Potentiation of sildenafil-induced hypotension is minimal with nitrates generating a radical intermediate

Ranolazine, a novel anti-anginal agent, does not alter isosorbide dinitrate- or sildenafil-induced changes in blood pressure in conscious dogs

Effects of ranolazine on isosorbide dinitrate- and on sildenafil-induced changes in mean arterial pressure and heart rate were assessed in conscious dogs. Dogs (n = 7) were chronically instrumented for measurements of mean arterial pressure and heart rate. Bolus intravenous injections of either isosorbide dinitrate (0.2 mg/kg) or sildenafil (0.5 mg/kg) caused biphasic changes in mean arterial pressure and heart rate: a transient (approximately 20 s) decrease in mean arterial pressure and an increase in heart rate, followed by prolonged (10-15 min) decreases in mean arterial pressure by 11 +/- 1.6 and 11 +/- 2.2 mm Hg, respectively. Infusion of ranolazine alone (plasma concentrations = 4 or 8 microM) for 10 min did not significantly affect mean arterial pressure and heart rate. The transient hypotension and tachycardia caused by isosorbide dinitrate were not altered by ranolazine. The sildenafil-induced transient tachycardia (Delta change: 114 +/- 10 beats/min) was significantly (P < 0.05) blunted by either 4 (Delta change: 71 +/- 8 beats/min) or 8 (Delta change: 66 +/- 9 beats/min) microM ranolazine. However, the sildenafil-induced transient decrease in mean arterial pressure was not altered by ranolazine. During ranolazine infusion (4-5 or 8-10 microM), isosorbide dinitrate and sildenafil caused prolonged decreases in mean arterial pressure. These results indicate that except for a blunting of the transient tachycardia caused by sildenafil, ranolazine at concentrations up to 10 microM does not alter changes in mean arterial pressure and heart rate induced by either isosorbide dinitrate or sildenafil in conscious dogs.

Effect of intravenous sildenafil on pulmonary hemodynamics and gas exchange in the presence and absence of acute lung injury in piglets

Sildenafil is becoming increasingly popular for the treatment of pulmonary hypertension. However, there are potential concerns regarding its effects on oxygenation and systemic hemodynamics that could theoretically reduce its utility in the neonatal population. We performed a prospective cumulative dose-response study of increasing doses of i.v. sildenafil (0.4, 1, and 3 mg/kg) on hemodynamics and oxygenation in 32 anesthetized piglets, of which 17 had meconium-induced pulmonary hypertension and lung injury, and 15 did not. Sildenafil caused a reduction in mean pulmonary artery pressure and pulmonary vascular resistance (PVR) at all doses, in non-lung-injured animals. There was no difference in pulmonary hemodynamics between doses. Oxygenation index [OI = mean airway pressure (cm H2O) * FiO2 * 100/PaO2 (mm Hg)] did not reach critical levels at any dose. In lung-injured animals, sildenafil also reduced mean pulmonary artery pressure and PVR by 30%. Again, this effect was achieved at the lowest dose, without subsequent changes at higher doses. However, in lung-injured animals, sildenafil produced a dose-related increase in oxygenation index. Sildenafil reduced the systemic vascular resistance (SVR) at the lowest dose in lung-injured animals, but this occurred only at higher doses in non-lung-injured animals. In conclusion, sildenafil is a potent pulmonary vasodilator. However, it should be administered with caution in the presence of lung injury because of a dose-related increase in oxygenation index and concomitant systemic vasodilatation.

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

BACKGROUND

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 beta1-adrenoceptor blocker with an additional, endothelium-dependent NO-liberating property, in comparison to the combination SIL/glycerol trinitrate (GTN).

METHODS AND RESULTS

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 (EC50) was GTN (0.08 microM) > SIL (1.25 microM) > or = NEB (3.5 microM). In the presence of both therapeutic (1 nM) and high (1 microM) concentrations of SIL, vasodilation of GTN was potentiated as indicated by a significant increase in vasodilatory potency (EC50 GTN + low SIL: 0.019 microM, EC50 GTN + high SIL: 0.002 microM; both P < 0.01 vs. GTN). In contrast, SIL did not potentiate the vasodilatory effect of NEB (EC50 NEB + low SIL: 5.01 microM, EC50 NEB + high SIL: 3.2 microM; n.s. vs. NEB).

CONCLUSIONS

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.

Atorvastatin enhances sildenafil-induced vasodilation through nitric oxide-mediated mechanisms

Statins have cholesterol-independent effects including an increased vascular nitric oxide (NO) activity and are commonly used by patients with cardiovascular disease. Such patients frequently have erectile dysfunction, which may be treated with sildenafil, a selective inhibitor of phosphodiesterase type 5. Since statins and sildenafil can activate the NO-cGMP pathway, we investigated whether pre-treatment with atorvastatin (0, 5 and 30 mg/kg/day) for 2 weeks affects sildenafil (1 pM-100 mM)-induced relaxation of aortic rings isolated from Wistar rats. We also examined the hemodynamic consequences of this interaction in Wistar rats. Plasma nitrite/nitrate (NOx) concentrations were determined using an ozone-based chemiluminescence assay. While pre-treatment with atorvastatin increased the potency of sildenafil-induced vasorelaxation (P<0.01), no differences were observed in the maximum sildenafil-induced relaxation. Pre-incubation of aortic rings with NG-nitro-L-arginine methyl ester (L-NAME) reversed atorvastatin-induced increase in the potency of sildenafil relaxation. In addition, pre-treatment with atorvastatin enhanced plasma NOx concentrations and sildenafil-induced hypotension and tachycardia (all P<0.05). These results suggest that atorvastatin increases the vascular sensitivity to sildenafil through NO-mediated mechanisms.

Sildenafil (Viagra) augments sodium nitroprusside-induced but not nitroglycerin-induced hypotension in dogs

We investigated whether sildenafil citrate (Viagra) may reduce the dose of nitrovasodilators to induce deliberate hypotension. Ten mongrel dogs were acutely instrumented with a femoral artery catheter and a pulmonary artery catheter. Sodium nitroprusside (SNP; 1-16 microg. kg(-1). min(-1)) or nitroglycerin (NTG; 2-32 microg. kg(-1). min(-1)) was IV given to induce hypotension. The study consisted of two occasions, in a random order, in each animal: one with sildenafil pretreatment (1 mg/kg IV followed by 0.3 mg. kg(-1). h(-1)) and the other without to serve as a control. Hemodynamic variables were continuously monitored. Plasma cyclic guanosine monophosphate (cGMP) concentrations were measured by radioimmunoassay. Both SNP and NTG produced dose-dependent decreases in mean arterial blood pressure without affecting the heart rate in the presence as well as in the absence of sildenafil. Systemic vascular resistance index and mean pulmonary arterial pressure were also decreased. The magnitude of mean arterial blood pressure and systemic vascular resistance index reductions caused by SNP was augmented by sildenafil, whereas that caused by NTG was not affected. Neither SNP nor NTG alone altered the plasma cGMP concentrations. Sildenafil increased the plasma cGMP concentration, which was further increased by SNP but not affected by NTG. These results indicate that sildenafil may reduce the dose of SNP in producing deliberate hypotension in the dog. The potentiation of SNP-induced hypotension by sildenafil may be related to an augmented accumulation of cGMP.

IMPLICATIONS

Sildenafil may reduce the dose of sodium nitroprusside required to induce deliberate hypotension and hence the potential for cyanide toxicity.