title: Melatonin receptor-mediated protection against myocardial ischaemia/reperfusion injury: role of its anti-adrenergic actions.
abstract: Melatonin has potent cardioprotective properties. These actions have been attributed to its free radical scavenging and anti-oxidant actions, but may also be receptor mediated. Melatonin also exerts powerful anti-adrenergic actions based on its effects on contractility of isolated papillary muscles. The aims of this study were to determine whether melatonin also has anti-adrenergic effects on the isolated perfused rat heart, to determine the mechanism thereof and to establish whether these actions contribute to protection of the heart during ischaemia/reperfusion. The results showed that melatonin (50 microM) caused a significant reduction in both isoproterenol (10(-7) M) and forskolin (10(-6) M) induced cAMP production and that both these responses were melatonin receptor dependent, since the blocker, luzindole (5 x 10(-6) M) abolished this effect. Nitric oxide (NO), as well as guanylyl cyclase are involved, as L-NAME (50 microM), an NO synthase inhibitor and ODQ (20 microM), a guanylyl cyclase inhibitor, significantly counteracted the effects of melatonin. Protein kinase C (PKC), as indicated by the use of the inhibitor bisindolylmaleimide (50 microM), also play a role in melatonin's anti-adrenergic actions. These actions of melatonin are involved in its cardioprotection: simultaneous administration of L-NAME or ODQ with melatonin, before and after 35 min regional ischaemia, completely abolished its cardioprotection. PKC, on the other hand, had no effect on the melatonin-induced reduction in infarct size. Cardioprotection by melatonin was associated with a significant activation of PKB/Akt and attenuated activation of the pro-apoptotic kinase, p38MAPK during early reperfusion. In summary, the results show that melatonin-induced cardioprotection may be receptor dependent, and that its anti-adrenergic actions, mediated by NOS and guanylyl cyclase activation, are important contributors.
authors.affiliation: Department of Biomedical Sciences, Division of Medical Physiology, Faculty of Health Sciences, University of Stellenbosch, Tygerberg, South Africa.
authors.forename: Sonia
authors.initials: S
authors.lastname: Genade
authors.forename: Amanda
authors.initials: A
authors.lastname: Genis
authors.forename: Kirsti
authors.initials: K
authors.lastname: Ytrehus
authors.forename: Barbara
authors.initials: B
authors.lastname: Huisamen
authors.forename: Amanda
authors.initials: A
authors.lastname: Lochner
mesh_terms: D018674:Adrenergic Antagonists / Q000494:pharmacology*; D000818:Animals; D005576:Colforsin / Q000494:pharmacology; D000242:Cyclic AMP / Q000378:metabolism*; D006162:Guanylate Cyclase / Q000378:metabolism; D006321:Heart / Q000187:drug effects / Q000502:physiology; D007211:Indoles / Q000494:pharmacology; D007545:Isoproterenol / Q000494:pharmacology; D008297:Male; D008301:Maleimides / Q000494:pharmacology; D008550:Melatonin / Q000819:agonists / Q000494:pharmacology*; D009203:Myocardial Infarction / Q000473:pathology; D015428:Myocardial Reperfusion Injury / Q000517:prevention & control*; D019331:NG-Nitroarginine Methyl Ester / Q000494:pharmacology; D009569:Nitric Oxide / Q000502:physiology; D010069:Oxadiazoles / Q000494:pharmacology; D011433:Propranolol / Q000494:pharmacology; D011493:Protein Kinase C / Q000378:metabolism; D011810:Quinoxalines / Q000494:pharmacology; D051381:Rats; D017208:Rats, Wistar; D044094:Receptors, Melatonin / Q000378:metabolism*; D014363:Tryptamines / Q000502:physiology; D048051:p38 Mitogen-Activated Protein Kinases / Q000378:metabolism
chemical_list: C095284:1H-(1,2,4)oxadiazolo(4,3-a)quinoxalin-1-one; D018674:Adrenergic Antagonists; D007211:Indoles; D008301:Maleimides; D010069:Oxadiazoles; D011810:Quinoxalines; D044094:Receptors, Melatonin; D014363:Tryptamines; C057154:luzindole; D005576:Colforsin; D009569:Nitric Oxide; D011433:Propranolol; D000242:Cyclic AMP; D011493:Protein Kinase C; D048051:p38 Mitogen-Activated Protein Kinases; D006162:Guanylate Cyclase; D008550:Melatonin; D007545:Isoproterenol; C088060:bisindolylmaleimide; D019331:NG-Nitroarginine Methyl Ester