Endotoxin challenge reduces aconitase activity in myocardial tissue

Sepsis impairs mitochondrial respiration but the mechanisms responsible are incompletely understood. We propose that Krebs cycle enzymes are inhibited in sepsis, contributing to reduced rates of oxidative phosphorylation. Hypothesis. The activities of Krebs cycle enzymes are decreased in endotoxemia and contribute to reduced rates of oxidative phosphorylation. Methods. Adult male rats received an intraperitoneal injection of either endotoxin or saline. Cardiac mitochondria were subsequently isolated and measures of mitochondrial respiration and enzyme activities performed. Main results. By 24 h post endotoxin administration, there was a 28% reduction in mitochondrial respiration (P = 0.0005) and a 24% reduction in aconitase activity (P = 0.001). Functional activity of the electron transport chain was unaffected. Conclusion. Our data demonstrate that in the heart, the administration of endotoxin significantly and selectively decreased aconitase activity in association with reduced rates of oxidative phosphorylation. We conclude that decreased activity of aconitase contributes to the endotoxin-stimulated reduction in mitochondrial respiration.