L-thyroxine treatment and neurotransmitter levels in the cerebrospinal fluid of hypothyroid patients: a pilot study

Monoamine precursors, neurotransmitters and their metabolites were studied in cerebrospinal fluid (CSF) obtained from nine newly diagnosed hypothyroid patients. Before treatment, the serum TSH correlated positively with the CSF concentr ations of tyrosine and phenylalanine. During treatment, the levels of the precursors tryptophan, phenylalanine an d tyrosine decreased significantly, as was also the case with dopamine and the noradrenaline metabolite 4-hydroxy-3-methoxyphenylglycol (HMPG), but no t with serotonin, noradrenaline and the serotonin metabolite 5-hydroxyindol eacetic acid, nor the dopamine metabolites homovanilic acid and dihydroxyph enylacetic acid. The study provided some indication that the CSF levels of phenylalanine and tyrosine are related to thyroid function. Furthermore, we have found an indication that L-thyroxine treatment affects the CSF levels of the precursors as well as dopamine and HMPG. Our results support the no tion that there is an interaction between thyroid function and CSF disposit ion of monoamine compounds.