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Department of Veterinary Biomedical Sciences, Dalton Cardiovascular Research Center, University of Missouri, Columbia, Missouri 65211
The effect of
cardiovascular deconditioning on central nervous system processing of
baroreceptor afferent activity was evaluated following 14 days of
hindlimb unloading (HU). Inactin-anesthetized rats were instrumented
with catheters, renal sympathetic nerve electrodes, and aortic
depressor nerve electrodes for measurement of mean arterial pressure,
heart rate, renal sympathetic nerve activity (RSNA), and aortic
depressor nerve activity (ADNA). Baroreceptor and baroreflex functions
were assessed during infusion of phenylephrine and sodium
nitroprusside. Central processing of baroreceptor afferent input was
evaluated by linear regression relating RSNA to ADNA. The maximum
baroreflex-elicited increase in RSNA was significantly reduced in HU
rats (122 ± 3.8 vs. 144 ± 4.9% of baseline RSNA), whereas ADNA was not altered. The slope (
0.18 ± 0.04 vs.
0.40 ± 0.04) and
y-intercept (121 ± 3.2 vs. 146 ± 4.3) of the linear regression relating increases in efferent RSNA
to decreases in afferent ADNA during hypotension were significantly
reduced in HU rats. There were no differences during increases in
arterial pressure. Results demonstrate that the attenuation in
baroreflex-mediated increases in RSNA following HU is due to changes in
central processing of baroreceptor afferent information rather than
aortic baroreceptor function.
microgravity; hindlimb suspension; cardiovascular deconditioning; bed rest; orthostatic intolerance
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