IDENTIFICATION OF BETA-ADRENERGIC-RECEPTOR SUBTYPES MEDIATING RELAXATION IN ISOLATED EQUINE ILEUM

Objective-To identify beta-adrenergic receptor subtypes in ileum smoot h muscle of the horse. Sample Population-isolated strips of equine lon gitudinal ileum smooth muscle and membrane preparations from smooth mu scle of the intestinal wall. procedure-Functional assays and radioliga nd binding assays. Results-Relaxation of ileum longitudinal smooth mus cle proved to be mainly caused by stimulation of beta-atypical and bet a(2)-adrenergic receptors. Binding studies on cell membranes indicated that the total beta-adrenergic receptors population consists of 54% b eta-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 importa nt role of beta-atypical adrenergic receptor subtypes in the relaxatio n of equine ileum suggests possible clinical use of selective beta-aty pical receptor agonists to control intestinal disturbances.