ASSESSMENT OF MYOCARDIAL GLUTAMATE REQUIREMENTS EARLY AFTER CORONARY-ARTERY BYPASS-SURGERY

Glutamate is an important substrate for the intermediary metabolism of the heart, particularly in association with ischemia. Early after cor onary artery bypass surgery (CABG) myocardial uptake of glutamate seem s to be limited by substrate availability (arterial levels). However, glutamate is not an innocuous substrate. As arterial levels of glutama te are important both for myocardial uptake and adverse effects, an at tempt was made to determine a minimum dose of glutamate sufficient to supply the needs of the heart after CABG. Ten patients received and in fusion of 220-240 mi of 0.1 M L-glutamic acid solution at varying rate s during two 30-min periods, starting 2 h after uncomplicated elective CABG. Intravenous glutamate infusion caused a dose-dependent Linear i ncrease in arterial glutamate and an increased myocardial uptake of gl utamate. However, myocardial uptake of glutamate correlated with arter ial levels only at lower infusion rates. Although maximal peak uptake in individual patients (6.6 +/- 1.1 mu mol/min) occurred at an average increase of arterial whole blood glutamate of 172 +/- 34 mu mol/L, th e greatest impact on myocardial glutamate uptake was achieved by incre asing arterial whole blood glutamate by less than 100 mu mol/L. This i mplies that an infusion rate of 30-40 mg glutamate/kg BW/h could suffi ce to achieve a maximal or near maximal myocardial glutamate uptake in most patients after CABG. The adequacy of this dosage remains to be c onfirmed in high-risk patients.