Amylin (islet amyloid polypeptide) inhibition of insulin release in the perfused rat pancreas: implication of the adenylate cyclase/cAMP system.

Amylin inhibits glucose-induced insulin secretion in the rat pancreas. To study the mechanism by which amylin acts on the B-cell, we have investigated, in the perfused rat pancreas, the effect of synthetic rat amylin (75 pM) on insulin release elicited by secretagogues acting on the B-cell via the adenylate cyclase/cAMP system, i.e., glucagon (10 nM), gastric inhibitory polypeptide (GIP, 1 nM), forskolin (1 microM) and isobutylmethylxanthine (IBMX, 75 microM). In addition, we examined the effect of amylin on GIP-induced insulin release in pancreata from rats pretreated with pertussis toxin, an agent which inactivates certain Gi proteins coupled to adenylate cyclase. Amylin inhibited the insulin response to glucagon (approx. 70%), GIP (approx. 90%), IBMX (approx. 75%) as well as the early phase of forskolin-induced insulin output (approx. 74%). However, amylin failed to modify GIP-induced insulin release in pancreata obtained from pertussis toxin pretreated rats. These results would indicate that the inhibitory effect of amylin on insulin secretion could be, at least in part, attributed to its interfering with the adenylate cyclase/cAMP system. Furthermore, prevention of the inhibitory effect of amylin on GIP-induced insulin output by pertussis toxin pretreatment, supports the concept that amylin can inhibit insulin release via a pertussis toxin-sensitive Gi protein coupled to the adenylate cyclase system.