Changes in efferent pulmonary sympathetic nerve activity during
systemic hypoxia in anesthetized cats.
Shirai, Mikiyasu, Kanji Matsukawa, Naoki Nishiura, Akira T. Kawaguchi,
and Ishio Ninomiya.
Department of Cardiac Physiology, National Cardiovascular Center
Research
APStracts 2:0185R, 1995.
Changes in efferent sympathetic nerve activity to the pulmonary
vessels during systemic hypoxia have yet to be elucidated. The
purpose of this study was to determine the pulmonary sympathetic
nerve activity (PSNA) changes in response to acute systemic hypoxia
before and after sinoaortic denervation (SAD) plus vagotomy in
anesthetized cats. The denervation was performed in order to estimate
the central nervous system-mediated peripheral chemo/baroreceptor
independent PSNA change. PSNA was recorded from the central end of
the cut nerve bundle which was isolated from the lobar artery
supplying the diaphragmatic lobe. Renal sympathetic nerve activity
(RNA), and systemic and pulmonary arterial pressures were also
measured simultaneously. The animals were submitted to _3 min periods
of graded hypoxia (16, 12, 8, 5, and 3% O2 inhalations). PSNA did not
change from normoxia down to a Pao2 of _45 Torr (with 12-21% O2
inhalations). Below this level PSNA began to increase, and markedly
so (_2.5-fold) at a Pao2 of _15 Torr (with 3% O2). The hypoxic PSNA
increase was significantly larger than that for RNA with a Pao2
< _30 Torr (with 3-8% O2). Particularly at a Pao2 of _15 Torr
the magnitude of the PSNA increase was two times greater than that
for RNA. After the denervation, the hypoxic PSNA increase was
significantly attenuated at a Pao2 of _25-_45 Torr (with 5-12% O2),
but the attenuation was very small; therefore most of the PSNA
increase persisted. The hypoxic RNA increase, in contrast, was mostly
abolished after the denervation. The data indicate that the neural
reflex effect of systemic hypoxia on PSNA is significantly greater
than that on RNA, and suggest that the hypoxic PSNA increase is
mostly mediated by central mechanisms, while that for RNA is chiefly
caused by peripheral chemoreceptors.
Received 7 December 1994; accepted in final form 26 June 1995.
APS Manuscript Number R691-4.
Article publication pending Am. J. Physiol. (Regulatory Integrative
Comp. Physiology).
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on 18 July 1995.