Journal of Applied Physiology, Vol 67, Issue 4 1331-1335, Copyright © 1989 by American Physiological Society
Response to acetylcholine and myosin content of isolated canine airways
C. E. Mapp, P. Chitano, N. De Marzo, P. Di Blasi, M. Saetta, A. Di Stefano, V. M. Bosco, L. Allegra and L. M. Fabbri
Institute of Occupational Medicine, University of Padua, Italy.
Contractility of tracheal smooth muscle strips and spiral strips of fourth
to fifth generation bronchi was studied in organ baths. The relationship
among contractility, airway smooth muscle myosin, and smooth muscle
thickness was also examined. The trachea was divided into three segments,
each consisting of 12-14 rings. Smooth muscle strips from each of the three
regions (top, middle, and bottom of the trachea) and from fourth to fifth
generation bronchi were studied. Acetylcholine (ACh) sensitivity (-log
EC50) was 8.1, 7.1, 7.9, and 6.1 for the top, middle, and bottom of the
trachea and the bronchi, respectively. At P = 0.01, the EC50 ACh value of
the top of the trachea differed from the EC50 value of the bronchi. Maximal
tension (Tmax) generated in bronchi (3.2 g) was lower (P less than 0.01)
than in the top (10.4 g), middle (7.1 g), and bottom of the trachea (5.1
g). Differences between trachea and bronchi disappeared when Tmax was
corrected for smooth muscle myosin content. Thickness of smooth muscle in
bronchi was less (P less than 0.01) than in the three regions of trachea.
Tmax was significantly correlated with airway smooth muscle thickness (r =
0.56; P less than 0.05). These results suggest that in mongrel dogs
sensitivity to ACh shows a gradient from the top of the trachea to the
bronchi and that Tmax is greater in the trachea than in the bronchi and is
significantly correlated with thickness of smooth muscle.
