On the interaction of rabbit antithrombin III with the luminal surface of the normal and deendothelialized XXXX thoracic aorta in vitro.

@entity95 @entity11328
Pure rabbit antithrombin III was isotope labeled (with 125I or 3H) by two different methods; neither procedure caused a loss of antithrombin activity although both methods affected the affinity of the protein for Sepharose-heparin. From segments from freshly excised @entity95 aorta, the uptake of isotope-labeled antithrombin III by the endothelium was rapid and saturable, although relatively small compared to the uptake of @entity11328 ; binding of 3H-antithrombin III to the endothelium resembled that of 125I-antithrombin III. Transendothelial passage of antithrombin III into the subendothelial layers (intima-media) was slow and progressive. Endothelium binding was not affected by pretreating the vessel with either heparin, @entity11328 , or glycosaminoglycan-specific enzymes. Endothelium-bound antithrombin III was not selectively displaced by either heparin or @entity11328 . In contrast, endothelium-bound @entity11328 was rapidly dislodged by antithrombin III as a @entity11328 -antithrombin III complex. The surface of the deendothelialized aorta (ie, subjected to a balloon catheter) bound antithrombin III avidly. Pretreatment of the deendothelialized vessel with glycosaminoglycan-specific enzymes, particularly heparitinase, decreased intima-media binding by up to 80%. 125I-antithrombin III, when bound to the deendothelialized vessel surface, was actively displaced by either heparin, @entity11328 , or by unlabeled antithrombin III. The relatively poor binding of antithrombin III compared with that of @entity11328 by the endothelium in vitro supports an earlier proposal (Lollar P, Owen WG: J Clin Invest 66:1222-1230, 1980) that @entity11328 bound to high-affinity sites, possibly pericellular proteoglycan, of the endothelium is inactivated by plasma antithrombin III in vivo. Such a situation probably holds for large arteries at least.
