Table 1.

¹³C fractional enrichment of glutamate and glutamine in positions C4 and C3 for [2-¹³C]acetate, [1-¹³C]glucose, and [3-¹³C]lactate infusions in the human occipito-parietal lobe at the end of 2 h of infusions

	[3-13C]Lactate	[1-13C]Glucose	[2-13C]Acetate
fe[GluC4]	6.7 ± 0.6	19.4 ± 1.2	5.4 ± 0.5
fe[GluC3]	4.7 ± 0.4	14.7 ± 0.8	5.0 ± 0.5
fe[GlnC4]	5.2 ± 0.6	16.7 ± 0.8	16.0 ± 2.4
fe[GlnC3]	3.7 ± 0.4	12.0 ± 0.7	7.9 ± 1.0
fe[GlnC4]/fe[GluC4]	0.78 ± 0.04	0.87 ± 0.04*	2.90 ± 0.22**

At the bottom line, the [4-¹³C]glutamine/[4-¹³C]glutamate labeling ratio is calculated for each individual experiment and averaged. Fractional enrichment values are in percentage, means ± SD, n = 9 for lactate group and n = 7 for the glucose and acetate group. The natural abundance (1.1%) is not subtracted.

Kolmogorov–Smirnov two-sample tests for difference between lactate and other groups: *p = 0.14 with glucose, and **p = 1 with acetate.