Dopaminergic Control of Gonadotropin Secretion in Male Senescence

Abstract

To verify the role of the dopaminergic mechanism in the control of gonadotropin secretion and aging of this mechanism in men, we studied serum gonadotropin response to LH-RH (100 micrograms i.v.) in basal condition and during dopamine infusion (DA 4 micrograms/kg/min). Seven young males (24-29yr.) and twenty aged males (50-80yr.) without endocrinological diseases were included in the present study. Aged male subjects were divided into hyperresponders, in whom maximal LH response to LH-RH without DA infusion exceeded 153.5mIU/ml (mean + 2SD of young male subjects), and non-hyperresponders, in whom maximal LH responses to LH-RH without DA infusion were less than 153.5mIU/ml. In hyperresponders, serum LH response at 30 minutes after LH-RH administration was significantly (p less than 0.05) suppressed by DA infusion. In non-hyperresponders and young male subjects, however, serum LH response to LH-RH was not affected by DA infusion. Basal levels of serum LH and FSH in hyperresponders tended to be higher than that of non-hyperresponders. Total serum testosterone, free testosterone and estradiol levels of hyper and non-hyperresponders failed to reveal any significant differences. These observations suggest that 1) DA directly suppresses gonadotroph responsiveness to LH-RH, 2) in aging men, inhibitory tone imposed on gonadotrophs by DA is decreased, and 3) this decline of DA system can cause hypergonadotropism in aging men, independent of serum sex steroids levels.