Tissue iodoprotein formation during the peripheral metabolism of the thyroid hormones

• Text
• PDF

Abstract

The formation of tissue iodoproteins during the peripheral metabolism of the thyroid hormones was examined by determining the concentration of nonethanol-extractable 125I (NE125I) in various tissues after the intravenous injection of 3,5,3′-triiodo-L-thyronine (T3-125I) and L-thyroxine-125I (T4-125I) in groups of rats with iodide-blocked thyroid glands. 3 days after T3-125I and 7 days after T4-125I injection the concentration of NE125I in the liver and kidney was 5-10 times greater than in plasma. Smaller but nonetheless significant concentrations of NE125I were demonstrated in skeletal and cardiac muscle. Hepatic subcellular fractionation studies revealed that the major portion of the liver NE125I was in the microsomal fraction. Lower concentrations of NE125I were present in the nuclear, mitochondrial, and soluble fractions. When similar studies were performed in groups of rats pretreated with phenobarbital, an increase in the metabolic clearance of T3-125I (30%) and T4-125I (100%) was observed along with a highly significant increase in the NE125I concentration of the liver and plasma. The increase in hepatic NE125I in these studies was primarily due to the microsomal component.

Authors

Martin I. Surks, Harold L. Schwartz, Jack H. Oppenheimer