Guanylyl cyclase activators evoke nitric oxide release in the intact rat superior mesenteric artery

University of Bristol (2005) J Physiol 567P, C81

Oral Communications: Guanylyl cyclase activators evoke nitric oxide release in the intact rat superior mesenteric artery

Stankevicius, Edgaras; Wegener, Greger; Mulvany, Michael; Simonsen, Ulf;

1. Pharmacology, University of Aarhus, Aarhus, Denmark. 2. Physiology, Kaunas University of Medicine, Kaunas, Lithuania, Lithuania.

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The purpose of the present study was to investigate the role of the cyclic GMP-pathway in acetylcholine (ACh)-evoked nitric oxide (NO)-mediated relaxation in rat superior mesenteric artery. Segments from humanely killed animals were mounted in microvascular myographs and by introduction of a NO specific microelectrode in the lumen of the artery simultaneous measurements of NO concentration and isometric force were performed. In the presence of indomethacin (3μM) and contracted with noradrenaline (0.5μM), ACh (10μM) increased NO concentration 11.3±1.9 nM and relaxed the arteries 99±1 % (n=6). The selective guanylyl cyclase activators, YC-1 (10μM) and BAY 412272 (10μM), increased NO concentration by, respectively, 11.3±4.7 nM (n=6) and 5.9±1.1 nM, and relaxed the arteries by, respectively, 94±2 % (n=6) and 95±1 % (n=6). These responses were reversed by oxyhaemoglobin (OxHb). In arteries without endothelium, BAY 412272 did not increase NO concentration and relaxation was reduced to 59±1 % (n=6). An inhibitor of soluble guanylyl cyclase, ODQ (3μM), reduced ACh-evoked increases (n=6) in NO and relaxations, and abolished S-nitroso-N-acetylpenicillamine (SNAP) relaxation without changing increases in NO concentration. An inhibitor of phosphodiesterase type 5, sildenafil (1μM) caused endothelium-dependent relaxations sensitive to OxHb, without increasing NO concentration (n=6), and leftward shifted concentration-relaxation curves for acetylcholine and SNAP. The protein kinase G (PKG) activator, 8-br-cGMP (400μM), did not increase NO concentration, but caused relaxation which was inhibited by the PKG inhibitor, 8br-PET-cGMPS (30μM). 8br-PET-cGMPS and an inhibitor of PKA, Rp-8Br-cAMPS (50μM), did not change ACh-induced increases in NO concentration. An inhibitor of heat shock protein (HSP90), geldanamycin rightward shifted acetylcholine concentration-relaxation curves. The present study provides evidence for a guanylyl cyclase-dependent mechanism, which probably independent of protein kinase G activation enhances ACh-evoked release of NO. We propose a model, where conformation changes in guanylyl cyclase induced by NO or guanylyl cyclase activators through the scaffold protein HSP90 increases endothelial NO synthase activity and enhances NO formation. The effect on relaxation of sildenafil and ODQ confirms a role for a smooth muscle cyclic GMP-pathway in acetylcholine-evoked relaxation.



Where applicable, experiments conform with Society ethical requirements.

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