An evaluation of vardenafil as a calcium channel blocker in pulmonary artery in rats

OBJECTIVE: Vardenafil was reported to relax rat pulmonary artery through endothelium-dependent mechanisms. The aim of this in vitro study was to investigate other related mechanisms for this effect. MATERIALS AND METHODS: Endothelium-intact and denuded artery rings were suspended in order to record isometric tension. In the rings with or without endothelium, the concentration-response curves for vardenafil were generated. In the rings without endothelium the contractile response induced by phenylephrine (Phe) or KCl was assessed in the presence or absence of vardenafil. In the last set of experiments, pulmonary artery rings were exposed to calcium-free isotonic depolarizing solution and the contractile response induced by the addition of calcium was evaluated in the presence or absence of vardenafil, nifedipine, verapamil or 1H-[1,2,4] oxadiazolo[4,3-a] quinoxalin-1-one (ODQ). RESULTS: Vardenafil attenuated pulmonary artery contraction induced by phenylephrine in the presence and absence of endothelium. In addition, vardenafil attenuated both Phe or KCl-induced contraction but, it's effect on the KCl dose-response curve was more significant. Vardenafil also inhibited the contractile response induced by calcium in a dose-dependent manner. Addition of nifedipine or verapamil did not significantly alter this effect while ODQ incubation significantly inhibited vardenafil-induced relaxation. CONCLUSION: From these findings, it was proposed that vardenafil relaxed rat pulmonary artery through inhibiting calcium influx.