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Department of Physiology and Biophysics, University of Nebraska College of Medicine, Omaha, Nebraska 68198-4575
Previous studies from our
laboratory have shown that the cardiac sympathetic afferent reflex is
enhanced in dogs with experimental heart failure. The aim of the
present study was to determine if the central gain of the cardiac
sympathetic afferent reflex was also enhanced in dogs with heart
failure. Fifteen dogs with pacing-induced heart failure were used in
this study. Seventeen sham-operated dogs served as control. At the time
of the acute experiment the dogs were anesthetized with 
-chloralose.
Arterial blood pressure, heart rate, and renal sympathetic nerve
activity were recorded. After sinoaortic denervation and cervical
vagotomy, a thoracotomy was performed in the second intercostal space.
The left stellate ganglion was identified, and the left cardiac
sympathetic nerves were cut. The central end of the left cardiac
sympathetic nerves was placed on bipolar stimulating electrodes. The
renal sympathetic nerve activity responses to electrical stimulation
(30 Hz, 1 ms with varying voltages from 1 to 10 V; or 10 V, 1 ms with
varying frequencies from 1 to 30 Hz) of the afferent cardiac
sympathetic nerves were compared between sham and heart failure groups.
Reflex renal sympathetic nerve activity responses to stimulation of the cardiac sympathetic nerves were significantly greater in the heart failure group compared with that in the sham group (21.4 ± 3.2 vs.
9.8 ± 2.9% at 10 V, 30 Hz and 27.7 ± 4.5 vs. 9.9 ± 3.4% at 30 Hz, 10 V, heart failure vs. sham group, respectively;
for both relationships, P < 0.05).
This enhanced central gain of the cardiac sympathetic afferent reflex
in the heart failure group was significantly attenuated after
intravenous and cerebroventricular injection of the angiotensin II
receptor antagonist losartan (5 mg/kg iv and 0.125 mg/kg in 0.1 ml
icv). These data suggest that the central gain of the cardiac
sympathetic afferent reflex is enhanced in dogs with heart failure and
central angiotensin II plays an important role in this enhanced
response.
renal sympathetic nerve activity; reflex control; angiotensin II; losartan; pacing
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