DER EINFLUSS VON 2-THIOURAZIL UND THIAMAZOL AUF DIE AKTIVITÄT DER L-α-GLYZEROPHOSPHAT-OXIDASE DER RATTENLEBER IN ABHÄNGIGKEIT VON L-THYROXIN, L-3′, 3,5-TRIJODTHYRONIN UND L-3′-ISOPROPYL-3,5-DIJODTHYRONIN

Abstract

ABSTRACT The activity of the L-α-glycerophosphate dehydrogenase (EC. 1. 1. 2. 1.) was measured in rat liver mitochondria after thyroidectomy and substitution with L-3′-isopropyl-3,5-diiodothyronine (iPT2), L-3′,3,5-triiodothyronine (T3), and L-thyroxine (T4). A substitution with 0.18, 0.46, and 3.7 μg per 100 g animal weight and day of iPT2, T3, and T4 for 10 days was necessary to reach normal range activity. In intact rats an ED50 of 1.4. 3.4, and 15.6 μg/100 g/day of iPT2, T3, and T4 respectively was found. 2-Thiouracil and 1-methyl-2-mercapto-imidazole (methimazole, thiamazole) decreased the effectivity of T4. The effectivity of T3 was unaltered by 2-thiouracil and methimazole and that of iPT2 enhanced by 2-thiouracil and not altered by methimazole. 2-Methylmercapto-imidazole was found to be without any effect on the increased activity of L-α-glycerophosphate dehydrogenase induced by thyroxine analogues. The activation of thyroxine by deiodination and the inhibition of this reaction by 2-thiouracil and methimazole are discussed.