The influence of glucagon on hepatic glycogen mobilization in exercising rats

Summary The significance of glucagon for the alterations in carbohydrate and fat metabolism during swimming has been evaluated. Fed, male rats were used. Blood was drawn by cardiac puncture for glucose analysis and either rabbit-antiglucagonserum (A-rats) or normal rabbitserum (N-rats) injected. Twentynine rats were then forced to swim (S-rats) with a tail weight for 60 min, while 16 rats were resting controls (C-rats). Subsequently blood was drawn and samples of liver and muscle tissue collected. In SN-rats glucagon concentrations increased from 152±18 (S.E.) pg/ml (CN-rats) to 332±61 (P<0.05), while liver glycogen decreased (P<0.001) and blood glucose increased (P<0.05). In SA-rats, however, the changes in liver glycogen and blood glucose were halved indicating that increased glucagon secretion enhances hepatic glycogen depletion during prolonged exercise. NEFA rose in SA-rats (P<0.005) as well as in SN-rats (P<0.05). Glycerol concentrations, however, only increased in SA-rats (P<0.05) indicating a shift towards lipid combustion in antibody treated rats. Muscle glycogen and plasma insulin diminished and blood lactate increased uniformly in exercised rats.