The hypothalamic-pituitary-thyroid axis in depressive patients and healthy subjects in relation to the hypothalamic-pituitary-adrenal axis.

Serum levels of thyroid stimulating hormone (TSH), triiodothyronine (T3), free T3 index (fT3i), thyroxine (T4), and free T4 index (fT4i) were measured before and after administration of 1 mg of dexamethasone in 54 depressive patients and 54 matched healthy subjects. A followup study at a mean of 2 years was performed in 28 patients in remission. Basal TSH levels were lower and fT4i levels were higher in major depressive patients compared with healthy subjects. After dexamethasone administration, there was no significant change in any of the hormones in a subgroup of 46 major depressive patients in contrast to matched healthy subjects, who showed a significant decrease in the levels of TSH, T3, and fT3i. The magnitude of the TSH response to dexamethasone in the major depressive patients was related to the level of nocturnal urinary cortisol excretion and pathological dexamethasone suppression test results. The level of TSH in depressive patients during remission did not return to levels similar to those found in the healthy subjects.