Benign prostate hyperplasia is the most common disease in the aging male, often comorbid with erectile dysfunction. Phosphodiesterase type 5 (PDE5) inhibitors (sildenafil, tadalafil, and vardenafil) decrease lower urinary tract symptoms in patients with erectile dysfunction and BPH. We studied PDE5 expression and activity in the human bladder and PDE5i effects both in vitro (human and rat) and in vivo (rat). PDE5 is highly expressed in rat and human bladder and immunolocalized in vascular endothelium and muscle fibers. Sildenafil, tadalafil, and vardenafil blocked 70% of the total cGMP-catabolizing activity; vardenafil was the most potent (IC(50) = 0.3 nm). In human bladder cells and in rat strips, a PDE-resistant cGMP analog, SP-8-Br-PET-cGMPS, induced, respectively, a consistent antiproliferative and relaxant effect. In contrast, the nitric oxide donor sodium nitroprusside (SNP) was almost ineffective. However, blocking PDE5 with vardenafil increased SNP antiproliferative and relaxant activity up to the level observed with SP-8-Br-PET-cGMPS. We also found that castration decreased, and T supplementation restored, PDE5 gene expression in rat bladder. Accordingly, bladder strips from castrated rats were more sensitive to SNP-induced relaxation than strips from control or T-replaced rats, whereas in the presence of vardenafil, all groups showed the same SNP sensitivity. To discover whether vardenafil affects bladder activity in vivo, the rat bladder outlet obstruction model was used. Chronic treatment with 10 mg/kg.d vardenafil significantly reduced nonvoiding contractions (47%, P < 0.05 vs. placebo) up to tamsulosin level (51%). Overall, these results demonstrate that PDE5 regulates bladder smooth muscle tone, strongly limiting the nitric oxide/cGMP signaling, and that vardenafil, by blocking PDE5, may be a possible therapeutic option for bladder dysfunction by ameliorating irritative lower urinary tract symptoms.