['To investigate the efficacy of oral L-citrulline for erectile dysfunction and penile structure disruption in a rat model.', "Male Wistar-ST rats aged 15 weeks were randomly divided into three groups as follows: sham-operated rats (control group), surgically castrated rats (castrated group) and surgically castrated rats subsequently treated with 2% L-citrulline water (castrated + L-citrulline). At 4 weeks postoperative, erectile function was assessed based on intracavernous pressure changes, followed by electrostimulation of cavernous nerves and calculation of maximum intracavernous pressure/mean arterial pressure. Penile structure was evaluated by Masson's trichrome staining and the smooth muscle-to-collagen ratio was calculated. The serum bioavailable testosterone, L-arginine, L-citrulline, N(G),N(G) -dimethylarginine and nitrogen oxide levels were evaluated.", 'The bioavailable testosterone concentrations were decreased in the castrated and castrated + L-citrulline groups compared with the control group at 4 weeks after surgery. The intracavernous pressure-to-mean arterial pressure and smooth muscle-to-collagen ratios were significantly decreased in the castrated group compared with the control group, but significantly increased in the castrated + L-citrulline group compared with the castrated group. The serum L-citrulline, L-arginine and N(G),N(G)-dimethylarginine levels, and the L-arginine-to-N(G),N(G)-dimethylarginine ratios were significantly increased in the castrated +L-citrulline group compared with the castrated group. The serum nitrogen oxide levels were increased in the castrated + L-citrulline group compared with the castrated group.'] Does oral L-citrulline supplementation improve erectile function and penile structure in castrated rats?