Journal of Applied Physiology, Vol 66, Issue 6 2629-2634, Copyright © 1989 by American Physiological Society
Effect of PAF on parasympathetic contraction of canine airways
R. A. Bethel, S. P. Curtis, D. C. Lien, C. G. Irvin, G. S. Worthen, A. R. Leff and P. M. Henson
National Jewish Center for Immunology and Respiratory Medicine, Department of Medicine, University of Colorado Health Sciences Center, Denver 80206.
Platelet-activating factor (PAF) increases the bronchoconstrictor response
of mammalian airways to cholinergic agonists and is thus implicated as a
potential mediator of airway hyperreactivity. This study further defines
the nature of the increase in airway responsiveness induced by PAF. We
employed an in situ canine tracheal preparation, which allows
differentiation of the effects PAF has on airway smooth muscle contraction
from confounding effects it has on inducing airway edema and secretions. We
found that PAF, infused regionally into tracheal arteries, increases the
responsiveness of the trachealis muscle to parasympathetic stimuli in a
dose-dependent manner. This effect occurred within 15 min. To determine
whether the increase in trachealis muscle responsiveness resulted from
effects localized to the trachea, we compared the effect of PAF on the
tracheal segment with effects of the lower airways of the lung. Delivered
to the arteries perfusing the tracheal segment, PAF did not increase lung
resistance during vagus nerve stimulation. These data indicate that airway
hyperresponsiveness elicited by PAF results from regional stimulation
and/or release of mediators that augment tracheal contractility and that
this effect is distinct from systemic effects elicited by PAF.
