Insulin Inhibits Somatostatin-Like Immunoreactivity Release Stimulated by Intragastric HCI

To determine the effect of an increase in insulin levels within the range occuring under physiologic conditions on the protein- and acid-induced release of splanchnic somatostatin, insulin was infused in dogs for 1 h following the intragastric instillation of a neutral protein load (20% liver extract at pH 7), a weak stimulus of somatostatin-like immunoreactivity (SLI), and after an intragastric HCI, a strong stimulus of SLI release, instilled 30 min later. Insulin levels between 50 and 60 μU/ml significantly reduced the rise in peripheral venous SLI levels elicited by the acid load from a mean integrated incremental value of 1705 ±182 pg/ml in controls to 840 ± 312 in the insulininfused group (P < 0.05). Prevention of the insulininduced hypoglycemia and the secondary rise in glucagon, a known stimulus of pancreatic somatostatin secretion, by means of a concomitant infusion of glucose, did not modify the reduction in acid-induced increase in plasma SLI concentration associated with hyperinsulinemia. Insulin-glucose infusion significantly lowered the SLI in the pancreaticoduodenal vein, and in the gastroepiploic vein draining the antrum (P < 0.02; P < 0.05), but not in the short gastric veins draining the fundus of the stomach in response to the acid load. It is concluded that a physiologic elevation of insulin levels causes significantly reduced response of SLI to an intragastric acid load in dogs. This reduction is explained by a diminished increment of SLI in the venous effluent of the pancreas and the antrum.