The role of thyronine in thyroid hormone metabolism.

Thryonine (T0) has been identified in human urine using gas chromatography-mass fragmentography (G.C.M.F.). In 22 normal individuals urinary T0 concentration was found to range between 8--25 nmol/24h. Assuming the mean normal thyroxine (T4) production rate to be approximately 100 nmol/24h, our findings indicate that less than 20% of this could be accounted for as urinary T0 excretion, thus supporting earlier findings that the peripheral metabolism of T4 is not limited solely to deiodination.