The role of peroxynitrite in chemical preconditioning with 3-nitropropionic acid in rat hearts.

Objectives: 3-Nitropropionic acid (3-NP), an irreversible inhibitor of succinate dehydrogenase, has been shown to protect against ischemic injury in the brain and in the heart via a preconditioning-like effect; however, the cellular mechanism is not known. The aim of the present study was to investigate if 3-NP pretreatment reduces infarct size and if altered metabolism of nitric oxide and reactive oxygen species are involved.

Methods: Hearts were assigned into 3 groups: 3 intermittent cycles of 5 min no-flow ischemia separated by 5 min aerobic perfusion protocol were used to induce ischemic preconditioning as a positive control; a time-matched non-preconditioning group served as control; and 3-NP (20 mg/kg, i.p.) was injected 3 h before the perfusion protocol to induce pharmacological preconditioning. Hearts from all groups were then subjected to 30 min global ischemia followed by 120 min reperfusion.

Results: Infarct size and lactate dehydrogenase release were significantly reduced after ischemia/reperfusion. While cardiac nitric oxide (NO) was increased, superoxide formation, nitrotyrosine level, and cardiac NADH oxidase and xanthine oxidase (XO) activities were markedly reduced by 3-NP administration. Cardiac activities of NO synthase and superoxide dismutase were not changed by 3-NP.

Conclusion: This is the first demonstration in the rat myocardium that 3-NP induces pharmacological preconditioning, thereby limiting infarct size, and that this effect is associated with increased NO bioavailability and reduced peroxynitrite formation due to inhibition of superoxide formation by XO and NADH oxidase.