cAMP Signal Transduction, A Potential Compensatory Pathway for Coronary Endothelial NO Production After Heart Failure

OBJECTIVE: This study investigated whether cAMP signal transduction regulates coronary microvascular NO production after heart failure (HF), a state in which endothelial NO synthase (eNOS) is downregulated. METHODS AND RESULTS: Myocardial microvessels were isolated. Nitrite, the hydration product of NO, from these vessels was quantified by using the Griess reaction. Forskolin (10(-4) mol/L), 8-bromo-cAMP (10(-2) mol/L), isoproterenol (10(-4) mol/L), or adrenomedullin (10(-6) mol/L) significantly increased nitrite release by 78+/-8, 84+/-14, 71+/-11, and 73+/-15 pmol/mg, respectively, from isolated microvessels from normal canine hearts (P<0.05 versus control). Bradykinin (10(-5) mol/L) and acetylcholine (10(-5) mol/L) increased nitrite release by 83+/-13 and 72+/-6 pmol/mg, respectively (P<0.05 versus control). However, NO production induced by bradykinin and acetylcholine was markedly reduced after HF (46+/-7 and 39+/-7 pmol/mg, respectively; P<0.05 versus normal), reflecting eNOS downregulation (55% in eNOS protein). Surprisingly, NO production in response to forskolin, 8-bromo-cAMP, isoproterenol, and adrenomedullin not only was preserved but also was substantially enhanced in these microvessels after HF (121+/-14, 124+/-21, 107+/-18, and 122+/-16 pmol/mg, respectively; P<0.05 versus normal group) and was associated with an upregulation of protein kinase B (220% increase in protein kinase B protein). All these responses were in an NO synthase or a protein kinase A inhibitor-blockable manner. CONCLUSIONS: Our data indicate that cAMP signal transduction may be an important potential compensatory pathway to increase myocardial microvascular NO production after HF when eNOS is downregulated.