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1 Department of Surgery, Vanderbilt University, and the Nashville VA Medical Center; 2 Department of Molecular Physiology and Biophysics, Vanderbilt University, Nashville, Tennessee 37232; and 3 Division of Endocrinology, Department of Medicine, Albert Einstein College of Medicine, New York, New York 10461
The purpose of this study was to
compare the assessment of gluconeogenesis (GNG) in the overnight- and
prolonged-fasted states and during chronic hypercortisolemia using the
arteriovenous difference and
[14C]phosphoenolpyruvate-liver biopsy
techniques as well as a combination of the two. Two weeks before a
study, catheters and flow probes were implanted in the hepatic and
portal veins and femoral artery of dogs. Animals were studied after an
18-h fast (n = 8), a 42- or 66-h fast
(n = 7), and an 18-h fast plus a continuous infusion of
cortisol (3.0 µg · kg
1 · min
1) for
72 h (n = 7). Each experiment consisted of an
80-min tracer ([3-3H]glucose and
[U-14C]alanine) and dye equilibration period (
80 to 0 min) and a 45-min sampling period. In the cortisol-treated group,
plasma cortisol increased fivefold. In the overnight-fasted group,
total GNG flux rate (GNGflux), conversion of glucose
6-phosphate to glucose (GNGG-6-P
Glc), glucose
cycling, and maximal GNG flux rate (GNGmax) were 0.95 ± 0.14, 0.65 ± 0.06, 0.62 ± 0.06, and 0.70 ± 0.09 mg · kg
1 · min
1,
respectively. In the prolonged-fasted group, they were 1.50 ± 0.18, 1.18 ± 0.13, 0.40 ± 0.07, and 1.28 ± 0.10 mg · kg
1 · min
1, whereas in
the cortisol-treated group they were 1.64 ± 0.33, 0.99 ± 0.29, 1.32 ± 0.24, and 0.91 ± 0.13 mg · kg
1 · min
1. These
results demonstrate that GNGG-6-P
Glc and GNGmax were almost identical. However, these rates were
15-38% lower than GNGflux generated by a
combination of the two methods. This difference was most apparent in
the steroid-treated group, where the combination of the two methods
(GNGflux) detected a significant increase in gluconeogenic flux.
fasting; cortisol
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