DIRECT EFFECT OF INSULIN AND INSULIN-LIKE GROWTH FACTOR-I ON THE SECRETORY ACTIVITY OF RAT PANCREATIC BETA-CELLS

Purified pancreatic Beta cells were labelled with 3H-tyrosine before studying their secretory activity in perifusion. At 1.4 mmol/l glucose, the cells released similar fractions (0.01% per min) of their contents in preformed and in newly formed insulin. At 20 mmol/l glucose plus 10-8 mol/l glucagon, these fractional release rates increased by 16 and 40-fold respectively. The preferential release of newly synthesized as compared to stored insulin is attributable to a heterogeneity in individual cell responses. The secretory responsiveness to glucose plus glucagon was completely suppressed by 10-7 mol/l clonidine. Insulin induced a 20% reduction at 10-6 mol/l, but remained without effect at 10-7 mol/l. Insulin-like growth factor-I provoked a 30% decrease at 5.10-9 mol/l. It is concluded that the type-I insulin-like growth factor receptors on pancreatic Beta cells mediate a suppressive action on the insulin release process. Their high affinity for insulin-like growth factor-I allows physiologic levels of this peptide to participate in the regulation of insulin release. Their low affinity for insulin provides the basis for a minor feedback action by this hormone at concentrations exceeding the normal circulating levels. © 1990 Springer-Verlag.