Protein synthesis in perfused rat liver following thyroidectomy and hormone treatment.

Rat livers perfused in situ were used to investigate the effects of thyroid hormone deficiency and subsequent hormone replacement on hepatic protein synthesis and secretion. Following surgical thyroidectomy, production of albumin and total secretory proteins was reduced by 50%, whereas the synthesis of retained intracellular proteins was reduced by only 20% compared to the respective control rates. The 28% reduction in the synthesis of total liver proteins (secreted plus retained) was associated with a fall of similar magnitude in the tissue RNA level. Treatment of thyroidectomized rats with various doses of thyroid hormones indicated a regimen that restored the rate of synthesis of total liver proteins and the concentration of RNA to normal levels. This treatment regimen increased the synthesis of retained proteins to 115% of the control rate, but produced only modest increases in the production of albumin and total secretory proteins. These findings indicated an impairment in protein secretion in livers of thyroidectomized rats that persisted after the defect in protein synthesis was corrected by thyroid hormone treatment.