The metabolic clearance rate and uterine extraction of progesterone at midgestation

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.

In vivo aspects of progesterone distribution and metabolism

The end-organ response of any hormone is the result of many factors which precede the event, including biosynthesis, secretion, transport, distribution, and metabolism. These factors vary among different species. The metabolic clearance rate (MCR) of progesterone varies between 40 and 180 L./day/Kg. in man (60 to 70), monkey (40 to 50), rabbit (55 to 60), sheep (110), rat (120), and guinea pig (180). Major sites of clearance include liver, brain, and uterus. Specific metabolites of progesterone include 20 alpha-hydroxypregn-4-en-3-one (20 alphaOHP) and alpha-pregnan-3,20-dione (5 alpha-DPH). Liver, brain, and uterine clearances, extractions, and conversions of progesterone to these metabolites have been studied in various species under apparent steady-state conditions. A specific hormone action of progesterone, the appearance of uteroglobin in the rabbit uterus, has also been studied in varying horomonal states (estrogen, estrogen plus progesterone, and progesterone alone). These have all been used as examples of progesterone distribution and metabolism.