title: Relaxation of equine tracheal muscle in vitro by different adrenoceptor drugs.
abstract: Strips of tracheal smooth muscle from 12 horses were contracted by carbachol in tissue baths under isometric conditions. This contraction (approximately 50% of maximum: EC50) was relaxed completely with adrenoceptor drugs. The only exception was clenbuterol, where the degree of relaxation was approximately 90%. In all horses the EC50-value for isoprenaline (mean 1.6 x 10(-8) M) was less than that for adrenaline (mean 9.6 x 10(-8) M) and noradrenaline (mean 1.8 x 10(-6) M). The potency ratio was 1 < 6 < 110 which indicates that the beta 2-subtype dominates among the beta-adrenoceptors of equine airways. All preparations were also very sensitive to the specific and potent beta 2-receptor agonists clenbuterol (mean 5.7 x 10(-9) M) and procaterol (mean 3.6 x 10(-10) M). No differences in EC50-values due to age, sex and breed were observed in this material. The standard deviation of the mean EC50-values seems to be larger for the specific beta 2-adrenoceptor agonists than for the unspecific. A reason for this could be differences in the pattern of the beta-adrenoceptor population.
authors.affiliation: Swedish University of Agricultural Sciences, Faculty of Veterinary Medicine, Department of Pharmacology and Toxicology, Uppsala, Sweden.
authors.forename: K
authors.initials: K
authors.lastname: Törneke
authors.forename: C I
authors.initials: CI
authors.lastname: Larsson
authors.forename: L E
authors.initials: LE
authors.lastname: Appelgren
mesh_terms: D000318:Adrenergic beta-Agonists / Q000494:pharmacology*; D000818:Animals; D002217:Carbachol / Q000037:antagonists & inhibitors; D004305:Dose-Response Relationship, Drug; D005260:Female; D006736:Horses; D008297:Male; D009126:Muscle Relaxation / Q000187:drug effects*; D009130:Muscle, Smooth / Q000187:drug effects*; D010277:Parasympathomimetics / Q000037:antagonists & inhibitors; D014132:Trachea / Q000187:drug effects
chemical_list: D000318:Adrenergic beta-Agonists; D010277:Parasympathomimetics; D002217:Carbachol