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First published online on September 7, 2006.
Experimental Physiology (2006)
DOI: 10.1113/expphysiol.2006.034868
© The Physiological Society 2006
A more recent version of this article appeared on November 1, 2006
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Received June 22, 2006
Revised July 25, 2006
Accepted after revision August 30, 2006

Autonomic Neuroscience [200]

Sympathoexcitatory response to peripheral chemoreflex activation is enhanced in juvenile rats exposed to chronic intermittent hypoxia

Valdir A Braga 1, Renato N Soriano 1, Benedito H Machado 1*

1 School of Medicine of Ribeirão Preto, University of São Paulo

* To whom correspondence should be addressed. E-mail: bhmachad{at}fmrp.usp.br.


  Abstract
In the present study we tested the hypothesis that chronic intermittent hypoxia (CIH) produces changes in the autonomic and respiratory responses to acute peripheral chemoreflex activation. To reach this goal, juvenile rats previously submitted to CIH were used to obtain the working heart-brainstem preparation (WHBP) and, under this unanaesthetized experimental condition, the chemoreflex was activated with potassium cyanide (KCN) and the thoracic sympathetic nerve activity (tSNA), heart rate (HR) and phrenic nerve discharge (PND) were recorded. Three-week-old rats were exposed to 10 days of CIH (6% O2 during 40 sec at 9 min intervals; 8h/day). CIH (n=12) and control (n=12) rats were used to perform the experiments in the WHBP, which allows HR, PND and tSNA recordings. KCN (0.05%) was injected via the perfusion system. CIH rats, when compared to control, presented the following significant changes in response to chemoreflex activation: a) an increase on the tSNA (78±4 vs 48±3 %); b) a long-lasting increase in the frequency of the PND at 20 (0.52±0.03 vs 0.36±0.03 Hz) and 30 sec (0.40±0.02 vs 0.31±0.02 Hz) after the stimulus; and c) a greater bradycardic response (-218±20 vs -163±16 bpm). These results indicate that the autonomic and respiratory responses to chemoreflex activation in juvenile rats previously submitted to CIH are greatly increased.

Key Words: Chemoreceptor, Hypoxia, Sympathetic activity




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