Estrogen and Progestin Regulation of the Progesterone Receptor Concentration in Human Endometrium*

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Abstract
The concentration of the progesterone receptor (PR), both cytosol and nuclear, has been measured in the endometrium of 31 normal menstruating women during the 2 phases of their menstrual cycle and compared with the plasma 17β-estradiol and progesterone concentrations. There was no relationship between PR concentrations and the plasma steroid levels when the 2 phases of the cycle were considered; however, a statistically significant correlation (r = 0.70; P <0.005) was observed between PR concentration and plasma 17β-estradiol when only the follicular phase was considered. PR was then measured in the endometrium of 14 postmenopausal patients treated with ethinylestradiol at increasing doses with or without association of chlormadinone acetate. Ethinylestradiol was shown to increase PR concentration (P < 0.05), and chlormadinone acetate was found to prevent this increase. These data suggest that in humans, as in other mammalian species, the endometrial PR concentration is under estrogen and progestin control.