Age-related differences in the effect of glucagon on metabolism in rat liver.

The authors found differences in the metabolic response of 10- and 120-day-old rats to glucagon. In 10-day-old young, the administration of glucagon was followed in 5 min by an abrupt small increase in the blood sugar level, which continued to rise and attained the maximum 2 hours after the injection of glucagon. In adult rats there was an abrupt large increase in the blood sugar level in the first minutes after administering glucagon; after that the blood sugar level fell, but remained significantly higher than in the controls. In a series of experiments on the isolated perfused liver, no differences were found in glucose and protein release from the liver into the perfusion medium, but the protein concentration in the liver of the younger rats fell. The results show that the liver of young rats, after the injection of glucagon, draws on its own protein resources for the substrates needed for gluconeogenesis.