Acute effects of sildenafil and dobutamine in the hypertrophic and failing right heart in vivo

Riociguat, sildenafil and inhaled nitric oxide reduces pulmonary vascular resistance and improves right ventricular function in a porcine model of acute pulmonary embolism

BACKGROUND

Pulmonary vasodilators as add-on to current treatment strategies in acute pulmonary embolism may improve right ventricular unloading and hence improve patient outcome. We aimed to investigate whether stimulation of the nitric oxide (NO)-soluble guanylate cyclase (sGC)-cyclic guanosine monophosphate (cGMP) pathway with riociguat, sildenafil or inhaled NO causes pulmonary vasodilation and improves right ventricular function in a porcine model of acute intermediate risk pulmonary embolism.

METHODS

Two large autologous blood clots were administered to the pulmonary circulation of 28 pigs (60 kg). Animals were randomized to four increasing, clinically equivalent doses of riociguat (n=6), sildenafil (n=6), inhaled NO (n=6) or vehicle (n=6). Sham animals (n=4) did not receive pulmonary embolism or treatment. Haemodynamic responses were evaluated at baseline, after pulmonary embolism and after each dose using invasive pressure measurements, transoesophageal echocardiography, respiratory parameters and blood analysis.

RESULTS

Pulmonary embolism caused a three-fold increase in pulmonary vascular resistance compared with baseline (pulmonary embolism: 352±29 vs. baseline: 107±6 dynes, p<0.0001). All treatments lowered pulmonary vascular resistance compared with vehicle (riociguat: -158±35, sildenafil: -224±35, inhaled NO: -156±35 dynes, p<0.0001). Sildenafil, but neither inhaled NO nor riociguat, caused a decrease in systemic vascular resistance (sildenafil 678±41 vs. vehicle 1081±93 dynes, p=0.02) and increased cardiac output (sildenafil 8.8±0.8 vs. vehicle: 5.9±0.2 L/min, p<0.001). Systemic blood pressure was unaltered in all treatment groups.

CONCLUSION

Stimulation of the NO-sGC-cGMP pathway by riociguat, sildenafil and inhaled NO reduces pulmonary vascular resistance in a porcine model of acute pulmonary embolism without lowering systemic blood pressure.

Prostacyclins have no direct inotropic effect on isolated atrial strips from the normal and pressure-overloaded human right heart

Prostacyclins are vasodilatory agents used in the treatment of pulmonary arterial hypertension. The direct effects of prostacyclins on right heart function are still not clarified. The aim of this study was to investigate the possible direct inotropic properties of clinical available prostacyclin mimetics in the normal and the pressure-overloaded human right atrium. Trabeculae from the right atrium were collected during surgery from chronic thromboembolic pulmonary hypertension (CTEPH) patients with pressure-overloaded right hearts, undergoing pulmonary thromboendarterectomy (n = 10) and from patients with normal right hearts operated by valve replacement or coronary bypass surgery (n = 9). The trabeculae were placed in an organ bath, continuously paced at 1 Hz. They were subjected to increasing concentrations of iloprost, treprostinil, epoprostenol, or MRE-269, followed by isoprenaline to elicit a reference inotropic response. The force of contraction was measured continuously. The expression of prostanoid receptors was explored through quantitative polymerase chain reaction (qPCR).

Iloprost, treprostinil, epoprostenol, or MRE-269 did not alter force of contraction in any of the trabeculae. Isoprenaline showed a direct inotropic response in both trabeculae from the pressure-overloaded right atrium and from the normal right atrium. Control experiments on ventricular trabeculae from the pig failed to show an inotropic response to the prostacyclin mimetics. qPCR demonstrated varying expression of the different prostanoid receptors in the human atrium. In conclusion, prostacyclin mimetics did not increase the force of contraction of human atrial trabeculae from the normal or the pressure-overloaded right heart. These data suggest that prostacyclin mimetics have no direct inotropic effects in the human right atrium.

Comparison of preventive effect of sildenafil and therapeutic effect of sildenafil treatment in rats with monocrotaline-induced pulmonary arterial hypertension

This study aimed to investigate the potential effects of sildenafil on pulmonary hypertension (PH) in the monocrotaline (MCT)-induced PH rat. Twenty-four, 12-week-old, male Sprague-Dawley rats were injected with MCT or saline solution. After injection of MCT, rats received oral sildenafil immediately (early-phase treatment group: E group), 4 weeks after injection (late-phase treatment group: L group) or no treatment (MCT group) until 6 weeks after injection. Serial echocardiography and right ventricular systolic pressure (RVSP) measurements via a cardiac catheter were performed. RVSP was reduced in the E and L groups compared with the MCT group. Echocardiography indicated that sildenafil therapy prevents an increase in RVSP and preserves diastolic function, and this effect is not dependent on timing of initiation of therapy.