Effects of glucose, exogenous insulin, and carbachol on C-peptide and insulin secretion from isolated perifused rat islets

Abstract

Isolated perifused rat islets were stimulated with glucose, exogenous insulin, or carbachol. C-peptide and, where possible, insulin secretory rates were measured. Glucose (8-10 mM) induced dose-dependent and kinetically similar patterns of C-peptide and insulin secretion. The addition of 100 nM bovine insulin had no effect on C-peptide release in response to 8-10 mM glucose stimulation. The addition of 100 nM bovine insulin or 500 nM human insulin together with 3 mM glucose had no stimulatory effect on C-peptide secretion rates from perifused rat islets. Stimulation with carbachol plus 7 mM glucose enhanced both C-peptide and insulin secretion, and the further addition of 100 nM bovine insulin had no inhibitory effect on C-peptide secretory rates under this condition. Perifusion studies using pharmacologic inhibitors (genistein and wortmannin) of the kinases thought to be involved in insulin signaling potentiated 10 mM glucose-induced secretion. The results support the following conclusions. 1) C-peptide release rates accurately reflect insulin secretion rates from collagen. ase-isolated, perifused rat islets. 2) Exogenously added bovine insulin exerts no inhibitory effect on release to several agonists including glucose. 3) In the presence of 3 mM glucose, exogenously added bovine or human insulin do not stimulate endogenous insulin secretion.