Antithrombin III-/J Associates More Readily Than Antithrombin Ill-or With Uninjured and De-endothelialized Aortic Wall In Vitro and In Vivo

The properties of two isoforms, or and fi, of rabbit antithrombin III (ATIII) were compared in the presence of undamaged or de-endothelialized rabbit aortic wall. Similar quantities of ATIII-tt and ATUI-fi bound to and rapidly saturated the endothelium in vitro, but the rate of transendothelial passage of ATIII-/3 exceeded that of ATIII-a by 22%. Furthermore, ATIII-0 was adsorbed approximately twice as rapidly as ATlII-a by the subendothelium of the de-endothelialized aorta. Binding of both isoforms was decreased (ATIII-/3 more than Al'lU-or) by pretreating the subendothelial surface with heparitinase. Also, subendothelium-bound ATIII-/J was desorbed more readily than bound ATlII-aby thrombin. In vivo, the rate of uptake of iodine-131-labeled ATI1I-/3 from the circulation by the aortic wall and the major organs was 30-50% faster than that of iodine-125-labeled ATIII-o: In contrast, the uptake of I-ATIII-0 by the de-endothelialized aorta in vivo was three times faster than that of '"I-ATlII-a. By these criteria, ATIII-^ is the more active of the two isoforms. We surmise that plasma and, consequently, vessel wall levels of ATIII-/3 may be vital for controlling thrombogenic events caused by injury to the vascular wall. (Arteriosclerosis and Thrombosis 1991;ll:530-539)