The effects of estrogens on sodium and potassium metabolism in rats

Male Wistar rats, housed in individual metabolism cages and fed standard rat chow, received, after a two-week acclimation period, daily intramuscular injections of 17beta-estradiol (0.17 mug/gram body weight) in peanut oil or 0.1 ml peanut oil alone for four days. Water and food intake were measured daily, as were urinary volume and electrolytes. 17beta-estradiol administration resulted in significant decreases in food and sodium and potassium intake and in urinary sodium and potassium excretion. In a second series of experiments, male rats treated with 17beta-estradiol or peanut oil as above had access to sodium-free food, water, and saline. In this group of animals, 17beta-estradiol administration resulted in a significant decrease in food intake but no significant changes in sodium intake or excretion. Potassium intake and excretion decreased as above. In a third experiment, sodium intake and output in female rats on standard rat chow correlated with the phase of the estrous cycle, being lowest during proestrus and estrous and highest during metestrus and diestrus. The data indicate that 17beta-estradiol reduces the renal excretion of sodium and potassium primarily as a consequence of a reduction in food intake and exerts no specific effect on either sodium or potassium metabolism.