Abstract

PIP: Estradiol, estrone, and progesterone levels in serum and tissue were determined radioimmunologically from 160 endometrium and serum samples taken at various phases of the menstrual cycle in female patients who had undergone either curettage or hysterectomy for medical reasons. In addition, the cytoplasmatic estradiol and progesterone receptor concentrations and the (17beta-HSD) 17-beta-hydroxysteroid dehydrogenase activities in the endometrium were measured. In 132 cases, it was possible to correlate the endometrial histological findings and serum hormone levels with a particular phase of the cycle. The serum concentrations of sexual steroids displayed the usual biphasal pattern for estradiol and estrone with the postovulatory increase in progesterone. The tissue levels of these hormones followed a course partly paralled to and partly opposed to the serum levels. The progesterone profile in tissues essentially matches that in the serum except that the endometrium concentrations showed a marked prevulatory increase, with no appreciable postovulatory rise. The midcycle estradiol peak was also observed in the endometrium. After ovulation, the estradiol concentration in the tissue declined significantly. The changes in estrone levels in the secretory endometrium were at variance with those in the serum, increasing sharply after ovulation. The cytoplasmic estradiol receptor concentration exhibited a maximum in the middle of the proliferative phase and declined steadily over the rest of the cycle. The number of progesterone-binding receptors is only enhanced at midcycle. The concentration changes in the progesterone receptors could be clearly correlated with the estradiol peak in serum and tissue at midcycle. A 10-fold increase in 17beta-HSD activity is observed after ovulation, affecting changes in the tissue/serum estradiol and estrone ratios. The estradiol shifts ratio in favor of the serum during postovulatory phase, whereas the estrone ratio is displaced in favor of the tissue. A regulatory model for the endometrial cells during the menstrual cycle is suggested on the basis of the results obtained.