Pituitary-Thyroid State Correlates with Central Dopaminergic and Serotonergic Activity in Healthy Humans

Data from lower animals suggest anatomic and physiological interactions between brain dopamine and serotonin (5-hydroxytryptamine, 5-HT) systems and the hypothalamic-pituitary-thyroid axis. However, in humans, investigations of interactions between these central neurochemical systems (especially the dopaminergic system) and thyroid function are rare; in healthy humans they are practically nonexistent. Using cerebrospinal fluid (CSF) and blood samples simultaneously obtained from indwelling subarachnoid and venous catheters in healthy humans, we determined the CSF concentrations of homovanillic acid (HVA) and 5-hydroxyindolacetic acid, the major metabolites of dopamine and 5-HT, and plasma concentrations of TSH, total triiodothyronine (T3), free T3, total thyroxine (T4) and free T4. CSF HVA concentrations were significantly and negatively correlated with plasma TSH and T3 (free and total), but not with T4 (free or total). CSF 5-HIAA concentrations were significantly and negatively correlated with plasma TSH and total T3 but not with free T3 or T4 (free or total). These results indicate that CNS monoamine-thyroid interactions are of physiological significance in the normal, euthyroid human.

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