Is Heparin an Antiprothrombin?

Abstract

Heparin while not itself an antithrombin will react with an unknown substance in the plasma to form a strong antithrombin. 1 Obviously it is essential to eliminate or correct for this antithrombic reaction in any experiment designed to determine whether heparin can also act as an antiprothrombin. A simple means to accomplish this has been found. Eagle 2 has shown that by passing carbon dioxide through plasma diluted with distilled water, prothrombin with some fibrinogen and a small amount of other constituents are precipitated. This precipitate when dissolved and neutralized is readily converted to thrombin by the addition of calcium. If heparin is an antiprothrombin it should prevent this conversion. The details of the experiment and the results are as follows:

Ten cc. of oxalated human plasma were diluted with 100 cc. cold distilled water and carbon dioxide bubbled through for 10 minutes. The precipitate was removed by centrifugation, dissolved in 8 cc. of normal saline, neutralized to pH 7.0, diluted to 9 cc, and divided into 2 equal portions. To the first were added 0.5 cc. heparin solution containing 5 mg. and 0.2 cc. of 0.1M calcium chloride, to the second, which served as control, 0.5 cc. saline and 0.2 cc. calcium chloride. A clot formed in both but appeared somewhat later in the solution containing heparin. After the removal of the fibrin, both were tested for their thrombic activity. 0.2 cc. of fibrinogen solution was mixed with 0.1 cc. of the thrombin solution and the clotting time determined. The reaction was carried out at a temperature of 39°-40°C. With this procedure, the coagulating potency of progressive dilutions of both thrombin preparations were determined. The results were:

The fibrinogen was prepared from rabbit plasma.