Phosphodiesterase type 5 inhibitor sildenafil citrate does not potentiate the vasodilative properties of nebivolol in rat aorta

Sildenafil citrate (SIL) is contraindicated in patients with coronary heart disease who are treated with nitric oxide (NO) donators such as organic nitrates, as it potentiates NO-mediated vasodilation. The present study investigated whether SIL also affects the vasodilatory effects of nebivolol (NEB), a selective β 1-adrenoceptor blocker with an additional, endothelium-dependent NO-liberating property, in comparison to the combination SIL/glycerol trinitrate (GTN). Experiments were performed in isolated vessel rings of rat aorta (Wistar rats, 8–12 weeks), which had been pre-contracted with phenylephrine (10 − 5 M). Isometric tension was measured by a force transducer, and cumulative concentration–response curves were obtained for each drug. The rank order of vasodilatory potency as measured by the concentration needed to achieve 50% relaxation (EC 50) was GTN (0.08 μM) > SIL (1.25 μM) ≥ NEB (3.5 μM). In the presence of both therapeutic (1 nM) and high (1 μM) concentrations of SIL, vasodilation of GTN was potentiated as indicated by a significant increase in vasodilatory potency (EC 50 GTN + low SIL: 0.019 μM, EC 50 GTN + high SIL: 0.002 μM; both P < 0.01 vs. GTN). In contrast, SIL did not potentiate the vasodilatory effect of NEB (EC 50 NEB + low SIL: 5.01 μM, EC 50 NEB + high SIL: 3.2 μM; n.s. vs. NEB). These data demonstrate that SIL does not potentiate NEB-induced vasodilation in vitro. These findings indicate that the interaction between SIL and NO-donators/organic nitrates does not apply to the NO-liberating properties of NEB. Our findings suggest that SIL may safely be used in hypertensive patients treated with NEB.