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Abstract
To define hemoglobin-based oxygen carrier (HBOC) vasoactivity, a preliminary study with isolated vascular ring preparations was performed. Transverse ring segments of pulmonary artery and aorta were obtained from male SD rats, mounted in a tissue bath containing Krebs buffer (pH=7.4, 37C) and instrumented to isometrically record changes in circumferential tension. Norepinephrine (NE) 0.1-70uM significantly increased vascular tension (N=8, P<0.01). Human stroma-free Hb (SFH) at 1.8nM to 1.8uM Hb caused a dose dependent increase in isometric tension while methemoglobin 2nM-1.2uM had no significant effect (P>0.05). Vessels preconstricted with SFH significantly relaxed (P<0.05) with sodium nitroprusside, glyceryl trinitrate, and isoproteranol. SFH at micromolar concentration causes substantial vasoconstriction in isolated vessel preparations. The mechanism of SFH mediated vasoactivity appears to involve Hb interaction with endothelium derived nitric oxide and was reversible with nitrogenous vasodilators and a beta receptor agonist indicating pharmacologic modulation may be possible.