Effects of different oxidative insults on intermediary metabolism in isolated perfused rat hearts

¹³C and ³¹P NMR were used to evaluate exogenous substrate utilization and endogenous phosphate metabolites in perfused rat hearts exposed to tert- butylhydroperoxide (tert-BOOH) and hydrogen peroxide (H₂O₂). Both reagents caused a reduction in developed pressure compared to controls and, in agreement with previous ³¹P NMR data, had different effects on intracellular high-energy phosphates and glycolysis. ¹³C Isotopomer analysis of tissue extracts showed that H₂O₂ and tert-BOOH also had significantly different effects on substrate utilization by the citric acid cycle. The contribution of exogenous lactate and glucose to acetyl-CoA was 43% in controls and increased to over 80% in the presence of either oxidant. With tert-BOOH, exogenous glucose and lactate were both significant contributors to acetyl-CoA (44 ± 2 and 41 ± 3%). However, with H₂O₂, exogenous lactate supplied a much higher fraction of acetyl-CoA (72 ± 2%) than glucose (9 ± 1%). Also, when [2¹³C] glucose was supplied, accumulation of [2-¹³C] and 15-¹³C]fructose 1,6-bisphosphate was observed in the presence of H₂O₂, indicating inhibition of glyceraldehyde-3- phosphate dehydrogenase. These results indicate that despite this glycolytic inhibition, H₂O₂ increased the utilization of pyruvate precursors when lactate was present as an alternative carbohydrate substrate.