Differences between longitudinal and circular smooth muscle in beta-adrenergic control of motility of isolated equine ileum.

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.