title: Kyotorphin has a novel action on rat cardiac muscle.
abstract: Several endogenous peptides for G-protein-coupled receptors have been found to play physiological roles in muscle contraction in addition to their well-demonstrated actions in other tissues. To further identify such peptides, we screened over 400 peptides using an isometric tension assay of rat papillary muscle. Here, we report that kyotorphin, which is known as an analgesic dipeptide, has a cardiac effect. Although kyotorphin had no effect on the twitch tension itself, it inhibited beta-adrenergic agonist isoprenaline-induced increases in twitch tension in a dose-dependent manner. Leu-Arg, a selective antagonist of kyotorphin, reversed this inhibitory effect. The inhibitory effect was also reversed by naloxone, an opioid receptor antagonist. These results suggest that kyotorphin may release opioid peptides from rat cardiac muscle and have an indirect regulatory role in beta-adrenergic action through cross-talk with opioid receptors.
authors.affiliation: Department of Pharmacology, Saitama Medical School, Moroyama 38, Iruma-gun, Saitama 350-0495, Japan.
authors.forename: Yue
authors.initials: Y
authors.lastname: Li
authors.forename: Yumiko
authors.initials: Y
authors.lastname: Saito
authors.forename: Masahiko
authors.initials: M
authors.lastname: Suzuki
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Ueda
authors.forename: Makoto
authors.initials: M
authors.lastname: Endo
authors.forename: Kei
authors.initials: K
authors.lastname: Maruyama
mesh_terms: D000818:Animals; D004305:Dose-Response Relationship, Drug; D004338:Drug Combinations; D004723:Endorphins / Q000008:administration & dosage*; D066298:In Vitro Techniques; D007537:Isometric Contraction / Q000187:drug effects / Q000502:physiology*; D007545:Isoproterenol / Q000008:administration & dosage*; D008297:Male; D009200:Myocardial Contraction / Q000187:drug effects / Q000502:physiology*; D010210:Papillary Muscles / Q000187:drug effects / Q000502:physiology*; D051381:Rats; D017208:Rats, Wistar
chemical_list: D004338:Drug Combinations; D004723:Endorphins; C019448:kyotorphin; D007545:Isoproterenol