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The aim of this work was to investigate the possible effects of resveratrol on the mitochondrial respiratory chain in rat brains. Isolation of mitochondria was performed at 4 degrees C using differential centrifugation. Mitochondrial respiration rate (0.4 mg of protein/ml) was determined by measuring mitochondrial oxygen consumption with a Clark electrode at 37 degrees C. Respiratory control ratio (RCR) was evaluated as the state 3/state 4 ratio of oxidative phosphorylation with substrates adenosine 5'-diphosphate (ADP) and malate plus glutamate, respectively in the presence and in the absence of resveratrol. The rate of oxygen consumption by the different complexes was checked using rotenone (2 microM), malonate (10 mM), antimycin A (1 microM), potassium cyanide (KCN) (0.3 mM) and oligomycin (10 microM) to inhibit complexes II, III, IV, V and I, respectively. Moreover, enzyme activity determinations were checked as follows: the activities of complexes II-III were measured as the rate of cytochrome c reduction at 550 nm (37 degrees C) successively triggered either by succinate (complexes II and III) or by decylubiquinol (DUQH2) (complex III), in the presence and in the absence of resveratrol. Adenosine 5'-triphosphate (ATP) synthase activity was checked as ATP hydrolysis (ATPase) at 37 degrees C for 10 min from purified mitochondria on Percoll gradient. The inorganic phosphate (Pi) concentration was measured by the Fiske and Subbarow method. When complexes I to V were activated by glutamate plus malate, resveratrol (10(-11) - 10(-4) M) significantly decreased RC (p < 0.001) following a biphasic curve with two EC50 values, 0.162 +/- 0.072 microM and 24.5 +/- 4.0 microM, representing about 56% of total oxygen consumption inhibition. We also observed a concentration-dependent effect on state 3 with two EC50 values, 2.28 +/- 0.87 nM and 27 +/- 5 microM respectively. On the other hand, resveratrol inhibited state 4 following a concentration-dependent curve with an EC50 of 37 +/- 11 microM. When complex IV operated alone, resveratrol (100 microM) did not modify oxygen consumption compared with control, indicating that this molecule did not inhibit complex IV. Thus resveratrol inhibits the mitochondrial respiratory chain through complexes I to III. In order to confirm these data, we measured the enzymatic activity of ubiquinol cytochrome c reductase alone and in the presence of resveratrol. In the presence of disrupted mitochondria, after freeze thawing cycles (three times), resveratrol inhibited about 20% of complex III activity. These results suggest that resveratrol and DUQH2 could be competitive on complex III. Resveratrol significantly inhibited ATPase activity (p < 0.001) following a biphasic curve with two EC50 values, 0.39 +/- 0.15 nM and 23.1 +/- 6.4 microM, both representing about 80% of oligomycin-dependent ATPase total activity. Resveratrol was effective as a protecting agent on the three models of oxidation. On lipid peroxidation of brain synaptosomes induced by the Fenton reaction, it was three times more potent than DUQH2. Its effectiveness in reducing 1,1-diphenyl-2-picryl hydrazyl radical (DPPH degrees) showed a stoichiometry of two, indicating that two hydrogen atoms of resveratrol were abstracted by the process. Resveratrol was also able to scavenge the superoxide anion (O2 degrees) generated from rat forebrain mitochondria in a concentration dependent manner. In conclusion, resveratrol can decrease complex III activity by competition with coenzyme Q. This property is especially interesting as this complex is the site where reactive oxygen substances (ROS) are generated. By decreasing the activity of complex III, resveratrol cannot only oppose the production of ROS but can also scavenge them.