Involvement of superoxide radical in the impaired endothelium-dependent relaxation of cavernous smooth muscle in hypercholesterolemic rabbits

Involvement of the superoxide radical in impaired relaxation of penile cavernous smooth muscle in hypercholesterolemia was investigated. New Zealand White rabbits (n = 40) were randomly divided into control and treatment groups. The control group (n = 20) received a regular diet while the treatment group (n = 20) was fed a diet of 2% cholesterol for 8 weeks. Blood level of cholesterol in the cholesterol-fed group was significantly higher than that of the control group. The contraction responses of cavernous tissues to norepinephrine were not significantly different in the two groups. The relaxation responses to endothelium-dependent agents (acetylcholine, bradykinin) were significantly reduced in the hypercholesterolemic group compared with the control group. However, the relaxation responses to endothelium-independent agents (papaverine, verapamil) were not significantly different in the two groups. The production of superoxide radicals was significantly higher in the hypercholesterolemic group than in the control group (P < 0.01). The activity of superoxide dismutase (total SOD, Mn-SOD, Cu,Zn-SOD) increased significantly in the hypercholesterolemic group compared with the control group (P < 0.05). The activities of catalase and glutathione peroxidase also increased in the hypercholesterolemic group, but were not significantly higher than those of the control group. Therefore, production of the superoxide radicals in rabbit cavernous tissues increases in the state of hypercholesterolemia, which may lead to functional impairment of cavernous smooth muscle relaxation in response to endothelium-mediated stimuli.