Concentration of Unconjugated Estrone and Estradiol in Peripheral Plasma in Nonpregnant Women Throughout the Menstrual Cycle, Castrate and Postmenopausal Women and in Men1

Abstract

The concentrations of unconjugated estrone and estradiol in 20 ml samples of plasma from ambulant human subjects were measured using a double-isotope derivative method (1). The concentration of estradiol (ng/100 ml plasma ±se) showed a biphasic curve throughout the menstrual cycle rising from a mean value of 2.9±0.7 during menstruation to a maximum of 31.8±2.7 around midcycle. There was a sharp fall (11.7±2.0) in the few days following ovulation, with a smaller secondary rise (19.1±2.0) in the midluteal phase. The rise in concentration of estrone was less marked than that of estradiol (4.0±0.4 during menstruation to 17.0±1.3 at midcycle). The ratio of estradiol/estrone rose significantly from 0.67±0.13 during menstruation to 1.90±0.12 around midcycle, indicating the increasing predominance of estradiol throughout the menstrual cycle. In contrast, the concentration of estrone in men (5.7±0.8), castrate (11.6±4.5) and postmenopausal women (7.1±2.7) was approximately 3-fold higher than that of estradiol (1.9±0.2, 3.6±1.3 and 1.3±0.2, respectively). The midcycle peak of concentration of LH in plasma as measured by radioimmunoassay corresponded with the maximum concentration of estradiol in all 7 subjects.