THE EFFECTS OF CORTISOL AND TESTOSTERONE ON RENAL-FUNCTION IN MALE ANTECHINUS-STUARTII (MARSUPIALIA)

Seasonal changes in the physiology of Antechinus stuartii result in co mplete male mortality after mating. The most important endocrine chang es in males are large rises in plasma testosterone and cortisol concen trations. Glomerular filtration rate (GFR) in males declines coinciden t with high plasma testosterone and cortisol. In the present study GFR s were measured in males captured in May (when endogenous plasma testo sterone and cortisol levels are low) and given depot injections of eit her saline, testosterone-only, cortisol-only or testosterone plus cort isol at doses designed to mimic plasma levels during the mating period . GFR decreased significantly with testosterone injection, independent of cortisol treatment. Urinary concentrations of sodium and chloride, and osmolality decreased significantly with cortisol treatment, altho ugh the addition of testosterone reversed the effect. Total urinary ex cretion of electrolytes was similar between groups. Plasma potassium l evels significantly increased in testosterone plus cortisol treated ma les. Plasma sodium levels significantly increased and plasma chloride significantly decreased in all groups treated with cortisol. Water con sumption significantly increased in all cortisol-treated males and foo d consumption significantly increased in all testosterone-treated male s. The seasonal renal functional changes observed in A. stuartii were mimicked by testosterone administration.