[Negative feedback in the epiphyseal-thyroid system].

The negative feedback mechanism in the epiphyseal-thyroid system was studied. The activating thyroxin influence upon hydroxy-indole-O-methyl-transferase, being the main enzyme of melatonin biosynthesis, was found in experimental Wistar rats. The "dose-response" curves were examined at varying times after thyroxin injections. The results obtained confirm the previous data concerning the activating effect of rat chronic hyperthyroidization on hydroxy-indole-O-methyl-transferase and intensified melatonin excretion with the urine in patients with pronounced thyrotoxicosis.