Protein synthesis in the tumor-influenced hepatocyte.

Total body protein turnover is elevated in the Fischer 344 rat bearing a subcutaneous transplantable methylcholanthrene-induced sarcoma. To assess the contribution of the liver, we have measured protein synthesis by hepatocytes freshly isolated from tumor-bearing animals over a range of tumor burdens and from sham-inoculated nontumor bearers. Synthetic rates of total hepatocyte protein were more than twofold greater in hepatocytes from tumor-bearing animals (P less than 0.005) and the increase was proportional to the tumor burden in individual animals (n = 19; r = 0.68; p less than 0.005). When compared with pair-fed nontumor bearers, the differences in rates of total hepatocyte protein synthesis reached statistical significance only when the tumor burden exceeded 5% of total body weight. The stimulation in synthetic rates applied equally to secretory and nonsecretory hepatocyte protein. Furthermore, a lack of net protein accrual in the livers of tumor-bearing animals suggests a concomitant increase in the rate of hepatic protein degradation.