[Effect of acute and chronic administration of L- thyroxine and methimazole on blood levels of tryptophane, serotonin and 5-hydroxyindoleacetic acid in plasma of rats].

The effects of hyperthyreosis induced by the administration of thyroxine and hypothyreosis induced by the administration of methimazole on the levels of tryptophane, serotonin and 5-hydroxyindoleacetic acid in low-platelet blood plasma have been studied in Wistar rats. Thyroxine administration (120 micrograms/kg/24 h, intraperitoneally) lasting 7 days caused a decrease in serotonin concentration by 38 per cent. The level of this amine in rats receiving thyroxine during three months was elevated by almost three times. Tryptophane concentration did not change following thyroxine administration. Methimazole administration lasting 14 days (oral dose 15 mg/kg/24 h) caused an increase in tryptophane concentration by 34 per cent and in serotonin concentration by 24 per cent. Long-term hypothyreosis induced by methimazole administration lasting three months caused an 39 per cent increase in tryptophane and 38 per cent increase in serotonin concentration. Neither hyperthyreosis induced by thyroxine administration nor hypothyreosis induced by methimazole++ caused any changes in the concentration of 5-hydroxyindoleacetic acid. The importance of serotonin in pathogenesis of clinical symptoms accompanying the states of deficit or excess of thyroid hormones needs further elucidation.