Sex Difference in Fluid Exchange During Food Deprivation in the Rabbit

Daily measurements of body weight, water and food intakes and urinary Na+, K+, Cl-, osmolarity and volume were made during 7 days of ad lib. feeding, followed by 7 days of food deprivation in normal male, and normal and ovariectomized female rabbits. Male rabbits deprived of food show a marked increase in fluid intake and urine output which is associated with an enhanced Na+ excretion. In contrast, female rabbits display a diminished or even depressed fluid exchange during food withdrawal; the onset of the increased Na+ excretion, although present as in the male, is delayed. Ovariectomy converts the female type of response to that of the male, i.e., a polyuria and polydipsia. Diethylstilbestrol (100 μg/day) or estradiol (100 μg/ day) given to the male on the 3rd and 4th days of food deprivation results in a significantly reduced water intake and urine output and increased urinary osmolar concentration; similar results are obtained in estradioltreated ovariectomized rabbits. Possible mechanisms of this est...