cAMP Signal Transduction Cascade, a Novel Pathway for the Regulation of Endothelial Nitric Oxide Production in Coronary Blood Vessels

Abstract

Abstract-The aim of this study was to determine whether cAMP signal transduction plays a role in the regulation of endothelial nitric oxide (NO) production. Canine coronary blood vessels were isolated, and nitrite, the hydration product of NO, from these vessels was quantified by using the Griess reaction. Forskolin (10 Ϫ4 mol/L), 8-bromo-cAMP (10 Ϫ2 mol/L), or isoproterenol (10 Ϫ4 mol/L) significantly increased nitrite release to 168Ϯ10, 162Ϯ13, or 149Ϯ13 pmol/mg, respectively, from isolated coronary microvessels (all PϽ0.05; control, 86Ϯ3 pmol/mg). Adrenomedullin and calcitonin gene-related peptide (CGRP), both potent vasodilator peptides, also increased coronary microvascular nitrite production. N -nitro-L-arginine methyl ester, a competitive inhibitor of NO synthase, or Rp-cAMP, a protein kinase A inhibitor, markedly blocked the nitrite release induced by these agents. Forskolin and adrenomedullin also potentiated coronary NO production induced by bradykinin. In large coronary arteries, removal of the endothelium eliminated nitrite production to both forskolin and acetylcholine. Our data demonstrate that stimulation of cAMP signal transduction can substantially increase coronary NO production, indicating that there is a cAMP-mediated, endothelial NO-forming system in coronary blood vessels. Because the cAMP signal cascade can be activated by CGRP or adrenomedullin and enhance kinin-mediated nitrite production, the cAMP-NO pathway may play an important role in the regulation of cardiovascular function. Key Words: cAMP Ⅲ nitric oxide Ⅲ endothelium Ⅲ protein kinase B Ⅲ coronary blood vessels ␤ -Adrenoceptor agonists and adenosine have been regarded as "archetypal" endothelium-independent vasodilators that cause vasodilation by increasing intracellular cAMP, with subsequent activation of protein kinase A (PKA) and myosin light-chain kinase within smooth muscle cells. [1][2][3][4][5][6] However, recent studies have challenged this concept. Growing evidence indicates that a number of classic endotheliumindependent vasodilator drugs also cause endotheliumdependent vasodilation, and this process seems to be related to endothelial NO production. [7][8][9][10][11][12][13][14][15][16][17][18][19] These include (1) the inhibition of isoprenaline-induced vasorelaxation in rat aorta by hemoglobin and methylene blue 11,12 ; (2) the inhibition of prostacyclin-and forskolin-induced vasorelaxation in pig coronary artery in vitro by hemoglobin and methylene blue 13 ; (3) the inhibition of salbutamol-and epinephrine-induced vasorelaxation in vivo and in vitro in the rat by the NO synthase (NOS) inhibitor N -nitro-L-arginine methyl ester (L-NAME); 14 -16 (4) the inhibition of isoproterenol-induced resistance coronary vessel dilation in the conscious dog by L-NAME 17,18 ; and (5) the inhibition of isoproterenol-induced vasodilation in human forearm by N -monomethyl-Larginine. 19 These results indicate that in blood vessels, there is an NO component to the vasorelaxant response to all of See page 729 these agonists. This may be of...

Shear stress stimulates phosphorylation of protein kinase A substrate proteins including endothelial nitric oxide synthase in endothelial cells

“…Therefore, it is suggested that PKA-dependent eNOS phosphorylation provides a compensatory mechanism for the enzyme activation without involving intracellular Ca 2+ increase. In consistent with this notion, a critical role of PKA in vascular nitric oxide production as a compensatory mechanism has also been demonstrated previously in coronary blood vessels (Zhang and Hintze, 2001). …”

Adrenomedullin and CGRP interact with endogenous calcitonin-receptor-like receptor in endothelial cells and induce its desensitisation by different mechanisms

“…Blockade or insufficient AM cross-talk between endothelial cells through juxtacrine loops mediated by laterally expressed EndoCL might contribute to hyperpermeability of the endothelial monolayer in response to stress stimuli, such as polymorphonuclear-leukocyte-derived oxygen metabolites (Hippenstiel et al, 2002). Apically expressed EndoCL might mediate endothelium-dependent AM-induced vasodilatation (Hinson et al, 2000;Zhang and Hintze, 2001). Similarly, EndoCL could be important in mediating CGRP-mediated proliferation (Haegerstrand et al, 1990) and migration (present study) of endothelial cells.…”

Aldosterone Regulates Vascular Reactivity

“…NOS can also be activated through the adenylyl cyclase/ PKA pathway. 24,25 Therefore, the short-term effect of aldo- sterone on the adenylyl cyclase/PKA pathway in ECs was assessed. Aldosterone (10 pmol/L to 10 nmol/L) had no effect on isoproterenol-, forskolin-, or cAMP-mediated PKA activity (data not shown).…”