The endogenous concentration of estradiol and estrone in normal human postmenopausal endometrium

Sununary--The endogenous estrone (E,) and estradiol (E2) levels @g/g tissue) were measured in 54 postmenopausal, atrophic endometria and compared with the E, and E2 levels in plasma (pg/ml). The results from the tissue levels of both steroids showed large variations and there was no significant correlation with their plasma levels. The mean & concentration in tissue was 420 pg/g, 50 times higher than in plasma and the E, concentration of 270 pg/g was 9 times higher. The Q/E, ratio in tissue of 1.6, was higher than the corresponding Es/E, ratio in plasma, being 0.3. We conclude that normal postmenopausal atrophic endometria contain relatively high concentrations of estradiol and somewhat lower estrone levels. These tissue levels do not lead to histological effects. Epidemiolo~cal studies have identified a number of risk factors for endometrial cancer. Several of these factors are clearly related to the endogenous production of estrogens; in addition the use of exogenous estrogens in postmenopausal women is associated with an increased risk for endometrial cancer [l-4]. Obesity, considered to be the most important risk factor for endometrial pathology, is thought to act through its contribution to the peripheral conversion of androstenedione to estrone [S-6]. Especially in the postmenopause, the resulting continuous exposure of target tissues to the unopposed action of estrogens may be a causal factor in the development of endometrial cancer [7-91. However, recent studies have shown that the production rate and the peripheral blood levels of estrone (E,) and estradiol (Er) are very similar in patients with this cancer, as compared to controls matched for body weight [l&12]. Although the predominant circulating estrogen in postmenopausal women is estrone, Tseng and Gurpide did show that the estrogen tightly bound to the nuclei of superfused human endometrium was not estrone but estradiol [13]. In a previous in vivo study we have shown that after a constant infusion of labelled E, for 12 h to postmenopausal women, there is a higher Er/E, ratio in endometrial tissue as compared with peripheral plasma. In the cell nucleus only E, was accumulated even after an infusion of E, [14-151. We therefore considered the possibility that tissue