Abstract
Presumably, the vasorelaxant properties of phosphodiesterase type 5 (PDE5) inhibitors are similar in isolated blood vessels. We aimed to explore the mechanisms underlying the vasorelaxation induced by the selective PDE5 inhibitors sildenafil, vardenafil, and tadalafil in the rat aorta. Aortic rings were mounted in 5-ml organ baths, and concentration-response curves for PDE5 inhibitors (0.0001-10 μM) were constructed in phenylephrine (PE)-precontracted endothelium-intact and -denuded rings. Cyclic nucleotides were measured using enzyme immunoassay kits. Sildenafil, vardenafil, and tadalafil concentration dependently relaxed aortic rings and increased cGMP, but not cAMP, concentrations. Endothelium denudation caused marked rightward shifts in the curves to sildenafil (45-fold), tadalafil (21-fold), and vardenafil (251-fold). Maximal responses to sildenafil and tadalafil were substantially reduced (38 ± 1% and 53 ± 2%, respectively), whereas that evoked by vardenafil was not affected. Likewise, inhibition of NO synthase (Nω-nitro-l-arginine methyl ester, 100 μM), guanylyl cyclase (1H-[1,2,4]oxadiazolo [4,3,-a]quinoxalin-1-one, 10 μM), or scavenging of NO ([carboxy-PTIO (2-(4-carboxyphenyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide), 100 μM]) caused similar attenuation of the vasorelaxations evoked by PDE5 inhibitors. Sildenafil, tadalafil, and vardenafil significantly potentiated relaxations mediated by glyceryl trinitrate (0.0001-3 μM; 8-13-fold) and atrial natriuretic peptide (0.1-100 nM; 2-3-fold). Contractions evoked by CaCl2 (0.01-5 mM) in PE-treated rings were significantly reduced (26 ± 4%) by vardenafil, but not sildenafil or tadalafil, whereas phorbol 12,13-dibutyrate-induced contractions were not affected. Ouabain, cyclopiazonic acid, and calyculin A failed to affect vasorelaxations induced by the PDE5 inhibitors. These results suggest that vardenafil, but not sildenafil or tadalafil, affects Ca2+ handling in the rat aorta in addition to increasing cGMP levels through inhibition of PDE5 to cause relaxation.
Footnotes
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This work was supported by the National Institutes of Health (Grants HL-71138 and HL-74167). C.E.T. is funded by a postdoctoral fellowship (0425437B) from the American Heart Association (Southeast Affiliate). F.B.M.P. is supported by a doctoral fellowship from Fundação de Amparo à Pesquisa do Estado de São Paulo (São Paulo, Brazil).
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doi:10.1124/jpet.105.092544.
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ABBREVIATIONS: NO, nitric oxide; sGC, soluble guanylyl cyclase; PDE, phosphodiesterase; PDE5, phosphodiesterase type 5; ACh, acetylcholine; PE, phenylephrine; l-NAME, Nω-nitro-l-arginine methyl ester; ODQ, 1H-[1,2,4] oxadiazolo [4,3,-a]quinoxalin-1-one; ANP, atrial natriuretic peptide; PDBu, phorbol 12,13-dibutyrate; CPA, cyclopiazonic acid; carboxy-PTIO, 2-(4-carboxyphenyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide; GTN, glyceryl trinitrate; SERCA, sarco(endo)plasmic reticulum ATPase.
- Received July 13, 2005.
- Accepted October 3, 2005.
- The American Society for Pharmacology and Experimental Therapeutics
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