Biosynthesis of plasminogen by the perfused rat liver

We investigated synthesis of plasminogen by the isolated rat liver perfused in vitro for 10 hours. Studies were performed under basal conditions as well as under conditions of hormone stimulation known to augment synthesis of acute-phase reactant proteins by the isolated perfused rat liver. In six control perfusions, mean cumulative synthesis of plasminogen after 10 hours of perfusion was 1.61 +/- 0.11 mg/300 cm2 body surface area of the rat liver donor, and in six "acute-phase" experiments, mean cumulative synthesis was 1.55 +/- 0.07 mg. When cycloheximide was added to the liver perfusate at the outset to inhibit protein synthesis, production of plasminogen was greatly reduced. Synthesis of fibrinogen in these same perfusions was characteristic of the known acute-phase reactant proteins. In control perfusions, 68.85 +/- 6.19 mg fibrinogen was produced in 10 hours compared with 106.20 +/- 6.93 mg in acute-phase perfusions. These studies indicate substantial synthesis of plasminogen by the isolated perfused rat liver, but suggest that synthesis of this protein is not affected by those conditions that enhance synthesis of known acute-phase reactant proteins.