Effect of Thyroxine and 5,5-Diphenyl-2-Thiohydantoin on Enzyme Activities of Rat Liver and Kidney

Abstract

Injected L-thyroxine causes an increase in the activities of pyruvate carboxylase (E.C. 6.5.1.1), phosphoenolpyruvate carboxykinase (E.C. 4.1.1.32), glucose-6-phosphatase (E.C. 3.1.3.9), and malic enzyme (E.C. 1.1.1.40) in rat liver. Dietary 5,5-diphenyl-2-thiohydantoin blocks the thyroxine-stimulated increase of these activities. Neither thyroxine nor diphenylthiohydantoin affect the liver activities of fructose-1,6-diphosphatase (E.C. 3.1.3.11), total hexose monophosphate shunt dehydrogenases (E.C. 1.1.1.49 and E.C. 1.1.1.44), TPN-linked isocitric dehydrogenase (E.C. 1.1.1.42), and cytosolic a-glycerophosphate dehydrogenase (E.C. 1.1.1.8). In kidney, the only enzymes affected were malic enzyme, pyruvate carboxylase, and glucose-6-phosphatase. Those liver enzyme activities stimulated by thyroxine all show a decrease in activity 29 hr after a single dose of diphenylthiohydantoin. Our results suggest that diphenylthiohydantoin is highly effective in blocking the stimulation by thyroxine of several enzyme activities, and that the mechanism of inhibition may be similar for these enzymes, since they all showed decreases in activity at approximately the same time after a single injection of diphenylthiohydantoin. (Endocrinology90: 1521, 1972)