SEASONAL-CHANGES IN GLOMERULAR-FILTRATION RATE IN ANTECHINUS-STUARTII(MARSUPIALIA, DASYURIDAE)

The small marsupial Antechinus stuartii experiences a synchronised lif e cycle that culminates in complete male mortality (within 3 weeks) fo llowing the 1 week mating period in mid-August (late winter). There ar e pronounced physiological changes in male A. stuartii over the life c ycle and renal function was assessed for correlation with these change s. Glomerular filtration rare and urine and plasma electrolytes were d etermined in male and female A. stuartii in February. May, July and Au gust. Females showed little change in glomerular filtration rate, exce pt for pre-mating values in August which decreased. In contrast, glome rular filtration rate of males decreased significantly in July and Aug ust. Plasma sodium and chloride levels were higher in males than femal es and were higher in animals in July and August than in February and May. Plasma potassium levels dropped in both males and females in July and August. Plasma osmolality was higher in animals in February compa red to animals from May and August. However, there were no significant sex or seasonal differences in urine electrolytes, although urea conc entration was higher in females than males. Urine osmolality was highe r in both sexes in July and August. There were no significant differen ces in total excretory rates of sodium, potassium or chloride between sexes or between seasons. Many of the alterations in renal function ar e correlated with known physiological and hormonal profiles in A. stua rtii. This is the first observation of seasonal changes in glomerular filtration rate that are unrelated to dietary and water stresses.