Effects of prolonged elevation of plasma adrenaline concentration in vivo on insulin-sensitivity in soleus muscle of the rat

1. Prolonged elevation of the plasma adrenaline concentration was produced in rats by implantation of adrenaline-releasing retard-tablets. With this technique, a hyperadrenalinaemic state is maintained for at least 5 days. 2. At 6 h after implantation of the retard-tablet it was found that plasma glucose and fatty acid concentrations increased and insulin concentration decreased compared with values obtained from placebo-tablet-implanted rats. Administration of a subcutaneous glucose load demonstrated an impaired glucose tolerance in vivo, and incubation of soleus muscle strips from 6 h-hyperadrenalinaemic rats in vitro demonstrated a decreased sensitivity of the rates of glycolysis and glucose transport to insulin. 3. The sensitivities of the rates of glycolysis, glucose transport and glycogen synthesis to insulin were determined for the incubated soleus muscle preparation isolated from animals after 48 h, 72 h and 120 h duration of hyperadrenalinaemia. At 48 h after retard-tablet implantation, the sensitivity of the processes of glucose transport and glycolysis was decreased; at 72 h, the insulin-sensitivities of the rates of glycolysis and glucose transport in skeletal muscle were similar to those determined for control animals; at 120 h, however, the sensitivities of the processes of glucose transport and glycolysis were both statistically significantly increased. In contrast, no changes in the sensitivity of the process of glycogen synthesis were observed at any of the time intervals studied. 4. The possible biochemical basis for the observed changes in skeletal-muscle insulin-sensitivity with prolonged hyperadrenalinaemia is discussed.