AJP - Endocrinology and Metabolism, Vol 268, Issue 4 E652-E659, Copyright © 1995 by American Physiological Society

ARTICLES

Stable isotope determination of plasma lactate conversion into glucose in fasting infants

P. F. Bougneres, F. Rocchiccioli, N. Nurjhan and J. Zeller
Institut National de la Sante et de la Recherche Medicale Unite 342, Hopital Saint Vincent de Paul, Paris, France.

To quantify lactate gluconeogenesis, we developed a gas chromatography-mass spectrometry method based on the infusion of [6,6-2H2]glucose and [3-13C]lactate tracers to 12 infants aged 1-25 mo fasting for 11.5 +/- 1.5 h. Both rates of appearance of plasma glucose (26.7 +/- 2.6 mumol.kg-1.min-1, 4.8 +/- 0.5 mg.kg-1.min-1) and lactate (30.8 +/- 3.1 mumol.kg-1.min-1, 2.8 +/- 0.3 mg.kg-1.min-1) were remarkably elevated compared with adult values. The interconversion of plasma lactate and glucose was determined by 1) measuring the incorporation of 13C from [3-13C]lactate into plasma glucose; 2) correcting for the metabolic exchange of carbon atoms in the tricarboxylic acid cycle. For this purpose, an additional group of six infants was infused with [3-13C]lactate, and the distribution of 13C at specific carbon positions in the glucose molecule was determined using relevant ions in the electron-impact mass spectrum of its 1,2,5,6-diisopropylidene-3-O-acetyl-alpha-furanosyl derivative; and 3) measuring the reverse conversion of glucose to lactate in five other infants infused with [1-13C]glucose. We found that 54 +/- 2% of glucose was derived from plasma lactate (14.4 +/- 1.3 mumol.kg-1.min-1, 2.6 +/- 0.2 mg.kg-1.min-1). Lactate and glucose rates of appearance were correlated (r = 0.58, P < 0.05) and decreased with fasting duration (r = 0.66, P < 0.02). The correction factor for carbon exchange in the tricarboxylic acid cycle was 1.14 +/- 0.11.(ABSTRACT TRUNCATED AT 250 WORDS)

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