RELATION BETWEEN THE BILIARY EXCRETION OF THYROXINE AND ITS BINDING BY THE SERUM PROTEINS IN MONKEYS.

Abstract

Nonradioactive thyroxine (T4) and sodium salicylate were injected intravenously into monkeys given intravenous 13lI-labeled T4 24 hr before the injection. Nearly all the m I in the bile, before and after the injections, was in the form of glucuronides or sulfate esters, both of which require intracellular enzymes for their synthesis. Injections of T4 caused an increase in the proportion of free to bound T4 by decreasing the concentration of free binding sites on the serum thyroxine-binding globulin (TBG), a fall in the plasma concentration of radioactive protein-bound iodine (PB131I), and a rise in the concentration of 13lI in the bile. T4 had no effect on bile flow. Salicylate, injected after nonradioactive T4, increased the proportion of free to bound T4 in the plasma by displacing T4 from albumin, and caused a fall in the plasma PB131I concentration and a rise in the concentration of mI in the bile. Salicylate stimulated the bile flow. These findings are consistent with the hypothesis that only the fre...