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 (T(max)) generated in bronchi (3.2 g) was lower (P <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 T(max) was corrected for smooth muscle myosin content. Thickness of smooth muscle in bronchi was less (P <0.01) than in the three regions of the trachea. T(max) was significantly correlated with airway smooth muscle thickness (r = 0.56; P <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 T(max) is greater in the trachea than in the bronchi and is significantly correlated with thickness of smooth muscle.
|Number of pages||5|
|Journal||Journal of Applied Physiology|
|Publication status||Published - 1989|
ASJC Scopus subject areas
- Orthopedics and Sports Medicine
- Physical Therapy, Sports Therapy and Rehabilitation