NADPH oxidase- and mitochondrion-derived superoxide at rostral ventrolateral medulla in endotoxin-induced cardiovascular depression

We evaluated the contribution of superoxide anion (O2−) generated by NADPH oxidase or mitochondria in the rostral ventrolateral medulla (RVLM), where sympathetic premotor neurons for arterial pressure maintenance are located, on cardiovascular depression induced by inducible nitric oxide synthase-derived NO after Escherichia coli lipopolysaccharide (LPS) treatment. In Sprague–Dawley rats maintained under propofol anesthesia, microinjection of LPS bilaterally into the RVLM induced progressive hypotension, bradycardia, and reduction in sympathetic vasomotor outflow over our 240-min observation period. This was accompanied by an increase in O2− production (60–240 min) in the RVLM, alongside phosphorylation of p47phox or p67phox, upregulation of gp91phox or p47phox protein, and increase in Rac-1 or NADPH oxidase activity (60–120 min), and a depression of mitochondrial respiratory enzyme activity (120–240 min). Whereas inhibition of NADPH oxidase or knockdown of the gp91phox or p47phox gene blunted the early phase (60–150 min), coenzyme Q10 or mitochondrial KATP channel inhibitor antagonized the delayed phase (120–240 min) of LPS-induced increase in O2− production in RVLM and cardiovascular depression. We conclude that, whereas NADPH oxidase-derived O2− in RVLM participates predominantly in the early phase, O2− generated by depression in mitochondrial respiratory enzyme activity or opening of mitoKATP channels mediates the delayed phase of LPS-induced cardiovascular depression.