Glutamate metabolism of the heart during coronary artery bypass grafting

Glutamate infusion has been shown to exert beneficial hemodynamic effects in patients with heart failure after cardiac surgery. To elucidate the underlying mechanism we studied the possibility that glutamate is a Krebs-cycle precursor in the human heart. Therefore [1-13C]glutamate was infused in order to show production of 13CO2 by the heart. In five patients a primed constant infusion of [1-13C]glutamate was started 2 h before the start of sampling from coronary sinus and arterial blood. Plasma concentrations of glutamate and glutamine were determined by high pressure liquid chromatography. Blood concentration of CO2 and enrichment of [1-13C]glutamate, [1-13C]glutamine and 13CO2 were measured by GC-IRMS. The results show that approximately 85% of [1-13C]glutamate taken up by the heart is released as 13CO2. These results show that synthesis of Krebs-cycle intermediates is a major fate of the glutamate extracted by the human heart.