Altered sympathetic reflexes and vascular reactivity in rats after exposure to chronic intermittent hypoxia.

J Physiol. 2011 Mar 15;589(Pt 6):1463-76. Silva AQ, Schreihofer AM. “Exposure to chronic intermittent hypoxia (CIH) yields persistent elevations in sympathetic nerve activity (SNA) and mean arterial pressure (MAP) with exaggerated sympathetic chemoreflexes”. The authors determined whether rats that were exposed to CIH produce exaggerated sympathetic responses. They hypothesized that sympathetic reflexes initiated by peripheral nerves would be exaggerated after exposure to CIH. They also determined whether exposure to CIH enhanced sympathoexcitation produced by glutamatergic stimulation of the RVLM. The authors found that sympathoexcitatory reflexes initiated by peripheral nerves other than the carotid sinus nerve produced exaggerated increase in SNA after exposure to CIH. Also stimulation of the RVLM, produced an augmented increase in SNA after CIH. Interestingly, the sympathoexcitatory responses were not accompanied by enhanced pressor changes. This could be because of reduced pressor reactivity to adrenergic stimulation seen after CIH. To summarize, the authors suggest that sympathoexciatory responses may be exaggerated because of increased excitability of the RVLM and reduced adrenergic vascular reactivity after exposure to CIH.-Madhan