University of Arkansas, Fayetteville Division of Agriculture


Nitric oxide (NO) plays an important role in physiological functions like vasodilation, neurotransmission, and inhibition of platelet aggregation. The endothelium-derived NO diffuses into the vascular lumen where it interacts with flowing blood as well as the smooth muscles where it modulates vascular tone. However, uncertainty exists on how NO escapes the rapid scavenging by hemoglobin (Hb) and reaches smooth muscles. Several proposed hypotheses include 1) a reduced reaction rate of NO with Hb contained inside red blood cells (RBCs) and 2) NO preservation in the bound form of s-nitrosohemoglobin or nitrite. The mechanism and magnitude of reduction of NO reaction rate with Hb contained inside RBCs are not well established. In this study, an in vitro experimental system was designed to expose stirred RBC suspension to physiologically relevant NO flux. NO-RBC interactions were studied by measuring the reaction products, nitrite and total NOx, using chemiluminescence method. We studied the effect of increasing hematocrit from 5% to 45% on NO-RBC interaction under oxygenated condition. Results show that the system maintained a steady state in the bioreactor and could be easily modified to control NO delivery flux. An increase in product concentration was observed by increasing the hematocrit from 5% to 45%. The study is clinically important as the understanding of molecular interaction of NO with Hb in RBCs and mode of NO transport in microcirculation may provide therapeutic opportunities in the biomedical field in areas as diverse as sickle cell anemia, septic shock, hypoxic pulmonary vasoconstriction, and blood substitutes.