In vivo carbon-13 nuclear magnetic resonance studies of heart metabolism.

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Abstract
Guinea pig heart metabolism was studied in vivo by 13C NMR at 20.18 MHz. High quality proton-decoupled 13C NMR spectra with excellent signal-to-noise ratios and resolution could be obtained in 6 min. Natural-abundance spectra showed resonances that could be assigned to fatty acids, but glycogen was not seen. During i.v. infusion of D-[1-13C]glucose and insulin, the time course of myocardial glycogen synthesis was followed serially for up to 4 h. 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 and glutamine, reflecting scrambling of the label expected from tricarboxylic acid cycle activity. Examination of the 31P NMR spectrum of the guinea pig heart in vivo demonstrated no change in the high-energy phosphates during the time periods of the 13C NMR experiments. 13C NMR apparently is a unique nondestructive tool for the study of heart mechanism in vivo.