Effect of cortisol on utilization and hepatic release of glucose in the marsupial brush-tailed opossum, Trichosurus vulpecula.

Brush-tailed opossums were prepared surgically with indwelling heatic and jugular venous catheters for blood sampling without disturbance in the conscious state. Hepatic extraction of Rose Bengal was 21 +3 (s.d.) % and hepatic clearance, used as a measure of hepatic blood flow, was 42.5 +7 ml/kg/min. Hepatic relaease of new glucose, calculated from the thorias vena caval-hepatic venous difference in glucose specific activity at equilibrium during i.v. infusion of [14C]glucose and hepatic blood flow, was 3.5 + o.0 mg/kg/mim. This was not changed by i.v. infusions of 10% ethanolic aline or cortisol in ethanolic saline, at 1mg/kg/h for 90 min, although the cortisol infusion caused the peripheral blood glucose concentration to rise form 56.5 + 7.3 to 83.2 + 10.3 mg/100ml. The rate of metabolic clearance of glucose fell from 6.1 +1.1 to 4.2 +0.9 ml/kg/min during i.v. cortisol infusion. Daily i.m. injection of 1 mg cortisol accetate/kg for 5 days caused an increase in hepatic new glucose release to 8.0 + 1.6 mg/kg/min. The findings support the propostion that, in the marsupial, the short-term effect of cortisol on plasma glucose concentration is due to inhibition of peripheral glucose utilization, whereas the long-term effect is due to increased hepatic glucose production.