EFFECT OF CORTISOL ON UTILIZATION AND HEPATIC RELEASE OF GLUCOSE IN THE MARSUPIAL BRUSH-TAILED OPOSSUM, TRICHOSURUS VULPECULA

Abstract

SUMMARY Brush-tailed opossums were prepared surgically with indwelling hepatic and jugular venous catheters for blood sampling without disturbance in the conscious state. Hepatic extraction of [125I]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 release of new glucose, calculated from the thoracic 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 ± 0·8 mg/ kg/min. This was not changed by i.v. infusion of 10% ethanolic saline or cortisol in ethanolic saline, at 1 mg/kg/h for 90 min, although the cortisol infusion caused the peripheral blood glucose concentration to rise from 56·5 ± 7·3 to 83·2 ± 10·3 mg/100 ml. 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 acetate/kg for 5 days caused an increase in hepatic new glucose release to 8·0 ± 1·6 mg/kg/min. The findings support the proposition that, in this 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.