Myocardial glutamate and alanine exchanges related to carbohydrate metabolism in patients with normal and stenotic coronary arteries.

Myocardial exchanges of glutamate, alanine, glucose, lactate, free fatty acids (FFA) and oxygen in resting state were determined in nine subjects (controls) without and in 28 patients with coronary artery disease (CAD). Patients with CAD showed increased myocardial glutamate uptake (2.51 +/- 0.60 mumol/min) and alanine release (1.25 +/- 0.60 mumol/min) compared to controls (glutamate uptake: 1.66 +/- 0.79 mumol/min; alanine release: 0.63 +/- 0.41 mumol/min). Myocardial glucose and lactate uptake was augmented in CAD patients, whereas FFA arteriovenous differences were decreased in patients with three-vessel-disease. The amount of glutamate taken up by the heart correlated positively to lactate uptake in all subjects (r = 0.84) and to external glucose utilization in patients with CAD (r = 0.72). Myocardial alanine release was positively related to glucose and lactate uptake in controls and in patients with only moderate CAD (one-vessel-disease). Glucose and FFA uptake correlated inversely in controls (r = 0.84), but not in CAD patients. A tight relation between exchanges of glutamate/alanine and carbohydrate metabolism in human heart is demonstrated. The data suggest altered myocardial substrate exchange towards augmented carbohydrate utilization in CAD patients in resting state. The results agree with in vitro and animal studies suggesting extraction of glutamate from the circulation to be of importance for maintaining carbohydrate consumption in chronic ischaemic heart disease.