Studies Involving Administration of Exogenous Hormone during Suppression of Endogenous Hormone Secretion with Somatostatin

A B S T R A CT To study the individual effects of glucagon and growth hormone on human carbohydrate and lipid metabolism, endogenous secretion of both hormones was simultaneously suppressed with somatostatin and physiologic circulating levels of one or the other hormone were reproduced by exogenous infusion. The interaction of these hormones with insulin was evaluated by performing these studies in juvenile-onset, insulin-deficient diabetic subjects both during infusion of insulin and after its withdrawal. Infusion of glucagon (1 ng/kg min) during suppression of its endogenous secretion with somatostatin produced circulating hormone levels of approximately 200 pg/ml. When glucagon was infused along with insulin, plasma glucose levels rose from 94±8 to 126±+12 mg/100 ml over 1 h (P <0.01); growth hormone, P-hydroxybutyrate, alanine, FFA, and glycerol levels did not change. When insulin was withdrawn, plasma glucose, fi-hydroxybutyrate, FFA, and glycerol all rose to higher levels (P < 0.01) than those observed under similar conditions when somatostatin alone had been infused to suppress glucagon secretion. Thus, under appropriate conditions, physiologic levels of glucagon can stimulate lipolysis and cause hyperketonemia and hyperglycemia in man; insulin antagonizes the lipolytic and ketogenic effects of glucagon more effectively than the hyperglycemic effect. Infusion of growth hormone (1 Ag/kg . h) during suppression of its endogenous secretion with somatostatin