title: Chronic fenoterol exposure increases in vivo and in vitro airway responses in guinea pigs.
abstract: We tested the hypothesis that the regular inhalation of a beta 2-adrenergic receptor (beta 2AR) agonist increases airway responsiveness in guinea pigs. A potent beta 2AR agonist, fenoterol hydrobromide, in sublaryngeal doses equivalent to maximal doses used in the treatment of asthma on a weight basis (5.28 micrograms/kg), was administered by nebulizer three times a day for 6 weeks to normal adolescent guinea pigs (FEN, n = 10) and to ovalbuminsensitized guinea pigs challenged twice weekly with ovalbumin (OA + FEN, n = 20), although not in the 12 h prior to or 4 h after antigen challenge. Controls included saline-treated normal animals (CON, n = 10) and ovalbumin-sensitized animals treated with repeated antigen challenge and saline (OA, n = 20). At 72 h after the last administration of saline, fenoterol, and ovalbumin, the dose-response relationship between pulmonary resistance (RL) and nebulized acetylcholine (ACh) was measured. RLmax increased 2-fold and the ACh concentration causing a 10-fold increase in RL (PC10) decreased 4-fold in the FEN, OA, and OA + FEN groups as compared to the CON group. In the FEN, OA, and OA + FEN groups, in vitro tracheal smooth-muscle contractile responses to maximal concentrations of acetylcholine increased 2-fold, and this increase was not due to increased smooth-muscle mass. There was no evidence for beta 2AR desensitization as judged by in vitro tracheal smooth-muscle relaxant responses to fenoterol. These results suggest that chronic beta 2AR stimulation increases airway smooth-muscle contractility and in vivo airways responsiveness to a degree similar to that induced by chronic antigen exposure. A similar effect in human asthmatics may explain the adverse effects observed during prolonged treatment with these drugs.
authors.affiliation: University of British Columbia Pulmonary Research Laboratory, St. Paul's Hospital, Vancouver, Canada.
authors.forename: Z L
authors.initials: ZL
authors.lastname: Wang
authors.forename: A M
authors.initials: AM
authors.lastname: Bramley
authors.forename: A
authors.initials: A
authors.lastname: McNamara
authors.forename: P D
authors.initials: PD
authors.lastname: Paré
authors.forename: T R
authors.initials: TR
authors.lastname: Bai
mesh_terms: D000336:Aerosols; D000704:Analysis of Variance; D000818:Animals; D001980:Bronchi / Q000187:drug effects* / Q000502:physiology; D004305:Dose-Response Relationship, Drug; D005280:Fenoterol / Q000008:administration & dosage*; D006168:Guinea Pigs; D066298:In Vitro Techniques; D008297:Male; D009119:Muscle Contraction / Q000187:drug effects; D009130:Muscle, Smooth / Q000187:drug effects / Q000502:physiology; D009330:Nebulizers and Vaporizers; D010047:Ovalbumin / Q000008:administration & dosage; D015656:Respiratory Mechanics / Q000187:drug effects; D013997:Time Factors; D014132:Trachea
chemical_list: D000336:Aerosols; D005280:Fenoterol; D010047:Ovalbumin