© 1996 American Heart Association, Inc.
Articles |
Thrombin Inhibition by Antithrombin III on the Subendothelium Is Explained by the Isoform ATß
the Vascular Research Group, Department of Surgical Sciences, Karolinska Institute, and Pharmacia (S.I.), Stockholm, Sweden.
Correspondence to Jesper Swedenborg MD, Vascular Research Group, Department of Surgery, Karolinska Hospital, S-171 76 Stockholm, Sweden. E-mail kjsg@kir.ks.se.
Balloon injury of the rabbit aorta results in thrombin coagulant activity on the injured vessel wall that causes fibrin formation. The anticoagulant activity of both the intact and injured vessel wall has been partly explained by glycosaminoglycans with heparin-like activity that augment the activity of antithrombin III (AT). AT exists in two isoforms, 
and ß. ATß, which constitutes only 5% to 10% of AT in plasma, lacks one carbohydrate side chain, has higher affinity for glycosaminoglycans, and associates more readily with the subendothelium. This study evaluated whether AT can inhibit thrombin on the injured vessel wall and, if so, whether one of the isoforms is more effective then the other. The two isoforms were isolated from human plasma by heparin-Sepharose chromatography, and the purity was investigated by isoelectric focusing and crossed immunoelectrophoresis. Rabbits were subjected to balloon injury of the aorta; 3 hours after injury the aorta was excised. Thrombin coagulant activity on the aorta was measured by exposure to fibrinogen and thereafter by measuring the generation of fibrinopeptide A. Injured animals were treated with AT, AT, or ATß and were compared with control animals. AT was demonstrated on the injured vessel wall by using an immunohistochemical method. Animals receiving crude AT had significantly lower amounts of thrombin coagulant activity on the injured aortic wall than control animals, but AT at a comparable dose had no effect. ATß was given in the same dose as crude AT and also at a dose (10%) proportional to its presence in plasma. Animals receiving ATß had significantly lower values of thrombin on the injured aortic wall than control animals. We conclude that the inhibitory effect of AT on thrombin coagulant activity on the injured vessel wall is explained by its ATß content.
Key Words: antithrombin III • antithrombin isoform • thrombin • vascular injury • fibrin
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