The Effects of Estrogen and Progesterone on the Volume and Electrolyte Content of the Uterine Luminal Fluid of the Rat

Rat uterine luminal fluid sodium and potassium contents have been studied by an uterine washing method and the volume of uterine fluid in each washing has been calculated by use of a molar electrolyte dilution factor: Three daily intramuscular injections of 10 μg estradiol-17² in 0.1 ml of an inert vehicle (ethyl laurate) in 10-day spayed rats, caused a 3-fold increase in the empty uterine horn weight (from 58 to 168 mg) and a 400-fold increase in the uterine luminal fluid volume (from 1.2 μl to 550 μl). Progesterone, 5 mg daily, given with the estradiol, gave an uterine weight (158 mg) almost as great as estradiol alone, but the progesterone completely blocked the accumulation of uterine luminal fluid (2.5 μl). A fall in the Na/K molar ratio of the uterine fluid from 3.5 in spayed controls to 1.8 was observed following low dose estradiol (0.01 μg) which did not cause an increase in uterine fluid volume. A higher dose of estradiol (0.1 μg) caused a marked rise in the Na/K ratio to 9.3 with the onset of uterine fluid secretion. With even higher doses of estradiol (1.0, 10, 100 μg), the Na/K ratio returned closer to the castrate level and values of 3.6, 3.9 and 2.8, respectively, were observed. Different combinations of estradiol and progesterone had extremely complex effects on the Na/K ratio. (Endocrinology95: 1034, 1974)