Ageing of the Hypothalamo-Pituitary- Testicular Axis in Men

Abstract

In distinction to the course of reproductive ageing in women, men do not experience a rapid decline of Leydig cell function or irreversible arrest of reproductive capacity in old age. Hence, strictu sensu, the andropause does not exist. Nevertheless, both spermatogenesis and fertility as well as Leydig cell function do decline with age, as shown by a decrease of ± 35% of total and of 50% of free testosterone levels between the age of 20 and 80 years. The origin of this decline of Leydig cell function resides on the one hand in the testes, and is essentially characterized by a decreased number of Leydig (and Sertoli) cells and on the other hand in the hypothalamo-pituitary complex characterized by a decreased luteinzing hormone (LH) pulse amplitude, LH pulse frequency being maintained. As the responsiveness of the gonadotrophs to gonadotropin-releasing hormone (GnRH) remains unimpaired, one may assume that the amount of GnRH released at each pulse is also reduced, possibly as the consequence of a reduction of the cellular mass of GnRH neurones. Plasma levels of testosterone below the lower normal limit occur, however, only in a minority of elderly men from 7% in the age group 40-60, to 20% in the age group 60-80 and 35% in the age group over 80 years old. Factors influencing testosterone levels in elderly men are multiple: hereditary, environmental (obesity, stress), psychosocial (depression, smoking, drugs) or socioeconomical (diet, hygiene). Whether these elderly men should be substituted with androgens remains controversial. Beneficial effects, such as an increased feeling of well-being and fitness, increased muscle strength and endurance, decreased bone catabolism and increase of hematocrit, should be weighed against the risks of stimulation of growth of an occult, subclinical prostatic carcinoma (occurring with a high frequency in elderly males). Therefore, large scale androgen supplementation should await the results of well-controlled prospective studies.