RECOMBINANT HUMAN HEMOGLOBIN INHIBITS BOTH CONSTITUTIVE AND CYTOKINE-INDUCED NITRIC OXIDE-MEDIATED RELAXATION OF RABBIT ISOLATED AORTIC RINGS

A genetically engineered recombinant human hemoglobin (rHb1.1) was rec ently developed for use as a blood substitute (Nature 1992;356:258-60) . Like other mammalian hemoglobin (Hb) molecules, it might bind and an tagonize the actions of nitric oxide (NO). We used an isolated rabbit aortic ring preparation to examine the ability of rHb1.1 to inhibit ac etylcholine (ACh)- and interleukin-1 beta (IL-1 beta)-induced reductio ns of vasoconstrictor responses to the alpha-adrenoceptor agonist phen ylephrine (PE). rHb1.1 (0.04-4.4 mu M) rapidly and reversibly inhibite d, in a concentration-dependent manner, both ACh- and IL-1 beta-induce d decreases in PE contractile responses. These inhibitory effects of r Hb1.1 were noncompetitive and were equipotent to those of purified, ce ll-free human Hb (p.hHb). These two forms of soluble Hb were at least 10 times more potent than Hb in erythrocytes (red blood cells: RBC-Hb) . Both N-G-nitro-L-arginine (10 mu M) a NO synthase inhibitor, and LY- 83583 (10 mu M), a guanylyl cyclase inhibitor, mimicked the effects of rHb1.1. The inhibitory effects of rHb1.1 were not shared by either hu man serum albumin (HSA 44 mu M), which combines with but does not deac tivate NO, or cytochrome C (44 mu M), a heme-containing protein that d oes not bind NO; neither were they reversed by L-arginine (L-ARG) (1 m M), the presumed NO precursor. These and other results suggest that th e chemical antagonism of NO is likely to be the mechanism by which rHb 1.1 and other Hbs inhibit ACh- and IL-1 beta-induced decreases in the response to PE in rabbit aortic rings.-