ARTERIAL BLOOD-PRESSURE RESPONSES TO CELL-FREE HEMOGLOBIN-SOLUTIONS AND THE REACTION WITH NITRIC-OXIDE

Changes in mean arterial pressure were monitored in rats following 50% isovolemic exchange transfusion with solutions of chemically modified hemoglobins. Blood pressure responses fall into three categories: 1) an immediate and sustained increase, 2) an immediate yet transient inc rease, or 3) no significant change either during or subsequent to exch ange transfusion. The reactivities of these hemoglobins with nitric mo noxide ((NO)-N-.) were measured to test the hypothesis that different blood pressure responses to these solutions result from differences in (NO)-N-. scavenging reactions. All hemoglobins studied exhibited a va lue of 30 mu M-1 s(-1) for both (NO)-N-. bimolecular association rate constants and the rate constants for (NO)-N-.-induced oxidation in vit ro. Only the (NO)-N-. dissociation rate constants and, thus, the equil ibrium dissociation constants varied. Values of equilibrium dissociati on constants ranged from 2 to 14 pM and varied inversely with vasopres sor response. Hemoglobin solutions that exhibited either transient or no significant increase in blood pressure showed tighter (NO)-N-. bind ing affinities than hemoglobin solutions that exhibited sustained incr eases. These results suggest that blood pressure increases observed up on exchange transfusion with cell-free hemoglobin solutions can not be the result of (NO)-N-. scavenging reactions at the heme, but rather m ust be due to alternative physiologic mechanisms.