Biliary and fecal clearance of endogenous thyroid hormone in cold-acclimated rats

Abstract

The increase in fecal excretion of thyroid hormone by rats as a result of cold acclimation may result from a more rapid biliary excretion of the hormone and/or from a reduction in reabsorption of hormone from the intestinal tract. In the present study cold acclimation was found to increase both biliary and fecal clearances of endogenously labeled hormone. No evidence was found, under the conditions of the experiment, to support the possibility that the greater volume of food eaten in some way reduces reabsorption. Feeding a commercial rat chow led to higher values of both fecal and biliary clearances than feeding a test diet. Significant reabsorption of hormone was not evident. The linear correlation between fecal and biliary clearances indicates the removal of the hormone by the liver and excretion via the bile is the major mechanism governing rate of excretion in the feces.