VASOCONSTRICTOR EFFECTS IN ISOLATED RABBIT HEART PERFUSED WITH BIS(3,5-DIBROMOSALICYL)FUMARATE CROSS-LINKED HEMOGLOBIN (ALPHA-ALPHA-HB)

To study the mechanism by which cell-free hemoglobin preparations may alter coronary vascular reactivity, we investigated the effect of huma n hemoglobin cross-linked between alpha chains with bis(3,5-dibromosal icyl)fumarate (alpha alpha Hb) on the vasomotor response to acetylchol ine (ACh) in isolated perfused rabbit hearts. Dose-response curves wer e generated by monitoring the increase in coronary pressure during ser ial addition of 0.2-10 mu M ACh before, during and after 20 min infusi on of three test solutions: a) 0.1 g/dl alpha alpha Hb (62 mu M heme); b) 0.1 g/dl alpha alpha Hb plus 60 mu M deferoxamine (DFO); c) 50 mu M N-G-nitro-L-arginine methyl ester (L-NAME), a specific inhibitor of nitric oxide (NO) synthase. We found that the sensitivity to ACh-induc ed vasoconstriction was significantly potentiated in the presence of a lpha alpha Hb and L-NAME. In addition, this response was only partiall y reversed after removal of alpha alpha Hb, except when DFO was simult aneously infused with the alpha alpha Hb solution. These findings are consistent with the idea that both NO binding to hemoglobin and iron-m ediated oxygen free radical generation contribute to an altered corona ry vasomotor responsiveness induced by cell-free hemoglobin.