title: Parasympathetic and adrenergic contractile responses in canine trachea and bronchus.
abstract: We compared the sympathetic and parasympathetic contractile responses of tracheal and third-order bronchial smooth muscle simultaneously in 26 dogs in situ. Stimulus-response curves were generated by bilateral stimulation of the cervical vagus nerves in five dogs to determine the parameters (20 V, 15 Hz, 2-ms duration) causing maximal parasympathetic contraction in trachea and bronchus. In six adrenal-intact (ADi) and five adrenalectomized (ADx) dogs, sympathetically mediated alpha-adrenergic contraction was studied after muscarinic and beta-adrenergic blockade by administering intravenous (iv) 1,1-dimethyl-4-phenylpiperazinium iodide (DMPP). In ADi dogs, the maximal alpha-adrenergic contractile response to iv DMPP was 67.3 +/- 14.8% of the maximal parasympathetic response in trachea and 112 +/- 21% of the maximal parasympathetic response in bronchus (P less than 0.03). In ADx dogs, the maximal alpha-adrenergic-to-parasympathetic stimulation ratios were 17.6 +/- 1.3% in trachea and 41.4 +/- 2.5% in bronchus (P less than 0.001). Comparable relationships were also obtained in pharmacological studies of alpha-adrenergic and cholinergic responses in trachea and bronchus. We conclude that there is substantial heterogeneity in the physiological and pharmacological cholinergic and alpha-adrenergic contractile properties in trachea and bronchus. Relative to cholinergic contraction, both circulating catecholamines and sympathetic innervation cause substantially greater alpha-adrenergic contraction in bronchus than for tracheal smooth muscle.
mesh_terms: D000320:Adrenergic Fibers / Q000502:physiology; D000403:Airway Resistance; D000818:Animals; D001980:Bronchi / Q000294:innervation; D004246:Dimethylphenylpiperazinium Iodide / Q000494:pharmacology; D004285:Dogs; D005260:Female; D008297:Male; D008688:Methacholine Compounds / Q000494:pharmacology; D009119:Muscle Contraction; D009130:Muscle, Smooth / Q000187:drug effects / Q000502:physiology*; D010275:Parasympathetic Nervous System / Q000502:physiology*; D013564:Sympathetic Nervous System / Q000502:physiology*; D014132:Trachea / Q000294:innervation; D014630:Vagus Nerve / Q000502:physiology
chemical_list: D008688:Methacholine Compounds; D004246:Dimethylphenylpiperazinium Iodide