Effects of somatostatin on liver glycogen and fat metabolism in vivo.

Effect of somatostatin on liver glycogen metabolism and lipid metabolism were studied in rats in vivo. Somatostatin infused at a rate of 100 ng/min/100 g wt. into the femoral vein resulted in a marked decrease in the blood glucose concentration. The content of glycogen in the liver and the concentration of insulin in the portal vein were also decreased during somatostatin infusion. Glucose was infused at a constant rate of 1.25 mg/min/100 g wt. in combination with somatostatin to prevent the somatostatin-induced hypoglycemia. Under this condition, significant increase in liver glycogen was observed without significant changes in the blood glucose level. The liver glycogen synthase activity did not change significantly during infusion of somatostatin and/or glucose. In contrast, the glycogen phosphorylase activity was markedly inhibited by infusion of somatostatin plus glucose. Liver glycogen phosphorylase was inversely correlated with the blood glucose level. However, there was no correlation between the phosphorylase activity and blood glucose concentration during somatostatin infusion. Infusion of somatostatin alone caused an increase in the blood free fatty acid and a marked decrease in the blood ketone bodies. Glucose-induced decrease in the blood free fatty acids and ketone bodies were partially overcome by the simultaneous infusion of somatostatin. On the basis of these findings, possible physiological roles of somatostatin in regulation of carbohydrate metabolism were discussed.