the effect of glucagon splanchnic balances of glucose ... · ezrin, salter, ogryzlo,andbest...

Journal of Clinical InvestigationVol. 43, No. 5, 1964

The Effect of Glucagon on Net Splanchnic Balances ofGlucose, Amino Acid Nitrogen, Urea, Ketones,

and Oxygen in Man *ROBERTF. KIBLER,t W. JAPE TAYLOR,: ANDJACK D. MYERS

(From the Departments of Medicine, University of Pittsburgh School of Medicine, Pittsburgh,Pa., and Duke University School of Medicine, Durham, N. C.)

The demonstration by Unger, Eisentraut, Mc-Call, and Madison (1) that glucagon is present inthe pancreatic vein of dogs and that its concentra-tion varies in response to changes in blood sugarsuggests that glucagon is a hormone with a sig-nificant role in blood glucose regulation.

The intravenous administration of glucagcncharacteristically produces a sharp rise in the sys-temic blood sugar. For some time the liver hasbeen known to play a primary role in the mediationof this effect (2, 3). More recently, Shoemaker,Van Itallie, and Walker (4, 5) demonstrated amarked increase in hepatic glucose output in dogsafter the administration of glucagon. Similarstudies have not been made in man, since directsampling from the portal vein is not feasible inhuman subjects. The enhanced glucose outputfrom the liver induced by glucagon is presumablydue to an augmentation of hepatic glycogenolysis.An increased glycogenolysis in liver slices exposedto glucagon has been observed in vitro (6). Inthe intact dog, Cahill, Zottu, and Earle (7) foundthat a 4-hour infusion of glucagon severely de-pleted the trichloroacetic acid-soluble glycogencontent of the liver. The demonstration bySutherland and Cori (8) that glucagon activatesliver phosphorylase elucidates the mechanism ofthis effect.

A number of studies have shown that glucagonalso increases gluconeogenesis (9-16). Kalant(9) observed in fasted rats that after the initial

* Submitted for publication August 19, 1963; acceptedJanuary 2, 1964.

Presented in part at the meeting of the Southern So-ciety for Clinical Investigation, Atlanta, Ga., January 19,1952.

tPresently at the Emory University School of Medi-cine, Atlanta, Ga.

4Presently at the University of Florida School ofMedicine, Gainesville, Fla.

depletion of hepatic glycogen from a single in-jection of glucagon, the incorporation of C14-labeled glycine into glycogen was enhanced. Withrepeated injections of glucagon, less C14 went intoglycogen, and increased amounts of labeled CO2appeared, suggesting an increased rate of oxida-tion. Kalant suggested that these findings can beinterpreted either as a mass action effect resultingfrom the accelerated glycogenolysis or as a pri-mary effect of glucagon on intermediary metabo-lism at some point other than at the level of thephosphorylase enzyme. The latter alternative issupported by the work of Best and associates andIzzo and Glasser, who found in both the rat (10,15, 16) and in man (13, 14) a gluconeogenic ef-fect of glucagon that appeared to be independentof the effect on glycogen metabolism.

Reports of the effect of glucagon on ketone me-tabolism and peripheral glucose uptake have beenconflicting. Ketonemia in animals and ketoneproduction by rat liver slices have been reported tobe depressed (17), enhanced (18-20), and un-changed (21, 22). Similar discrepancies havebeen reported in man. Bondy and Cardillo (23)found no change in arterial blood ketone levelsin man during a 2-hour infusion of glucagon.Ezrin, Salter, Ogryzlo, and Best (13), on the otherhand, found ketosis in six patients receiving long-term iv glucagon therapy, an effect seemingly in-dependent of the level of blood sugar and occur-ring before the appearance of glycosuria. In fact,one patient developed ketosis without a rise inblood sugar. Salter, Ezrin, Laidlaw, and Gornall(24) reported similar results in human subjectson long-term glucagon administration. Drury,Wick, and Sherrill (25) found that glucagon de-creased the uptake of a constant infusion of glu-cose in the eviscerated and nephrectomized rab-bit. Van Itallie, Morgan, and Dotti (26) and

904

tFFECT OF GLUCAGONON SPLANCHNICMETABOLISMIN MAN

Bondy and Cardillo (23), on the other hand, havereported that the arteriovenous glucose differencesacross the arm in human subjects during glucagonadministration were similar to the differences en-countered with a comparable degree of hypergly-cemia induced by glucose administration. Similarstudies by Elrick, Hlad, and Witten (27) haveshown an enhancement of peripheral glucose up-take by glucagon.

Further delineation of the physiologic andmetabolic effects of glucagon is, therefore, ap-parently desirable. In our study, the effects of asingle injection and a continuous infusion of glu-cagon on net splanchnic glucose production in manwere determined. In man, net splanchnic glu-cose production closely approximates true hepaticglucose production in the fasting state (28).Concurrently, hepatic blood flow, Bromsulphaleinclearance, and splanchnic oxygen consumptionwere measured. In some subjects splanchnic bal-ances of urea, amino acids, and ketones were de-termined, and in others the arteriovenous glucosedifferences across the leg and brain were measured.

Methods

The glucagon used in these studies came from threedifferent lots of crude amorphous material, Lilly lotnumbers 208-158B-288, 11049, and 208-158B-197.1 Eachlot had been cysteine-treated to destroy insulin, and themanufacturer's assay of lot 208-158B-197 showed ap-proximately 50% glucagon. The relative potency of thelots was determined by comparing the effect of a givendose on blood glucose or net splanchnic glucose produc-tion (NSGP), utilizing the patients reported in thisstudy, as well as other human subjects, for this purpose.We found, for example, that 5 mg of lot 208-158B-197produces the same rise in blood glucose or NSGPas 3mg of lot 208-158B-288. Similarly, 10 mg of lot 208-158B-197 produces changes in these parameters equiva-lent to 6 mg of lot 208-158B-288. Therefore, we ex-pressed all dose levels in terms of the amount of lot no.208-158B-288 producing an equivalent response. Sincethe same subjects were not used for many of these com-parative studies, however, dose levels must be consideredrough approximations only.

The subjects of these experiments were adult pa-tients without metabolic or hepatic disorders. Theywere adequately nourished and had been eating well ofthe routine hospital diet. They were fasted 6 to 14hours before study, and in some instances 90 mg pheno-barbital was given orally 1 hour before the experiment.

1 Eli Lilly, Indianapolis, Ind.

Catheterization of the hepatic vein was accomplished un-der fluoroscopic guidance, and a Cournand-type needlewas inserted into the femoral artery. After a stabiliza-tion period of 10 to 15 minutes, paired, simultaneousblood samples were collected at 5- to 10-minute intervalsfrom the femoral artery and hepatic vein. Glucose,Bromsulphalein (BSP), oxygen, and, in certain instances,amino acid nitrogen, urea, and ketones were determined.A weighed amount of glucagon, dissolved in 2 ml ofphysiological saline and acidified with acetic acid, wasthen either administered as a single, rapid iv injectionor further diluted in normal saline and infused througha calibrated Murphy drip at a constant rate for 1 to 2hours. The injection or infusion was accomplished with-out further distress to the patient by utilizing a Cour-nand-type needle that had been inserted in the ante-cubital vein during the initial part of the study. Bloodsamples were again collected for the appropriate deter-minations at 5- to 10-minute intervals after t'.e singleinjection of glucagon or during the constant infusion ofglucagon.

In five subjects a Cournand-type needle was also in-serted into the femoral vein of the opposite leg. Sampleswere drawn from the two leg needles as simultaneouslyas possible 2 every 10 minutes during a constant 1-hourinfusion of glucagon. In four other subjects blood sam-ples were obtained from the femoral artery and jugularbulb. In these latter subjects the hepatic vein was notcatheterized.

Hepatic blood flow (HBF), by the technique of he-patic venous catheterization and the BSP method (28, 29),was determined in six subjects before and after ad-mipistration of glucagon. The results obtained in thesesubjects (Table I) showed that glucagon has no effecton HBF or splanchnic oxygen consumption. There-fore, in the remaining subjects HBF was determinedonly during the control period. Hepatic arteriovenous(a-v) oxygen differences, however, were measured inboth the control and experimental periods. Since HBFand hepatic a-v oxygen differences have a reciprocal re-lationship when splanchnic oxygen consumption is con-stant, that these differences did not change significantly(Table III) supports the assumption that HBF wasstable throughout in these subjects. Net splanchnic bal-ances of oxygen, glucose, urea, amino acid nitrogen, andketones were estimated from the product of their re-spective hepatic venous-arterial (hv-a) difference andthe HBF.

Blood oxygen was determined by the spectrophotometricmethod of Hickam and Frayser (30), blood glucose bythe method of Somogyi as modified by Nelson (31),blood urea by the colorimetric method described byArchibald (32), blood amino acid nitrogen by the colori-metric method of Frame, Russell, and Wilhelmi (33),and blood ketones by the method of Werk and associates(34).

2 Blood was withdrawn from the arterial needle firstand immediately thereafter from the venous needle.

905

ROBERTF. KIBLER, W. JAPE TAYLOR, AND JACK D. MYERS

TABLE I

The effect of a single rapid iv injection of glucagon on splanchnic circulation in six subjects,with comparative data for epinephrine

Splanchnic oxygenHepatic blood flow consumption Splanchnic glucose production

Glucagon* Epinephrinet Glucagon Epinephrine Glucagon Epinephrine

mi/min/m2 mi/min/m2 mg/min/m2Control 753434t 820±t80 34±2.9 40±6 48±5.1 51±7After 723±-47 1,345 ± 136 35±-3.0 65 ±8 175±-9.9 150±i19%Change -0.5 +64§ +3 +60§ +260§ +194§

* Six patients: 3 received 3 mg and 3 received 6 mg.t Ten patients: 0.05 ml of a 1: 1,000 dilution intramuscularly.t Standard errors.§p <0.01.

Results

Figure 1 shows the effect of a single iv injectionof glucagon on the arterial and hepatic venousblood glucose levels. In six subjects (group A),3 mg of glucagon produced a mean maximal risein arterial blood glucose of 21 mg per 100 ml, 10minutes after injection; in six other control sub-jects (group B), 6 mg gave a mean maximal riseof 36 mg per 100 ml at 15 minutes. The eleva-tion of hepatic venous blood glucose in each group

was even more marked and resulted in a strikingincrease in the hv-a glucose differences (Figure1, shaded area). In group A the mean, controlhv-a difference of 6 + 1 3 mg per 100 ml rose at

21 minutes to a mean, maximal value of 23 + 1mg per 100 ml. Comparable values in group Bwere 7 ± 1 and 28 ± 4 mg per 100 ml at 5 min-utes. The p values for these changes were lessthan 0.01. Since glucagon did not alter HBF(Table I; see also Methods), these increases inhv-a glucose difference indicate fourfold increases

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FIG. 2. NET SPLANCHNIC GLUCOSE PRODUCTION AFTER

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EFFECT OF GLUCAGONON SPLANCHNICMETABOLISMIN MAN

TABLE II

The effect of a single rapid iv injection of glucagon on arterial blood glucose, hepaticvenous-arterial glucose differences, and splanchnic glucose production

Change in arterial Hepatic venous-arterial Splanchnic glucoseblood glucose glucose difference production

Time Group A* Group Bt Group A Group B Group A Group B

min mg/100 ml mg/100 ml mg/min/m20 (78)t (89) 6±0.6 7±1.1 48±5.1 5246.8

After glucagon2.5 +8±1§ 23±11 175±10115 +20±1 +24±2 23±11 28±411 160±lljf 217±1411

10 +21±2 +35±2 6±2 21±4311 39±16 1614191115 +15±2 +36±3 5±42 10±42 32±14 82±1720 +11±2 +30±4 3±1 4±2 20±7 30±13

* Group A: six patients, 3 mg glucagon each.t Group B: six patients, 6 mgglucagon each.I Figures in parentheses represent absolute values for the fasting blood glucose.§ Standard errors.II P <0.01.

in NSGPat 2j and 5 minutes, respectively. Fig-ure 2 illustrates the individual and mean re-sponses of the NSGPfor both groups of controlsubjects. After 5 minutes the NSGPfell rapidlyin all patients and reached control levels or belowin the next 5 to 15 minutes. The reduction inNSGPbelow control levels in some subjects mayhave resulted from the suppression of NSGPby the persistence of hyperglycemia (28) at atime when the glycogenolytic effect of glucagonhad subsided.

The total, mean increases in NSGP after asingle injection of glucagon can be calculated

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FIG. 3. INCREASES IN ARTERIAL AND HEPATIC VENOUS

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Shaded areas represent hv-a glucose differences.

from the areas beneath the mean curves of Figure2. These increments are 700 and 1,400 mg glu-cose per square meter of body surface for groupsA and B, respectively. These seem adequate toaccount for the accompanying 21 and 36 mg per100 ml maximal, mean elevation in arterial bloodglucose. It is also apparent that the relativemagnitude of these total increases in NSGPisdirectly related to the difference in the two dosesof glucagon. The mean data of Figures 1 and 2are presented in Table II.

The effects of a continuous infusion of glu-cagon in six patients are shown in Figures 3through 6. No mean data for this group have

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been calculated because of the wide range of doseused. Figures 3 and 5 are comparable to Figure1. They show that a brisk rise in arterial bloodglucose is accompanied by an even sharper eleva-tion of the hepatic venous blood glucose, so thatthe hv-a glucose differences increase significantly.The curves for NSGPin Figures 4 and 6 havebeen calculated from the product of these hv-aglucose differences and the control HBF (seeMethods). In all subjects the major incrementin NSGPoccurred during the first 10 minutes ofthe infusion. With one exception, the NSGPthen gradually fell to control or slightly belowcontrol levels; in three subjects there was asubsequent modest rise. In subject M.D. (Fig-ulre 6) the NSGPremained elevated throughout

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FIG. 7. INCREASE IN ARTERIAL GLUCOSECONCENTRATIONDURING A 3N-HOUR IV INFUSION OF GLUCAGONIN A CON-TROL SUBJECT.

the entire 110-minute period of infusion. Arterialhyperglycemia was reasonably well maintained inall subjects during the infusion. Figure 7 showsthat a fairly constant hyperglycemia can be main-tained by an infusion of glucagon for as long as3A hours. The individual data for Figures 3through 6 are presented in Table III.

Tables IV through VI demonstrate the effectof glucagon on blood amino acid nitrogen (TableIV), urea (Table V), and ketones (Table VI).Each table includes data for both a single injectionand a continuous 1-hour infusion of glucagon.Arterial levels and hv-a differences only are re-corded; for the sake of brevity, splanchnic bal-ances are not included. Data have already been

TABLE IV

The effect of glucagon on the arterial concentration andarterial-hepatic venous difference of amino acid nitrogen

Arterial-hepatic venousArterial blood amino amino acid nitrogen

acid nitrogen difference

Time R.B.* E.S. C.W. K.S. R.B. E.S. C.W. K.S.

min mg/100 ml mg/100 ml

-20 4.3 4.9 4.6 4.9 0.3 0.4 0.1 0.4-15 4.2 4.8 4.6 4.9 0.2 0.5 0.1 0.4-10 4.3 4.7 4.4 4.8 0.2 0.3 0.2 0.4- 5 4.4 5.0 4.6 4.9 0.3 0.4 0.2 0.4

After glucagon5 4.6 4.6 4.1 0.7 0.7 0.7

10 4.5t 4.3 0.6 0.515 4.3 4.8f 4.4t 5.0 0.3 0.7 0.6 0.720 4.1 4.4 4.4 0.1 0.5 0.630 4.2 4.7 5.0 0.2 0.9 0.845 4.9t 0.560 4.7 0.3

FIG. 6. NET SPLANCHNIC GLUCOSEPRODUCTIONDURING

THE IV INFUSION OF GLUCAGONIN THE SUBJECTS OF * Single injection of glucagon: R.B., 3 mg; E.S., 3 mg; C.W., 6 mg;K.S., 7 mgglucagon per hour.

FIGURE 5. t Time of maximal arterial blood glucose rise.

909

ROBERTF. KIBLER, W. JAPE TAYLOR, AND JACK D. MYERS

TABLE V

The effect of glucagon on arterial urea concentrations and hepatic venous-arterial urea differences

Arterial blood urea Hepatic venous-arterial urea difference

Time M.W.* A.L. J.R. R.J. V.J. J.R. L.B. M.W. A.L. J.R. R.J. V.J. J.R. L.B.

min mg/100 ml mg/100 ml

-20 14.4 25.0 48.1 27.2 11.6 0.7 1.3 0.5 1.0 0.5-15 14.4 25.0 25.8 48.6 11.7 1.1 1.1 0.4 0.3 0.7-10 14.4 25.0 48.6 16.6 26.8 0.8 1.3 0.5 1.1 1.0- 5 14.6 24.9 25.6 16.9 1.1 1.3 0.6 0.8

After glucagon5 14.2 24.9 25.4 26.3 11.6 0.8 0.8 0.8 0.7 0.6

10 24.0 25.2 46.9 16.2 24.9 1.3 0.5 0.0 0.7 0.915 t 24.9 26.7t 2.3 1.620 14.4 25.0t 26.7 46.6 16.4 11.5t 0.3 0.2 -0.1 0.3 0.7 0.930 14.8 26.9 46.1 16.4 0.4 0.2 0.3 1.245 45.6t 24.0t 11.2 0.4 0.5 0.660 45.9 t 22.5 11.4 1.1 0.9 1.0

* Single injection of glucagon: M.W., 6 mg; A.L., 6 mg; J.R., 6 mg. Glucagon per hour: R.J., 7 mg; V.J., 11 mg;J.R., 3 mg; L.B., 7 mg.

t Time of maximal arterial blood glucose rise.

presented indicating that HBF did not change, so

that the hv-a differences may be considered to re-

flect directly any change in the splanchnic balancesof these substances. It is apparent from TableIV that glucagon had no significant effect on ar-

terial blood amino acid nitrogen levels. Therewas, however, an approximate twofold increase inthe normal, small hepatic a-v differences in thefour subjects during the first 15 to 30 minutes af-ter glucagon, so that splanchnic amino acid nitro-gen uptake was also doubled, i.e., an increase froman average control value of 2.2 mg per minute per

m2 to a value of 4.5 mg per minute per m2 after

glucagon. There was no corresponding increasein either the arterial level or hv-a differences ofurea (Table V). Table VI shows that glucagondid not significantly alter either the arterial levelor the hv-a differences of blood ketones. Most ofthe minor changes observed are within the range

of error for the method.Figures 8 and 9 and Table VII present data

relevant to the effect of glucagon on glucose up-

take. A single, rapid injection of 10 mg of glu-cagon had little effect on the cerebral, a-v glucosedifferences of four control subjects (Figure 8).The only significant change was an increased a-v

TABLE VI

The effect of glucagon on arterial ketone concentrations and hepatic venous-arterial ketone differences

Arterial blood ketones Hepatic venous-arterial ketone difference

Time C.W.* R.B. E.S. K.S. L.B. C.W. R.B. E.S. K.S. L.B.

min mg/10O ml mg/100 ml

-20 0.8 2.6 0.7 1.9 1.2 0.1 1.0 0.1 0.7 0.4-15 0.7 2.4 0.6 1.9 1.2 0.2 1.0 0.2 0.8 0.3-10 0.8 2.7 0.6 2.1 1.0 0.2 0.6 0.2 0.4 0.5- 5 0.8 2.3 0.6 1.8 1.1 0.1 1.0 0.0 0.6 0.5

After glucagon5 0.7 1.6 0.4 1.4 0.1 0.9 0.4 0.4

10 0.6 1.6t 0.4 1.2 0.2 1.1 0.3 0.615 0.8t 1.8 0.6t 1.7 0.0 1.0 0.0 0.320 0.7 2.0 0.5 1.0t 0.2 0.2 0.2 0.430 0.8 0.5 1.5 0.0 0.245 1.4t 0.8 0.2 0.160 1.1 0.4

* Single injection of glucagon: C.W., 6 mg; R.B., 3 mg; E.S., 3 mg. Glucagon per hour: K.S., 7 mg; L.B., 7 mg.t Time of maximal arterial blood glucose rise.

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circulation time throuththe organ will cause thevenous concentration to lag behind the arterial.Under these circumstances a falsely high a-v dif-ference will be recorded. The value of 8 mg per100 ml for the mean, control cerebral a-v glucose

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1-HOUR, IV INFUSION OF GLUCAGONON THE FEMORALA-V

GLUCOSEDIFFERENCESOF FIVE SUBJECTS. The values abovethe bars represent standard errors.

difference compares favorably with the value of10 mg per 100 ml reported by Scheinberg andStead (35). The mean, cerebral, a-v oxygen dif-ference was 8.33 vol per 100 ml during the con-

trol period and 8.57 vol per 100 ml after glucagon.Since there was no apparent anxiety in these pa-

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oxygen differences suggest that cerebral blood flowand, hence, cerebral glucose uptake were not af-fected by glucagon.

TABLE VIIThe effect of glucagon on cerebral and femoral arteriovenous glucose differences

4 control subjects, 5 control subjects10 mg glucagon 2 mg glucagon

(single injection) (per hour)

Change in arterial Cerebral a-v Change in arterial Femoral a-vTime blood glucose glucose difference blood glucose glucose difference

min mg/1OG ml mg/1OG ml mg/1OG ml mg/1OG ml-20 (88) 4±1-10 (103)* 8±1 0 4±1- 5 0 8±lt N

0 0 8±1 0 4±1

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10 +30 13±6 + 4 4±115 +26 9±120 +18 10±1 + 7 4±230 +16 7±1 +11 5±245 +10 4±4160 +10 3±2

* Figures in parentheses represent absolute values for the fasting blood glucose.t Standard errors.Ip <0.02, >0.01.

I

911


As shown in Figure 9, an infusion of 2 mg ofglucagon per hour had no significant effect on thea-v glucose differences across the leg in five con-trol subjects. Again, the only change occurredat a time when the arterial blood glucose was ris-ing rapidly. The small dose of glucagon was givendeliberately to produce a degree of hyperglycemiathat would not stimulate the release of insulin bythe pancreas. The mean, fasting a-v glucose dif-ference of 4 mg per 100 ml agrees closely withthe value of 3.4 mg per 100 ml obtained by Belland Burns (36) by a more accurate method ofglucose determination. Although no attempt wasmade to estimate blood flow through the leg inthe present studies, Bondy and Cardillo (23)have observed in two control subjects that glu-cagon does not affect blood flow through anextremity.

Discussion

In these studies glucagon produced a rapid andstriking increase in NSGPin man. Since HBFdid not change, the augmented glucose productionwas due to the increase in hv-a blood glucose dif-ferences alone. It is unlikely that a decrease inglucose uptake by the extrahepatic tissues of thesplanchnic bed contributed significantly to theincrease in these differences in the absence of ademonstrable effect of glucagon on peripheralglucose uptake. The assumption appears justified,therefore, that the changes noted in "net splanch-nic glucose production" were in fact changes inhepatic glucose production. Nevertheless, theterm "net splanchnic glucose production" ratherthan "hepatic glucose production" is used through-out this report.

Within the dose range used in these studies, thetotal increase in NSGPwas proportional to thedose of glucagon administered. Calculations basedupon the data provided in Figure 2 (see Results)indicate that doubling the amount of glucagonfrom 3 to 6 mg resulted in a doubling of the totalincrease in NSGPfrom 700 to 1,400 mg of glu-cose per M2, respectively. The arterial blood glu-cose response also reflected differences in the doseof glucagon, but these changes were not so directlyproportional to dose as were the changes inNSGP. This is not surprising since arterial bloodglucose is influenced by peripheral glucose diffu-sion and utilization as well as by hepatic glucose

production. Despite these considerations andthe fact that our dose levels were only rough ap-proximations, it is difficult to understand whyLoube, Campbell, and Mirsky (37), Helmer andRoot (38), and Carson and Koch (39) found nodifference in the hyperglycemic response to gradeddoses of glucagon in either animals or humansubjects.

The continuous infusion of glucagon produced aprolonged increase in NSGP. In all subjects theincrement in NSGP persisted for 30 minutes,even when the administered dose was quite low.The largest dose of glucagon, 15 mg per hour,resulted in a threefold increase in NSGP for 2hours in one of two subjects who received thisamount. This high level of NSGP continueddespite the fact that the arterial blood glucose con-centration remained elevated throughout the infu-sion period. Hyperglycemia of the degree attainedhere, when produced by an infusion of glucose, issufficient to abolish the normal hepatic glucoseproduction (28). Clearly, the continuing actionof glucagon was sufficient to counter this opposingeffect of hyperglycemia on NSGP. Figure 5shows that a fairly constant level of hyperglyce-mia may be maintained for as long as 3j hoursduring glucagon infusion. These results contrastto the substantial drop in blood glucose noted byVan Itallie and associates (26) during the last30 minutes of a 1-hour infusion of glucagon intwo subjects.

In contrast to epinephrine, which also enhancesNSGPin man, glucagon had no significant effecton HBF or splanchnic oxygen consumption (Ta-ble I). In dogs, however, Shoemaker and his as-sociates (4, 5) have found that glucagon doublesthe HBF during the first 30 minutes after injec-tion. Similar findings in dogs are reported byLandau, Leonards, and Barry (40). Since themethod of estimating HBF and the observationperiods were the same in the animal and in thepresent human experiments, this discrepancy maxrepresent a species difference.

Although glucagon had no significant effect onsplanchnic balances of urea or oxygen, the dou-bling of the normally small, fasting splanchnicamino acid nitrogen uptake suggests some stimula-tion of gluconeogenesis. It is not known whatcontribution the extrahepatic tissues of thesplanchnic bed may have made to the changes

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noted in a-hv amino acid nitrogen differences.That these changes were probably hepatic in ori-gin is suggested by the work of Shoemaker andVan Itallie (5), who sampled the portal and he-patic veins directly in dogs and found a fourfoldincrease in amino acid nitrogen uptake within 45minutes after a single injection of glucagon. Inour study the magnitude of the amino acid ni-trogen uptake after glucagon was still of a loworder of magnitude, and that gluconeogenesis con-tributed significantly to the large amounts of glu-cose released by the liver during this time seemsunlikely. Wepresume, therefore, that glycogen-olysis was largely responsible for the increasedglucose output from the liver. The small magni-tude of the change in amino acid nitrogen uptakewithout significant alterations in splanchnic bal-ances of urea or oxygen suggests that the changesobserved were merely secondary to the effect ofglucagon on glycogenolysis. There is considerableevidence, however, from studies on the long-termeffects of glucagon in favor of a direct action ofglucagon on protein catabolism. Salter, Davidson,and Best (10) demonstrated that intact, fastingrats injected with 400 jug of glucagon every 8hours excreted 40% more urinary nitrogen thancontrol animals, although the rats showed no hy-perglycemia or glycosuria. Izzo and Glasser ( 15 ),comparing the effects of glucagon and epinephrineadministered to fasted rats over a 5-day period,found that although both cause a similar depletionof liver glycogen, only glucagon brings about an in-crease in protein catabolism. In a further study,Glasser and Izzo (16) found a gluconeogenic ef-fect of glucagon in the adrenalectomized fastedrat similar to that in the intact, fasted rat without,however, an effect on liver glycogen. Duringprolonged iv glucagon therapy in patients withrheumatoid arthritis, Ezrin and colleagues (13)had one patient who showed a negative nitrogenbalance with normal blood sugar concentrations.Izzo (14) gave repeated im injections of glucagon( 1 to 2 mg every 8 hours) for 3 to 9 days to well-regulated diabetic patients and found not onlyhyperglycemia and glycosuria but also an increasein urinary nitrogen. Comparable or greater de-grees of hyperglycemia and glycosuria seen in twosuch patients while off insulin were accompaniedby less nitrogen excretion than that seen with glu-cagon. In one patient, simultaneous administra-

tion of carbutamide virtually abolished the hyper-glycemic-glycosuric response to glucagon but hadno effect on the increased nitrogen excretion in-duced by glucagon.

Neither the blood ketone levels nor the ketoneoutput by the liver was altered by glucagon underthe conditions of the present experiments; all thesubjects were well-nourished and had low fastingblood ketone levels and small hv-a ketone differ-ences. Our results are contrary to the long-termstudies in which ketosis has been observed in theabsence or independent of hyperglycemia and gly-cosuria (13, 24).

That glucose differences across the leg andbrain did not change significantly except duringthe period of a rapidly rising arterial blood glu-cose level suggests that glucagon does not affectperipheral glucose uptake. The advantages ofusing the leg rather than the forearm for makingthese observations on glucose utilization in thelimbs have been discussed elsewhere (28). How-ever, since our studies were not controlled by ob-servations during a comparable degree of hyper-glycemia with infused glucose and since leg andcerebral blood flow were not measured, the dataon a-v glucose differences serve only to excludegross changes. As noted previously, Bondy andCardillo (23) observed no effect of glucagon onextremity blood flow in two subjects. Hennemanand Shoemaker (41), on the other hand, foundthat glucagon decreases blood flow in the hind limbof the unanesthetized dog. Despite this decreasein blood flow, glucose uptake was enhanced. Butfrom further observations in fasted dogs, theseauthors concluded that this effect of glucagon onperipheral glucose uptake is secondary to thechanges in blood glucose. As already discussed,the dose of glucagon used in the present study ofa-v glucose differences across the leg was rela-tively small in order to minimize the effect of arise in blood sugar per se in bringing about changesin peripheral glucose uptake. Conceivably, largerdoses of glucagon may have a direct effect onperipheral glucose uptake.

Thus, in the present acute experiments in man,glucagon brought about marked increases in NSGPwithout significant changes in other metabolic andcirculatory parameters except for a small increasein net splanchnic amino acid nitrogen uptake. Inthe light of these findings, the impressive changes

913


in protein and ketone metabolism reported in theliterature with long-term glucagon administrationmay well be phenomena secondary to the exhaus-tion of liver glycogen rather than primary effectsof glucagon. This interpretation is at variance,however, with the changes, noted above, in pro-tein and ketone metabolism in the absence or in-dependent of changes in glucose metabolism.Our studies have no direct bearing on recent re-ports that glucagon affects the plasma levels ofnonesterified fatty acids (42, 43), total lipids(44, 45), and cholesterol (46). Dreiling and as-sociates (43) consider the changes in plasma non-esterified fatty acids to be independent of thehepatic glycogenolytic effect of glucagon, since thechanges were noted in patients with liver diseasein whom the hyperglycemic response to glucagonwas reduced or absent. A word of caution isjustified, however, in the interpretation of thisand other studies that are based on blood glucosevalues alone and propose to show an effect of glu-cagon in the absence of an effect on carbohydratemetabolism. As previously indicated, the changein blood sugar is probably a less sensitive index ofthe glycogenolytic action of glucagon than is thechange in NSGP.

Summary

Glucagon by intravenous injection or infusionproduced a rapid and marked increase in netsplanchnic glucose production in the normal fast-ing human subject. The magnitude of this re-sponse seems adequate to account for the degreeof hyperglycemia observed. Responses to gradeddoses of glucagon are better compared on thebasis of total increases in net splanchnic glucoseproduction than on increases in blood glucoseconcentrations alone.

Glucagon had no effect on hepatic blood flow,splanchnic oxygen consumption, or Bromsulphaleinclearance. In this respect, it differs from epi-nephrine.

Glucagon had no appreciable effect on splanch-nic balances of urea or oxygen. It caused adoubling of the normally small, amino acid nitro-gen uptake by the liver, but the magnitude of thiseffect does not seem sufficient to account for themarked changes in net splanchnic glucose produc-tion. Presumably, therefore, glycogenolysis was

largely responsible for the increased glucose out-put from the liver.

Glucagon had no effect on splanchnic ketoneoutput.

Glucagon did not significantly alter the arterio-venous glucose differences across the leg or brain.We conclude, therefore, that glucagon does notmodify peripheral glucose uptake under the con-ditions of these experiments.

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the effect of glucagon splanchnic balances of glucose ... · ezrin, salter, ogryzlo,andbest...

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