Effects of supranormal liver glycogen content on hyperglucagonemia-induced liver glycogen breakdown

The purpose of the present study was to test the hypothesis that a higher hepatic glycogen level is associated with higher glucagon-induced hepatic glycogen depletion. Four groups of anesthetized rats received three injections (at times 0, 30, and 60 min) of glucagon (intravenously, 20?μg/kg). Among these groups, hepatic glycogen levels had previously been manipulated either by an overloading diet (Fast-refed), a reduction in food intake (1/2-fast), or exercise (75?min of running, 26?m/min, 0% grade). A fourth group had normal hepatic glycogen levels. A fifth group of rats was injected only with saline (0.9% NaCl). Liver glycogen concentrations were measured every 30?min during the course of the 90-min experiment, using liver samples obtained from the open liver biopsy technique. Plasma glucagon concentrations were significantly higher (P?P?P?P?