Beneficial Effects of Phosphodiesterase 5 Inhibition in Pulmonary Hypertension Are Influenced by Natriuretic Peptide Activity

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Abstract
Background— Phosphodiesterase type 5 (PDE5) inhibitors (eg, sildenafil) are a novel, orally active approach to the treatment of pulmonary arterial hypertension. The role of natriuretic peptides in the response to sildenafil was examined in mice lacking NPR-A, a guanylyl cyclase-linked natriuretic peptide receptor, in which pulmonary hypertension was induced by hypoxia. Methods and Results— Mice homozygous for NPR-A (NPR-A+/+) and null mutants (NPR-A−/−) were studied. Sildenafil inhibited the pressor response to acute hypoxia in the isolated perfused lungs of both genotypes. This effect was greater in the presence of atrial natriuretic peptide in the perfusate in NPR-A+/+ mice but not NPR-A−/− animals. In vivo, NPR-A mutants had higher basal right ventricular (RV) systolic pressures (RVSPs) than did NPR-A+/+ mice, and this was not affected by 3 weeks of treatment with sildenafil (25 mg · kg−1 · d−1). Both genotypes exhibited a rise in RVSP and RV weight with chronic hypoxia (10% O2 for 21 days); RVSP and R...