Relationships between basal hypothalamic- pituitary-thyroid-axis activity and plasma haptoglobin levels in depression

The present study was carried out to investigate the relationship between basal hypothalamic- pituitary-thyroid (HPT)-axis function and the acute phase (AP) response in depression. Toward this end, the authors measured serum concentrations of basal thyroid-stimulating-hormone (TSH), free thyroxine (FT4) and free triiodothyronine (FT3), and plasma levels of an AP protein, i.e. haptoglobin (Hp) in 38 depressed in-patients and in 11 normal controls. In depression, basal TSH was significantly and negatively related to Hp values, whereas in normal controls a trend toward a positive correlation between both factors was found. Depressed patients with increased Hp levels (≥250 mg/dl) showed significantly lower basal TSH levels than patients with normal Hp levels. No significant correlations were found between Hp plasma levels and either FT4 or FT3 serum concentrations. The results support the hypothesis that lower TSH secretion in major depression may be related to the AP response in that illness, and may constitute an expression of a coordinated neuroendocrine-immune response to nonthyroidal illness.