Action of Adrenal Corticoids on Protein Metabolism in the Thiouracil-Treated Rat

Abstract

When fed a casein diet containing 0.5% thiouracil, male Wistar rats (150 g) had increased liver weights and protein/ DNA ratios but unaltered RNA/DNA ratios. When the adrenocorticoids—cortisone and corticosterone—were administered to these goitrogen-fed animals at a dose of 0.5 or 1.5 mg/day, there were decreases in liver size, protein/RNA and protein/DNA ratios. Concomitantly, at the 1.5 mg/day corticoid treatment, the free amino acid pool, RNA/DNA ratios, and the ability to incorporate labeled methionine into liver protein all increased. The biochemical profile of the gastrocnemius muscle of goitrogen-fed rats was characterized by a decreased protein/RN A ratio and a diminished ability to incorporate amino acids. When adrenal steroids were administered to these hypothyroid animals, there was a decrease in the muscle free amino acid pool and further reduction in the amino acid incorporation rate. Administration of adrenal corticoids (1.5 mg/day) to control-fed animals resulted in lower protein/DNA and protein/RNA ratios and an elevated esssentialrnonessential free amino acid ratio. The incorporation rate of 35S from methionine into muscle protein was elevated at the 0.5 mg level of adrenal corticoid, but equal to control at the 1.5 mg/day dose. The lower protein/RNA ratios in liver and muscle and the elevated essential: nonessential free amino acid ratios in muscle are suggestive of enhanced catabolism. One action of cortisone and corticosterone, an apparent enhancement of protein catabolic activity in the liver and muscle, is more readily observed in the goitrogen-fed rat. (Endocrinology76: 418, 1965)