Effects of progestins on estradiol receptor levels in human endometrium

Medroxyprogesterone acetate (Provera) was administered orally during 2-4 days to women undergoing endometrial curettage during the follicular phase of the menstrual cycle. Estradiol (E2) receptor levels were estimated from the amounts of 2H-E2 tightly bound in nuclei after incubation of endometrial tissue with an excess of the labeled hormone. An average value (9 subjects) of 1.5 pmole E2/mg DNA +/- 0.7 (mean +1- SD) was found. This value is significantly lower than the average E2 receptor levels in proliferative endometrium of untreated subjects (3.2 +/- 1.3, n = 33) and equals the level observed in the early secretory phase (1.5 +/- 0.5, n = 5). These results indicate that one of the progestin effects on human endometrium is the reduction of E2 receptor levels.