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Department of Physiology, School of Medicine of Ribeirão Preto, University of São Paulo, 14049-900 Ribeirão Preto, São Paulo, Brazil
Changes in
mean arterial pressure (MAP), heart rate (HR), and vascular resistance
(hindquarter and mesenteric territories) in response to electrical
stimulation (ES) of the aortic depressor nerve (ADN) were evaluated in
conscious freely moving rats. Platinum electrodes were implanted into
the ADN of all rats studied, and some of these animals were also
implanted with miniaturized Doppler probes around the superior
mesenteric artery and inferior abdominal aorta (hindquarter). In both
groups, the femoral artery and vein were catheterized one day before
the experiments. In the first group of rats
(n = 7), the control ES of the ADN in
the range from 0.5 to 3.0 V (50 Hz, 10 ms) produced bradycardia and
hypotension in an intensity-dependent manner, and treatment with
methylatropine (intravenously) blocked the bradycardia but produced no
significant changes in the hypotensive response. In a second group
(n = 6), ES of the ADN was performed
with the intensity fixed at 3 V and the frequency of the stimuli
varying from 10 to 50 Hz. In this group, the hypotensive response was
frequency dependent, whereas the bradycardic response was not. In a
third group of rats (n = 6), ES of the
ADN (2.5 V) produced hypotension (
35 ± 4 mmHg), minor
changes in the mesenteric (+5 ± 14%), and
vasodilation in hindquarter (32 ± 6%) vascular beds. The
data show that 1) ES of the ADN
produces a fall in pressure, bradycardia, vasodilation in the
hindquarter, and no changes in the mesenteric vascular resistance,
2) methylatropine blocked the
bradycardia and produced no effect on the hypotensive response to ES of
the ADN, and 3) the baroreceptor
afferent fibers involved in the hypotensive response to ES of ADN are
sensitive to the variation of the frequency of the stimuli, whereas the
fibers involved in the bradycardic response are not.
arterial baroreceptors; heart rate; blood pressure; blood flow; vascular resistance; baroreflex; frequency; intensity
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