Abstract
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 increase, or 3) no significant change either during or subsequent to exchange transfusion. The reactivities of these hemoglobins with nitric monoxide (.NO) were measured to test the hypothesis that different blood pressure responses to these solutions result from differences in .NO scavenging reactions. All hemoglobins studied exhibited a value of 30 microM-1 s-1 for both .NO bimolecular association rate constants and the rate constants for .NO-induced oxidation in vitro. Only the .NO dissociation rate constants and, thus, the equilibrium dissociation constants varied. Values of equilibrium dissociation constants ranged from 2 to 14 pM and varied inversely with vasopressor response. Hemoglobin solutions that exhibited either transient or no significant increase in blood pressure showed tighter .NO binding affinities than hemoglobin solutions that exhibited sustained increases. These results suggest that blood pressure increases observed upon exchange transfusion with cell-free hemoglobin solutions can not be the result of .NO scavenging reactions at the heme, but rather must be due to alternative physiologic mechanisms.
Highlights
Changes in mean arterial pressure were monitored in rats following 50% isovolemic exchange transfusion with solutions of chemically modified hemoglobins
Hemoglobin solutions that exhibited either transient or no significant increase in blood pressure showed tighter 1⁄7NO binding affinities than hemoglobin solutions that exhibited sustained increases. These results suggest that blood pressure increases observed upon exchange transfusion with cell-free hemoglobin solutions can not be the result of 1⁄7NO scavenging reactions at the heme, but rather must be due to alternative physiologic mechanisms
Isovolemic exchange transfusions in rats with a solution of ␣␣-Hb resulted in a significant increase in mean arterial pressure (MAP), whereas PEG-Hb solutions caused no significant change in blood pressure
Summary
Hemoglobin Solutions—Chemically modified hemoglobin preparations were dissolved in Ringer’s lactate to make the solutions used for both exchange transfusion experiments and in vitro kinetic studies. The deoxyhemoglobin was eluted off the column through a needle directly into a tonometer containing 1 atm of 1⁄7NO gas, prepared as described above, and equilibrated to produce a [1⁄7NO] ϭ 1.97 mM Hb-NO solution This solution was used directly for dissociation experiments or diluted with appropriate volumes of anaerobic and 1⁄7NO-equilibrated buffers to produce Hb-NO samples at a heme concentration of 100 M, and a defined 1⁄7NO concentration, for laser photolysis experiments. The time courses were fitted to a single exponential expression, taking into account the shape of the laser pulse and the response time of the instrument, using an iterative non-linear least squares algorithm to obtain the observed rate constants (kobs) Under these conditions, the reaction is pseudo first order and the bimolecular association rate constants were obtained by dividing the observed rate constants by the 1⁄7NO concentration (kЈ ϭ kob1⁄7sN/[O1⁄7NOu]n).imolecular dissociation kinetics were measured by ligand displacement reactions. The bimolecular rate constants were obtained by dividing the observed rate constants by the 1⁄7NO concentration (koЈx ϭ kobs/[1⁄7NO])
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
