Adrenocortical functions in a macropodid marsupial Thylogale billardierii

In a study of adrenocortical functions in macropodid marsupials, measurements were made of the effects of ACTH infusion, ether stress and adrenaline infusion on plasma corticosteroid and glucose concentrations in wallabies (Thylogale billardierii) provided with indwelling venous catheters. The mean plasma total glucocorticoid concentration in undisturbed males and females was 80 +/- 5 (S.E.M.) micrograms/l, of which more than 90% was cortisol. This fraction declined to 68% of the total at the highest ACTH-stimulated concentration of 225 micrograms/l, due to an increase in the contribution by 11-deoxycortisol. Although maximal ACTH stimulation (4.5 i.u./kg per h) caused a five- to sixfold increase in cortisol secretion rate, as measured by isotope dilution during constant-rate tracer infusion, plasma cortisol concentration rose only two- to threefold, due to a marked increase in metabolic clearance. Plasma glucose concentration did not change significantly during either short-term (1 h) i.v. infusion or long-term (8 days) i.m. injection of ACTH, even though plasma cortisol concentration was significantly increased. Ether anaesthesia caused a marked hyperglycaemia that preceded an increase in plasma cortisol concentration and was not sustained while plasma cortisol concentration continued to increase. Infusion of adrenaline i.v. at rates sufficient to cause a similar hyperglycaemia had no significant effect on plasma cortisol concentration. A marked hyperglycaemia during xylazine anaesthesia was not associated with an increase in plasma cortisol concentration and was attributable to suppression of insulin secretion.(ABSTRACT TRUNCATED AT 250 WORDS)