TRH-induced hormonal responses: the effect of pizotifene and naloxone

We examined the effects of the serotonin antagonist pizotifene (4 mg daily for 3 days orally), and the opiate antagonist naloxone-HCI (0.8 mg intravenously) on the TRH-induced thyrotropin (TSH), growth hormone (GH), and prolactin (PRL) response in female psychiatric inpatients with adjustment disorder or alcohol abuse. All the patients were free from interfering endocrine and metabolic illness and had not received major psychotropic medication before the investigation. Pizotifene caused a small but significant decrease of the TRH-induced TSH response in 8 patients, two of them changed their responses from normal (i.e. above 5 mU/l) to blunted. Neither GH nor PRL changed significantly after pizotifene. Naloxone-HCI, 30 min before the TRH challenge, did not produce any significant change in the TSH, GH or PRL responses, nor did it cause any significant change in the plasma level of these hormones by itself. The hormonal responses to TRH remained unaltered in ten other patients who had repeated tests without any drug treatment between the two occasions. The results suggest that serotonin deficiency may play a role in the blunted TSH response to TRH, while opiate mechanisms do not appear to have a primary influence on these endocrine effects of TRH.