title: Hypobaric intermittent hypoxia attenuates hypoxia-induced depressor response.
abstract: BACKGROUND
  Hypobaric intermittent hypoxia (HIH) produces many favorable effects in the cardiovascular system such as anti-hypertensive effect. In this study, we showed that HIH significantly attenuated a depressor response induced by acute hypoxia.
  
  
  RESULTS
  Sprague-Dawley rats received HIH in a hypobaric chamber simulating an altitude of 5000 m. The artery blood pressure (ABP), heart rate (HR) and renal sympathetic nerve activity (RSNA) were recorded in anesthetized control rats and rats received HIH. The baseline ABP, HR and RSNA were not different between HIH and control rats. Acute hypoxia-induced decrease in ABP was significantly attenuated in HIH rat compared with control rats. However, acute hypoxia-induced increases in HR and RSNA were greater in HIH rat than in control rats. After removal of bilateral ascending depressor nerves, acute hypoxia-induced depressor and sympathoexcitatory responses were comparable in control and HIH rats. Furthermore, acute hypoxia-induced depressor and sympathoexcitatory responses did not differ between control and HIH groups after blocking ATP-dependent K(+) channels by glibenclamide. The baroreflex function evaluated by intravenous injection of phenylephrine and sodium nitroprusside was markedly augmented in HIH rats compared with control rats. The pressor and sympathoexcitatory responses evoked by intravenous injection of cyanide potassium were also significantly greater in HIH rats than in control rats.
  
  
  CONCLUSIONS
  Our findings suggest that HIH suppresses acute hypoxia-induced depressor response through enhancement of baroreflex and chemoreflex function, which involves activation of ATP-dependent K(+) channels. This study provides new information and underlying mechanism on the beneficiary effect of HIH on maintaining cardiovascular homeostasis.
authors: Department of Physiology, Hebei Medical University, Shijiazhuang, China.
authors: Fang
authors: F
authors: Cui
authors: Lu
authors: L
authors: Gao
authors: Fang
authors: F
authors: Yuan
authors: Ze-Fei
authors: ZF
authors: Dong
authors: Zhao-Nian
authors: ZN
authors: Zhou
authors: David D
authors: DD
authors: Kline
authors: Yi
authors: Y
authors: Zhang
authors: De-Pei
authors: DP
authors: Li
mesh_terms: D000531:Altitude; D000818:Animals; D017704:Baroreflex / Q000187:drug effects; D001794:Blood Pressure / Q000187:drug effects; D004780:Environment, Controlled; D005905:Glyburide / Q000494:pharmacology; D006339:Heart Rate / Q000187:drug effects; D000860:Hypoxia / Q000378:metabolism / Q000503:physiopathology*; D054086:KATP Channels / Q000378:metabolism; D007668:Kidney / Q000294:innervation; D008297:Male; D019331:NG-Nitroarginine Methyl Ester / Q000494:pharmacology; D051381:Rats; D017207:Rats, Sprague-Dawley; D013564:Sympathetic Nervous System / Q000187:drug effects / Q000378:metabolism / Q000503:physiopathology*; D013997:Time Factors
chemical_list: D054086:KATP Channels; D005905:Glyburide; D019331:NG-Nitroarginine Methyl Ester