PERFUSED WITH BIS(3,S-DIBROMOSAL1CYL)FUMARATE CROSS-LINKED HEMOGLOBIN (aaHb)

To study the mechanism by which cell-free hemoglobin preparations may alter coronary vascular reactivity, we investigated the effect of human hemoglobin cross-linked between alpha chains with bis(3,5-dibromosalicyl)fumarate (aaHb) on the vasomotor response to acetylcholine (ACh) in isolated perfused rabbit hearts. Dose-response curves were generated by monitoring the increase in coronary pressure during serial addition of 0.2-10 pM ACh before, during and after 20 min infusion of three test solutions: a) 0.1 g/dl aaHb (62 pM heme); b) 0.1 g/dl aaHb plus 60 pM deferoxamine (DFO); c) 50 pM NG-nitro-L-arginine methyl ester (L-NAME), a specific inhibitor of nitric oxide (NO) synthase. We found that the sensitivity to ACh-induced vasoconstriction was significantly potentiated in the presence of aaHb and LNAME. In addition, this response was only partially reversed after removal of aaHb, except when DFO was simultaneously infused with the mHb solution. These findings are consistent with the idea that both NO binding to hemoglobin and iron-mediated oxygen free radical generation contribute to an altered coronary vasomotor responsiveness induced by cell-free hemoglobin.