Dual carbon-labeled isotope experiments using D-[6-14C] glucose and L-[1,2,3-13C3] lactate: a new approach for investigating human myocardial metabolism during ischemia.

Simultaneous lactate production and extraction have been previously demonstrated in the myocardium in patients with coronary artery disease. To quantitate this lactate production and determine its source, dual carbon-labeled isotope experiments were performed. L-[1,2,3-13C3] lactate and D-[6-14C] glucose were infused in 10 patients with significant coronary artery disease. Metabolic samples were obtained at rest and during atrial pacing. Despite net chemical myocardial lactate extraction in the 10 patients at rest and no evidence of clinical ischemia, the L-[1,2,3-13C3] lactate analysis demonstrated that lactate was being released by the myocardium. During atrial pacing, seven patients did not develop clinical symptoms of ischemia, and the chemical lactate analysis showed net lactate extraction. However, tracer analysis demonstrated that there was a significant increase in the lactate released during atrial pacing (from 6.9 +/- 2.3 to 16.2 +/- 10.1 mumol/min) (p less than 0.05). In these seven patients, circulating glucose was the source of 23 +/- 15% of the lactate released at rest, and there was no significant change during pacing. The remaining three patients had mild chest pain and net chemical lactate production during pacing. Lactate release detected by the tracer increased from 5.7 +/- 3.0 mumol/min at rest to 50.9 +/- 16.8 mumol/min during pacing (p less than 0.01). In these patients, the contribution of glucose to lactate production increased significantly during pacing-induced clinical ischemia from 25 +/- 22 to 67 +/- 14% (p less than 0.005). Thus, dual carbon-labeled isotopic experiments are powerful tools for investigating myocardial metabolic pathways.(ABSTRACT TRUNCATED AT 250 WORDS)