Abstract 510: Regulation of Coronary Vascular Tone via Redox Modulation in the Alpha-Adrenergic-Angiotensin-Endothelin Axis of the Myocardium
Recently we reported alpha-adrenoceptor stimulation of cardiac myocytes resulted in the production of angiotensin II, which stimulated the coronary vascular production of endothelin (ET) resulting in vasoconstriction. Because signaling induced by these agonists influences the redox state of many cells, we hypothesized that manipulating the redox state of cells may influence the extent of coronary vasoconstriction. To determine the role of the redox state in this pathway, we measured vasoconstriction of isolated, pressurized rat coronary arterioles (74±8μm, diameter) to supernatant collected from enzymatically isolated cardiac myocytes, which were stimulated with an alpha1-adrenoceptor agonist phenylephrine (PH) 50μM. PH increased production of superoxide in cardiac myocytes [dihydroethidium fluorescence (DHE) for oxidative stress 6.2±0.8 fold vs. quiescent myocytes, n=8, p<0.01]. Vasoconstriction was determined under control conditions, and following treatment of the isolated arterioles with angiotensin receptor antagonist olmesartan (1μM, n=8) or ETA receptor antagonist TA0201 (5μM, n=8). Addition of supernatant 100, 200, 500 μl from PH stimulated myocytes to a 2 ml vessel bath (n=8, each) caused dose-dependent vasoconstriction (500μl: 11.2±1.6%). Olmesartan eliminated vasoconstriction (500μl: 0.5±1.2%, p<0.01) or TA0201 converted vasoconstriction to vasodilation (500μl: 1.2±0.5%, p<0.01) to the supernatant from PH stimulated myocytes. Treatment of cardiac myocytes with N-acetylcysteine (10mM, n=8) decreased PH induced production of superoxide (DHE 0.88±0.12 fold, p<0.01) and vasoconstriction was reduced (500μl: 1.8±0.4%, p<0.01). Treatment of arterioles with NADPH oxidase inhibitor apocynin (30μM, n=8) reduced vasoconstriction to the supernatant from PH stimulated myocytes (500 ±l: 3.8±0.6%, p<0.01). From these results, we speculate superoxide mediated redox signaling modulates both angiotensin production in myocytes and endothelin release through NADPH oxidase in coronary arterioles. Thus, coronary vasocon-striction via the alpha-adrenergic-angiotensin-endothelin axis appears to require redox mediated signaling in cardiac and vascular cells.