AJP - Regulatory, Integrative and Comparative Physiology, Vol 261, Issue 6 1579-R1586, Copyright © 1991 by American Physiological Society
Neural and humoral effects on hindlimb vascular resistance of ducks during forced submergence
A. M. Lacombe and D. R. Jones
Department of Zoology, University of British Columbia, Vancouver, Canada.
Circulating catecholamines increase by three orders of magnitude in forced
submerged ducks; their role in promoting vascular resistance was studied
using vascular perfusion of hindlimbs. Perfusion pressure and blood flow
were recorded simultaneously in hindlimbs of ducks during forced
submergence. One leg was perfused with blood mixtures devoid of
catecholamines (test leg) and compared with the other autoperfused leg.
Perfusion pressures in test legs perfused with hyperoxic and hypocapnic
blood or with hypoxic and hypocapnic blood were not significantly different
from those in the matching autoperfused legs. However, when test legs were
perfused with hypercapnic blood, regardless of whether blood was hypoxic or
hyperoxic, perfusion pressures were significantly lower than in
autoperfused legs. Adding catecholamines to test legs perfused with hypoxic
and hypercapnic blood, after 3 min submergence, significantly enhanced
vasoconstriction. Hypercapnia acts directly on the peripheral vascular beds
and impairs the neurally mediated vasoconstriction during submergence,
while circulating catecholamines restore peripheral vasoconstriction. Thus
circulating catecholamines are needed to compensate for the depressant
action of hypercapnia on neurally mediated vasoconstriction.
