AJP - Heart and Circulatory Physiology, Vol 256, Issue 1 291-H296, Copyright © 1989 by American Physiological Society
Relative importance of four pressoregulatory mechanisms after 10% bleeding in rabbits
N. Katoh, D. D. Sheriff, C. O. Siu and K. Sagawa
Department of Biomedical Engineering, School of Medicine, Johns Hopkins University, Baltimore, Maryland 21205.
Four physiological mechanisms are known to be important for recovery of
arterial pressure (AP) after acute hemorrhage. These are the sino-aortic
baroreflex (SA), the vagally mediated cardiopulmonary baroreflex (CP), the
renin-angiotensin system (RA), and the vasopressin system (VP). We
evaluated in anesthetized rabbits the relative importance of these
mechanisms by repeating rapid, 10% arterial hemorrhage (6.5 ml/kg) once
before and once after eliminating one of them and comparing the
posthemorrhage hypotension. The study was conducted in two series. In the
first series, we randomly grouped 24 rabbits into four groups, i.e., a
sinoaortic baroreceptor-denervated group (SA) a vagotomized group (CP), a
renin-angiotensin-blocked group (RA), and a vasopressin-blocked group (VP).
In control conditions, AP fell to 88% at 2 min and 92% at 6 min after
completing the hemorrhage. Significantly greater hypotension (e.g., 74% at
6 min) occurred only in the SA group. In the second series, we randomly
classified 18 rabbits into three groups, i.e., an autonomic
ganglion-blocked group (AB) plus a RA group and a VP group as before.
Hypotension significantly greater than control (68% opposed to 91% at 6
min) occurred only in the AB group. We submit that as far as restoration of
arterial pressure after rapid, mild hemorrhage in the rabbit is concerned,
the arterial baroreceptor reflex system plays a far more important role
than the vagally mediated cardiopulmonary baroreflex, the vasopressin
system, or the renin-angiotensin system triggered directly by a fall in
renal arterial pressure.
