Propylthiouracil and hepatic clearance of thyroid hormones

Abstract

Biliary radioactivity derived from injected tracer amounts of either radioactive thyroxin or triiodothyronine was increased following injection of propylthiouracil (PTU). In one experiment PTU was administered 18 hr and again 1 hr before the measurement of biliary radioactivity. The tracer hormones were injected just prior to the first of four hourly periods of bile collection. Total radioactivity and trichloroacetic acid-soluble radioactivity were determined in hourly plasma samples. In another experiment, thyroxin was injected 18 hr prior to bile collection. Radioactivity in bile collected from each animal for 1 hr was measured and then PTU was infused at a rate of 5 mg/hr intravenously by constant infusion pump for the next 2 hr. While large alterations were occurring in radioactivity of bile, no discernible alterations were seen in either total plasma counts or counts in the trichloroacetic acid-soluble fraction of the plasma. These results, considered along with those of other investigators, were interpreted to mean that PTU probably has more than one extrathyroidal effect on the metabolism of thyroid hormones.