Romain Adelin Lefebvre1, Chana Callens2, Inge Van Colen1, Catherine John Ghislaine Delesalle3. 1. Heymans Institute of Pharmacology, Faculty of Medicine and Health Sciences, De Pintelaan 185, B-9000 Gent, Belgium. 2. Department of Industrial Biological Sciences-Kortrijk, Faculty of Bioscience Engineering, Graaf Karel de Goedelaan 5, 8500 Kortrijk, Belgium. 3. Department of Comparative Physiology and Biometrics, Faculty of Veterinary Medicine, Ghent University, Salisburylaan 133, 9820 Merelbeke, Belgium. Electronic address: Catherine.Delesalle@UGent.be.
Abstract
BACKGROUND: Postoperative ileus (POI) remains an important cause of death in horses. The recently developed selective 5-HT4 receptor agonists such as prucalopride target 5-HT4 receptors on myenteric cholinergic neurons to enhance acetylcholine release and GI motility. No clearcut in vitro evaluation whether highly selective 5-HT4 receptor agonists enhance submaximal cholinergic neurotransmission towards the muscle layer has been performed in horses. OBJECTIVES: To identify functional 5-HT4 receptors in equine jejunum. STUDY DESIGN: In vitro experimental study. METHODS: Circular and longitudinal smooth muscle strips (mid-jejunum) were mounted in organ baths between 2 platinum electrodes allowing electrical field stimulation (EFS). To delineate the conditions to obtain purely cholinergic responses, voltage-response curves were studied. To investigate the influence of prucalopride and 5-HT, submaximal cholinergic contractions at a single voltage were induced. RESULTS: In circular and longitudinal strips, EFS induced voltage-dependent neurogenic on-contractions when the bathing medium contained a NO-synthesis inhibitor and apamin to prevent inhibitory responses to NO and ATP. Contractions at a voltage inducing 50% of maximal amplitude were cholinergic, as they were blocked by atropine. These contractions were not influenced by prucalopride (up to 3μM), even in the presence of the phosphodiesterase inhibitor isobutyl-methyl-xanthine to inhibit breakdown of the second messenger of 5-HT4 receptors, cAMP. Also the full 5-HT4 receptor agonist 5-HT did not influence the EFS-induced submaximal cholinergic contractions. Moreover, prucalopride did not influence muscle tone continuously enhanced with KCl. CONCLUSIONS: There are no functional 5-HT4 receptors on myenteric cholinergic neurons nor muscular 5-HT4 receptors in equine jejunum.
BACKGROUND: Postoperative ileus (POI) remains an important cause of death in horses. The recently developed selective 5-HT4 receptor agonists such as prucalopride target 5-HT4 receptors on myenteric cholinergic neurons to enhance acetylcholine release and GI motility. No clearcut in vitro evaluation whether highly selective 5-HT4 receptor agonists enhance submaximal cholinergic neurotransmission towards the muscle layer has been performed in horses. OBJECTIVES: To identify functional 5-HT4 receptors in equine jejunum. STUDY DESIGN: In vitro experimental study. METHODS: Circular and longitudinal smooth muscle strips (mid-jejunum) were mounted in organ baths between 2 platinum electrodes allowing electrical field stimulation (EFS). To delineate the conditions to obtain purely cholinergic responses, voltage-response curves were studied. To investigate the influence of prucalopride and 5-HT, submaximal cholinergic contractions at a single voltage were induced. RESULTS: In circular and longitudinal strips, EFS induced voltage-dependent neurogenic on-contractions when the bathing medium contained a NO-synthesis inhibitor and apamin to prevent inhibitory responses to NO and ATP. Contractions at a voltage inducing 50% of maximal amplitude were cholinergic, as they were blocked by atropine. These contractions were not influenced by prucalopride (up to 3μM), even in the presence of the phosphodiesterase inhibitor isobutyl-methyl-xanthine to inhibit breakdown of the second messenger of 5-HT4 receptors, cAMP. Also the full 5-HT4 receptor agonist 5-HT did not influence the EFS-induced submaximal cholinergic contractions. Moreover, prucalopride did not influence muscle tone continuously enhanced with KCl. CONCLUSIONS: There are no functional 5-HT4 receptors on myenteric cholinergic neurons nor muscular 5-HT4 receptors in equine jejunum.