A quantitative study of glucagon-induced hepatic glycogenolysis

¹ Departments of Biochemistry, Medicine and Surgery, School of Medicine, Western Reserve University, Cleveland, Ohio

Hepatic vein, portal vein and arterial plasma glucose concentrations, plasma galactose and glucose radioactivity, and hepatic blood flow were measured in dogs following the infusion of galactose-C¹⁴ and subsequent glucagon administration. Galactose uptake by the liver was rapid and associated with the release of glucose-C¹⁴. Following the glucagon injection there was an immediate release of labeled glucose into the hepatic vein; the peak radioactivity occurring prior to the maximum release of hepatic glucose. With small doses of glucagon small quantities of glucose and radioactivity were released into the circulation. With larger doses of glucagon less radioactivity relative to the quantity of glucose was released. These findings are interpreted to be a consequence of the incorporation of C¹⁴ predominantly in the outer tiers of glycogen. The observation of a nearly constant glucose specific activity following insulin administration is discussed as a possible expression of the release of these labeled outer tiers.