Sympathetic control of hepatic glycogenolysis during glucopenia in man

Abstract

Liver glycogen stores may be mobilized during hypoglycemia by release of adrenomedullary catecholamines, by release of norepinephrine from sympathetic nerve endings and by release of glucagon. To clarify the nature of peripheral sympathetic control of hepatic glycogenolysis during glucopenia in man, 2-deoxy-d-glucose (2 DG), a competitive inhibitor of glucose metabolism, was infused intravenously (50 mg/kg) to nine normal volunteers and four adrenalectomized patients for 20 min. In normal volunteers, the initial elevation of free fatty acids (FFA) and growth hormone (HGH) correspond with the rise in total catecholamines, with maximal levels attained at 60 min; lactate and cortisol rose at a slower rate, no change in IRI was noted. Plasma glucose levels were 148% of preinfusion values by 120 min and remained elevated. In adrenalectomized subjects, despite no change in plasma FFA, lactate, catecholamines and glucagon, glucose rose 20% by 150 min; the growth hormone and insulin responses were similar to normals. A significant increase in glucose response from 60 min onward was found in the 2 DG infusion studies when compared to cortisone administration, alone. Thus, during glucopenia, plasma glucose rose in spite of unchanged adrenomedullary catecholamine and glucagon levels. The findings indicate that the sympathetic neurotransmitter, norepinephrine, contributes to counterregulatory events during 2 DG-induced glucopenia presumably via its release from hepatic sympathetic nerve endings.