Metabolic dysfunction and depletion of mitochondria in hearts of septic rats

Abstract

Our previous studies indicate that hearts from septic rats have decreased work with oxygen wasting. The present studies test if there is energy deficit, changes in cardiac mitochondrial content and caspase activation during sepsis. Anesthetized, male Sprague-Dawley rats received no surgical treatment (control), laparotomy (sham), or laparotomy with cecal ligation and puncture (CLP) to induce polymicrobial septic shock. Hearts were isolated 12-14 h later. Cardiac work, oxygen consumption, substrate oxidation and energy stores were measured in perfused hearts. Normalized density of mitochondria was determined in ventricles without perfusion by morphometric analysis with electron microscopy. Citrate synthase activity was assessed in homogenates and isolated mitochondria. Cardiac work decreased significantly in CLP (47%), while oxygen consumption and glucose oxidation were unchanged compared with control or sham hearts (oxygen and substrate wasting). Tissue adenosine triphosphate, creatine phosphate and glycogen were lower in CLP hearts (energy deficit). Mitochondrial grid intersects decreased significantly from 151 +/- 8 sham to 130 +/- 4 CLP out of 361 possible intersects and autophagy was observed in CLP hearts. Total activity of citrate synthase decreased in homogenates (99 +/- 8 micromol/min/g wet weight sham vs. 62 +/- 7 CLP, P < 0.05) and in the mitochondrial fraction (27 +/- 1 micromol/min/g wet weight sham to 22 +/- 1 CLP, P < 0.05). Calculated mitochondrial content decreased from 63 +/- 4 mg protein/g wet weight sham to 46 +/- 5 CLP, P < 0.05 (mitochondrial depletion). Caspase-3 activity doubled and tumor necrosis factor alpha content tripled in CLP hearts. CONCLUSIONS. - Oxygen and substrate wasting in CLP occurs with fewer mitochondria and energy deficit, processes that are coincident with caspase-3 activation.