Evidence for superoxide anion generation in aortas of cholesterol-fed rabbits treated with L-arginine

The inducible form of nitric oxide synthase (iNOS) is present in advanced atherosclerotic lesions. The aim of the present paper was to compare the functionality of iNOS in rabbits fed a 0.3% cholesterol-diet for 24 weeks (Baseline), and 36 weeks, with l-arginine (l-Arg) or vehicle supplementation (Saline) for the last 12 weeks. N-iminoethyl-l-lysine (l-NIL; 10 microM), a selective inhibitor of iNOS, potentiated the contractions to phenylephrine in aortas from Baseline, Saline and l-Arg rabbits confirming the presence of a functional iNOS. In l-Arg rabbits, the contractions induced by l-NIL were less pronounced than those noted in Baseline and Saline rabbits; superoxide dismutase (150 U/ml) significantly increased the phenylephrine-induced contractions only in the l-Arg rabbits. In the presence of NADPH, aortas from l-Arg rabbits produced more superoxide anions than aortas from saline rabbits as evidenced by the lucigenin-enhanced chemiluminescence technique. In conclusion, our results show functional and biochemical evidence for an increased superoxide anion production in atherosclerotic aortas from hypercholesterolemic rabbits treated with l-Arg for 12 weeks. These data may thus help to explain the lack of beneficial effects of l-Arg on atherosclerosis progression in long-term experimental hypercholesterolemia as well as in severely atherosclerotic humans.