Comparative distribution of cholinomimetic and parasympathetic contractile responses in the major diameter airways of dogs.

The distribution of cholinomimetic and parasympathetic contractile responses in the major diameter airways and the simultaneous change in lung resistance was examined in 10 mongrel dogs in vivo. The airways of animals anesthetized with chloralose-urethane were insufflated with tantalum, and responses in airway generations 0 (trachea) through 5 were assessed as the change in airway diameter (dDaw) at functional residual capacity (FRC). All animals had beta-adrenergic blockade with propranolol to block reflex sympathetic effects resulting from hypotension. Sequential dose-response curves to 10(-10) to 10(-7) mol/kg iv methacholine (MCh; n = 5) were elicited; in separate studies, stimulus-response curves were generated (1-20 Hz; n = 5) at 7 min intervals. Tantalum bronchograms were obtained at each point on the stimulus/dose-response curve for each animal. Maximal parasympathetic stimulation caused a 28.8 +/- 4.35% dDaw in trachea, a 37.2 +/- 2.33% dDaw in generation 1 airways and a 42.4 +/- 3.63% dDaw in generation 5 airways. In contrast, cholinomimetic stimulation caused substantially less narrowing of trachea (dDaw = 8.04 +/- 2.60%; P less than 0.001 vs cholinomimetic stimulation) and generation 1 airways (21.6 +/- 2.06%; P less than 0.001) and substantially less change in airway resistance (981 +/- 107% for MCh vs 1634 +/- 173% P less than 0.01) when diameter changes in generation 5 airways were comparable (45.6 +/- 7.38% vs 42.4 +/- 3.63%; P = NS).(ABSTRACT TRUNCATED AT 250 WORDS)