Airway responses to aerosolized methacholine in the cat. Effects of partial or complete vagosympathectomy.
To explore the role of airway innervation as a determinant of airway responsiveness to inhaled cholinergic agonists, we studied the effects of partial or complete section of the cervical vagosympathetic trunk on the magnitude of methacholine-induced bronchoconstriction in the chloralose-urethane-anesthetized, mechanically ventilated cat. An initial concentration-response curve to methacholine was constructed to identify the concentration required to cause a twofold to threefold rise in mean pulmonary resistance (RL). Using this concentration, 3 consecutive challenges (C1, C2, and C3) were then performed at 30-min intervals in 4 groups of cats. After a control challenge (C1), the parasympathetic (n = 9), sympathetic (n = 6), or both branches (n = 4) of the cervical vagosympathetic trunks were sectioned. Sham cats (n = 7) showed reproducible increases in RL (C1, delta RL = 15.1 +/- 2.7 cm H2O X 1(-1) X s; C2, delta RL = 15.7 +/- 3.0; C3, delta RL = 13.1 +/- 2.9; mean +/- 1 SE). After parasympathectomy there was an increase in responsiveness after C3 (C1, delta RL = 15.0 +/- 4.3; C2, delta RL = 16.4 +/- 6.4; C3, delta RL = 29.9 +/- 11.6; p less than 0.01). Sympathectomy and vagosympathectomy did not significantly alter responsiveness. The results suggest that vagally mediated inhibitory influences modulate the bronchial response to aerosolized methacholine in the cat.
D000336:Aerosols; D000403:Airway Resistance / Q000187:drug effects; D000818:Animals; D001980:Bronchi / Q000187:drug effects* / Q000294:innervation; D002415:Cats; D003250:Constriction; D004305:Dose-Response Relationship, Drug; D005260:Female; D005726:Ganglia, Parasympathetic; D005728:Ganglia, Sympathetic; D008297:Male; D016210:Methacholine Chloride; D008688:Methacholine Compounds / Q000494:pharmacology*; D013562:Sympathectomy / Q000379:methods*; D014628:Vagotomy / Q000379:methods; D014630:Vagus Nerve / Q000502:physiology*
D000336:Aerosols; D008688:Methacholine Compounds; D016210:Methacholine Chloride