Characterization of the in vitro responses of equine cecal longitudinal smooth muscle to endothelin-1.
OBJECTIVE
To characterize the in vitro response of equine cecal longitudinal smooth muscle (CLSM) to endothelin (ET)-1 and assess the role of ETA and ETB receptors in those ET-1-induced responses.


METHODS
36 horses without gastrointestinal tract disease.


METHODS
To determine cumulative concentration-response relationships, CLSM strips were suspended in tissue baths containing graded concentrations of ET-1 (10(-9) to 10(-6)M) with or without BQ-123 (ETA receptor antagonist); with or without IRL-1038 (ETB receptor antagonist); or with both antagonists at concentrations of 10(-9), 10(-7), and 10(-5)M. To determine the percentage change in baseline tension of CLSM, the areas under the curve during the 3-minute periods before and after addition of each dose were compared. Also, the effects of ET-1 and a combination of selective ETA and ETB receptor antagonists on electrically evoked contractions were studied.


RESULTS
ET-1 caused sustained increases in CLSM tension in a concentration-dependent manner. Contractile responses to ET-1 were not significantly inhibited by either BQ-123 or IRL-1038 alone at any concentration; however, responses were significantly inhibited by exposure to the antagonists together at a concentration of 10(-5)M. Electrical field stimulation did not change the spontaneous contractile activity of CLSM and did not significantly alter the tissue response to ET-1, BQ-123, or IRL-1038.


CONCLUSIONS
Results indicated that ET-1 has a contractile effect on equine CLSM that is mediated via ETA and ETB receptors. In vitro spontaneous contractions of equine CLSM apparently originate in the smooth muscle and not the enteric nervous system.
Chidambaram
Ramaswamy M
RM
Equine Health Studies Program, Department of Comparative Biomedical Sciences, School of Veterinary Medicine, Louisiana State University, Baton Rouge, LA 70803-8410, USA.
Eades
Susan C
SC
Moore
Rustin M
RM
Hosgood
Giselle
G
Venugopal
Changaram S
CS
D000818:Animals; D002432:Cecum / Q000502:physiology*; D004305:Dose-Response Relationship, Drug; D065128:Endothelin Receptor Antagonists; D019332:Endothelin-1 / Q000494:pharmacology / Q000502:physiology*; D016232:Endothelins / Q000494:pharmacology; D006736:Horses / Q000502:physiology*; D066298:In Vitro Techniques; D009119:Muscle Contraction / Q000187:drug effects / Q000502:physiology*; D009130:Muscle, Smooth / Q000502:physiology*; D010446:Peptide Fragments / Q000494:pharmacology; D010456:Peptides, Cyclic / Q000494:pharmacology
D065128:Endothelin Receptor Antagonists; D019332:Endothelin-1; D016232:Endothelins; D010446:Peptide Fragments; D010456:Peptides, Cyclic; C077420:Cys(11)-Cys(15)-endothelin-1 (11-21); C072247:cyclo(Trp-Asp-Pro-Val-Leu)