Estrogen-progesterone interactions in uterus and brain of intact and adrenalectomized immature and adult rats.

Abstract

The uptake and metabolism of progesterone following estrogen pretreatment. was examined in immature and adult rats. In the first experiment 31, 45 and 60-day-old ovariectomized rats, half of which were pretreated with 0.325 μg estradiol/100 g body wt/day for 3 days, were given 40 μCi tritiated progesterone. With increasing age there was a decline in uterine uptake of radioactivity. Estradiol pretreatment reduced the uptake of radioactivity in the 31-day-old but not in the 45 or 60-day-old rats. Age differences could not be explained on the basis of uterotropic effects. The same effect was obtained in 31 and 60-day-old rats given estradiol and a higher dose (52 μCi/100 g) of tritiated progesterone. Greater uptake in immature rats and estrogen-induced inhibition of uptake in immature but not mature rats were again found when the last estrogen injection preceded the injection of tritiated progesterone by 12 hr instead of 24 hr. The proportion of radioactivity identified chromatographically as progesterone wa...