Effect of TRH on TSH and prolactin levels in affective disorders

The thyrotropin-releasing hormone (TRH) test was studied in 32 patients with acute major depressive disorder, 16 patients with recurrent unipolar (n = 8) or bipolar (n = 8) affective disorder in remission, and 22 healthy control subjects. Twenty-six of the 32 acutely ill patients were also studied when in remission. Outcome in these patients was correlated to serum levels of triiodothyronine (T3), 3,3',5'triiodothyronine (reverse T3), thyroxine (T4), thyroid-stimulating hormone (TSH), prolactin (PRL), melatonin, dexamethasone suppression test (DST) results, and clinical symptoms assessed by the Comprehensive Psychopathological Rating Scale (CPRS). The TSH response to TRH (delta TSH) was decreased in the acutely ill patients, but no difference was found between patients in remission and controls. The delta TSH was correlated to TSH but not to T3 and T4 levels in both acutely ill and control subjects. In the acutely ill group, delta TSH did not distinguish between patients with normal and abnormal DST results. Thus, abnormalities in the hypothalamic-pituitary-thyroid (HPT) axis are not correlated to abnormalities in the hypothalamic-pituitary-adrenal (HPA) axis. Moreover, delta TSH did not differentiate between melancholic (DSM-III) and nonmelancholic patients or between patients with primary and secondary depression. No correlation was found between delta TSH and CPRS scores. Patients with observable agitation greater than 0.25 points (item range 0-3) had higher levels of delta TSH than patients with lower levels. No significant correlation was found between delta TSH and seven specific symptom clusters on the CPRS. However, there was a possible relation between low delta TSH and violent suicide attempts or suicide. PRL levels did not distinguish acutely ill patients from controls. Finally, there was no significant regression between delta TSH and melatonin levels. The decrease in delta TSH seen in the acutely ill patients was too small to be of diagnostic value as a laboratory measure differentiating acutely ill and healthy subjects. The mechanism underlying the HPT alterations in acute major depressive disorder may be a desensitization of the TRH receptor in the thyrotrophs secondary to an increased endogenous TRH stimulation.