EFFECTS OF INTRAVENOUS GLUTAMATE ON SUBSTRATE AVAILABILITY AND UTILIZATION ACROSS THE HUMAN HEART AND LEG

To study the effect of monosodium glutamate on hemodynamics and on substrate metabolism in cardiac and skeletal muscle, an intravenous (IV) dose of 1.2, 2.5, or 5.0 mg/kg body weight was administered to 27 patients during arterial-coronary sinus catheterization (15 patients) or arterial-femoral vein catheterization (13 patients). Data were obtained for 25 minutes after the injection. Arterial glutamate concentrations increased 2.5-5 fold in a dose-related manner. Glutamate administration reduced arterial levels of free fatty acids by 25% (P < .001), of lactate by 13% (P < .05), and of alanine by 6% (P < .05). Arterial glucose increased by 10% (P < .001) and arterial insulin was increased threefold (P < .01). Myocardial uptake of free fatty acids decreased by 25% (P < .001), whereas uptakes of glutamate and glucose increased by 60% (P < .001) and 100% (P < .001), respectively. Cardiac release of citrate increased transiently (P < .05), whereas consumption of lactate and releases of alanine were unchanged by the glutamate. Across the leg, the arteriovenous differences of glutamate were elevated threefold to eightfold (dose-related) (P < .001), and that of glucose was doubled (P < .01). The release of citrate increased (P < .01). Arterial-femoral vein gradients of free fatty acids, lactate, and alanine remained unchanged. Heart rate, blood pressure, coronary sinus flow, coronary vascular resistance, and cardiac oxygen uptake were unmodified by glutamate. Six patients complained of short-lasting burning sensations after the highest glutamate doses. In conclusion, glutamate administration stimulates insulin secretion and changes substrate availability and utilization in human cardiac and skeletal muscle from free fatty acids toward glucose and glutamate. © 1991.