THE DISTRIBUTION OF THYROXINE IN RAT LIVER CELL FRACTIONS1

Abstract

Il31-labeled thyroxine administered to thyroidectomized rats 3,6,12, or 24 hrs. prior to sacrifice, assumes a characteristic distr. in the rat liver cell. The nuclear, mitochondrial, and supernatant fractions accounted for 18, 23, and 54%, respectively, of the total thyroxine in the homogenates. Approx. half the thyroxine in the supernatant fraction was associated with the microsomes, Somewhat similar distrs. were observed when either I131-thyroxine or a labeled mitochondrial prepn. (from a rat given I13l.-thyroxine) were mixed with a normal liver homogenate in vitro. There was no indication that thyroxine concentrates in any of the cellular fractions. The available evidence indicates that thyroxine may, and does enter the rat liver cell.