Carbon-13 and phosphorus-31 nuclear magnetic resonance studies of myocardial metabolism in live guinea pigs.

Myocardial metabolism in live guinea pigs was investigated by 13C and 31P nuclear magnetic resonance (NMR) at 20.18 and 32.5 MHz, respectively. 13C NMR studies allowed monitoring of myocardial glycogen synthesis during intravenous infusion of D-[1-13C]glucose and insulin. Anoxia resulted in degradation of the labeled glycogen within 6 min and appearance of 13C label in lactic acid. Infusion of sodium [2-13C]acetate resulted in incorporation of label into the C-4, C-2, and C-3 positions of glutamate, reflecting "scrambling" of the label expected from tricarboxylic-acid-cycle activity. 31P NMR spectra of heart in live guinea pigs were obtained continuously in 20.5-sec time blocks during 3 min of anoxia, during subsequent reoxygenation, and, in separate animals, during terminal anoxia. Reversible anoxia resulted in rapid degradation of phosphocreatine (t1/2 = 54.5 +/- 2.5 sec), which recovered fully during reoxygenation. Heart inorganic phosphate increased during anoxia and returned to basal levels after oxygen was restored. During 3 min of anoxia, no significant changes in ATP levels or pH were detected.