title: Inhibition of endothelium-dependent relaxation by hemoglobin in rabbit aortic strips: comparison between acellular hemoglobin derivatives and cellular hemoglobins.
abstract: Hemoglobin (Hb)-based artificial oxygen carriers are supposed to induce vasoconstriction through the inactivation of endothelium-derived relaxing factor (EDRF). We examined the vasoconstrictive activity of acellular Hb and cellular Hb solutions in rabbit aortic strips. Unmodified Hb, pyridoxalated Hb, bovine unmodified Hb, haptoglobin-Hb complex (Hp-Hb), and polyoxyethylene glycol-conjugated Hb (PEG-Hb) were used as acellular Hbs having different molecular masses. Cellular Hbs included liposome-encapsulated Hb and red blood cells (RBC). In the first experiment, Hb (10 ng/ml to 1 mg/ml) was cumulatively added to the tissues in which steady-state relaxation was evoked by acetylcholine (ACh) after precontraction induced by phenylephrine. Although all Hb solutions induced a dose-dependent reversal of ACh-induced relaxation, the most potent vasoconstrictive effect was noted with acellular Hbs, and their contractile activities were almost the same independent of molecular mass. On the other hand, liposome-Hb and RBC showed reduced potencies in this order. These results indicate the importance of cellularity as the major factor determining Hb-related EDRF inactivation. In another experiment, the tissues were exposed to Hb at 0.01, 0.1, or 1 mg/ml for 30 min and ACh-induced relaxation was recorded after the complete removal of Hb in an organ bath chamber. Exposure to unmodified Hb at > 0.1-mg/ml concentrations significantly reduced the ACh-induced relaxation, whereas the relaxation was not affected by PEG-Hb, Hp-Hb, liposome-Hb, or RBC. These results suggest that unmodified Hb might be persistently associated with tissues and thereby inhibit ACh-induced relaxation. From these findings, we propose two attributes of Hb-related inhibition of endothelium-dependent relaxation: Acellular Hbs inhibit EDRF more efficiently in the luminal space than cellular Hbs, and unmodified Hb can also inhibit it adluminally and/or adventitially.
authors.affiliation: Department of Cell Processing, Institute of Medical Science, University of Tokyo, Japan.
authors.forename: K
authors.initials: K
authors.lastname: Nakai
authors.forename: T
authors.initials: T
authors.lastname: Ohta
authors.forename: I
authors.initials: I
authors.lastname: Sakuma
authors.forename: K
authors.initials: K
authors.lastname: Akama
authors.forename: Y
authors.initials: Y
authors.lastname: Kobayashi
authors.forename: S
authors.initials: S
authors.lastname: Tokuyama
authors.forename: A
authors.initials: A
authors.lastname: Kitabatake
authors.forename: Y
authors.initials: Y
authors.lastname: Nakazato
authors.forename: T A
authors.initials: TA
authors.lastname: Takahashi
authors.forename: S
authors.initials: S
authors.lastname: Sadayoshi
mesh_terms: D000109:Acetylcholine / Q000494:pharmacology; D000818:Animals; D001011:Aorta / Q000187:drug effects* / Q000502:physiology; D004305:Dose-Response Relationship, Drug; D004730:Endothelium, Vascular / Q000187:drug effects* / Q000502:physiology; D005260:Female; D006454:Hemoglobins / Q000494:pharmacology*; D066298:In Vitro Techniques; D008297:Male; D011817:Rabbits; D014664:Vasodilation
chemical_list: D006454:Hemoglobins; D000109:Acetylcholine