Early effects of estradiol and cortisol on water and electrolyte shifts in the uterus of the immature rat

Abstract

The influences of estradiol on the uptake of water and radioactive electrolytes in the uterus of the immature rat were studied in short term experiments to determine the earliest manifestations of estrogen stimulation and to ascertain whether differential accumulation of these constituents occurred in the presence of the steroid. Immature rats were given a single i.v. dose of estradiol and sacrificed at intervals of 1 hour or less. Analyses of uteri for Na²⁴ revealed: a) a short period of equilibrium followed by a gradual rise above control levels beginning at 1 hour and, b) a marked increase in the rate of uptake between the 2nd and 3rd hours, reaching a maximum 2 3/4 hours after estrogen injection. A fluid uptake occurred parallel in time and proportional in magnitude to the net accumulation of Na²⁴. No significant change could be detected in uterine K or in the content of Na or of water in extrauterine tissues up to 6 hours following estrogen treatment. In longer term experiments, changes in uterine Na were observed and interpreted as reflecting increases in intracellular water. Cortisol blocked the increases in uterine water and Na produced at 4 hours by estradiol alone. The relationship of the results of these studies to the vascular changes induced in the uterus by estrogen is discussed.