Mitochondrial function and substrate availability.

Carbohydrates and lipid oxidations support energy metabolism by distinct pathways exhibiting similarities and differences. Alterations of energy metabolism during sepsis are well recognized; however, failure of oxygen or substrate supply is not a prominent cause. The occurrence of a "mitochondrial cytopathy" induced by sepsis explains some of these abnormalities, which may represent a "metabolic hibernation," a potential strategy of defense during the very acute phase of the illness. Our view of the involvement of mitochondrial metabolism in cell signaling has evolved considerably. Because of the structure of the respiratory chain, the way electrons are provided (upstream or downstream of complex 1 [i.e., nicotinamide adenine dinucleotide {reduced form} or flavin adenine dinucleotide {reduced form}]) plays an important role in the regulation of several functions, including the yield of adenosine triphosphate synthesis and the production of reactive oxygen species. Moreover, the modern view of energy channeling and compartmentation in the cell may open attractive hypotheses regarding the changes in cellular energy distribution in pathologic states, such as sepsis.