AJP - Heart and Circulatory Physiology, Vol 257, Issue 5 1347-H1353, Copyright © 1989 by American Physiological Society
Cardiac and peripheral vascular contributions to hypotension in spinal cats
C. P. Yardley, C. L. Fitzsimons and L. C. Weaver
John P. Robarts Research Institute, University of Western Ontario, London, Canada.
On transection of the cervical spinal cord, substantial decreases in
systemic arterial pressure and in discharge of many sympathetic nerves
suggest the absence of sympathetic support to the cardiovascular system.
However, discharge of mesenteric and splenic nerves is well maintained in
spinal cats (R. L. Meckler and L. C. Weaver. J. Physiol. Lond. 396:
139-153, 1988; R. D. Stein and L. C. Weaver. J. Physiol. Lond. 396:
155-172, 1988). We proposed that the low arterial pressure in spinal
animals was caused predominantly by decreased cardiac output and
vasodilation in muscle and some visceral vascular beds but that sustained
mesenteric and splenic discharge was causing significant splanchnic
vasoconstriction and partial support of arterial pressure. Therefore,
changes in cardiac output, total peripheral resistance, and resistance of
constant-flow-perfused mesenteric visceral and hindlimb skeletal muscle
vascular beds caused by interruption of cervical spinal pathways were
assessed. Blockade of cervical pathways decreased arterial pressure as much
by decreasing cardiac output as by decreasing total peripheral resistance.
Resistances of the muscle and mesenteric vascular beds decreased equally.
In conclusion, hypotension in spinal cats is caused by decreased cardiac
output and by vasodilation, which is as prominent in mesenteric as it is in
muscle vascular beds. The maintained mesenteric sympathetic discharge in
spinal cats appears unable to produce significant support of vascular
arterial resistance.
