[Dopaminergic control of gonadotropin secretion in male senescence]

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.