Respiratory Alterations Due to Chronic Long-Term Intermittent Hypobaric Hypoxia in Rabbits: Importance of Peripheral Chemoreceptors

Altered mitochondrial biogenesis and its fusion gene expression is involved in the high-altitude adaptation of rat lung

Intermittent hypobaric hypoxia-induced preconditioning (IHH-PC) of rat favored the adaption of lungs to severe HH conditions, possibly through stabilization of mitochondrial function. This is based on the data generated on regulatory coordination of nuclear DNA-encoded mitochondrial biogenesis; dynamics, and mitochondrial DNA (mtDNA)-encoded oxidative phosphorylation (mtOXPHOS) genes expression. At 16th day after start of IHH-PC (equivalent to 5000m, 6h/d, 2w of treatment), rats were exposed to severe HH stimulation at 9142m for 6h. The IHH-PC significantly counteracted the HH-induced effect of increased lung: water content; tissue damage; and oxidant injury. Further, IHH-PC significantly increased the mitochondrial number, mtDNA content and mtOXPHOS complex activity in the lung tissues. This observation is due to an increased expression of genes involved in mitochondrial biogenesis (PGC-1α, ERRα, NRF1, NRF2 and TFAM), fusion (Mfn1 and Mfn2) and mtOXPHOS. Thus, the regulatory pathway formed by PGC-1α/ERRα/Mfn2 axes is required for the mitochondrial adaptation provoked by IHH-PC regimen to counteract subsequent HH stress.

The effect of chronic long-term intermittent hypobaric hypoxia on bone mineral density in rats: role of nitric oxide

Intermittent hypoxia is the most common pattern of hypoxic exposure in humans. The effect of chronic long-term intermittent hypobaric hypoxia (CLTIHH) on bone metabolism is not investigated. We examined the effect of CLTIHH on bone metabolism and the role of nitric oxide (NO) in this process. The rats were divided into three groups in this study. The animals in groups I and II have been exposed to CLTIHH. The animals in group II were also treated with nitric oxide synthase inhibitor NG-nitro-L-arginine methyl ester. To obtain CLTIHH, rats were placed in a hypobaric chamber (430 mm Hg; 5 h/day, 5 days/week, 5 weeks). The group III (control) rats breathed room air in the same environment. At the begining of the experiments, bone mineral density (BMD) of the animals were measured, and blood samples were collected from the tail vein. After the 5-week CLTIHH period, the same measurements were repeated. Parathyroid hormone, calcium, phosphate, bone alkaline phosphatase (b-ALP), NO, interleukin 1 beta, interleukin 6, and tumor necrosis factor alpha levels were determined. The cytokines, NO levels, and BMD in CLTIHH-induced rats were higher compared with baseline and control values. The cytokines, b-ALP, and BMD increased while NO levels decreased in the group II compared with baseline values. BMD values of group II were lower than group I but higher than control group. Our results suggested that CLTIHH has positive effects on bone density. Intermittent hypoxia protocols may be developed for treatment and prevention of osteopenia and osteoporosis.