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

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 degrees C using cortisol gave a high-affinity binding constant of 95 +/- 5.2 litres/mumol 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.

Seasonal changes in the testis, accessory glands and ejaculate characteristics of the southern hairy‐nosed wombat, Lasiorhinus latifrons (Marsupialia: Vombatidae)

“…In general, all of these variables increased significantly between January and September, the breeding season, and were minimal from November through to May, the non-breeding season. The affects of androgens on the accessory reproductive organs are well known (Taggart & Temple-Smith, 1990;Bradley & Stoddart, 1992). The significant changes observed in prostate and Cowper's gland weight in L. latifrons in this study corresponded well with data collected from previous studies in other marsupial species (Rodger & Hughes, 1973;Brandes, 1974;Brooks et al, 1978;Taggart & Temple-Smith, 1990).…”

Ultradian, circadian and seasonal rhythms in cortisol secretion and adrenal responsiveness to ACTH and yarding in unrestrained red deer (Cervus elaphus) stags

“…In addition, androgens can influence HPA axis activity by competing with cortisol for binding sites on carrier proteins such as corticosteroid binding globulin (CBG) (Bradley & Stoddart 1992) and plasma albumin (Ward et al 1992). Androgens can also suppress hepatic synthesis of CBG (Gala & Westphal 1965) effectively increasing unbound concentrations of cortisol.…”

Plasma binding proteins as mediators of corticosteroid action in vertebrates

“…In mammals, CBG capacity is lower during the breeding season (Bradley & Stoddart 1992, Boonstra et al 2001. In birds, however, CBG capacity is elevated during all or part of the breeding season (Assenmacher et al 1975, Daniel et al 1981, Silverin 1986, Romero & Wingfield 1998, Romero et al 1998b,c, Breuner & Orchinik 2001.…”