Secretion of adrenal steroids in female sheep of differing body size and composition

The relationship between body composition and secretion of adrenal steroids was examined in the lightest and heaviest Merino ewes selected from a flock that was grazing pasture during the breeding season. Animals were placed in individual pens in an animal house, fed to maintain live weight and given exogenous progestagen to establish uniform endocrine conditions similar to the luteal phase. Heavy ewes had a greater weight-to-height ratio than light ewes and carried significantly more omental, perinephric and subcutaneous rib fat, There were no significant differences between the groups in diurnal patterns or mean daily concentration of cortisol or dehydroepiandrosterone (DHEA),but mean daily concentration of dehydroepiandrosterone sulphate (DHEAS) was significantly higher in heavy ewes than in light ewes. Dexamethasone reduced the concentration of DHEAS in light ewes significantly more than in heavy ewes. Stimulation with ACTH increased the concentrations of cortisol, DHEA and DHEAS in both groups of animals, Cortisol response was greater in light ewes than in heavy ewes, whereas the concentrations of DHEAS and DHEA increased similarly in both groups. Apart from establishing values for DHEA and DHEAS in normal healthy ewes over a range of body conditions during the breeding season, these results also show that body size or composition affect the control of secretion of both cortisol and DHEAS. However, there appears to be a compensatory mechanism involved because resting plasma concentrations of these steroids did not differ between heavy and light ewes. This information provides the basis to structure investigations into effects of the adrenal gland on reproductive function.