Attenuation of tracheal smooth muscle contraction by connective tissue.

Removing the fibroelastic connective tissue, which surrounds the smooth muscle of the pig trachea, enhanced contractions and decreased desensitization in vitro in response to histamine. There were no differences between the preparations in the presence of indomethacin. The magnitude of contraction to acetylcholine was not significantly different. Incubation of the connective tissue in histamine solution caused the appearance of a substance(s) which relaxed other, precontracted tracheal muscles. Propranolol did not block this relaxation. Intact connective tissue appears to reduce the reactivity of the tracheal smooth muscle to histamine.