The uptake of fibrin and fibrin-degradation products by the isolated perfused rat liver.

The uptake of Se75-labeled rat fibrin and a specific preparation of fibrin degradation products by an isolated, perfused liver was studied. The rapid phase T ½ for fibrin in the perfusate was approximately 9 minutes. This is comparable to that found for aggregated I131 B.S.A. and colloidal gold in the same system. The loss of activity from the blood closely paralleled the increased activity recorded in the liver. No radioactivity was found in the bile samples or the T.C.A.-soluble fraction of plasma. Microradioautographs of washed liver tissue following the labeled, fibrin perfusion suggest the presence of the label on or in the Kupffer cells. Labeled rat fibrin preparations, digested by the action of "cold" rat plasmin to a distinct endpoint, were found to contain 3 distinct fractions on paper electrophoresis. Addition of these fractions to the perfusate resulted in approximately 25 per cent clearance of radioactivity over a 3-hour period. Hence, clearance of this specific F.D.P. preparation occurs at a much slower rate than that of fibrin. The T ½ as found to be in excess of 12 hours. These findings appear to confirm Lee’s observation that cells of the reticuloendothelial system are involved in the elimination of free circulating fibrin and its metabolic products.