In vitro effects of estradiol, testosterone or progesterone on luteal steroidogenesis in the pregnant rat

In order to assess the direct luteotropic effects of steroids, dispersed luteal cells from rats on day 8 or 16 of pregnancy were incubated for 2 h with various concentrations of estradiol (1-1000 ng/ml), testosterone (1-100 ng/ml) or progesterone (1-100 ng/ml). Estradiol, at any concentration, did not cause significant changes in the in vitro accumulation of progesterone, 20 alpha-dihydroprogesterone (20 alpha-OHP) or testosterone by dispersed luteal cells on both days 8 and 16. Addition of testosterone (1-100 ng/ml) increased the accumulation of estradiol on day 8 with estrone synthesized at half to one third the rate of estradiol. On day 16, accumulation of estradiol by dispersed luteal cells was more sensitive to 1 ng/ml testosterone than on day 8 with a concomitant drop in estrone synthesis. Although luteal secretion of estradiol was readily stimulated by testosterone, there were no corresponding changes in the production of progesterone or 20 alpha-OHP. Although the addition of a small amount of progesterone did not cause the anticipated increase in accumulation of 20 alpha-OHP, 100 ng/ml progesterone elicited a slight but significant increase in accumulation of 20 alpha-OHP on day 8. Thus, none of 3 steroids added was found to exert any direct in vitro luteotropic action in the pregnant rat, in acute experiments.