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ABSTRACT
The effects of cortisol, ACTH, adrenalin and insulin on indices of carbohydrate, fat and protein metabolism were investigated in the conscious marsupial sugar glider Petaurus breviceps.
Short-term i.v. infusion of cortisol at dose rates of 0·02, 0·2 and 1·0 mg/kg per h caused the plasma glucose concentration to rise sharply from the normal range of 3·3–4·4 to 8·1–8·7 mmol/l at the end of the infusion period without significant alteration in plasma free fatty acid (FFA), amino acid or urea concentrations. Infusions of ACTH at dose rates of 0·02, 0·06 and 0·45 IU/kg per h caused a similar rise in plasma glucose concentration; however, this was now accompanied by an elevation in plasma FFA concentration, but again without significant changes in either plasma amino acid or urea concentrations. Infusion of adrenalin at 10 μg/kg per h caused an increase in the plasma concentrations of both glucose and FFA. Intravenous injections of 0·15 IU insulin/kg caused a rapid and marked decrease in the plasma glucose concentration within 30 min and an increase in the plasma free cortisol concentration. Associated with this change was a marked rise in the plasma concentration of both FFA and free cortisol. The rise in free cortisol was, however, significantly reduced by infusion of glucose. Pretreatment with five daily i.m. injections of 1 mg cortisol acetate/kg, which produced an increase in plasma free cortisol concentration to near the maximum of the physiological range, caused a marked reduction in insulin sensitivity. Cortisol pretreatment caused an increase in the plasma FFA and amino acid concentrations.
Petaurus breviceps is highly sensitive to the metabolic effects of glucocorticoids and is similar in this respect to the brush-tailed possum Trichosurus vulpecula. The interactive effects between insulin and glucocorticoids on carbohydrate, fat and protein metabolism in Petaurus breviceps are similar to those shown by Trichosurus vulpecula and some eutherian mammals but contrast with the pattern described for two macropodid marsupials, the red kangaroo Macropus rufus and the quokka Setonix brachyurus.
Journal of Endocrinology (1990) 127, 203–212
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ABSTRACT
An investigation spanning two breeding seasons was carried out to examine endocrine changes associated with reproduction in a wild population of the marsupial sugar glider Petaurus breviceps, a small arboreal gliding possum.
Using techniques of equilibrium dialysis and polyacrylamide gel electrophoresis at steady-state conditions, a high-affinity, low-capacity glucocorticoid-binding protein was demonstrated in the plasma of Petaurus breviceps.
Equilibrium dialysis at 36 °C using cortisol gave a high-affinity binding constant of 95 ± 5·2 litres/μmol for a presumed corticosteroid-binding globulin (CBG) while the binding constant for the cortisol-albumin interaction was 3·5 ± 0·4 litres/mmol.
There was no difference between the sexes in the affinity of binding of cortisol to CBG; however, the cortisol-binding capacity underwent seasonal variation in both sexes. Progesterone was bound strongly to the presumed CBG while neither oestradiol nor aldosterone appeared to be bound with high affinity to P. breviceps plasma.
In the males, peaks in the plasma concentration of testosterone coincided with the July–September breeding season in both years. A significant inverse relationship was shown to exist between the plasma testosterone concentration and the CBG-binding capacity.
In both sexes an increase occurred in the plasma concentration of free cortisol during the first breeding season, a pattern which was not repeated in the subsequent breeding season, possibly due to a lower population density in that year.
Journal of Endocrinology (1992) 132, 21–31
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Departments of *Physiology and †Zoology, Monash University, Clayton, Victoria 3168, Australia
(Received 19 December 1974)
In the shrew-like marsupial Antechinus stuartii from eastern Australia, there is an abrupt and total mortality of males after a 7 to 10-day mating period in August or September (Woolley, 1966; Wood, 1970). Males isolated in the laboratory before mating survive beyond the time of natural mortality (Wood, 1970).
Barnett (1973) observed increased peripheral corticosteroid concentrations in males taken from natural populations in the last weeks of life. To test whether this change could be a cause of the mortality, exogenous cortisol was injected into laboratory-held males.
Male A. stuartii were captured before the mating period in July 1973 and 1974 at Powelltown, Victoria, and caged singly under the natural Melbourne photoperiod. Their average initial body weight was 30·1 ± 3·6 g (n = 38). In each year they were divided into three groups: two
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Departments of Physiology and *Zoology, Monash University, Clayton, Victoria, Australia
(Received 24 February 1976)
In natural populations of the shrew-like marsupial Antechinus stuartii all the males die within 3 weeks of the beginning of a single mating period in late winter. Males captured before this period begins and caged singly survive well beyond the time of natural mortality. During the mating period the males become extremely aggressive; vagrancy and interactions increase greatly and copulatory activity is frequent and prolonged (Woolley, 1966, Wood, 1970; Braithwaite, 1974). This is associated with evidence of increased adrenocortical activity (Barnett, 1973). Administration of cortisol to males captured and caged singly before the breeding period causes a significant dose-related mortality (Bradley, McDonald & Lee, 1975). However, the mortality is only 45% even when the plasma total corticosteroid concentration is well above the natural breeding level. Also, the plasma corticosteroid concentration of females in natural populations is
