PROTHROMBIN SYNTHESIS: AN EXAMPLE OF HEPATIC FUNCTION

Prothrombin, a plasma protein valuable in blood coagulation, appears to be produced exclusively by liver parenchymal cells. Immunuofluorescent procedures were applied to various organs from bovine, canine and human sources. Since antiprothrombin was species specific, each species required its own fluorescent antiprothrombin as a cellular marker. Reticuloendothelial cells were not reactive with fluorescent antiprothrombin. In normal individuals prothrombin synthesis occurred in a cyclic asynchronous fashion with significant quantities of prothrombin contained in only 10-30% of the hepatocyte population. Essentially all hepatocytes were able to synthesize prothrombin when stimulated by vitamin K 1 . The rate of prothrombin synthesis depended upon both the level of plasma prothrombin and the amount of vitamin K 1 , available to the hepatocytes. From quantitation of plasma prothrombin during drug alteration of prothrombin synthesis in dogs the average prothrombin replacement time was calculated as 9½ hr.