Erectile dysfunction (ED) frequently coexists with coronary artery disease (CAD) and has been proposed as a potential marker for silent CAD in type 2 diabetes. In the present study we comparatively assessed the structural and functional changes of both penile arteries (PA) and coronary arteries (CA) from a prediabetic animal model. PA and CA from 17-18 weeks old Obese Zucker rats (OZR) and from their control counterpart Lean Zucker rats (LZR) were mounted in microvascular myographs to evaluate vascular function and stained arteries were subjected to morphometric analysis. Endothelial nitric oxide (NO) synthase (eNOS) protein expression was also assessed. Lumen and vessel areas were reduced and the media to-lumen area ratio was increased in PA from OZR, but structure was preserved in CA. Acetylcholine-elicited relaxations were severely impaired in PA but not in CA from OZR although eNOS expression was unaltered. Contractions to noradrenaline and 5-hydroxytryptamine (5-HT) were significantly enhanced in both PA and CA, respectively, from OZR. Blockade of NOS abolished endothelium-dependent relaxations in PA and CA, and potentiated noradrenaline and 5-HT contractions in arteries from LZR but not from OZR. The vasodilator response to the phosphodiesterase 5 (PDE5) inhibitor, sildenafil, was reduced in both PA and CA from OZR. Pretreatment with superoxide dismutase (SOD) reduced the enhanced vasoconstriction in both PA and CA from OZR but did not restore acetylcholine-induced relaxations in PA. In conclusion, the present results demonstrates vascular inward remodeling in PA and a differential impairment of the endothelial relaxant responses in PA and CA from insulin-resistant OZR. Enhanced superoxide production and reduced basal NO activity seem to underlie augmented vasoconstriction in both PA and CA. The severity of the structural and functional abnormalities in PA might anticipate the vascular dysfunction of the more preserved coronary vascular bed.