Effect of sepiapterin on voltage-dependent erectile response. Following the untreated voltage series (open bars), 10 µM sepiapterin was injected intracavernosally, and a voltage series was applied 30-minutes postinjection (hatched bars). No treatment effects were observed in rats fed the control diet (A), whereas rats fed the WD for 4 weeks (B), 8 weeks (C), and 12 weeks (D) demonstrated an enhanced erectile response with sepiapterin treatment. *P < 0.05, ***P < 0.001. Reported are means ± SEM for 4–6 animals in each group. ICP = intracavernosal pressure; MAP = mean arterial pressure; SEM = standard error of the mean; WD = Western diet.