Key Points
- Quantitatively evaluate in vivo myocardial substrate uptake, fuel preference, and carbon metabolism in a closed-chest model using carbon-13 nuclear magnetic resonance spectroscopy.
- Administered intravenous infusions of non-radioactive carbon-13-labeled glucose, 3-hydroxybutyrate, and acetate into overnight-fasted Sprague-Dawley rats.
- Acquired in vivo 7 T carbon-13 NMR spectra from rat myocardium at a temporal resolution of 6 minutes.
- Harvested heart tissue extracts post-infusion for high-resolution carbon-13 NMR spectroscopy to corroborate in vivo kinetic measurements.
- Acetate and 3-hydroxybutyrate supplied 53 ± 9% and 42 ± 6% of the acetyl-CoA entering the tricarboxylic acid cycle, respectively, whereas glucose did not contribute to oxidative metabolism despite being extracted.
- In vivo myocardial tricarboxylic acid cycle turnover was 1.34 ± 0.07 µmol/min/g wet weight, and myocardial oxygen consumption was 2.95 ± 0.16 µmol/min/g wet weight.
- In vivo myocardial glutamine synthesis occurred at 0.14 ± 0.02 µmol/min/g wet weight and alpha-ketoglutarate-glutamate exchange at 1.22 ± 0.08 µmol/min/g wet weight, differing from isolated heart preparations.
Structured PICO
PPopulationOvernight-fasted Sprague-Dawley rats
IInterventionIntravenous infusions of non-radioactive 13C-labeled glucose, 3-hydroxybutyrate, and acetate with in vivo 13C NMR spectroscopy at 7 T
OOutcomeQuantitative appraisal of myocardial metabolism in vivo (substrate uptake, preference, and metabolism)surrogate
In vivo 13C NMR spectroscopy is feasible in intact rats and provides quantitative insights into myocardial substrate metabolism, revealing that ketone bodies and acetate are preferred over glucose for oxidative metabolism in the fasted state.