Figure 4.

(A) Representative ¹³C NMR spectra of a perfused rat heart injected with co-polarized [1-¹³C]pyruvate and [1,3-¹³C₂]AcAc, showing resonances of [1-¹³C]pyruvate (P), [1,3-¹³C₂]AcAc (A and A´), and their downstream metabolites. P₁-P₄ = metabolic products of [1-¹³C]pyruvate; A₁-A₄ = metabolic products of [1,3-¹³C₂]AcAc. (B) Representative sequential ¹³C NMR spectra, displayed as stacked plots, of the perfused hearts following the injection of co-polarized [1-¹³C]pyruvate and [1,3-¹³C₂]AcAc. Each spectrum was acquired every 2 s. Corresponding summed spectra of these arrays are shown in panel (C). Averaged normalized signal intensities (4 hearts per group) of HP [1-¹³C]lactate and C-1 of HP [1,3-¹³C₂]β-HB plotted as a function of perfusion time are shown in panels (D) and (E), respectively. At a given time point, the HP [1-¹³C]lactate signal was normalized to the total HP ¹³C signals of downstream metabolites originated from HP [1-¹³C]pyruvate summed over the NMR acquisition time window for each heart, ~150 s. Meanwhile, the HP [1-¹³C]β-HB signal was normalized to the total metabolites originated from HP [1,3-¹³C₂]AcAc during the same time window.