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.


METHODS
Isolated strips of equine ileum circular smooth muscle and membrane preparations from circular and longitudinal muscle layers.


METHODS
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.


CONCLUSIONS
Findings support the important role of beta-atypical adrenoceptors in the inhibitory regulation of equine ileum motility.
Belloli
C
C
Institute of Veterinary Pharmacology and Toxicology, University of Milan, Italy.
Re
G
G
Arioli
F
F
Badino
P
P
Carcano
R
R
Odore
R
R
Girardi
C
C
Beretta
C
C
D000322:Adrenergic Agonists / Q000494:pharmacology; D000818:Animals; D001485:Basement Membrane / Q000737:chemistry / Q000378:metabolism / Q000502:physiology; D002976:Clenbuterol / Q000494:pharmacology; D000242:Cyclic AMP / Q000096:biosynthesis; D004280:Dobutamine / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D005260:Female; D005769:Gastrointestinal Motility / Q000187:drug effects / Q000502:physiology*; D006736:Horses / Q000378:metabolism / Q000502:physiology*; D007082:Ileum / Q000737:chemistry / Q000378:metabolism / Q000502:physiology*; D007545:Isoproterenol / Q000494:pharmacology; D008297:Male; D009119:Muscle Contraction / Q000187:drug effects / Q000502:physiology; D009130:Muscle, Smooth / Q000737:chemistry / Q000378:metabolism / Q000502:physiology*; D011869:Radioligand Assay / Q000662:veterinary; D011943:Receptors, Adrenergic, beta / Q000032:analysis / Q000187:drug effects / Q000502:physiology*
D000322:Adrenergic Agonists; D011943:Receptors, Adrenergic, beta; D004280:Dobutamine; D000242:Cyclic AMP; D007545:Isoproterenol; D002976:Clenbuterol