Insulin Release from Collagenase-lsolated Islets of Rat Pancreas in the Presence of Cyclic AMP and Somatostatin

Abstract

In order to study the role of cyclic AMP in the inhibition by somatostatin of glucose-induced insulin release, the effect of somatostatin on the potentiation by dibutyryl-cyclic AMP (db-cAMP) of insulin release from isolated pancreatic islets of rats was examined. Isolated islets were obtained from the rat pancreas by the collagenase method. Ten islets were incubated for periods of 30 min in Krebs-Ringer bicarbonate buffer containing albumin and glucose 2.0 mg/ml in the presence or absence of somatostatin (1 µg/ml or 100 ng/ml) and/or db-cAMP 1 mM. Glucose-induced insulin release was reduced by somatostatin in concentrations of 1 µg/ ml. Somatostatin in a concentration of 100 ng/ml significantly abolished the potentiation by db-cAMP of insulin release (p <0.01), in spite of exerting no inhibition of glucose-induced insulin release. However, in the presence of theophylline 5 mM, somatostatin 100 ng/ml did not show that inhibitory effect on the potentiated insulin release. These results strongly suggest that cAMP plays an important role in the inhibiting mechanism of insulin release by somatostatin. 2 Supported by Deutsche Forschungsgemeinschaft, Bad Godesberg.