Insulin within islets is a physiologic glucagon release inhibitor.

To determine if glucagon secretion is under physiological control of intra-islet insulin, pan- creata from normal rats were perfused at a 100 mg/dl glucose concentration with either guinea pig antiinsulin serum or normal guinea pig serum in a nonrecirculating system. Perfusion of antiserum was followed within 3 min by a significant rise in glucagon that reached peak levels three times the base-line values and assumed a hectic pattern that returned rapidly to base-line levels upon termination of the antiserum perfusion. Nonim- mune guinea pig serum had no effect.