NORMAL I131L-THYROXINE METABOLISM IN THE PRESENCE OF POTASSIUM PERCHLORATE AND INTERRUPTED BY PROPYLTHIOURACIL1

Abstract

The urinary and fecal excretions of I131 were studied during chronic administration of I131 L-thyroxine to rats fed a low iodine, low residue diet. Control rats and those fed KClO4 were in iodine balance when they excreted 70% of the daily I131 dose in the urine. Rats fed propylthiouracil (PTU) accumulated radio-thyroxine in their bodies and at equilibrium they excreted only 30% of the daily I131 dose in the urine and 70% in the feces. Paper chromatograms showed the fecal I131 was predominately thyroxine but an unknown I131-labeled material was also present in the feces. Fifty micrograms of PTU per rat per day was enough to cause the PTU effect on thyroxine metabolism. The distribution of urinary and fecal I131 was independent of thyroxine dose in these experiments.