Steroid Endocrinology after the Menopause: A Review

The menopause is defined as the last menstrual period in a woman's life. It is the inevitable consequence of the natural rate of atresia of ovarian follicles. Because in premenopausal women 95% of circulating oestradiol-171B is secreted by these follicles, the menopause is associated with a reduction of oestrogen secretion. Measurement of oestrogens by biological techniques showed, many years ago, that blood levels in postmenopausal and castrate women were lower than in preimenopausal women. However, even 40 years ago it was realized that oestrogens were not always undetectable in postmenopausal women (Fluhmann 1936). The development of biochemical methods of measurement made it possible to investigate extraovarian sources of steroids after the menopause. Direct secretion of oestrogens by the adrenal gland had been inferred by Brown et al. (1959) after noting premenopausal levels of urinary oestrogens in an ovariectomized woman who had been treated with corticotrophin (ACTH). Direct ovarian and adrenal secretion of steroids after the menopause has since been studied by determining hormone concentrations in the blood draining these glands. Although this method of collection of blood samples itself may disturb glandular secretion, the studies reported have suggested that neither the adrenal cortex nor the ovarian stroma makes a significant direct contribution to circulating oestrogens after the menopause (Baird, Uno & Melby 1969, Judd et al. 1974). Extraglandular production of oestrogens through aromatization of androgens was first recognized in humans by West et al. (1956), who identified oestrone and oestradiol in the urine of 2 adrenalectomized, ovariectomized women after injections of testosterone propionate. The subsequent development ofisotopic techniques has allowed this aspect ofsteroid endocrinology to be studied in greater detail. The peripheral pathways of conversion and interconversion of androgen and oestrogens suggested by the isotopic studies of Baird, Horton et al. (1969) are as follows: Androstenedione Oestrone