PDE5A and bronchopulmonary dysplasia: This explanation is supported by the beneficial effects of agents that increase intracellular cGMP levels, either by stimulating the NO-eNOS-cGMP pathway with inhaled NO, apelin or soluble guanylate cyclase modulators or inhibiting cGMP breakdown with the specific cGMP-selective PDE5 inhibitor sildenafil, in newborn rats with experimental BPD that our group and others described previously [9, 50, 56–58].