Effect of glucose on adenosine 3', 5'-monophosphate levels in rat pancreatic islets

Time course of the changes in insulin release and cyclic AMP levels in isolated rat islets incubated in media containing 5 or 16.7 mM of glucose were followed. The higher glucose concentration caused a slight but significant increase of cyclic AMP levels after 10 min incubation, but not 5 min incubation, whereas the stimulation of insulin release by 16.7 mM of glucose was apparent in both incubation times. Theophylline increased cyclic AMP levels markedly but did not stimulate insulin release when the glucose concentration was 5 mM. A slight augmentation by theophylline of insulin release was observed in the incubation medium containing 16.7 mM glucose. All these findings suggest that the elevation of cyclic AMP in islets may not play a role for the initiation of the insulin release induced by glucose, though it may act to modulate the glucose effect.