AJP - Lung Cellular and Molecular Physiology, Vol 258, Issue 2 52-L56, Copyright © 1990 by American Physiological Society
Epithelial effects on tracheal smooth muscle tone: influence of muscarinic antagonists
A. Lev, G. C. Christensen, R. A. Zhang and S. G. Kelsen
Department of Medicine, Temple University School of Medicine, Philadelphia, Pennsylvania 19140.
The tracheobronchial epithelium produces factor(s) that modulate the
constrictor and relaxant response of airway smooth muscle. The present
study sought to determine whether the tracheobronchial epithelial
inhibitory effect on trachealis smooth muscle tension is under muscarinic
receptor control. Studies were performed on 195 strips from 13 rabbits. In
strips in which the epithelium was intact, pirenzepine (an M1 receptor
antagonist) produced a dose-related (10(-8) and 10(-7)M) rightward shift (P
less than 0.01 for each) and gallamine (an M2 antagonist) produced a
progressive (10(-8) and 10(-7)M) leftward shift of the acetylcholine
concentration responses (P less than 0.01 for each). In strips in which the
epithelium was removed mechanically, neither pirenzepine nor gallamine had
any effect on the acetylcholine responses. In acetylcholine precontracted
(5 x 10(-6) M) muscle strips with epithelium intact, addition of
pirenzepine (10(-7)M) produced a significant (P less than 0.01) reduction
in steady-state tension, whereas administration of gallamine tended to
increase tension, (P = NS). Neither pirenzepine nor gallamine had any
effect on steady-state tension in strips in which the epithelium was
removed. These results indicate that the magnitude of the tracheobronchial
epithelial inhibitory effect on smooth muscle tension is under muscarinic
control. Specifically, M1 receptor blockade augments and M2 receptor
blockade inhibits the magnitude of the tracheobronchial epithelial effect.
