AJP - Heart and Circulatory Physiology, Vol 236, Issue 1 165-H173, Copyright © 1979 by American Physiological Society
Pressor response buffering by beta-adrenergic and cholinergic vasodilation in tranquilized dogs
J. M. Evans, C. F. Knapp and T. R. Lowery
Buffering of alpha-receptor-mediated pressor responses by beta-adrenergic
or cholinergic vasodilation in tranquilized, chronically instrumented gos
was investigated. Increases in aortic pressure were produced in the same
animal by intravenous injections of phenylephrine in the control state and
in three successive experimental states by 1) pacing the heart to remove
the reflex capability to lower heart rate, 2) pacing the heart and
beta-blockade to remove beta-adrenergic vascular buffering, and 3)
beta-blockade plus atropine to also remove cholinergic vascular buffering.
The pressor response in each experimental state was greater than that in
the state preceding it. With the combined beta-adrenergic and cholinergic
blockade, the pressor response to an alpha-receptor stimulation was three
times greater than that of the control state. From an analysis of the
components of the pressor response, cardiac output, and peripheral
resistance, it is suggested that normal buffering of an alpha-mediated
pressor response may include beta-adrenergic and cholinergic vascular
dilation in addition to a decrease in heart rate.
