THE CATABOLISM OF 131I-LABELLED HOMOLOGOUS γ-GLOBULIN IN NORMAL, HYPERTHYROID AND HYPOTHYROID RATS

Abstract

SUMMARY: The biological half-life of injected homologous ¹³¹I-γ-globulin was found to be 4·8 days in euthyroid, 5·8 days in thyroidectomized, and 3·8 days in thyroxine-treated rats. The catabolic rate of homologous γ-globulin, expressed as a percentage of the intravascular protein broken down per day, was decreased from 25·5% in normal rats to 22·5% in thyroidectomized animals, and increased to 39·2% by thyroxine treatment. Total serum protein levels were not affected by thyroxine treatment (0·02 mg/kg) in the rat, but increased after thyroidectomy. This increase was chiefly due to an increased γ-globulin level, and it is postulated that catabolism of γ-globulin in the thyroidectomized rat is decreased to a greater extent than is γ-globulin synthesis.