Me. Kreider et al., STEADY-STATE AND NON-STEADY-STATE MEASUREMENTS OF PLASMA GLUTAMINE TURNOVER IN HUMANS, American journal of physiology: endocrinology and metabolism, 35(4), 1997, pp. 621-627
To compare steady-state glutamine turnover using nitrogen, carbon, and
hydrogen tracers and to test the validity of monocompartmental equati
ons to determine plasma glutamine turnover under non-steady-state cond
itions, we infused 10 normal postabsorptive volunteers simultaneously
with [3,4-H-3]glutamine, [2-N-15]glutamine, and [U-C-14]glutamine for
4 h to isotopic steady state. Eight of the ten subjects were subsequen
tly infused in a stepwise fashion with exogenous glutamine. Plasma glu
tamine enrichment and specific activities fit a monoexponential model
well (r = 0.89, 0.92, and 0.92 for [2-N-15]-, [U-C-14]-, and [3,4-H-3]
glutamine, respectively). Volumes of distribution for each tracer (362
+/- 58, 433 +/- 51, and 446 +/- 63 ml/kg) and the transfer rate const
ants (0.0224 +/- 0.0020, 0.0222 +/- 0.0020, and 0.0240 +/- 0.0023 min(
-1)) for [2-N-15]-, [U-C-14]-, and [3,4-H-3]glutamine, respectively, w
ere not significantly different from one another. However, turnover of
glutamine determined with [3,4-H-3]glutamine (6.14 +/- 0.54 mu mol .
kg(-1). min(-1)) exceeded that determined with [U-C-14]glutamine (5.72
+/- 0.541 mu mol . kg(-1). min(-1); P < 0.03), which in turn exceeded
that determined with [2-N-15]glutamine (4.67 +/- 0.39 mu mol . kg(-1)
. min(-1), P < 0.01). The monocompartmental non-steady-state equations
of both DeBodo et al. (DeBodo, R., R. Steele, A. Dunn, and J. Bishop.
Rec. Prog. Horm. Res. 19: 445-448, 1963) and Finegood et al. (Finegoo
d, D., R. Bergman, and M. Vranic. Diabetes 36: 914-924, 1987) yielded
acceptable approximations of predicted rates of glutamine plasma appea
rance with deviations from predicted rates from 0.2 to 1.6% (Finegood
et al.) and from 0.1 to 8.2% (DeBodo et al.). Use of a 0.75 pool fract
ion most closely approximated predicted rates.