Metabolism of progesterone in rat uterus

The in vitro metabolism of progesterone was studied in uteri of untreated and estrogen stimulated immature rats. In intact uteri the rate of metabolism varied with the hormonal status of the animal in a concentration dependent manner. At a low (3 × 10^?9M) progesterone concentration the rate of ring A reduction was decreased in estrogen stimulated uteri. At a high progesterone concentration (3 × 10^?6M) the rate of ring A reduction was increased after estrogen treatment. The rate of reduction of the C20 ketone was increased after estrogen treatment at all concentrations of incubated progesterone. In dilute homogenates of uterus, estrogen stimulation always increased the rate of progesterone metabolism.Estrogen stimulation results in increased concentration of progesterone receptor in the uterus. It is proposed that increased activity of ring A reductases also occurs. The relative influence of these two factors on the metabolism of progesterone is dependent on the progesterone concentration in the incubation medium.