The action of diaspirin cross-linked haemoglobin blood substitute on human arterial bypass conduits

Immediately available blood substitutes could transform medicine. In coronary artery surgery, vasoconstriction induced by some of these agents could have serious implications. We have examined some of the vasoactive effects of one of these blood substitute, diaspirin cross-linked haemoglobin (DCLHb), on isolated rings of human arterial conduits.

Sections of human left internal mammary artery (LIMA) and radial artery (RA) were cut into 3-mm rings, mounted in individual organ baths containing aerated (95% O(2)/5% CO(2)) Krebs-Heinseleit solution at 37 degrees C and attached to isometric strain gauge for measurements of tension. All rings were tested for the presence of endothelium by addition of carbachol to rings pre-contracted with phenylephrine. The relative importance of nitric oxide (NO) in contraction mediated by the addition of DCLHb was studied.

Carbachol relaxed phenylephrine precontracted LIMA by 72.3+/-1.7% and RA by 97+/-0.7% confirming the presence of a functional endothelium. Sodium nitroprusside (SNP) caused complete relaxation of LIMA with an EC(50) value of 2.0+/-0.1x10(-8) M and RA with an EC(50) value of 1. 9+/-0.1x10(8) M. In the presence of DCLHb (10(-7) M), carbachol-induced relaxation was significantly reduced to 46.3+/-0. 7% (P<0.01) and the BC(50) value for SNP relaxation increased to 1. 2+/-0.1x10(-7) M (P<0.01). DCLHb caused rings to contract in the absence of phenylephrine with EC(50) values of 1.6+/-0.1x10(-7) M (LIMA) and 1.8+/-0.1x10(-7) M (RA). Presence of L-NAME (300 microM) caused no alteration in DCLHb-induced contraction.

In this study of isolated rings of human vessels, DCLHb causes a significant reduction in relaxation mediated by carbachol and SNP, which is likely to be due to its ability to bind NO. However, it is possible that other mechanisms might contribute to the vasoconstrictor effects of DCLHb and these might be amenable to anti-vasospastic strategies.