Potassium and sodium content of uterine and seminal vesicle secretions

K and Na concentrations of the fluid which accumulates in the uterine lumen of the rat during proestrus were studied before and after the animals were mated. The K in the resting uterine secretion was 37, the Na 115 mEq/l. The sum of the K plus Na in the resting uterine secretion did not differ from the sum of the K plus Na in serum samples obtained simultaneously. The seminal vesicle secretion of the rat contained 1.1 mEq/l. of K and 34 of Na. The fluid obtained from the uterine lumen after mating with a vasectomized male did not show a significant reduction in K, but the Na concentration was reduced 11%. The high K/Na ratio found in the rat uterine fluid is similar to the K/Na ratios reported by others for the seminal plasma of several mammals.