Production and release of plasminogen by isolated perfused rat liver.

Abstract

In view of conflicting evidence for a major hepatic role in the synthesis of circulating plasminogen, the precursor of the fibrinolytic enzyme plasmin, a sensitive assay was used to study the accumulation of small quantities of plasminogen in a recycling rat liver perfusion system. Plasminogen was purified from Sprague-Dawley rat plasma and a monospecific antiserum against it was raised in rabbits. Isolated rat liver perfusions were performed with an oxygenated recycling perfusate consisting of a perfluorotributylamine/Pluronic F-68 emulsion (Fluosol 43) free of plasma proteins and blood cells. The system was capable of synthesizing albumin and transferrin. The cumulative appearance of plasminogen in the perfusate was measured by a sensitive, specific radioimmunoassay. Plasminogen concentration increased progressively during the first 2 h of perfusion; the observed average net synthesis in 5 separate experiments was .apprx. 35 .mu.g/h per 100 g of body wt. Exposure of the perfused liver to 18 .mu.M cycloheximide inhibited additional increase in the titer of plasminogen. Evidence for de novo synthesis was provided by the incorporation of 14C-labeled leucine into specific immunoprecipitates of plasminogen and the inhibition of this incorporation by cycloheximide. Analysis of the immunoprecipitates by sodium dodecyl sulfate/polyacrylamide gel electrophoresis revealed a single peak of radioactivity corresponding to MW of 82,000. The liver is apparently a major site of plasminogen production.