title: Inhibitory effects of clonidine on bronchospasm induced in guinea-pigs by vagal stimulation or antigen challenge.
abstract: The effects of clonidine on the bronchospastic responses induced by vagal stimulation or antigen challenge were studied in anaesthetized guinea-pigs. Electrical stimulation of the vagus nerves by 2-4 Hz induced a vigorous, mainly atropine-sensitive bronchoconstriction, which was strongly inhibited by clonidine (0.05 mg/kg i.v.). The inhibitory effect of clonidine was significantly reduced by the alpha 2-adrenoceptor antagonist yohimbine (1 mg/kg i.v.). Another series of experiments was done with ovalbumin-sensitized guinea-pigs. Respiratory anaphylaxis was induced by antigen inhalation resulting in an increase of pulmonary resistance from 100% (baseline) to about 190% in the control group. Animals pretreated with a clonidine aerosol (0.03%) showed a marked inhibition of the bronchospastic response. It is suggested that the inhibition of the bronchospastic responses induced by clonidine may be mediated by a stimulation of alpha 2-adrenoceptors, which exerts an inhibitory control of the excitatory vagal activity in the guinea-pig airways.
mesh_terms: D000707:Anaphylaxis / Q000209:etiology / Q000503:physiopathology; D000818:Animals; D000941:Antigens / Q000008:administration & dosage; D001986:Bronchial Spasm / Q000188:drug therapy* / Q000209:etiology / Q000503:physiopathology; D003000:Clonidine / Q000494:pharmacology*; D004558:Electric Stimulation; D006168:Guinea Pigs; D007114:Immunization; D008297:Male; D010047:Ovalbumin / Q000276:immunology; D011942:Receptors, Adrenergic, alpha / Q000187:drug effects / Q000502:physiology; D014630:Vagus Nerve / Q000502:physiology
chemical_list: D000941:Antigens; D011942:Receptors, Adrenergic, alpha; D010047:Ovalbumin; D003000:Clonidine