Department of Physiology, Hebei Medical University, Shijiazhuang, China.
PLoS One. 2012;7(7):e41656. doi: 10.1371/journal.pone.0041656. Epub 2012 Jul 27.
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.
METHODOLOGY/PRINCIPAL FINDINGS: 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/SIGNIFICANCE: 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.
低压间歇性低氧（HIH）对心血管系统产生许多有利影响，如抗高血压作用。在这项研究中，我们表明 HIH 可显著减弱急性低氧引起的降压反应。
方法/主要发现：Sprague-Dawley 大鼠在模拟海拔 5000 米的低压舱中接受 HIH。在麻醉对照大鼠和接受 HIH 的大鼠中记录动脉血压（ABP）、心率（HR）和肾交感神经活动（RSNA）。HIH 和对照大鼠之间的基础 ABP、HR 和 RSNA 没有差异。与对照大鼠相比，HIH 大鼠的急性低氧诱导的 ABP 下降明显减弱。然而，急性低氧诱导的 HR 和 RSNA 增加在 HIH 大鼠中大于对照大鼠。在去除双侧升压板神经后，对照和 HIH 大鼠的急性低氧诱导降压和交感兴奋反应相当。此外，在使用格列本脲阻断 ATP 依赖性 K(+) 通道后，对照和 HIH 组之间的急性低氧诱导降压和交感兴奋反应没有差异。与对照大鼠相比，HIH 大鼠的静脉注射苯肾上腺素和硝普钠评估的压力反射功能明显增强。静脉注射氰化钾引起的升压和交感兴奋反应在 HIH 大鼠中也明显大于对照大鼠。
结论/意义：我们的发现表明，HIH 通过增强压力反射和化学反射功能来抑制急性低氧诱导的降压反应，这涉及到 ATP 依赖性 K(+) 通道的激活。这项研究提供了关于 HIH 对维持心血管稳态有益影响的新信息和潜在机制。
