AJP - Regulatory, Integrative and Comparative Physiology, Vol 263, Issue 3 693-R702, Copyright © 1992 by American Physiological Society
Baroreflex control of arterial blood pressure during involuntary diving in ducks (Anas platyrhynchos var.)
F. M. Smith and D. R. Jones
Department of Zoology, University of British Columbia, Vancouver, Canada.
The dynamic role of arterial baroreceptors in control of mean arterial
blood pressure (MAP), heart rate (HR), cardiac output (CO), hindlimb
vascular (HLVR) and total peripheral (TPR) resistance responses to forced
dives was investigated in acutely and chronically barodenervated ducks. To
activate the baroreflex, the proximal end of one aortic nerve was
stimulated electrically with bipolar electrodes that had been implanted
under pentobarbital sodium anesthesia. Predive nerve stimulation caused CO
to fall (by reducing HR; stroke volume remained constant), producing a
decrease in MAP to half the prestimulation level. During diving (for
2.5-min periods) nerve stimulation did not affect HR and MAP after the
first minute of submersion. Neither HLVR nor TPR contributed to the fall in
MAP during aortic nerve stimulation before or during diving. The effects of
nerve stimulation on HR and MAP were maintained to the end of dives in
animals given 100% O2 to breathe before diving. In separate experiments,
increasing arterial chemoreceptor input by perfusing one vascularly
isolated carotid body with venous blood caused a reduction in the effects
of aortic nerve stimulation on MAP. Arterial baroreceptors may thus act on
HR to alter MAP early in the dive, but as the dive progresses the
baroreflex is attenuated by an increase in peripheral chemoreceptor drive.
