Sildenafil, a type 5 phosphodiesterase inhibitor, lowers pulmonary ascular resistance in pulmonary hypertension by augmenting intracellular leels of the nitric oxide second messenger, cyclic GMP.

• 昔多芬是一种磷酸二酯酶抑制剂，在肺动脉高压时，它可通过增加细胞内NO第二信使-cGMP水平来降低肺血管阻力。