Direct observation of lactate and alanine by proton double quantum spectroscopy in rat hearts supplied with [3-13C]pyruvate.

The 13C-fractional enrichments in the lactate and alanine methyl carbon positions were determined by 1H NMR spectroscopy of extracts of rat hearts perfused with various concentrations of [3-13C]pyruvate +/- unlabeled glucose or acetate. In general, the 13C-fractional enrichment of the alanine methyl carbon pool paralleled the 13C-fractional enrichment of the acetyl-CoA which entered the TCA cycle (as determined by 13C-isotopomer analysis) while the 13C-fractional enrichment of the lactate methyl carbon was always significantly lower, consistent with a pool of lactate which does not mix with exogeneous [3-13C]pyruvate. This has also been examined in intact, perfused, KCl-arrested rat hearts supplied with [3-13C]pyruvate by proton double quantum metabolite specific spectroscopy (MSS). A comparison of MSS spectra of intact hearts with one pulse spectra of extracts of those same hearts indicates there is a sizeable non-enriched pool of lactate in the intact hearts which is not visible by NMR spectroscopy.