Equine coronary artery responds to 5-hydroxytryptamine with relaxation in vitro.
Isolated equine coronary arteries responded to 5-hydroxytryptamine (5-HT) with relaxations in both endothelium-dependent and endothelium-independent mechanisms. Experiments were designed to characterize the 5-HT receptor subtype mediating these relaxations. Both 5-HT and alpha-methyl-5-HT (alpha-Me-5-HT; 5-HT2 agonist) produced concentration-dependent relaxations in equine coronary arteries precontracted with a thromboxane A2 derivative (ONO11113). The degree of the maximal relaxation induced by alpha-Me-5-HT was about one-half of that induced by 5-HT. In the coronary arteries without endothelium, alpha-Me-5-HT produced no relaxation, but 5-HT caused relaxation, which was inhibited by a 5-HT1 antagonist (methysergide, mianserin and methiothepin), but was inhibited neither by ketanserin (5-HT2 antagonist) nor by MDL72222 (5-HT3 antagonist). In the coronary arteries with endothelium, however, the relaxation induced by alpha-Me-5-HT was inhibited by ketanserin, L-nitro-arginine (NO synthase inhibitor) and methylene blue (soluble guanylate cyclase inhibitor). These results suggest that the relaxation induced by 5-HT in equine coronary arteries depends mainly on the stimulation of both 5-HT1 receptor subtype on smooth muscle cells directly, and 5-HT2 receptor subtype on endothelial cells indirectly by liberating endothelium-derived NO.
Obi
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Department of Veterinary Pharmacology, Faculty of Agriculture, Kagoshima University, Japan.
Kabeyama
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Nishio
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D000818:Animals; D001158:Arteries; D003331:Coronary Vessels / Q000187:drug effects*; D004594:Electrophysiology; D004730:Endothelium, Vascular / Q000378:metabolism; D006736:Horses; D066298:In Vitro Techniques; D009126:Muscle Relaxation / Q000187:drug effects*; D009131:Muscle, Smooth, Vascular / Q000187:drug effects; D011985:Receptors, Serotonin / Q000378:metabolism; D012701:Serotonin / Q000031:analogs & derivatives / Q000494:pharmacology*; D012702:Serotonin Antagonists / Q000494:pharmacology
D011985:Receptors, Serotonin; D012702:Serotonin Antagonists; D012701:Serotonin