Objective: To identify beta-adrenoceptor subtypes involved in motility inhibition of circular and longitudinal smooth muscle layers of equine ileum.
Sample population: Isolated strips of equine ileum circular smooth muscle and membrane preparations from circular and longitudinal muscle layers.
Procedure: Functional assays of circular muscle preparations and radioligand binding assays and measurements of cAMP production in smooth muscle membranes from circular and longitudinal layers.
Results: Selective beta-adrenergic agonists exerted inhibitory effects on circular muscle preparations. Binding studies of cell membranes indicated that the density and distribution of 3 beta-adrenoceptor subtypes did not differ between longitudinal and circular muscle layers. Measurement of cAMP production in membrane preparations of longitudinal and circular muscle after selective beta-stimulation confirmed presence of the 3 adenylate cyclase-coupled beta-adrenoceptor subtypes; however, preparations from the 2 layers had differing cAMP production efficacy.
Conclusions: The data may partly explain the differing functional responses between circular and longitudinal muscle preparations.
Clinical relevance: Findings support the important role of beta-atypical adrenoceptors in the inhibitory regulation of equine ileum motility.