Uterine metabolism of gonadal steroids during the menstrual cycle.

The metabolic clearance rate and uterine extraction of (3H)progesterone, (3H)estradiol, and (14C)estrone were studied at the time of hysterectomy in six women on or before day 12 of the menstrual cycle, in three women after day 12, and in one postmenopausal woman. The metabolic clearance rates of progesterone, estradiol, and estrone were in the same range as for normal women as previously reported by us. The uterine extraction for progesterone ranged between 12% and 37% on or before day 12 and 0% to 5% after day 12, and was 7.4% in the postmenopausal woman. The uterine extraction of estradiol was 0% to 25% on or before day 12, and 0%, 4%, and 22% after day 12 and was 18% in the postmenopausal woman. The uterine extraction of estrone was 7% to 24.5% on or before day 12 and 0% after day 12 and was 18% in the postmenopausal woman. The across-uterine interconversion of estradiol to estrone was 0% to 2.7% and of estrone to estradiol 0% to 2.6%. Both conversions appeared to be independent of the day of the menstrual cycle. The results suggest that the uterine metabolism of progesterone and estrone and perhaps estradiol is lower in the luteal phase of the cycle as compared to the follicular phase and that the conversion of estradiol to estrone may not be a major reaction of estradiol metabolism in the human uterus.