Episodic luteinizing hormone (LH) secretion and the response of LH and follicle-stimulating hormone to LH-releasing hormone in aged men: evidence for coexistent primary testicular insufficiency and an impairment in gonadotropin secretion.

The influence of aging on episodic LH secretion and the release of LH and FSH after LRH administration was studied in 14 healthy men, aged 65-80 yr. Mean morning serum testosterone levels were reduced by 16% (P less than 0.05) and serum LH and FSH concentrations were increased by nearly 2- and 3-fold, respectively (P less than 0.01), compared to levels in young men. LH secretory episodes were evident and did not differ significantly in either amplitude or frequency from those of young men in spite of the higher mean LH concentrations. The increments in serum LH and FSH levels after LRH and the areas under the response curves were similar in aged and young men. However, the time of the peak LH response was significantly delayed with aging (P less than 0.001), suggesting an alteration in the control of the releasable LH pool. Further, LH levels were slower to fall after the peak in elderly men (P less than 0.01), suggesting prolonged secretion of hormone after LRH stimulation. These changes did not relate to the basal hypersecretion of LH in elderly men, as the responses in young men with primary gonadal failure did not differ from those in healthy young men (P = NS). The possibility that increased LH molecular size leads to its reduced clearance was not supported by the similar Sephadex G-100 elution profiles for LH in both basal and post-LRH sera from young and old men. Our data indicate that Leydig cell function is impaired in healthy elderly men as a result of primary testicular insufficiency. These studies further reveal the presence of an additional hypothalamic-pituitary disorder of gonadotropin secretion associated with the aging process.