Difference Between Evening and Morning Thyrotropin Responses to Protirelin in Major Depressive Episode

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Abstract
• We studied the thyrotropin response to protirelin challenge (200 μg intravenously) at 8 AM and at 11 PM after a minimum washout period of 10 days in 29 euthyroid inpatients who met DSM-III-R criteria for major depressive episode and 20 normal volunteer controls. The maximum increment in thyrotropin above baseline (△thyrotropin) was significantly greater at 11 PM than at 8 AM both in patients and in controls. However, the difference between 11 PM △thyrotropin and 8 AM △thyrotropin (△△thyrotropin) was significantly lower in patients than in controls. The lower △△thyrotropin found in patients could not be explained by differences in age, body weight, sex, or thyroid functioning. In the overall population, △△thyrotropin correlated with circadian variables (ie, mesor and amplitude). With the use of a criterion of less than 3 mU/L to define a blunted △△thyrotropin, the diagnostic sensitivity was 89% and the specificity was 95%. We suggest that △△thyrotropin has the advantage of taking into account chronobiologic influences in the interpretation of the protirelin/thyrotropin challenge, and this may explain the improved diagnostic value derived from this measure in the diagnosis of major depressive episode.