Pituitary-gonadal function in the aged male (author's transl)

Abstract

The changes of hormone secretion and its control mechanism in the pituitary-gonadal axis in the aging male were studied, and the following results were obtained.1. The mean levels of serum total testosterone and free testosterone index declined progressively from the 5th decade with, however, a wide range of individual values, and the increments of serum testosterone after LH-RH or hCG administration were significantly reduced in the aged men studied. On the other hand, basal serum LH and FSH levels increased slowly after the 5th decade, indicating a more pronounced increase after the age of 70. The responses of these gonadotropins and LH subunits to LH-RH increased significantly in the aged group.2. Three days after daily administration of testosterone propionate, serum testosterone levels in the aged group were elevated more definitely than those in the young group, and basal LH and FSH levels in both groups were suppressed to nearly the same extent, but the responses of LH and FSH to LH-RH did not decrease except for a young group given a higher dose of testosterone propionate.3. Cytosol testosterone and 5a-dihydrotestosterone receptors in the hypothalamus and pituitary of aged male rats decreased to about 50% of those in the control young male rats, whereas estradiol receptors remained unchanged.These results indicate that the changes in pituitary-gonadal function in aging men may occur primarily in the testis and suggest the possibilities that (1) the feedback action of testosterone on gonadotropin secretion could be exerted at the hypothalamic level rather than at the pituitary level, and that (2) the set point of testosterone in its negative feedback control of gonadotropin secretion in the aged males might be reset at a higher level, probably due to the decrease in gonadal steroid hormone receptors in the hypothalamus and pituitary.