ABSTRACT
Hearts from Sprague-Dawley rats were perfused at constant flow and then exposed to 30 min global zero-flow ischemia followed by 15 min reperfusion. After ischemia-reperfusion, coronary arteries were dissected from the heart and segments 2 mm long were prepared for isometric tension recording in organ baths. Stimulation of the arteries with 5-hydroxytryptamine (10(-6) M) produced contraction, which was potentiated by treatment with endothelin-1 (3x10(-10); 10(-9) M). This potentiation was lower in the arteries from hearts after ischemia-reperfusion (for 3x10(-10) M, 15+/-5%; P>0.05; for 10(-9) M, 37+/-7%, P<0.01, n=5) than after control (for 3x10(-10) M, 34+/-4%; P<0.01; for 10(-9) M, 50+/-6%, P<0.01, n=5), and the potentiation was reduced by the inhibitor of nitric oxide synthesis l-NAME (10(-4) M), the antagonist of endothelin ET(A) receptors BQ123 (10(-6) M) and the antagonist of endothelin ET(B) receptors BQ788 (10(-6) M), but not by the cyclooxygenase inhibitor meclofenamate (10(-5) M). These results suggest that endothelin-1 at low concentrations potentiates coronary vasoconstriction, and this effect is reduced after ischemia-reperfusion, mediated by endothelin ET(A) and ET(B) receptors and dependent on nitric oxide release.
Subject(s)
Coronary Vessels/metabolism , Endothelin-1/metabolism , Myocardial Reperfusion Injury/metabolism , Vasoconstriction , 15-Hydroxy-11 alpha,9 alpha-(epoxymethano)prosta-5,13-dienoic Acid/pharmacology , Animals , Coronary Vessels/drug effects , Coronary Vessels/enzymology , Coronary Vessels/physiopathology , Cyclooxygenase Inhibitors/pharmacology , Endothelin A Receptor Antagonists , Endothelin B Receptor Antagonists , Enzyme Inhibitors/pharmacology , In Vitro Techniques , Male , Meclofenamic Acid/pharmacology , Myocardial Reperfusion Injury/physiopathology , NG-Nitroarginine Methyl Ester/pharmacology , Nitric Oxide Synthase/antagonists & inhibitors , Nitric Oxide Synthase/metabolism , Oligopeptides/pharmacology , Peptides, Cyclic/pharmacology , Perfusion , Piperidines/pharmacology , Rats , Rats, Sprague-Dawley , Receptor, Endothelin A/metabolism , Receptor, Endothelin B/metabolism , Serotonin/pharmacology , Vasoconstriction/drug effects , Vasoconstrictor Agents/pharmacologyABSTRACT
1 Urocortin is a vasodilator peptide related to corticotrophin-releasing factor, which may protect endothelial function during coronary ischemia-reperfusion (I-R). The aim of this study was to study the mechanisms of this protective effect. 2 Hearts from Sprague-Dawley rats were isolated and perfused at constant flow and then exposed to 15 min global zero-flow ischemia, followed by 15 min reperfusion. The relaxation to acetylcholine (10 nM-10 microM) was recorded after pre-constriction of the coronary vasculature with U46619 (100-300 nM) in ischemic-reperfused or time-control hearts. 3 After I-R, the coronary relaxation to acetylcholine was reduced and this reduction was attenuated by treatment with urocortin (10 pM), administered before ischemia and during reperfusion. 4 This urocortin-induced improvement of the relaxation to acetylcholine was not modified by tetraethylammonium (10 mM), blocker of Ca2+ dependent-potassium channels; glibenclamide (10 microM), blocker of K(ATP) channels; N(w)-nitro-L-arginine methyl ester (L-NAME, 100 microM), blocker of nitric oxide synthesis; or meclofenamate (10 microM), blocker of cyclooxygenase, but it was abolished by chelerythrine (3 microM), blocker of protein kinase C (PKC). 5 These results suggest that urocortin may protect coronary endothelial function during I-R by activation of PKC.
Subject(s)
Corticotropin-Releasing Hormone/pharmacology , Endothelium, Vascular/drug effects , Heart/drug effects , Myocardial Reperfusion Injury/physiopathology , Acetylcholine/pharmacology , Alkaloids , Animals , Benzophenanthridines , Cardiovascular Agents/pharmacology , Cyclooxygenase Inhibitors/pharmacology , Dose-Response Relationship, Drug , Endothelium, Vascular/physiopathology , Enzyme Inhibitors/pharmacology , Glyburide/pharmacology , Heart/physiopathology , In Vitro Techniques , Male , Meclofenamic Acid/pharmacology , NG-Nitroarginine Methyl Ester/pharmacology , Nitric Oxide Synthase/antagonists & inhibitors , Perfusion , Phenanthridines/pharmacology , Protein Kinase C/antagonists & inhibitors , Rats , Rats, Sprague-Dawley , Tetraethylammonium/pharmacology , Urocortins , Vasodilator Agents/pharmacologyABSTRACT
The effects of the duration of ischemia on coronary vasoconstriction after ischemia-reperfusion were analysed in rat hearts. After 15, 30 or 45 min of global zero-flow ischemia and 15 min reperfusion, the coronary response to endothelin-1 (10(-10)-10(-7) M) and the thromboxane A2 analogue 9,11-dideoxy-1a,9a-epoxymethanoprostaglandin F2alpha (U46691, 10(-8)-10(-6) M) was recorded. Vasoconstriction induced by endothelin-1 only increased after short 15 min periods of ischemia. In contrast, the vasoconstriction induced by U46619 remained unmodified by short ischemias but was reduced after longer periods of ischemia (30 and 45 min). Inhibition of nitric oxide synthesis with the Nw-nitro-L-arginine methyl ester (L-NAME, 10(-4) M) augmented the vasoconstriction induced by endothelin-1 in non-ischemic hearts, but not following ischemia. Similarly, L-NAME increased the vasoconstriction induced by U46619 to a greater extent in non-ischemic hearts than following ischemia. These results suggest that ischemia-reperfusion inhibits nitric oxide production, causing an increased coronary response to endothelin-1 after brief ischemias. Longer ischemias may non-specifically inhibit coronary vasoconstriction and reduce nitric oxide production.
