Influence of Thyroxine on Hexokinase, Succinoxidase and Choline Oxidase

Abstract

A NUMBER of workers have reported that the administration of either thyroxine or thyroid powder to a number of species results in significant changes in the activity of various tissue enzymes. Thus the D-amino-acid oxidase¹ and succinoxidase and cytochrome oxidase² activity of liver appears to be enhanced in hyperthyroid rats ; the activity of rat serum pseudo-choline-esterase is markedly decreased following thyroxine administration³, while the activity of rat liver arginase and acid phosphatase appears to be uninfluenced by thyroxine⁴. We have recently investigated the influence of thyroxine administration on the activity of certain enzymes in the liver and skeletal muscle of adult, male hooded rats. In view of the fact that thyroxine was administered over a period of some days prior to measuring the enzyme activities, the paired feeding technique was employed in order to eliminate alteration in the food intake of the thyroxine-treated animals as a factor responsible for any changes observed. In each series of experiments the animals were pair-fed on a synthetic diet supplemented with vitamins.