Non-anticoagulant heparin increases endothelial nitric oxide synthase activity: Role of inhibitory guanine nucleotide proteins

Heparin, which is widely used clinically, has recently been shown to have s pecific properties affecting the vascular endothelium, We hypothesized that heparin stimulates endothelial nitric oxide synthase (eNOS) activity by a mechanism independent of its anticoagulant properties and dependent on an i nhibitory guanine nucleotide regulatory protein (Gi). We determined the eff ect of both heparin and N-acetyl heparin (Non-Hep), a heparin derivative wi thout anticoagulant properties, on eNOS activity in cultured bovine aortic endothelial cells and on endothelium-dependent relaxation in isolated vascu lar rings. The eNOS activity was determined by measuring both citrulline an d nitric oxide (NO) metabolite formation. Heparin and Non-Hep dose-dependen tly increased basal eNOS activity (ED50 1.0 mu g/ml or 0.15 U/ml), an effec t that was significantly inhibited by pertussis toxin (100 ng/ml), a Gi-pro tein inhibitor. Agonist-stimulated (acetylcholine, 10 mu M) eNOS activity w as potentiated following pre-treatment with both heparin and Non-Hep and re versed by pertussis toxin. Heparin and Non-Hep induced a dose-dependent rel axation in preconstricted thoracic aortic rings, an effect that was signifi cantly inhibited by pertussis toxin, endothelial inactivation (following tr eatment with sodium deoxycholate) and N-G-nitro-L-arginine-methyl ester (L- NAME). We conclude that heparin and non-anticoagulant heparin induce endoth elium-dependent relaxation following activation of eNOS by a mechanism invo lving a Gi-protein. Administration of heparin derivatives without anticoagu lant properties may have therapeutic implications for the preservation of e NOS in conditions characterized by endothelial dysfunction. (C) 1998 Academ ic Press.