AJP - Heart and Circulatory Physiology, Vol 246, Issue 1 74-H79, Copyright © 1984 by American Physiological Society
Baroreflex regulation of hindquarter vascular resistance during acute blood volume expansion
G. B. Guo and D. R. Richardson
The baroreflex control of hindquarter vascular resistance in response to a
30% blood volume expansion (BVE) was examined in constant-flow perfused
hindlimbs of chloralose-urethan-anesthetized rats. Volume expansion
initially increased both systemic arterial pressure (SAP) and central
venous pressure (CVP) while decreasing hindquarter vascular resistance.
After these initial changes, there was a parallel return of
hindquarter-vascular resistance and CVP to pre-expansion levels, suggesting
that cardiopulmonary afferents play a major role in the vascular resistance
adjustments to volume expansion. This notion was supported in a separate
set of experiments in which CVP was elevated selectively while SAP was held
constant. This manipulation elicited a decrease in hindquarter vascular
resistance, which was significantly attenuated following vagal
cardiopulmonary denervation. The return of hindquarter vascular resistance
following BVE also occurred in the presence of elevated SAP in rats with
vagotomy and aortic nerve denervation, i.e., only the carotid sinus
baroreflexes intact, but the time course was much faster compared with
preparations with cardiopulmonary receptors intact. No response of
hindquarter vascular resistance to BVE was observed in rats with both
sinoaortic and cardiopulmonary baroreceptors denervated. These findings
suggest that the return of hindquarter vascular resistance following BVE
involves a gradual increase in sympathetic outflow to the hindquarters
resulting from both a decrease in cardiopulmonary afferent activity and a
rapid adaptation of arterial baroreflexes.
