Abstract

The hepatic extraction ratio, clearance and flux of thyroxine measured by brachial artery and hepatic vein catheterization in normal man yields values similar to those determined indirectly. The rate of thyroxine clearance by the liver is from 20 to 94 ml/min and the average thyroxine flux is about 1 μg of hormonal iodine/min/m2 of body surface area. The portal circulation does not contribute to the extraction ratio. The clearance by the liver exceeds that produced by biliary excretion by 100-fold. It accounts for 60% of the early rate of removal of labeled thyroxine from the blood. The hormonal molecule in the hepatic venous effluent was unchanged although traces of radioactivity with the mobility of tetraiodothyroacetic acid were found.

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