COMPARATIVE DISTRIBUTION OF SMOOTH-MUSCLE POSTSYNAPTIC CONTRACTILE RESPONSES IN CANINE TRACHEA AND BRONCHUS INVIVO

  • 1 January 1983
    • journal article
    • research article
    • Vol. 224  (2) , 259-264
Abstract
The response of canine tracheal and bronchial smooth muscle to i.a. [intraarterially] administered agonists causing smooth muscle contraction was compared in 22 mongrel dogs in vivo. Tracheal and bronchial contractile responses were measured isometrically in situ in the same dogs. In 9 dogs, dose-response curves were generated with i.a. acetylcholine and histamine (10-10 to 10-6 mol) in a 4-cm tracheal segment and a 1-cm segment of 3rd order bronchus. The tracheal response to i.a. histamine was 36.5 .+-. 4.48% of the response to equivalent doses of acetylcholine. In bronchus, the contraction caused by histamine was 81.0 .+-. 2.83% of the cholinergic contractile response (P < 0.001). In 5 dogs having .beta.-adrenergic blockade with propranolol, tracheal contraction to 10-8 to 10-6 mol i.a. norepinephrine was 27.3 .+-. 4.2% of the response to acetylcholine. In bronchus, contraction to norepinephrine was 218 .+-. 16.6% of the response to equivalent doses of acetylcholine (P < 0.001). Phentolamine (200-400 .mu.g/kg i.a.) caused 79-100% blockade of the tracheal and bronchial response to i.a. norepinephrine. Cholinergic contraction was blocked specifically with 5 .mu.g/kg i.a. of atropine. There is substantial heterogeneity in the contractile responses of canine trachea and bronchus in situ. Relative to cholinergic contraction, both histamine and .alpha.-adrenergic stimulation cause substantially greater contraction of airway smooth muscle in the 3rd order bronchus than in trachea.