Cardioprotection by L-glutamate during postischaemic reperfusion: Reduced infarct size and enhanced glycogen resynthesis in a rat insulin-free heart model

1. Previously, we found that administration of high-dose L-glutamate during postischaemic reperfusion improves haemodynamic recovery and enhances glycogen resynthesis. In the present study, we investigated whether the same effect occurs in an insulin-free model and whether glutamate administration reduces infarct size. Further, we studied whether the cardioprotective effect of glutamate depends on preserved glutamate transamination and K-ATP channel activity. 2. In a rat isolated, insulin-free, perfused heart model, we compared the effects of administration of L-glutamate (10 mmol/L) during either 45 min no-flow regional ischaemia plus 120 min reperfusion or reperfusion alone on infarct size and left ventricular (LV) recovery. The effect of glutamate on glycogen metabolism was studied in a model of 30 min global no-flow ischaemia and 60 min reperfusion. In both models, the effects of inhibition of glutamate transamination and K-ATP channel activity were examined by adding amino-oxyacetate (an aminotransferase inhibitor; 0.1 mmol/L) and glibenclamide (a K-ATP blocker; 10 mmol/L), respectively. 3. Administration of L-glutamate reduced infarct size by 60% (P < 0.01) and improved postischaemic LV function (developed pressure and rate pressure product; P < 0.05). L-Glutamate increased glycogen content after 60 min reperfusion by 65% (P < 0.01). Amino-oxyacetate, as well as glibenclamide, abolished the glutamate-mediated reduction in infarct size, haemodynamic improvement and glycogen resynthesis during reperfusion. 4. In conclusion, L-glutamate administration from the start of postischaemic reperfusion exerts cardioprotective effects, including reduced infarct size, improved haemodynamic recovery and enhanced glycogen resynthesis. These effects depend on preserved transamination of glutamate and K-ATP channel activity, but not on insulin administration.