Pedro Endocrino

Environmental Health Perspectives Supplements
101

(Suppl. 2): 91-100 (1993)

Environment, Human Reproduction, Menopause, and Andropause
by Alex Vermeulen
As the hypothalamic gonadotropin-releasing hormone (GnRH) pulse generator is an integrator of hormonal, metabolic, and neural signals, it is not surprising that the function of the hypothalamogonadal axis is subject to the influence of alarge array of environmental factors. Before puberty, the central nervous system (CNS) restrains the GnRH pulse generator. Undernutrition, low socioeconomic status, stress, and emotional deprivation, all delay puberty. During reproductive life, among peripheral factors that effect the reproductive system, stress plays an important role. Stress, via the release of corticotropin-releasing factor(CRF), eventually triggered by interleukin 1, inhibits GnRH release, resulting in hypogonadism. Effects of CRF are probably mediated by the opioid system. Food restriction and underweight (anorexia nervosa), obesity, smoking, and alcohol all have negative effects on the GnRH pulse generator and gonadal function. Age and diet are important determinants of fertility in both men and women. Theage-associated decrease in fertility in women has as a major determinant chromosomal abnormalities of the oocyte, with uterine factors playing a subsidiary role. Age at menopause, determined by ovarian oocyte depletion, is influenced by occupation, age at menarche, parity, age at last pregnancy, altitude, smoking, and use of oral contraceptives. Smoking, however, appears to be the major determinant.Premature menopause is most frequently attributable to mosaicism for Tlurner Syndrome, mumps ovaritis, and, above all, total hysterectomy, which has a prevalence of about 12-15% in women 50 years old. Premature ovarian failure with presence of immature follicles is most frequently caused by autoimmune diseases or is the consequence of irradiation or chemotherapy with alkylating cytostatics. Plasmaestrogens have a physiological role in the prevention of osteoporosis. Obese women have osteoporosis less frequently than women who are not overweight. Early menopause, suppression of adrenal function (corticoids), and thyroid hormone treatment all increase the frequency of osteoporosis. Aging in men is accompanied by decreased Leydig cell and Sertoli cell function, which has a predominantly primarytesticular origin, although changes also occur at the hypothalamopituitary level. Plasma testosterone levels, sperm production, and sperm quality decrease, but fertility, although declining, is preserved until senescence. Stress and disease states accelerate the decline on Leydig cell function. Many occupational noxious agents have a negative effect on fertility. There is evidence for a decline ofsperm quality in the general male population over the last two decades, probably a consequence of increasing pollution, irradiation, and population stress. If the evidence is confirmed, it might be mandatory to reduce drastically pollution, irradiation, and other noxious agents that may impair spermatogenesis.

Introduction
The human organism acquires its full reproductive capacity aftercompletion of puberty, the fertile period covering about 35 years in women, whereas in men reproductive capacity, although decreasing with age, persists until a very old age.

Puberty
Puberty represents the final stage of sexual differentiation during which time the individual acquires full reproductive capacity, with not only maturation of sexual organs
Department of Endocrinology and Metabolism,State University of Ghent, De Pintelaan 185, B-9000 GHENT, Belgium. This manuscript was presented at the Conference on the Impact of the Environment on Reproductive Health that was held 30 September-4 October 1991 in Copenhagen, Denmark.

and formation of the oocytes and mature spermatozoa, but also development of secondary sex characteristics under the influence of sex hormones. Puberty is...