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 (T(3)), free T(3), total thyroxine (T(4)) and free T(4). CSF HVA concentrations were significantly and negatively correlated with plasma TSH and T(3) (free and total), but not with T(4) (free or total). CSF 5-HIAA concentrations were significantly and negatively correlated with plasma TSH and total T(3) but not with free T(3) or T(4) (free or total). These results indicate that CNS monoamine-thyroid interactions are of physiological significance in the normal, euthyroid human.