Glucagon release precedes insulin release in response to common secretagogues

The dynamics and interrelationships of glucagon and insulin secretion were studied in the isolated perfused rat pancreas by utilizing a series of compounds that stimulate the release of both hormone. Leucine, arginine, prostaglandins F2alpha and E2, bovine growth hormone, and isoproterenol were administered individually over 60-second intervals. The release of glucagon preceded that of insulin in response to all compounds tested. The rapidity of glucagon release varied in response to different secretagogues; the time course of insulin release was fairly constant. The timing and the magnitude of glucagon and insulin release did not correlate statistically.

(1) pancreatic alpha cells respond more rapidly than beta cells to the same stimulus; (2) antecedent release of glucagon is not the principal mediator of insulin release in response to stimuli common to both hormones; and (3) endogenous glucagon may at best modify the release of insulin evoked by certain secretagogues.