Some Reactions of the Rat to Treatment with Progesterone and Estrone in Late Pregnancy.

Abstract

Proges-terone (2,5 mg. daily) beginning on the 19th day of pregnancy in intact rats prevents labor, uterine bleeding and parturition. Estrone (25 [mu]g.) started on the 19th or 20th day induces uterine bleeding, vigorous but ineffective labor and death of fetuses. Estrone (100 [mu]g.) begun on the 20th day in 1 animal brought about delivery of young 1 day premature. Spontaneous delivery occurred in 4 rats given 25 [mu]g. of estrone about 24 hrs. before time for delivery. Progesterone (2.5 mg.) given simultaneously with estrone (25 [mu]g.) beginning on the 20th day has the same effect as progesterone alone, preventing the above effects of estrone alone. It is suggested that estrone plays a role in the prevention of parturition in the rat other than by way of its action on the corpora lutea.