Figure 1.

Plasma samples were collected 0, 3 and 12 hr after [U-¹³C-Glc] infusion, as described in the Experimental Section. Unlabeled glucose and lactate concentrations were quantified by 1-D ¹H NMR using DSS as the calibration standard. Their % ¹³C enrichment was determined from the respective ¹³C satellite peaks in 1-D ¹H NMR spectra. Panel A illustrates the time course changes in glucose and lactate concentrations as well as their % ¹³C enrichment. Panel B shows the ¹³C satellite pattern of the 3-methyl group of lactate (¹³C-CH₃-lac) in the 1-D ¹H NMR spectrum of patient #6 after 3 hr of [U-¹³C-Glc] infusion. The chemical shifts of lactate and Ala reflected the acidic pH of the TCA extract.