Identification of ß-adrenergic receptor subtypes mediating relaxation in isolated equine ileum

OBJECTIVE: To identify beta-adrenergic receptor subtypes in ileum smooth muscle of the horse. SAMPLE POPULATION: Isolated strips of equine longitudinal ileum smooth muscle and membrane preparations from smooth muscle of the intestinal wall. PROCEDURE: Functional assays and radioligand binding assays. RESULTS: Relaxation of ileum longitudinal smooth muscle proved to be mainly caused by stimulation of beta-atypical and beta 2-adrenergic receptors. Binding studies on cell membranes indicated that the total beta-adrenergic receptors population consists of 54% beta-atypical, 34% beta 2- and 12% beta 1-subtypes. CONCLUSIONS: The data suggest that sympathetic relaxation of equine ileum smooth muscle depends mainly on beta-atypical receptor subtypes activation, with a minor contribution by beta 2-subtypes. CLINICAL RELEVANCE: The important role of beta-atypical adrenergic receptor subtypes in the relaxation of equine ileum suggests possible clinical use of selective beta-atypical receptor agonists to control intestinal disturbances.