Acute effects of sildenafil in patients with primary pulmonary hypertension receiving epoprostenol.

Epoprostenol therapy has improved survival in primary pulmonary hypertension; however, only two thirds of patients are alive 3 years after starting treatment. Combined therapy with sildenafil, a phosphodiesterase 5 inhibitor, may provide additional benefit. The authors prospectively evaluated the acute hemodynamic and biochemical effects of sildenafil and inhaled nitric oxide, alone and in combination, in 8 patients with primary pulmonary hypertension receiving chronic epoprostenol. Average duration of epoprostenol therapy was 2.9 +/- 1.6 years (mean +/- SD) and mean dose was 25.7 +/- 10.8 ng/kg/min. A single 50 mg dose of sildenafil decreased mean pulmonary arterial pressure 10% (P<.05), increased cardiac output 8%, and decreased pulmonary vascular resistance 24% (P<.005). Although nitric oxide led to a similar decrease in mean pulmonary arterial pressure of 10% (P<.05), cardiac output was unchanged, resulting in a decrease in pulmonary vascular resistance of only 13%, which was not statistically different from baseline. These results suggest that sildenafil has greater acute hemodynamic effects than nitric oxide and that it can further reduce pulmonary vascular resistance in patients already demonstrating a benefit from chronic epoprostenol.

Outcome in 91 consecutive patients with pulmonary arterial hypertension receiving epoprostenol.

Epoprostenol has markedly improved the treatment of pulmonary arterial hypertension, although predictors of outcome with epoprostenol are not well characterized. From June 1995 through August 2001, 91 patients with pulmonary arterial hypertension were treated with epoprostenol at our institution. We analyzed the effects of long-term epoprostenol treatment to determine features associated with outcome. Predictors of worse outcome included older age of disease onset (hazard ratio 3.2, 95% confidence interval 1.32-7.76 for patients above the median age of 44 years), World Health Organization functional Class IV, either at baseline or follow-up, (3.07, 1.42-6.62 compared with functional Class I, II, and III), and scleroderma spectrum of disease (2.32, 1.08-4.99). There were no baseline or follow-up hemodynamic factors predictive of outcome. Our results indicate that treatment with epoprostenol improves survival in patients with Primary Pulmonary Hypertension compared with that predicted by the National Institutes of Health Primary Pulmonary Hypertension Registry's survival equation and that their survival is significantly better than that of patients with scleroderma spectrum of disease (p = 0.001). Older patients treated with epoprostenol have significantly shorter survival, regardless of etiology.

[3H]sildenafil binding to phosphodiesterase-5 is specific, kinetically heterogeneous, and stimulated by cGMP.

Sildenafil (Viagra) potentiates penile erection by acting as a nonhydrolyzable analog of cGMP and competing with this nucleotide for catalysis by phosphodiesterase-5 (PDE5), but the characteristics of direct binding of radiolabeled sildenafil to PDE5 have not been determined. [3H]Sildenafil binding to PDE5 was retained when filtered through nitrocellulose or glass-fiber membranes. Binding was inhibited by excess sildenafil, 2-(2-methylpyridin-4-yl)methyl-4-(3,4,5-trimethoxyphenyl)-8-(pyrimidin-2-yl)methoxy-1,2-dihydro-1-oxo-2,7-naphthyridine-3-carboxylic acid methyl ester hydrochloride (T-0156), 3-isobutyl-1-methylxanthine, EDTA, or cGMP, but not by cAMP or 5'-GMP. PDE5 was the only [3H]sildenafil binding protein detected in human lung extract. Using purified recombinant PDE5, [3H]sildenafil exchange dissociation yielded two components with t1/2 values of 1 and 14 min and corresponding calculated KD values of 12 and 0.83 nM, respectively. This implied the existence of two conformers of the PDE5 catalytic site. [3H]Sildenafil binding isotherm of PDE5 indicated KD was 8.3 to 13.3 nM, and low cGMP decreased the KD to 4.8 nM but only slightly increased Bmax to a maximum of 0.61 mol/mol-subunit. Results suggest that these effects occur via cGMP binding to the allosteric cGMP binding sites of PDE5. Results imply that by inhibiting PDE5 and thereby increasing cGMP, sildenafil accentuates its own binding affinity for PDE5, which further elevates cGMP. The data also indicate that after physiological elevation, cGMP may directly stimulate the catalytic site by binding to the allosteric cGMP-binding sites of PDE5, thus causing negative feedback on this pathway.