ABSTRACT
Experiments were made on 100 random bred rats of various age groups, controls and animals exposed to single external gamma-radiation at a dose of 1 Gy on the 35th day of life. Thyroxine and triiodothyronine concentrations were investigated in peripheral blood and separately in arterial blood, in thyroid, portal and hepatic venous blood. The activity of T4 conversion into T3 by 5'-deiodinating enzymes of the liver microsomal fractions and the activity of the liver mitochondrial enzymes--cytochrome of C-oxidase and alpha-glycerophosphate dehydrogenase were also investigated. A decrease in thyroid excretion of T4 and T3 and T4 blood concentration was noted in rats exposed to irradiation. 5'-thyroxine deiodinating activity of the microsomal enzymes was elevated in the liver of such rats; a T3 ratio in the blood outflowing from the liver was on the increase. A conclusion has been made that 5'-deiodination in the liver of rats with postradiation hypothyrosis is effected as a result of increased production of the most active hormone T3 from less active T4.
