STUDIES ON THE EFFECT OF THYROXINE ADMINISSTRATION ON CATALASE ACTIVITY

Abstract

Liver, kidney and blood catalase activity was determined on normal rats and rats receiving injections of thyroxine. Thyroxine administration produced a decrease in liver and kidney catalase activity, but no change was detected in blood catalasc activity. Addition of thyroxine or 3,5,3′-triiodo-L-thyronine to liver homogenates did not alter the enzyme activity. When liver homogenates from normal and thyroxine-treated rats were mixed, the catalase activity of the mixed homogenate was equal to the activities of the separate fractions. Measurement of the incorporation of Fc⁵⁹ into liver catalase revealed a marked inhibition of radioiron utilization in thyroxine-treated animals. From these data it was concluded that the decreased catalase activity in the livers of thyroxine-treated rats was the result of an inhibition of enzyme formation.