The prolactin response to thyrotrophin-releasing hormone is intact in the human male castrate

This study has evaluated the role of the testis in the modulation of Prl secretion in the male. Six elderly male castrates aged 58-69 years, who had undergone bilateral orchidectomy for prostatic carcinoma, were challenged with LRH (100 μg) and TRH (200 μg) administered together as a bolus. Their response was compared to 8 elderly males aged 65-75 years. One additional male aged 26 years, who had lost both his testes following a war injury was also challenged with bolus LRH and TRH; in addition, he was given LRH, TRH and the dopaminergic antagonist, metoclopramide (MET) sequentially at 30 min intervals. On a subsequent occasion, MET was given also. The responses in this young castrate were compared to 24 young males who received the sequential protocol and 12 who received a solitary bolus of MET. In the castrate subjects, gonadotrophins were markedly elevated, whereas testosterone and oestradiol levels were significantly decreased as compared to the controls. The castrate subjects also had exaggerated LH and FSH responses to LRH. In contrast, basal Prl levels and the responses to TRH in the castrates were similar to the controls. In addition, the young male castrate showed a normal Prl response to metoclopramide, when this was given alone, or 30 min after TRH. The intact Prl profile in the castrate subjects should be contrasted to the exaggerated Prl response to TRH which has been described in patients with primary testicular failure and elevated LH and FSH levels. These results indicate that the presence of the testis is obligatory for the exaggerated Prl response to TRH observed in patients with primary testicular failure.