Melatonin attenuates the acetylcholine-induced contraction in isolated intestine of a teleost fish

• Published in: Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology Biochemical, systemic, and environmental physiology, 2009-11, Vol.179 (8), p.951-959
• Main Authors: Velarde, Elena, Alonso-Gómez, Angel Luis, Azpeleta, Clara, Isorna, Esther, Delgado, María Jesús
• Format: Article
• Language: English
• Subjects: Acetylcholine - pharmacology; Animal Physiology; Animals; Biochemistry; Biomedical and Life Sciences; Biomedicine; Calcium - metabolism; Dose-Response Relationship, Drug; Gastrointestinal Motility - physiology; Goldfish - physiology; Human Physiology; In Vitro Techniques; Intestines - physiology; Life Sciences; Melatonin - agonists; Melatonin - antagonists & inhibitors; Melatonin - physiology; Muscle Contraction - drug effects; Muscle Contraction - physiology; Original Paper; Zoology
• ISSN: 0174-1578; 1432-136X
• DOI: 10.1007/s00360-009-0373-1

The present study investigates the possible direct actions of melatonin (N-acetyl-5-methoxytryptamine) on intestinal motility in goldfish (Carassius auratus) using an in vitro system of isolated intestine in an organ bath engaged to an isometric transducer. The longitudinal strips from goldfish intestine in the organ bath showed a resting spontaneous myogenic rhythmic activity which is not altered by melatonin. The addition of acetylcholine (1 nmol l⁻¹-10 mmol l⁻¹) to the organ bath induces a significant contraction of the intestinal strips in a concentration-dependent manner. The addition of melatonin and its agonist, 2-iodomelatonin, induced a concentration-dependent attenuation of acetylcholine-induced contractile response. The specificity of this effect is tested by the preincubation of the intestine strips in the presence of two melatoninergic antagonists, luzindole (a non-selective MT₁/MT₂ melatonin receptor antagonist) and 4-P-PDOT (preferred antagonist of MT2 receptor subtype), which counteracted the melatonin-induced relaxation in a concentration-dependent manner. Finally, present results demonstrate that this melatoninergic effect on intestinal strips is a process highly dependent on extracellular calcium. In conclusion, this is the first study demonstrating the role of melatonin in the control of gut motility in a non-mammalian vertebrate. The melatonin effects on isolated intestine from goldfish are mediated by melatoninergic membrane receptors, and could suggest a delay in food transit time, supporting its anorectic effect reported on in vivo studies.