Recent studies have shown that statins seem to upregulate the endothelial NO synthase pathway (eNOS) and may, therefore, enhance NO availability, a direct scavenger of O2- and an inhibitor of oxidative enzymes.
Methods: To assess whether the oxidative stress produced by an in vivo exposure to nitroglycerin (NTG) is attenuated by statins, 4 groups of normocholesterolemic rats were treated; group 1 received pravastatin (20 mg/kg/d p.o) and group 2 atorvastatin (10 mg/kg/d) both for 5 weeks and the last 3 days, a cotreatment with the statin plus NTG (50 mg/kg/d, s.c. injections b.i.d.); group 3 (NTG) received only NTG (50 mg/kg/d, b.i.d. for 3 days) and group 4 served as control. Rings of thoracic aortas from these groups were studied in organ baths. Relaxations to NTG (0.1 nM to 0.1 mM) were determined on phenylephrine-preconstricted rings and O2- production (counts/10 s/mg) was assessed by lucigenin chemiluminescence technique.
Results: In vivo NTG exposure induced a rightward shift of the concentration-response curves to NTG: the pD2 (-log NTG concentration evoking a half maximal relaxation) was 5.8 +/- 0.3 (n=7) vs. 7.2 +/- 0.2 in the control group (not exposed to NTG, n=7) and O2- production was enhanced (1259 +/- 71 vs. 787 +/- 76, (n=5) P<.05). In contrast, groups 1 (n=7) and 2 (n=7) behaved as the control group (pD2 values were 7.4 +/- 0.1 (n=7) and 6.9 +/- 0.1 (n=7); O2- production was 721 +/- 109 and 647 +/- 121). The protective effect on nitrate tolerance disappeared when L-NAME (an eNOS inhibitor, 100 mg/kg/d) was co-administered with NTG in groups 1 and 2. Incubation of aortic rings with NAD(P)H (100 microM) also impaired the protective effect of both statins. Moreover, before NTG exposure, aortic cGMP content, reflecting EDNO availability, was significantly enhanced in group 1 (P<.05 vs. control).
Conclusion: Long-term statin treatment protects against nitrate tolerance by counteracting NTG-induced increase in O2- production. Both eNOS pathway and NAD(P)H oxidases seem to be involved in this protective mechanism.