Studies with High and Low Molecular Weight Tritium-Labelled Heparin in Vivo and in Vitro

Abstract

When defibrinated platelet-poor plasma 1s chromatographed on Sephadex G-200, fractions with antithrombin-heparin cofactor activity are found 1n only one area. When platelet-poor plasma treated with a tritium-labelled heparin is chromatographed on Sephadex G-200, radioactivity, signifying the presence of heparin, is spread across all of the protein fractions, whereas immediate antithrombin activity is located in two. main areas. Tritiated heparin produced from porcine intestinal mucosa was fractionated on a Sephadex G-200 column with separation of the higher and lower molecular weight fractions. These fractions were added to platelet-poor plasma which was then rechromatographed on Sephadex G-200.With the higher molecular weight, heparin radioactivity appeared in fractions which usually have immediate antithrombin activity, whereas, with the lower molecular weight heparin, it did not. A comparison of the activities of the higher and lower molecular weight material was made after intravenous injection into rats. The higher molecular weight heparin gave higher concentrations of radioactivity in the liver and blood. In addition, the anticoagulant activity as measured by a whole blood recalcification clotting time was maintained for a much longer period. The lower molecular weight heparin was excreted more rapidly in the urine. It is concluded that only the higher molecular weight heparins have anticoagulant activity 1n combining with antithrombin whereas lower molecular weight heparins do not combine with antithrombin but are eliminated in the urine.