AJP - Regulatory, Integrative and Comparative Physiology, Vol 258, Issue 4 895-R902, Copyright © 1990 by American Physiological Society
Effects of acute and chronic baroreceptor denervation on diving responses in ducks
F. M. Smith and D. R. Jones
Department of Zoology, University of British Columbia, Vancouver, Canada.
To investigate the effects of barodenervation on the cardiovascular
responses to forced submersion, we implanted snares around the aortic
nerves innervating the baroreceptors in anesthetized (pentobarbital sodium,
35-45 mg/kg) ducks (Anas platyrhynchos). Snares were withdrawn 1 wk after
surgery to effect barodenervation in the absence of complications from
surgical trauma or anesthesia. After barodenervation, resting heart rate
(HR), hind limb vascular resistance (HLVR), and mean arterial pressure
(MAP) all increased, with different time courses, over the 16-day
observation period. Bradycardia developed during forced submersion in ducks
before and after barodenervation, although this response was reduced for
1-3 days after nerve section. The HR response to diving intensified 4-5
days after denervation, and the level of dive bradycardia at 16 days was
similar to that before denervation. End-dive MAP fell further, as a
proportion of predive MAP, with time after baroreceptor loss. The absolute
level of HLVR reached during diving was unaffected by barodenervation.
These results show that diving responses develop in the absence of
baroreceptors, but MAP in the dive is not maintained as well in
barodenervates as in baroreceptor-intact animals.
