Hypoxia hypoxic-tolerance

Administration of oxygen-rich gas mixtures is useful in hypoxia, but 100% 02 is not often used. In chronic bronchitis, hypoxia and hypercapnia coexist, the respiratory centre in the medulla becomes tolerant to the high C02 content of blood and is relatively insensitive to it. Respiratory drive is maintained by hypoxia acting via chemoreceptors in the aorta and carotid body. Removal of the hypoxic stimulus to the respiratory centre in the medulla may actually stop the patient breathing. 

It is clear that the closure of voltage-gated K" " charmels by hypoxic exposure has implications for neuroprotection as demonstrated by K+ channel arrest in hypoxia-tolerant turtles (Pek and Lutz, 1997 Bidder and Buck, 1998 Hochachka and Lutz, 2001 Bidder and Donohoe, 2002), which reduces Ca" influx (Bidder and Buck, 1998). In some anoxia-tolerant spedes, neuronal energy is not only conserved by ion channel arrest but also by ATP-sensitive mitochondrial K+ channel arrest (reviewed by Buck and Pamenter, 2006). This may have implications for chnical interventions. 

Shams I, Avivi A, Nevo E. 2004. Hypoxic stress tolerance of the blind subterranean mole rat Expression of erythropoietin and hypoxia-inducible factor la. Proc Natl Acad Sci USA 101 9698-9703. 

Shimizu, T., Uehara, T., and Nomura, Y. 2004. Possible involvement of pyruvate kinase in acquisition of tolerance to hypoxic stress in gjial cells. Journal of Neurochemistry 91 167-175 Siddiq, A., Aminova, L.R., and Ratan, R.R. 2007. Hypoxia inducible factor prolyl 4-hydroxylase enzymes Center stage in the battle against hypoxia, metabolic compromise and oxidative stress. Neurochemical Research 32 931-946 Siesjo, B.K. 1978. Brain Energy Metabolism. WUeyChichesten... 

Vanhatalo et investigated the influence of dietary nitrate supplementation on muscle metabolism and oxidative function. P MRS showed muscle PCr, P and pH changed at a faster rate in hypoxic conditions with no dietary nitrate compared to hypoxia with nitrate or normoxia conditions. The limit of tolerance to exercise was similarly affected and there was also a longer recovery of PCr under hypoxic conditions with no nitrate supplementation. Davies et assessed the impact of exercise-induced muscle damage on muscle metabolic response to dynamic exercise. Incremental knee extensor exercise was performed inside the bore of a 1.5 T magnet before, and 48 h after, executing 100 squats with a load corresponding to 70% of body mass. 

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