The effect of steroids on mitosis and maintenance of pregnancy in spayed rats.

Abstract

AbstractRats were ovariectomized on the eighth day of pregnancy and either 10 or 20 mg of progesterone, 10 mg of progesterone with 1 μg estradiol benzoate or 1 μg estradiol benzoate alone were administered between the eighth and twelfth day. On the twelfth day tritiated thymidine was injected to study mitoses in the junctional zone cells of the placenta by autoradiography, and tracings of spontaneous uterine contractions were made. Twenty milligrams of progesterone daily sustained pregnancy to the twelfth day in spayed rats as effectively as it was sustained in the untreated normal rats; 10 mg progesterone daily was less effective and 10 mg progesterone with 1 μg estradiol benzoate did not maintain normal pregnancy. Progesterone produced normal rates of mitosis in the placental trophoblast cells of spayed rats. No correlation was found between the maintenance of pregnancy and decreased contractions of the myometrium in this study. The injection of 20 mg progesterone produced patterns of contraction similar to the normal contraction patterns and differing from those found in spayed rats and in rats injected with 10 mg progesterone, progesterone and estradiol benzoate or estradiol benzoate alone. It is concluded that a sufficient supply of progesterone maintains both normal mitotic activity in the trophoblastic cells and normal patterns of contraction by the muscle of the uterus.