Effect of Corticosterone on Carbamylcholine-, Leucine-, or Calcium-Induced Insulin Secretion by the Isolated Perfused Rat Pancreas*

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Abstract
Using the isolated pancreas of male Sprague-Dawley rats, 3 different concentrations of glucose were tested in the perfusion medium: 4.0, 6.7, and 9.4 mM. The insulinotropic effects of several potent secretagogues were examined with and without a 10-7-M corticosterone-21-acetate (CS) background. When the perfusion medium contained 4.0 mM glucose, there was no insulin secretion in the basal state, but 10-6 M carbamylcholine chloride, 5 mM L-Leu, and 5 mM calcium chloride elicited moderate but sharp responses of insulin output. When the secretagogues were superimposed on CS infusion, their stimulatory effects were abolished. When the perfusion medium contained 6.7 mM glucose, a steady insulin secretion was observed. A 4- to 5-fold stimulation of insulin release was elicited by carbamylcholine, Leu and Ca. With CS in the perfusate, the secretagogues were ineffective. However, at a higher glucose level (9.4 mM), the stimulants could partially escape the inhibitory effects of CS. CS may play a role in the regulation of insulin output by directly modulating the activities of some potent secretagogues.