THE INFLUENCE OF RESERPINE, SEROTONIN AND METABOLITES OF TRYPTOPHANE ON THE DEGRADATION OF THYROXINE AND ITS DERIVATIVES12

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Abstract
It has previously been reported that certain metabolites of tryptophane interfere with an action of thyroxine in vitro. The present stud}’ was undertaken to determine whether these compounds also influence the peripheral metabolism of thyroxine and its analogues. It was found that serotonin, 5-hydroxytryptophane, 5-hydroxyindole, 5-hydroxyindoleacetic acid, 3-hydroxyanthranilic acid and xanthurenic acid all depressed the degradation of thyroxine to inorganic iodide by homogenates of mammalian and amphibian tissues. A similar effect was obtained with reserpine. On the other hand, tryptophane, indole, indole-acetic acid, anthranilic acid, quinolinic acid, kynurenine, kynurenic acid and nicotinic acid were without effect. Both serotonin and reserpine also inhibited the formation of iodide from triiodothyronine, tetra- and triiodothyroacetic acids in these systems. In contrast, the deiodination of mono- and diiodotyrosine by mouse liver homogenatc was not altered by the presence of serotonin. Depressed degradation of thyroxine to iodide was also observed in liver obtained from tadpoles and mice pretreated with reserpine. Evidence was obtained that certain of the tissues used were capable of dcaminating thyroxine to its acetic acid analogue. In the presence of serotonin, increased amounts of tetraiodothyroacetic acid were formed. The implications of these findings are discussed.