IntroductionCurrent evidence suggests that erectile dysfunction (ED) may be an early marker of atherosclerosis and systemic vascular disease. Cardiovascular disease (CVD) and ED share many common risk factors such as age, hypertension, dyslipidemia, smoking, obesity, sedentary lifestyle, and diabetes. 1 These risk factors have been shown to predict the development of future ED. 2 Penile erection is the result of a complex and coordinated series of events involving vascular response, neuronal pathways, and psychosomatic stimulation. The nitric oxide (NO) pathway is activated upon sexual stimulation, and NO is released into penile smooth muscle from both the vascular endothelium of the penis and the autonomic, cavernous nerve terminals. Within the penile smooth muscle, NO activates guanylyl cyclase, which increases the concentration of the second messenger, cyclic guanosine monophosphate (cGMP). The elevated concentrations of cGMP result in relaxation of arterial smooth muscle in the penis and a marked rise in penile blood pressure. In addition, cGMP relaxes trabecular smooth muscle, which facilitates engorgement of the sinusoidal spaces, lengthening and enlargement of the penis, and compression of the subtunical venules. The net result is complete occlusion of penile venous outflow and trapping of blood within the corpus cavernosa.Phosphodiesterase-5 (PDE-5) inhibition enhances the normal erectile response by inhibiting the enzyme that degrades cGMP. This inhibition results in greater smooth muscle relaxation of both arterial smooth Abstract: Phosphodiesterase-5 (PDE-5) inhibitors are an effective therapy for the majority of men with erectile dysfunction (ED). However, many men with ED still report a suboptimal or partial response even after an adequate trial of oral PDE-5 therapy. Since ED is associated with impaired vascular function and both atorvastatin and quinapril have been previously shown to improve vascular function, we examined the effects of adjunctive treatment with these medications in men with vasculogenic ED who were suboptimal responders to 100 mg of sildenafil. Men with ED and suboptimal response to sildenafil were randomly assigned to 3 months of treatment with atorvastatin 40 mg (n ϭ 12), quinapril 10 mg (n ϭ 10), or placebo (n ϭ 13), along with continued adjunctive sildenafil use. Measured variables included: International Index of Erectile Function (IIEF) questionnaire, brachial artery flow-mediated dilation (FMD), endothelium-independent dilation (EID) via nitroglycerin, penile Doppler blood flow, blood pressure (BP), lipids, and C-reactive protein (CRP). Compared to placebo, quinapril (p Ͻ 0.01) significantly improved symptoms of ED as measured by the IIEF-5 questionnaire. There was a trend toward a significant improvement in IIEF-5 with atorvastatin. Similarly, quinapril significantly improved the IIEF ED Domain (p Ͻ 0.05). Other peripheral and penile vascular parameters were unchanged with drug therapy as compared to placebo.In conclusion, treatment with quinapril, in combination with si...