The Effect of Somatostatin on Glucose Uptake and Production by Rat Tissues in Vitro

Somatostatin has recently been used as a tool to investigate the roles of insulin and glucagon in the regulation of glucose metabolism in vivo. The alterations in glucose uptake and production that somatostatin causes have been attributed to the modifications it induces in pancreatic hormone levels rather than to effects of the peptide per se, although the direct effects of the latter on glucose turnover have not been clearly assessed. The aim of the present study therefore was to determine whether or not somatostatin directly affects either the rate of glucose uptake by fat and muscle or the rate of glucose production by the liver. Glucose uptake by the perfused rat hindquarter (skeletal muscle) was unaltered by somatostatin (10-1,000 ng./ml.) whether or not the process was stimulated by insulin (250 μU./ml.). Basal and insulin-(5-40 / μU./ml.)-stimulated glucose oxidation (uptake) by isolated rat adipocytes was also unaffected by somatostatin (5-500 ng./ml.). In addition, the peptide had no effect on basal or glucagon-(10 −l0 –10 −9 M)-stimulated glucose output by isolated rat liver cells. Somatostatin also failed to modify the actions of these sub-maximally effective levels of glucagon on either the intracellular level of cAMP or the activity of cAMP-dependent protein kinase. The present studies support the hypothesis that the acute changes in the level and turnover of glucose induced by somatostatin are attributable to its effect on the endocrine system rather than to its direct effects on glucose metabolism.