Hormonal response to thyrotropin-releasing hormone following rest-activity reversal in normal men

The prolactin (PRL) and thyrotropin (TSH) response to an intravenous dose (400 micrograms) of thyrotropin-releasing hormone (TRH) was studied in eight healthy young men in the morning (0800 hr), in the evening (2000 hr), and after an acute 12-hr shift of the rest-activity cycle. The PRL and TSH response to TRH was significantly greater in the evening than the morning. The increased PRL and TSH responses observed in the evening were significantly reduced following rest-activity reversal. Our findings underscore the importance of temporal factors in determining response to TRH. These factors may be relevant in clarifying the mechanisms underlying abnormal hormonal responses to TRH in patients with affective disorders.