Progesterone metabolism by uterine tissue of pregnant rats

Abstract

The amount of progesterone metabolized during one hour incubations of uterine tissue from pregnant rats was determined. A tenfold increase in metabolic activity was observed between day 11 and day 21 of pregnancy when the results were expressed as nanograms of progesterone metabolized per gram of tissue per hour. A seventyfold increase was observed in the same period when the results were expressed in terms of nanograms of progesterone metabolized per whole uterus per hour. The major products were identified as 5α-pregnane-3,20-dione and 3a-hydroxy-5α-pregnan-20-one. Administration of luteinizing hormone and estrone in midpregnancy significantly increased the rate of in vitro progesterone metabolism by the uterus. Administration of progesterone and prolactin afer day 18 prevented normal parturition and significantly decreased the rate of in vitvo progesterone metabolism by the uterus. The results suggest a possible relationship between the progesterone-reducing activity of the rat uterus and uterine progesterone concentration during pregnancy, and suggest an effect of several hormones on uterine enzyme activity.