Glucagon Secretion From the Perfused Rat Pancreas Following Acute and Chronic Streptozotocin Gordon C. Weir, Robert F. Atkins, and Donald B. Martin

O N T R O V E R S Y over the mechanism of the anomalous glucagon secretion of diabetes as a p r i m a r y or secondary alpha cell defect 1 p r o m p t e d studies in the perfused rat pancreas which support the concept that local insulin secretion within the islet exerts an important suppressive effect, 2 and demonstrates enhanced glucagon secretion following acute treatment with streptozotocin. Pagliara et al. performed a similar study but used rats with chronic streptozotocin and alloxan diabetes, and found reduced glucagon secretion. 3 The present study is an effort to clarify the differences between our studies in acutely diabetic rats and those in the chronically diabetic rats of Pagliara et al.

C

METHODS

Fasted male Sprague-Dawley rats (Charles River Breeding Laboratories) weighing 220-300 g were given intracardiac streptozotocin (Upjohn) at a dose of 75 m g / k g . F o u r to 6 wk later perfused pancreas studies were performed on these chronically treated rats (plasma glucose 502 4- 33 mg/dl). In the acute streptozotocin group 75 m g / k g o f the drug was administered intravenously l hr prior to perfusion, 2 using previously described technics. 4 Antisera 30K or 02K were used. Cumulative secretion was estimated by planimetry} RESU LTS

Baseline glucagon secretion (Fig. 1) is enhanced in the acutely treated group and diminished in the chronic groups as c o m p a r e d with controls. When both sets of baseline data are combined, with the zero and 4 min values averaged, 2 nondiabetic baseline glucagon secretion averaged 158 • 19 p g / m l (n = 35), that of the acute diabetic group 326 4- 37 p g / m l (n = 20), and that of the chronic group 54 4- 3 p g / m l (n = 11). Both streptozotocin groups differed from the control (p < 0.001). Glucagon secretion in the three groups in response to arginine and epinephrine is also shown in Fig. 1. Response to arginine is increased in the acutely diabetic group, but is decreased in the chronically diabetic group. With epinephrine infusion, the response of the acute group was indistinguishable from the control, but the response in the chronic group was reduced. Cumulative secretion during arginine perfusion was 49.8 4- 4.4 ng (n = 12) in the control group, 92.7 ~= 10.4 ng (n = 6, p < 0 . 0 0 5 ) i n the acutely diabetic group, and 22.6 + 2.0 ng (n = 6,p < 0.001) in the chronically diabetic group. The cumulaFrom the Diabetes Unit and the Department of Medicine, Massachusetts General Hospital and Harvard Medical School, Boston, Mass. Supported by the Juvenile Diabetes Foundation and by NIH Grant .4 M 18230. Reprint requests should be addressed to Gordon C. Weir, M.D., Diabetes Unit, Massachusetts General Hospital, Boston, Mass. 02114. 9 1976 by Grune & Stratton, Inc.

Metabolism, Vol. 25, No. 11, Suppl. 1 (November), 1976

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WEIR, ATKINS, A N D MARTIN

I ARGININE (lOmM)

5000 -

9 - Control o - Acute 9 - Chronic

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EPINEPHRINE (2.7 x 10"7M) D J

2000

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1_ 0

1A J - " " " ~=-

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ig Minutes

i

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;

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Fig. 1. Baseline and stimulated glucagon secretion from perfused pancreases of control rats and rats treated both acutely and chronically with streptozetecin. Perfusate glucose concentration throughout w a s 80 m g / d l .

tive secretion during epinephrine experiments was 33.4 • 4.1 ng (n = 13), 31.7 • 5.3 ng (n = 8), and 10.5 4- 2.6 ng (n = 5, p < 0.001) in the control, acutely, and chronically diabetic groups, respectively. DISCUSSION

T h e data from the present study indicate that the acutely streptozotocindiabetic perfused rat pancreas exhibits enhanced basal and arginine-stimulated glucagon secretion; whereas in the chronically diabetic pancreas secretion is diminished in the basal, arginine- and epinephrine-stimulated states. Even though the present study differs in some respects from the study of Pagliara et al., 3 we agree that reduction of glucagon secretion may be seen in the chronically diabetic model. Yet in chronically diabetic rats pancreatic glucagon content is normal and plasma glucagon levels are elevated? Perhaps sornatostatin, which we have shown is elevated in the islets of streptozotocin diabetic rats, 5 contributes to the diminished glucagon secretion. The increased plasma levels may also result from decreased renal clearance of glucagon in the severely diabetic state. 6 We have proposed that diminished local endogenous insulin secretion caused by acute streptozotocin administration accounts for the enhanced glucagon response to arginine; however, because endogenous insulin secretion is inhibited in both the nondiabetic and in acutely diabetkz pancreas by epinephrine, enhanced glucagon secretion does not occur in theSe groups. REFERENCES 1. Unger RH: Diabetes and the alpha cell. Diabetes 25:136-151, 1976

2. Weir G C , K n o w l t o n SD, Atkins RF, McKennan KX, Martin DB: Glucagon secre-

ACUTE AND CHRONIC SI"REPTOZOTOCIN

tion from the perfused pancreas of streptozotocin-treated rats. Diabetes 25:275-282, 1976 3. Pagliara AS, Stillings SN, Haymond MW, Hover BA, Matschinsky FM: Insulin and glucose as modulators of the amino acid-induced glucagon release in the isolated ~ancreas of alloxan and streptozotocin diabetic rats. J Clin Invest 55:244-255, 1975 4. Weir GC, Knowlton SD, Martin DB: Glucagon secretion from the perfused rat

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pancreas: Studies with glucose and catecholamines. J Clin Invest 54:1403-1412, 1974 5. Patel YC, Weir GC: Increased somatostatin content of islets from streptozotocindiabetic rats. Clin Endocrinol 5:191-194, 1976 6. Lefebvre PJ, Luyckx AS, Nizet AH: Renal handling of endogenous glucagon in the dog: comparison with insulin. Metab Clin Exp 23: 753-761, 1974