Physiological and pharmacological response of canine bronchial smooth muscle in situ

Publisher Website
Google Scholar
Abstract
The isometric response of bronchial smooth muscle in a single 3rd-order bronchus of 24 dogs was studied in situ. Length-tension studies were performed in 6 dogs by repeated injection of 10-5 mol acetylcholine (ACh) into the right bronchoesophageal artery; the resting tension (30.6 .+-. 6.9 g/cm) and length (0.76 .+-. 0.14 cm) permitting maximal contraction were determined. In 8 other dogs, dose-related bronchial contraction was obtained with 10-10 to 10-5 mol intra-arterial (ia) ACh. Supramaximal electrical stimulation of the right cervical vagus nerve and bronchial parasympathetic ganglion stimulation with ia 1-1-dimethyl-4-phenylpiperazinium (DMPP) also caused bronchial contraction. The maximal response to ia ACh (28.5 .+-. 1.7 g/cm), supramaximal electrical stimulation (15.2 .+-. 1.1 g/cm), and ia DMPP (10.5 .+-. 3.0 g/cm) was blocked by an ia dose of atropine (1-5 .mu.g/kg) that did not alter the sympathetic relaxation response in the trachea. In 4 dogs, the bronchial response to sympathetic activation was studied by i.v. bolus injection of DMPP after cholinergic blockade with atropine. DMPP (25 .mu.g/kg i.v.) caused 9.5 .+-. 2.2 g/cm bronchial relaxation, which was blocked completely by 2-4 mg/kg i.v. propranolol. In 6 other dogs, hypoxia induced by ventilation with pure nitrogen caused bronchial contraction, which was blocked by vagotomy, atropine and hexamethonium. A sensitive method for selective measurement of bronchial smooth muscle response in a single resistance bronchus is reported. This preparation preserves regional innervation and circulation and permits selective physiological stimulation in situ.