Effects of Pregnancy on Insulin and Glucagon Secretion by Perifused Rat Pancreatic Islets*

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Abstract
Pancreatic islet insulin and glucagon secretion was studied in 18-20 day pregnant rats (P) and age-matched virgin female animals (C). Pancreata were removed after overnight fasts. One hundred islets from P and C groups were isolated by a collagenase method, placed in 2 chambers, and perfused simultaneously at 37.degree. C with buffered albumin at 0.9 ml/min. A 30 min basal period preceded a 50 min continuous substrate challenge. Glucose (16.7 mM) elicited an acute and 2nd phase insulin secretion from P islets that significantly exceeded C values. Glucagon secretion was abruptly suppressed in both groups and was significantly lower in P islets at the 40 min interval. A 6 mM mixture of 20 amino acids (AA) stimulated biphasic insulin and glucagon secretion in both groups but differences were not significant. AA + 5.5 mM glucose stimuli resulted in higher insulin and lower glucagon secretion in P islets during the 2nd phase. AA + 16.7 mM glucose suppressed acute phase glucagon release significantly below that achieved by AA alone and to the same extent in both groups despite higher acute and 2nd phase insulin secretion in P animals. Insulin/glucagon molar secretory ratios were similar in P and C rats with AA challenges alone. With 16.7 mM glucose alone or glucose + AA, ratios were higher in P animals at several time intervals. In late rat gestation islet insulin secretion is excessive and predominates over secretion of glucagon when nutrient stimuli contain glucose or glucose + AA. Bihormonal islet secretion in response to AA alone is not altered appreciably by pregnancy under these experimental conditions.

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