Effects of short-term and prolonged infusions of somatostatin on endocrine pancreas, body weight and food intake in rats.

Infusion of cyclic somatostatin (700 mg/kg/min) for 4 h in rat fed and libitum suppressed basal insulin but not glucagon release. It was accompanied by hypoglycemia during the first hour whereas, at the end of the infusion, hyperglycemia was present. The same dose of somatostatin applied 60 min prior to and during a 30 min load of glucose or arginine significantly inhibited their effects on insulin and glucagon release. In contrast, when this dose of somatostatin was given during a 24 h period by the i.v. route it did not inhibit glucose induced insulin release though circulating somatostatin levels were constantly and markedly elevated. Furthermore, in rats continuously infused with somatostatin for 4 days, no effect was found either on plasma concentrations of glucose, insulin, glucagon, growth hormone and cyclic AMP, or on body weight gain, food consumption or water intake. The pancreases of these animals showed normal concentrations of insulin and glucagon and a normal nuclear area of D-cells. Our experiments demonstrate that, in short-term experiments in rats, somatostatin influences insulin and glucagon release as well as glucose homeostasis. Furthermore, they suggest that during prolonged i.v. administration of somatostatin, rats develop mechanisms counteracting the effect of the peptide, e.g., peripheral tachyphylaxis.