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1 Departments of Anesthesiology and Medicine, University of Washington, 98195; and 2 Veterans Affairs Puget Sound Health Care System, Seattle, Washington 98108
Red blood cells (RBCs) augment hypoxic
pulmonary vasoconstriction (HPV) in part by scavenging of nitric oxide
(NO) by Hb (Deem S, Swenson ER, Alberts MK, Hedges RG, and Bishop MJ,
Am J Respir Crit Care Med 157: 1181-1186, 1998). We
studied the contribution of the RBC compartmentalization of Hb to
augmentation of HPV and scavenging of NO in isolated perfused rabbit
lungs. Lungs were initially perfused with buffer; HPV was provoked by a
5-min challenge with hypoxic gas (inspired O2 fraction
0.05). Expired NO was measured continuously. Addition of free Hb to the
perfusate (0.25 mg/ml) resulted in augmentation of HPV and a fall in
expired NO that were similar in magnitude to those associated with a
hematocrit of 30% (intracellular Hb of 100 mg/ml). Addition of dextran
resulted in a blunting of HPV after free Hb but no change in expired
NO. Blunting of HPV by dextran was not prevented by NO synthase
inhibition with
N
-nitro-L-arginine and/or
cyclooxygenase inhibition. RBC ghosts had a mild inhibitory effect on
HPV but caused a small reduction in expired NO. In conclusion, the RBC
membrane provides a barrier to NO scavenging and augmentation of HPV by
Hb. Increased perfusate viscosity inhibits HPV by an undetermined mechanism.
anemia; nitric oxide; hypoxia; red blood cells
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