Metabolic effects of cortisol, ACTH, adrenalin and insulin in the marsupial sugar glider, Petaurus breviceps

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 micrograms/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.

Seasonal changes in plasma androgens, glucocorticoids and glucocorticoid-binding proteins in the marsupial sugar glider Petaurus breviceps

“…This study was undertaken as part of a larger study on chemical communication and reproduction in this species to describe glucocorticoid-protein interactions in the blood plasma and thus make possible measure¬ ments of the seasonal changes which occur in the partitioning of cortisol and also changes which occur in the plasma concentration of testosterone. Some metabolic effects which result from stress and stimulation of the pituitary-adrenal axis have been described for this species (Bradley & Stoddart, 1990).…”

Plasma androgen, social position, and response to GnRH in the marsupial sugar glider Petaurus breviceps (Marsupialia: Petauridae)

“…A blood volume equivalent to the dead space of the sampling line was withdrawn before, and replaced after, the blood sample which was to be assayed for testosterone. Plasma samples were collected and erythrocytes washed and returned at the end of an experiment to the animals as previously described (Bradley & Stoddart, 1990). All runs were completed during 2 successive days and the catheters were then removed.…”

Father and son sugar gliders: more than a genetic coalition?

“…Those individuals which are still kept in captivity are alive and well nearly 2 years after the last cardiac puncture was performed. The concentration of testosterone in the blood plasma was measured by radioimmunoassay (Bradley & Stoddart, 1990) and is the subject of a different study by B. Klettenheimer. An aliquot of each blood sample was used for DNA extraction to determine the genetic relatedness of animals in each group.…”

“…Although the sugar glider has been the subject of some studies (Smith, M. J., 1979, Smith, A. P., 1982Temple-Smith, 1984;Bradley & Stoddart, 1990,1992Mallick et al, 1994;Quin, 1995), relatively little work on the social group structure has been conducted. If the social structure was studied, only the social status of males was assessed by short-term behavioural observations or intruder experiments were performed.…”