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Departments of Internal Medicine and Physiology, University of Iowa College of Medicine; and Veterans Administration Medical Center, Iowa City, Iowa 52242
To examine the effect of activation of a
unique population of renal sympathetic nerve fibers on renal blood flow
(RBF) dynamics, anesthetized rats were instrumented with a renal
sympathetic nerve activity (RSNA) recording electrode and an
electromagnetic flow probe on the ipsilateral renal artery. Peripheral
thermal receptor stimulation (external heat) was used to activate a
unique population of renal sympathetic nerve fibers and to increase
total RSNA. Total RSNA was reflexly increased to the same degree with
somatic receptor stimulation (tail compression). Arterial pressure and heart rate were increased by both stimuli. Total RSNA was increased to
the same degree by both stimuli but external heat produced a greater
renal vasoconstrictor response than tail compression. Whereas both
stimuli increased spectral density power of RSNA at both cardiac and
respiratory frequencies, modulation of RBF variability by fluctuations
of RSNA was small at these frequencies, with values for the normalized
transfer gain being ~0.1 at >0.5 Hz. During tail compression
coherent oscillations of RSNA and RBF were found at 0.3-0.4 Hz
with normalized transfer gain of 0.33 ± 0.02. During external heat
coherent oscillations of RSNA and RBF were found at both 0.2 and
0.3-0.4 Hz with normalized transfer gains of 0.63 ± 0.05 at
0.2 Hz and 0.53 ± 0.04 to 0.36 ± 0.02 at 0.3-0.4
Hz. Renal denervation eliminated the oscillations in RBF at both 0.2 and 0.3-0.4 Hz. These findings indicate that despite similar
increases in total RSNA, external heat results in a greater renal
vasoconstrictor response than tail compression due to the activation of
a unique population of renal sympathetic nerve fibers with different
frequency-response characteristics of the renal vasculature.
somatic receptor; peripheral thermal receptor; spectral analysis
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