Localization Of Antithrombin III On The Vascular Endothelium And Its Function

<jats:p>Vessel wall is known to be rich in sulfated glycosamino glycans (GAGs) including heparin and they may serve as the natural catalysts of antithrombin III (AT III). This paper reports the possible role of AT III on the development of anticoagulant activity of activated AT m on the vessel wall. The freshly prepared rat aortic ring was washed in 0.05M Tris HC1 0.15M NaCl buffer (ph 7.5) with or without protamine, and was fixed for histochemical and immunofluo- rescent examinations. Anti-rat AT III serum was obtained from rabbit immunized with the purified AT III. Mucopolysaccharide stainings including Alcian Blue revealed the sulfated GAGs on the endothelium and the media. The GAGs on the endothelium corresponded with the specific AT III fluorescence localization. Protamine treatment disclosed the disappearance of the AT III fluorescence on the surface of endothelium. AT III-heparin complex was observed to be dissociated by protamine treatment through the investigations with affinity chromatography and sephadex G75 column chromatography, and the separated AT III was proved to recover the original progressive antithrombin activity.</jats:p><jats:p>Based on these experimental results it is concluded that the localized AT III on the surface of endothelium may be present in complexed with the exposed heparin or other GAGs and be present in activated, and that the complexed AT III is considered to inhibit proteases in situ in the circulating blood to prevent the activation of coagulation process. This phenomenon may have a clinical significance on the pathogenesis and treatment of thromboembolic vascular diseases.</jats:p>