Synthesis and half-life of a serum factor in normal and tumor-bearing animals

The synthesis and disappearance of a serum factor from the circulating blood of rats bearing Morris hepatomas 7777 or 7800 were described. We provided evidence that the factor was synthesized by the livers of normal rats and continued to be synthesized in tumor-bearing animals. Despite very low levels in the sera of tumor-bearing animals, the factor was synthesized at twice the rate in these animals compared to that in normal rats. The half-life of the total serum protein was 2 days in normal rats and 2.9 days in hepatoma 7777-bearing animals. The half-life of the serum factor, on the other hand, was 23 hours in normal rats but only 9 hours in hepatoma-bearing rats. This rapid disappearance of the factor from the circulating blood, despite an increased synthesis, accounts for the complete absence of the factor in the sera of hepatoma-bearing animals with tumor weights larger than the liver weights.