 min after which sampleswere taken from the top of the tubes for measure-ment of osmolality. The remainder of the urinewas mixed thoroughly and an aliquot was mixedwith an equal volume of 0.5 M LiOH solution todissolve the urate precipitate. Diluted urines werefrozen for later analysis. Haematocrits were mea-

Fig. 1. Ventral view of kidneys of bird with modified rightkidney. Dashed lines outline functional kidney tissue. Solidbar represents vascular clamp. The positions of the snares

on the iliac vein, portal vein, and ischiadic artery, and perivas-cular blood flow probes on the proximal ischiadic artery andrenal vein are shown.


sured on arterial blood by filling duplicate haema-tocrit tubes and centrifuging at 13,000 RPM for 3min. The remainder of the blood samples was cen-trifuged at 13,000 RPM and plasma frozen forlater analysis. Plasma and urine samples wereanalyzed for inulin (Waugh, ’77), PAH (Brun, ’57),osmolality (Wescor 5100C vapour pressure os-mometer), and sodium and potassium (flame pho-tometry).

The experimental set-up allowed the compre-hensive testing of the flow probes as a means ofmeasuring blood flow to the avian kidney. Threeexperimental protocols were followed, as shownin Table 1, to measure renal function with andwithout the presence of the venous probe and dis-tal ischiadic artery snare. It was important to as-sess whether the presence of the probe itself, orthe process of clearing around the vessel for place-ment of the probe, had an effect on renal func-tion. Blood flow in the renal portal system wasmodified by tightening the snares around the por-tal vessels.

Calculations and statisticsThe plasma clearance of inulin was determined

by dividing the rate of excretion of inulin by theplasma concentration and was used as a measureof glomerular filtration rate (GFR). The plasmaclearance of PAH provided an indication of totalrenal plasma flow. Arterial and venous plasmaflow was determined from the flow probes aroundthe proximal ischiadic artery and the renal vein,respectively. Renal portal plasma flow was calcu-lated as the difference between the arterial andvenous flow. In this experiment it was possible,for the first time, to estimate the true filtrationfraction for the avian kidney. This was achievedby dividing the GFR by the arterial plasma flowto the right kidney. Excretion of ions was calcu-

lated as the product of the urine concentration ofthe ion- and the urine-flow rate. Fractional excre-tion of an ion was determined by dividing theplasma clearance of the ion by GFR. For many ofthe measurements, data are expressed per gram ofkidney tissue to allow for the differences in size ofthe modified right and contralateral left kidneys.

Data were analysed by two factor analysis ofvariance (ANOVA). Differences between meanswere assessed by Fisher’s Protected Least Signifi-cant Difference (PLSD) tests. All statistical analy-ses were conducted using the Statistical AnalysisSystem (SAS Institute Inc., Cary, NC).

RESULTSThe presence of the flow probe on the renal vein

had no significant effect on any of the renal func-tion parameters measured. The presence of thedistal snare on the ischiadic artery had no sig-nificant effect on renal function except that theblood flow through the proximal ischiadic arterywas significantly higher when the distal snare wasloose than when the snare was tightened aroundthe artery. Therefore, data from all three experi-mental protocols were pooled and the four differ-ent treatment groups compared. These treatmentgroups were ambient arterial and ambient portalflow (AA/AP), ambient arterial and restricted por-tal flow with snare tightened on the caudal renalportal vein (AA/RP), ambient arterial and forcedportal flow with the snare tightened on the com-mon iliac vein (AA/FP), and restricted arterial andambient portal flow with the snare on the proxi-mal ischiadic artery tightened to achieve a pres-sure of 50 mm Hg (RA/AP).

Haematocrit was not significantly differentamong experimental treatments (Table 2). Simi-larly, plasma osmolality and plasma sodium con-centration were not significantly affected by

TABLE 1. Protocols for testing use of perivascular flow probes1

Protocol 1: with (+) or without (–) renal vein flow probe (n = 5)

AA/AP AA/AP RA/AP AA/AP AA/RP AA/FP(–) (+) (+) (+) (+) (+)

Protocol 2: with (+) or without (–) renal vein flow probe (n = 5)

AA/AP AA/AP AA/AP AA/RP AA/FP AA/AP RA/AP AA/AP(+) (–) (+) (+) (+) (+) (+) (+)

Protocol 3: with (+) or without (–) distal ischiadic artery snare (n = 5)

AA/AP AA/RP AA/FP AA/AP AA/AP AA/RP AA/FP AA/AP(–) (–) (–) (–) (+) (+) (+) (+)

1AA/AP, ambient arterial and ambient portal flow; AA/RP, ambient arterial and restricted portal flow (snare tightened on caudal renal portalvein); AA/FP, ambient arterial and forced portal flow (snare tightened on common iliac vein); RA/AP, restricted arterial and ambient portalflow (snare on proximal ischiadic artery tightened to pressure of 50 mm Hg).


treatment. However, plasma potassium was high-est for restricted arterial and ambient portal flow.Blood pressure to the left and right kidneys re-mained constant for all treatment groups exceptthe RA/AP group (restricted arterial, ambient por-tal) (Table 3). For this group, blood pressure inthe right ischiadic artery was significantly reducedwhen the snare around the ischiadic artery wastightened.

Urine-flow rate per gram of kidney tissue tendedto be higher from the left kidney and was signifi-cantly reduced from the right kidney when arte-rial flow was restricted (Table 3). Glomerularfiltration rate (GFR), expressed per gram of kid-ney tissue, did not vary between treatments orkidneys except for the RA/AP group where there

was a significant reduction in GFR of the rightkidney when the snare was tightened on the rightischiadic artery (Table 3). The clearance of PAHper gram of kidney tissue was not significantlyaffected by experimental treatment and the rateof clearance of PAH was not different between leftand right kidneys for any treatment (Table 3). Ar-terial plasma flow (per gram of kidney tissue) tothe right kidney remained similar for all treat-ment groups with ambient arterial pressure andwas significantly reduced when the snare wastightened on the right ischiadic artery (RA/AP)(Table 3). In contrast, venous plasma flow to theright kidney remained relatively constant acrossall treatment groups (Table 3). Filtration fractionwas an average of 21% during ambient arterial flow

TABLE 2. Blood and plasma values during changes in arterial and portal flow to the right kidney1

Experimental treatmentAA/AP AA/RP AA/FP RA/AP

(ambient arterial/ (ambient arterial/ (ambient arterial/ (restricted arterial/Measurement ambient portal) restricted portal) forced portal) ambient portal) P value

Haematocrit (%) 32.685 ± 0.924 32.516 ± 1.007 32.031 ± 0.965 32.375 ± 1.203 NSPlasma osmolality 311.149 ± 2.674 312.469 ± 3.140 312.000 ± 3.511 308.700 ± 3.249 NS(mOsm·kg–1)Plasma sodium (mM) 134.221 ± 1.694 132.441 ± 1.883 133.909 ± 1.805 138.290 ± 1.589 NSPlasma potassium B3.726 ± 0.075 B3.794 ± 0.108 AB3.957 ± 0.099 A4.118 ± 0.121 0.0329(mM)1Within a measurement, across experimental treatments, values with different superscripts are significantly different from one another. Theabsence of superscripts across a row indicates that experimental treatment had no statistically significant effect on the variable measured.Means ± S.E.

TABLE 3. Renal function in response to changes in arterial and portal flow to the right kidney1


(ambient arterial/ (ambient arterial/ (ambient arterial/ (restricted arterial/Measurement Kidney ambient portal) restricted portal) forced portal) ambient portal) P value

Blood pressure Left A131.736 ± 3.338 A131.969 ± 2.935 A129.312 ± 4.253 A133.733 ± 5.195 <0.0001mmHg Right A129.821 ± 3.488 A129.917 ± 3.086 A127.167 ± 3.834 B51.867 ± 1.768Urine-flow rate Left AB0.021 ± 0.002 AB0.023 ± 0.002 AB0.024 ± 0.002 A0.026 ± 0.003 <0.0001mL·(min·kg·g)–1 Right B0.018 ± 0.001 B0.018 ± 0.002 B0.019 ± 0.002 C0.009 ± 0.001Glomerular filtration Left A0.157 ± 0.010 A0.152 ± 0.013 A0.154 ± 0.011 A0.157 ± 0.016 0.0042rate mL·(min·kg·g)–1 Right A0.155 ± 0.008 A0.158 ± 0.009 A0.158 ± 0.008 B0.092 ± 0.010Clearance of PAH Left 1.509 ± 0.126 1.394 ± 0.175 1.470 ± 0.161 1.582 ± 0.206 NSmL·(min·kg·g)–1 Right 1.425 ± 0.129 1.223 ± 0.113 1.430 ± 0.114 1.379 ± 0.204Arterial plasma flow Right A0.848 ± 0.087 A0.956 ± 0.111 A0.854 ± 0.091 B0.396 ± 0.060 <0.0001mL·(min·kg·g)–1

Venous plasma flow Right 1.807 ± 0.240 1.737 ± 0.290 2.018 ± 0.363 1.870 ± 0.333 NSmL·(min·kg·g)–1

Portal plasma flow Right 1.127 ± 0.203 0.913 ± 0.234 1.264 ± 0.277 1.474 ± 0.343 NSmL·(min·kg·g)–1

Filtration fraction Right 0.218 ± 0.020 0.201 ± 0.022 0.221 ± 0.024 0.312 ± 0.071 NSright kidney1Within a measurement, across experimental treatments, values with different superscripts are significantly different from one another.Means ± S.E.


and was not significantly different during restrictedarterial flow although filtration fraction tended toincrease (31%) (Table 3). Mean portal plasma flowwas lowest during restricted portal perfusion andhighest during forced portal perfusion and when ar-terial flow was restricted (Table 3).

Osmolar clearance per gram of kidney tissuewas the same for both kidneys in all treatmentgroups except RA/AP where osmolar clearancefrom the right kidney was significantly reducedwhen arterial flow was restricted (Table 4).Freewater clearance per gram of kidney tissue wasconsistently lower for the right kidney and wasreduced to a small negative value in the right kid-ney when the arterial snare was tightened (Table4). Sodium excretion per gram of kidney tissuewas similar for both kidneys during all experi-mental treatments except for the right kidney dur-ing restriction of arterial pressure (Table 4).Reduced arterial perfusion of the right kidney re-sulted in a marked reduction in sodium excretion.However, despite a general tendency for the frac-tional excretion of sodium to be lower in the rightkidney for all treatment groups, this trend wasnot statistically significant. Potassium excretionper gram of kidney tissue was similar for bothkidneys across all treatments (Table 4). The frac-tional excretion of potassium was not significantlydifferent between left and right kidneys, nor wasit affected by treatment.

DISCUSSIONIn the present study, renal function in the do-

mestic fowl was not significantly affected by thepresence of either the flow probe on the renal vein

or the tightening of the distal snare on the distalright ischiadic artery. Blood pressure remainedrelatively constant for both left and right kidneysof all experimental treatments except for the RA/AP group where the blood pressure was restrictedto approximately 50 mm Hg by tightening thesnare on the ischiadic artery. This reduction inrenal arterial perfusion pressure (RAPP) to theright kidney was accompanied by a reduction inarterial plasma flow of approximately 55%. In ad-dition, reduced RAPP in the right kidney was as-sociated with a reduction in urine-flow rate ofapproximately 50% and a 40% reduction in glom-erular filtration rate (GFR). These findings areconsistent with those of previous studies (Wide-man and Gregg, ’88; Vena et al., ’90;) which dem-onstrated that a significant decrease in GFRoccurred at RAPP below 60 mm Hg. Moreover,both the present study and all previous studies(Wideman and Gregg, ’88; Vena et al., ’90; Wide-man, ’91; Wideman et al., ’92b; Glahn et al., ’93)found that the plasma clearance of PAH was notsignificantly affected by reduced RAPP. Vena andcoworkers (’90) speculated that this finding wasthe result of either an increase in renal portal flowor an increase in the extraction efficiency of PAH(EPAH). A later study (Wideman, ’91) found thatEPAH was not affected by reduced RAPP.

The present study was able to measure, directly,venous plasma flow from the right kidney. Venousplasma flow was not significantly affected by anyexperimental treatment, including the reducedRAPP, and the same was true for portal plasmaflow. However, there were numerical trends to adecrease in venous and portal plasma flow when

TABLE 4. Renal function in response to changes in arterial and portal flow to the right kidney1


(ambient arterial/ (ambient arterial/ (ambient arterial/ (restricted arterial/Measurement Kidney ambient portal) restricted portal) forced portal) ambient portal) P value

Osmolar clearance Left A0.016 ± 0.001 A0.017 ± 0.001 A0.017 ± 0.001 A0.019 ± 0.002 0.0011mL·(min·kg·g)–1 Right A0.016 ± 0.001 A0.017 ± 0.001 A0.017 ± 0.001 B0.009 ± 0.001Free water clearance Left AB0.005 ± 0.001 A0.007 ± 0.001 A0.007 ± 0.002 A0.006 ± 0.002 0.0003mL·(min·kg·g)–1 Right B0.002 ± 0.001 B0.002 ± 0.001 B0.002 ± 0.001 B–0.000 ± 0.000Sodium excretion Left A0.640 ± 0.072 A0.654 ± 0.071 A0.685 ± 0.105 A0.789 ± 0.133 0.0019µmoles·(min·kg·g)–1 Right A0.597 ± 0.070 A0.548 ± 0.082 A0.559 ± 0.086 B0.150 ± 0.043Fractional excretion Left 0.036 ± 0.005 0.040 ± 0.008 0.039 ± 0.008 0.038 ± 0.006 NS

of sodium Right 0.031 ± 0.005 0.029 ± 0.005 0.028 ± 0.005 0.013 ± 0.004Potassium excretion Left 0.233 ± 0.019 0.241 ± 0.025 0.265 ± 0.022 0.307 ± 0.028 NSµmoles·(min·kg·g)–1 Right 0.259 ± 0.022 0.282 ± 0.034 0.306 ± 0.032 0.215 ± 0.041Fractional excretion Left 0.426 ± 0.036 0.449 ± 0.044 0.461 ± 0.036 0.503 ± 0.045 NS

of potassium Right 0.454 ± 0.035 0.472 ± 0.044 0.486 ± 0.035 0.576 ± 0.0751Within a measurement, across experimental treatments, values with different superscripts are significantly different from one another.Means ± S.E.


the snare was tightened on the caudal renal por-tal vein and an increase in venous and portalplasma flow when the snare was tightened on thecommon iliac vein. To our knowledge, the presentstudy is the first to measure the relative contri-butions of renal portal and renal arterial plasmaflow to total renal plasma flow. Portal plasma flowand arterial plasma flow represented 57% and43%, respectively, of total renal plasma flow dur-ing ambient portal and ambient arterial flow. Pre-vious studies have utilised either radiographictechniques (Akester, ’64, ’67), standard renal clear-ance technique and the Sperber preparation(Shideman et al., ’81), microspheres (Odlind, ’78)or the thermal pulse decay (TPD) system (Wide-man et al., ’92b; Glahn et al., ’93). However, noneof these approaches has provided an accurate as-sessment of arterial versus renal portal flow. Theresults of the present study indicate that the rela-tive contributions of these two sources of bloodflow to the kidney may vary.

For the first time in an avian species, it waspossible to directly measure the arterial plasmaflow to the right kidney and to calculate the truefiltration fraction from the ratio of the arterialplasma flow to the GFR calculated from the clear-ance of infused inulin. Filtration fraction was 22%during ambient arterial and ambient portal flow(AA/AP) and remained relatively constant whenportal flow was either forced or restricted. Therewas no statistically significant effect on the truefiltration fraction of reduced RAPP although themean filtration fraction increased during the RA/AP treatment.

Wideman and coworkers (Wideman ’91; Wide-man et al., ’92b) investigated the effect of re-stricted renal portal flow on the renal response toreduced RAPP. These researchers found that GFRwas not affected by restricted portal flow but thatCPAH and renal plasma flow (calculated from CPAHand EPAH) were lower during reduced RAPP whenthe portal blood flow was restricted (Wideman ’91;Wideman et al., ’92b). In one of these studies(Wideman et al., ’92b), a thermal pulse decay(TPD) system was used to study blood flow in thekidney. This system involves the use of thermistorprobes that were inserted at different locationsin the kidney. The position of the probes was foundto influence the results obtained for renal bloodflow in response to different treatments (Widemanet al., ’92b).

Glahn and coworkers (’93) conducted furtherstudies using the TPD system. These authors re-ported positive correlations between CPAH, renal

plasma flow and renal blood flow as measuredfrom the CPAH and EPAH, and renal blood flow mea-sured using the TPD system. Glahn et al. (’93)used different combinations of ambient arterialflow (AA) or restricted arterial flow (RA) with am-bient portal (AP), forced portal (FP: achieved bytightening the snare on the common iliac vein) orrestricted portal flow (RP: snare tightened on thecaudal renal portal vein). In the present study,FP and RP treatments had no significant effecton arterial, venous, or portal plasma flow (PPF).However, the mean values for PPF and CPAH de-creased when portal flow was restricted (AA/RP)and increased during forced portal perfusion (AA/FP). Glahn et al. (’93) found that renal blood flow,as measured by the TPD system (RBFTPD), wassignificantly reduced during restricted portal flowbut not significantly higher for forced portal flowin comparison to ambient portal flow.

The mechanism by which renal blood flow ismaintained relatively constant under a range ofperfusion pressures is not fully understood.Wideman and colleagues (’92b) suggested that por-tal inflow and outflow via the ischiadic vein andvertebral sinuses may compensate for changes inperitubular sinusoid pressure during the experi-mental procedures of tightening the snares on thecaudal renal portal vein (restricted portal flow),the common iliac vein (forced portal flow), or proxi-mal ischiadic artery (restricted arterial flow). Thissuggested possibility is not easily tested becauseof the inaccessible location of the ischiadic veinand vertebral sinuses.

The use of the TPD system in two previous stud-ies (Wideman et al., ’92b; Glahn et al., ’93) indi-cated that the TPD system provides a reasonablyreliable measure of renal blood flow provided thatthe TPD probes are placed appropriately. The useof the Transonic perivascular flow probes removesmuch of this uncertainty as the perivascularprobes are placed directly around the major bloodvessels. However, care must be exercised in clear-ing along blood vessels and in placement of theflow probes to avoid deformation of blood vessels,particularly the veins. The technique of laserdoppler velocimetry, which has been used success-fully to measure blood flow to the skin (Vissing etal., ’94) and gastric mucosa (Gronbech and Lacy,’95) was judged to be less appropriate for thepresent study, owing to the location of the bloodvessels under investigation.

In conclusion, the results of the present studyindicate that the presence of the perivascular flowprobes and snares does not change the renal func-


tion parameters being measured. The presentstudy confirmed earlier findings that renal plasmaflow remains constant at renal arterial perfusionpressures (RAPP) of 50 mm Hg (below the GFRautoregulatory range). Also confirmed by thisstudy is that restricted RAPP to the right kidneyresulted in reductions in GFR, urine-flow rate andsodium excretion. For the first time, it was pos-sible to measure true filtration fraction in theavian kidney. It was also possible to assess in adirect way the relative contributions of arterialand renal portal flow to avian renal plasma flow.The use of Transonic perivascular blood flowprobes allows a direct assessment of patterns ofblood flow to the avian kidney.

ACKNOWLEDGMENTThis study was published as Arkansas Agricul-

tural Experiment Station manuscript number97018 with the approval of the Experiment Sta-tion Director.

LITERATURE CITEDAkester AR. 1964. Radiographic studies of the renal portal

system in the domestic fowl (Gallus domesticus). J Anat98:365–376.

Akester AR. 1967. Renal portal shunts in the kidney of do-mestic fowl. J Anat 101:569–594.

Brun C. 1957. A rapid method for the determination of para-aminohippuric acid in kidney function tests. J Lab Clin Med37:955–958.

Glahn RP, Bottje WG, Maynard P, Wideman RF Jr. 1993. Re-sponse of the avian kidney to acute changes in arterial per-fusion pressure and portal blood supply. Am J Physiol264(Regulatory Integrative Comp Physiol 33):R428–R434.

Gregg CM, Wideman RF Jr. 1990. Morphological and func-tional comparisons of normal and hypertrophied kidneys ofadult domestic fowl (Gallus gallus). Am J Physiol 258(Re-nal Fluid Electrolyte Physiol 27):F403–F413.

Gronbech JE, Lacy ER. 1995. Role of gastric blood flow in

impaired defence and repair of aged rat stomachs. Am JPhysiol 269(Gastrointest Liver Physiol 32):G737–G744.

Odlind B. 1978. Blood flow distribution in the renal portalsystem of the intact hen: a study of a venous system usingmicrospheres. Acta Physiol Scand 102:342–356.

Shideman JR, Evans RL, Bierer DW, Quebbemann AJ. 1981.Renal venous portal contribution to PAH and uric acid clear-ance in the chicken. Am J Physiol 240:F46–F53.

Vena VE, Lac TH, Wideman RF, Jr. 1990. Dietary sodium,glomerular rate autoregulation, and glomerular size distri-bution profiles in domestic fowl (Gallus gallus). J CompPhysiol 160:7–16.

Vissing SF, Scherrer U, Victor RG. 1994. Increase of sympa-thetic discharge to skeletal muscle but not to skin duringmild lower body negative pressure in humans. J Physiol481:233–241.

Waugh WW. 1977. Photometry of inulin and polyfructosanby use of a cysteine/tryptophan reaction. Clin Chem23:639–645.

Wideman RF Jr. 1991. Autoregulation of avian renal plasmaflow: contribution of the renal portal system. J Comp PhysiolB 160:663–669.

Wideman RF, Braun EJ. 1982. Ureteral urine collection fromanaesthetised domestic fowl. Lab Anim Sci 32:298–301.

Wideman RF, Gregg CM. 1988. Model for evaluating avianhemodynamics and glomerular filtration rate autoregula-tion. Am J Physiol 254(Regulatory Integrative CompPhysiol. 23):R925–R932.

Wideman RF Jr, Laverty G. 1986. Kidney function in domes-tic fowl with chronic occlusion of the ureter and caudal re-nal vein. Poult Sci 65:2148–2155.

Wideman RF, Holt L, Pla JS. 1992a. Glomerular size andvolume distributions for cranial, medial and caudal divi-sions of domestic fowl kidneys. Anat Rec 232:512–519.

Wideman RF Jr, Glahn RP, Bottje WG, Holmes KR. 1992b.Use of a thermal pulse decay system to assess avian renalblood flow autoregulation. Am J Physiol 262(Renal Integra-tive Comparative Physiol 31):R90–R98.

Wideman RF Jr, Mallinson ET, Rothenbacher H. 1983. Kid-ney function of pullets and laying hens during outbreaks ofurolithiasis. Poult Sci 62:1954–1970.

Wideman RF Jr, Nishimura H, Bottje WG, Glahn RP. 1993.Reduced renal arterial perfusion pressure stimulates reninrelease from domestic fowl kidneys. Gen Comp Endocrinol89:405–414.

blood flow to the avian kidney: the use of transit-time ultrasonic flow probes

Documents