METABOLIC EFFECTS OF CORTISOL AND CORTICOTROPHINS IN THE AUSTRALIAN BRUSH-TAILED OPOSSUM, TRICHOSURUS VULPECULA (KERR)

Abstract

SUMMARY The effect of cortisol and adrenocorticotrophic hormone (ACTH) administration on indices of carbohydrate, fat and protein metabolism was investigated in the conscious marsupial brush-tailed opossum Trichosurus vulpecula (Kerr). Short-term (1 h) i.v. infusions of cortisol at 0·02, 0·20 and 1·0 mg/kg/h caused plasma glucose concentration to rise rapidly from the normal range of 106–119 mg/100 ml to 145–163 mg/100 ml at the end of the infusion period without consistent changes in plasma urea, amino acid or free fatty acid (FFA) concentration. Similar infusions of porcine or synthetic ACTH at 0·45 i.u./kg/h increased plasma glucose concentration to similar levels without significant change in plasma urea or amino acid concentration, but with a marked increase in plasma FFA concentration. Daily injections of 1 mg cortisol acetate/kg for 8 days caused a moderate loss of weight, increased urinary nitrogen excretion and glycosuria in all animals. In one animal it was possible to associate these changes with an increase in plasma cortisol concentration to 8·6 μg/100 ml, and an increase in plasma glucose and urea concentrations to 172 and 52 mg/100 ml, respectively. Liver glycogen concentrations in normal and 24 h-fasted animals were 5·53 ± 0·73 and 0·20 ± 0·14 g/100 g respectively, and daily i.m. injections of 1 mg cortisol acetate/kg increased the liver glycogen concentration to 3·38 ± 0·63 g/100 g in 24 h-fasted animals. The erythrocytes contained only small amounts of glucose which increased during cortisol-induced hyperglycaemia. It is concluded that Trichosurus is highly sensitive to the metabolic effects of glucocorticoids, which resemble those found in eutherian mammals, particularly the rabbit.