Frequency response characteristic of sympathetic mediated vasomotor
waves in conscious rats.
Stauss, Harald M., and Kevin C. Kregel.
Department of Exercise Science, The University of Iowa, Iowa City,
Iowa 52242
APStracts 3:0099H, 1996.
Power spectrum analysis of arterial blood pressure (BP) and heart rate
(HR) has been used to investigate autonomic nervous system activity.
Sympathetic-mediated vasomotor tone has been attributed to the blood
pressure power at frequencies between 0.05 Hz and 0.15 Hz in humans
and dogs and between 0.2 Hz and 0.8 Hz in rats. In contrast, it has
been suggested that the sympathetic nervous system is too sluggish to
transmit frequencies higher than 0.017 Hz in dogs. Thus, we
investigated the frequency response characteristics of the
transmission of peripheral sympathetic nerve discharge to peripheral
vascular resistance and arterial blood pressure in conscious rats.
Eleven rats were instrumented with arterial catheters, nerve
electrodes on the sympathetic splanchnic nerve, and flow probes on
the superior mesenteric artery. The splanchnic nerve was cut proximal
to the electrode in order to avoid afferent nerve stimulation. The
next day the nerve was stimulated at frequencies of 0.05, 0.1, 0.2,
0.5, 1.0, and 2.0 Hz while mesenteric blood flow, BP, and HR were
recorded in conscious rats. Mesenteric resistance (MR) was calculated
off-line. Nerve stimulation at 0.05, 0.1, 0.2, 0.5, and 1.0 Hz
significantly increased the power in MR at these respective
frequencies. The greatest response was found between 0.2 Hz and 0.5
Hz. These oscillations in MR were translated to oscillations in BP
but not in HR. Nerve stimulation on the second day, when the nerve
was degenerated, did not elicit oscillations in MR or BP. We conclude
that the peripheral sympathetic nervous system in rats has the
capability to transmit signals at frequencies higher than those
traditionally assigned to sympathetic vasomotor activity in several
species, including humans, and may even overlap with the respiration
-related high frequency range.
Received 26 December 1995; accepted in final form 29 February
1996.
APS Manuscript Number H1209-5.
Article publication pending Am. J. Physiol. (Heart Circ. Physiology).
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 20 March 96