Hypobaric Hypoxia Induced Oxygen Dissociation Curve Contrarotation And Bohr Effect Hypersensitivity

Background:Change of intrinsic properties of hemoglobin is a universal mechanism to acclimatize various creatures to hypoxia environment. Such as bar-headed goose, a migrant bird which can fly over the Himalayas, has mutant hemoglobin that increase the oxygen affinity. Hemoglobin mutations also occurred in some fishes living under deeply sea and animals living underground or cave. However, the structural mutants don’t occur in hemoglobin of acclimatized or adapted people and animal such as high altitude native people, some high altitude native animals. So the regulatory changes might be occurred in the hemoglobin and play important roles in elevating the resistance to hypoxia. We consider certain mechanism might endow hemoglobin with oxygen dissociation curve(ODC) contrarotation and Bohr Effect hypersensitivity under hypoxia exposure. This hemoglobin possesses higher oxygen affinity to capture more oxygen in alkaline pulmonary alveolar capillary while the hemoglobin’s oxygen affinity might be rapidly reduced in acidic microenvironment such as muscle or brain capillary, which facilitate the oxygen unloading to tissue. Therefore, ODC contraotation and Bohr Effect hypersensitivity are very cost-effective compensatory mechanism in hypoxia. In fact, some animals such as bulltrout adopt the mechanism to live in hypoxia environment. But it is not reported whether human and mammal animal possess the mechanism by far.White blood cells(WBCs) and vascular endothelial cells(VECs), the most intimate partner of red blood cells(RBCs) can be activated and release some inflammatory mediators including cytokines and nitric oxide(NO) under hypoxia exposure. Some receptors such as Duffy Antigen Receptor for Chemokines are present on RBC to bind cytokines. NO is also a regulator of hemoglobin. So we speculate that hypoxia-activated WBCs and VECs might regulate RBCs in ODC contrarotation and Bohr Effect hypersensitivity by the inflammatory mediators.Objectives:This study planned to determine whether ODC contrarotation and Bohr Effect hypersensitivity are a novel anti-hypoxia mechanism, whether hypoxia-stimulated WBCs or VEC contribute to the mechanism.Methods:SD rats were exposed in hypobaric chamber simulating altitude of 5000 m for 1d, 7 d, 30 d. ODCs of the rats’ artery blood were measured in alkaline or acidic condition(7.45, 7.16 or 7.55)by an instrument HEMOX ANALYZER. The P50 and Hill constant were analyzed by the software of the instrument. And the index of sensitivity(SI) to alkaline or acid was calculated by the formula: SI =(P50 HCl- P50 Na OH)/ P50 CON×100 %;P50HCl is the P50 of ODC in acidic condition. P50 NaOH is the P50 of ODC in alkaline condition. P50 CON is P50 of the ODC in p H 7.45.After memory training in Morris water maze, SD rats were intraperitoneal injected by 5-hydroxymethylfurfural(5HMF) and fed in hypobaric chamber simulating altitude of 5000 m(as hypoxia group) or 400 m(as control) for 1 day. Then,repeated once intraperitoneal injection, and after 30 min, the number of crossing over at the original platform position and the time(s) spent in the target quadrant, as well as in the other quadrants were recorded to evaluate the mental performance capacity and the swimming exhaustive time in hypobaric chamber was recorded to assay the physical performance ability in the hypobaric chamber.After WBCs or VECs were exposed in hypoxia(5 % O2 or 1 % O2), the supernatants of the cells were collected. The purified RBCs were incubated for 2 hours in the ODC assay buffer containing the collected supernatants or cytokines(IL-1β, IL-6 or IL-8), then the ODC were recorded in p H7.45, 7.16, 7.55.Results:Hypobaric hypoxia for 7, 30 days induced ODCs contrarotation and more sensitive to p H change, higher Hill constant and SI as compared with normoxia group. Hypobaric hypoxia for 1 day did not induced ODC contrarotation and Bohr Effect hypersensitivity, but induced lower artery oxygen saturation, less number of crossing over at the original platform position, shorter time spent in the target quadrant of the Morris water maze or in the swimming until exhaustion. 5HMF induced ODC contrarotation and hypersentivity of Bohr Effect, significant increased the Hill constant and SI in vitro. Treatment of 5HMF significantly attenuated the hypoxia-induced impairment.Supernatants from hypoxia-stimulated WBCs or VECs significantly reduced P50 of ODC, and significantly increased the HC and SI, which were partially inhibited by L-NAME, an inhibitor of nitric oxide synthase. The cytokines(IL-1β, IL-6 and IL-8) dramatically increased the SI and decreased the P50.Conclusion:1 Hypobaric hypoxia induced the ODC contrarotation and sensitivity to pH changes(Bohr Effect hypersensitivity), as contributed to improve the physical and mental performance capacity in hypobaric hypoxia.2 Hypoxia-stimulated WBCs or VECs promoted the ODC contrarotation and Bohr Effect hypersensitivity, in which inflammatory mediators such as IL-1, IL-6, IL-8 and NO may be involved.