Biosynthesis of factor V by normal adult rat hepatocytes

The synthesis of coagulation factor V was investigated in isolated rat hepatocytes maintained in long-term primary culture. Two culture conditions were compared. A clotting assay and an immunoprecipitation experiment with rabbit anti rat factor V IgG were used to demonstrate not only the presence of factor V in the cells but also active secretion into the culture medium. Both the inhibition of the clotting reaction in presence of the antibody and absence of thrombin in culture media confirmed the specificity of the clotting assays. Electron microscopic examination located factor V in the endoplasmic reticulum and Golgi apparatus of hepatocytes in common with other liver specific plasma proteins. Examination of liver tissue sections confirmed the production of factor V in hepatocytes but not in hepatic endothelial cells although it did not exclude a transit pathway of factor V through these cells. Addition of Russell viper venom factor V activating enzyme to the culture medium had no effect on the factor V activity. In contrast, treatment of cell extracts did increase the coagulant activity. This suggests that hepatocytes contained principally an unactivated form or procofactor, whereas factor V present into the culture medium was mainly in an activated form. These data provide evidence for synthesis and secretion of an hepatocytic factor V.