Selective inhibitors of phosphodiesterase 5 (PDE5), which specifically hydrolyzes cGMP, are used to study signaling through the guanylate cyclase activator nitric oxide and to mediate smooth muscle relaxation and vasodilation triggered by cGMP. Vardenafil is a potent inhibitor of PDE5 (IC50 = 0.2-1.2 nM) that less effectively blocks the activities of PDE6, PDE1, and PDE11 (IC50s = 2, 230, and 130 nM, respectively). PDE5 inhibitors, including vardenafil, have applications in several conditions, including erectile dysfunction, pulmonary arterial hypertension, and lower urinary tract dysfunction.
