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Department of Molecular Physiology and Biophysics, Diabetes Research and Training Center and Department of Surgery, Vanderbilt University School of Medicine, Nashville, Tennessee 37232
The aim of this
study was to determine how gut and liver protein kinetics adapt to
acute exercise in the 18-h-fasted dog
(n = 7) and in dogs glycogen depleted
by a 42-h fast (n = 8). For this
purpose, sampling (artery and portal and hepatic veins) and infusion
(vena cava) catheters and Doppler flow probes (portal vein and hepatic
artery) were implanted with animals under general anesthesia. At least
16 days later, an experiment, consisting of a 120-min equilibration
period, a 30-min basal sampling period, and a 150-min exercise period,
was performed. At the start of the equilibration period, a constant
rate infusion of
[1-13C]leucine was
initiated. Gut and liver leucine appearance and disappearance rates
were calculated in these studies by combining a novel stable isotopic
method and arteriovenous difference methods. In the determination of
tissue leucine kinetics the tissue inflow of both
-[13C]ketoisocaproic
acid and [13C]leucine
was taken into account. The results of this study show that
1) the splanchnic bed (liver plus
gut) contributes ~40% to the whole body proteolytic rate in the
basal state and during exercise in dogs fasted for either 18 or 42 h,
2) the contributions of the gut and
liver to splanchnic bed proteolysis is about equal in the basal state
in both 18- and 42-h-fasted dogs, and
3) exercise in the 18-h-fasted dog
leads to a greater emphasis on gut proteolysis and a lesser emphasis on
hepatic proteolysis. These studies highlight the important contribution
of gut and hepatic proteolysis to whole body proteolysis and the
ability of the gut to acutely adapt to changes in physical activity.
gastrointestinal tract; ketoisocaproic acid; stable isotope; amino acid
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