DIRECT OBSERVATION OF LACTATE AND ALANINE BY PROTON DOUBLE QUANTUM SPECTROSCOPY IN RAT HEARTS SUPPLIED WITH [3-C-13]PYRUVATE

The C-13-fractional enrichments in the lactate and alanine methyl carbon positions were determined by H-1 NMR spectroscopy of extracts of rat hearts perfused with various concentrations of [3-C-13]pyruvate +/- unlabeled glucose or acetate. In general, the C-13-fractional enrichment of the alanine methyl carbon pool paralleled the C-13-fractional enrichment of the acetyl-CoA which entered the TCA cycle (as determined by C-13-isotopomer analysis) while the C-13-fractional enrichment of the lactate methyl carbon was always significantly lower, consistent with a pool of lactate which does not mix with exogeneous [3-C-13]pyruvate. This has also been examined in intact, perfused, KCl-arrested rat hearts supplied with [3-C-13]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.