Pioglitazone (PGZ) decreased enzymatic activity of complex I and III of the mitochondrial respiratory chain. (A) The in vitro enzymatic activity of mitochondrial respiratory chain (MRC) complexes was measured by spectrophotometry (as described in the Methods section) in isolated mouse liver mitochondria exposed to 0 to 15 μM PGZ for 30 minutes. Activities were expressed as nM of substrate used per minute per mg protein and referred to as the percentage of the specific activity of citrate synthase (CS) to correct for the hepatic content in mitochondria. NS, not significant. **, P <0.001; ***, P <0.001 vs control activity. (B) Effects of PGZ on the enzymatic activity of the MRC and complex V of the oxidative phosphorylation in mice treated with PGZ for 12 weeks. Ten C57BL/6J mice were treated with 10 mg/kg/day PGZ for 12 weeks. The enzymatic activity of MRC complexes was measured as indicated in the Methods section and expressed as nM of substrate used per minute per mg protein and, to correct for the hepatic content in mitochondria, referred as a percentage of the specific activity of citrate synthase (CS). NS, not significant.