Effect of inhaled nitric oxide on oxygen-carrying capacity of red blood cells and hypoxia tolerance in mice

Abstract

Objective To study the effects of nitric oxide (NO) inhalation on oxygen-carrying capacity of red blood cells and hypoxia tolerance in mice. Methods Peripheral blood from 8-week-old male mice was exposed to nitrogen gas containing NO in an oxygenation pool to generate the oxygen dissociation curve and calculate the oxygen affinity parameter P50 and the Hill coefficient. Fifty 8-week-old male C57 mice were randomized into 5 groups (n=10) and subjected to inhalation of 21% O2, 5% O2, or 5% O2 with 5, 10 or 20 mL/m3 NO under anesthesia. The oxygen saturation in the tail vein blood of the mice was measured with an oximeter following the exposures, and the survival time of the mice was recorded. Results The introduction of 100 and 200 mL/m3 NO into the pooled whole blood resulted in a significant left shift of the oxygenation curve, and significantly decreased P50 (P < 0.05) in a concentration-dependent manner. Hypoxic exposure of the mice caused a significant reduction in the oxygen saturation level in the tail vein blood, and this reduction was obviously attenuated by inhalation of 20 mL/m3 NO (P < 0.05). Compared with hypoxia exposure, inhalation of 5, 10, and 20 mL/m3 NO concentration-dependently prolonged the survival time of the mice, and the effect was statistically significantly in mice inhaling 10 and 20 mL/m3 NO (P < 0.05). In mice inhaling 20 mL/m3 NO, the survival time under hypoxic conditions was positively correlated with the level of blood oxygen saturation (P < 0.05). Conclusion Inhalation of NO increases hemoglobin oxygen affinity and improves blood oxygen saturation in mice exposed to hypoxic conditions. NO enhances hypoxia tolerance by improving the oxygen-carrying capacity of the red blood cells.

Keywords

• nitric oxide
• erythrocytes
• hemoglobin
• oxygen affinity
• hypoxia tolerance