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1 United States Department of Agriculture/Agricultural Research Service Children's Nutrition Research Center, Department of Pediatrics, Baylor College of Medicine, Houston, Texas 77030; 2 United States Department of Agriculture/Agricultural Research Service Growth Biology Laboratory, Beltsville, Maryland 20705; and 3 Department of Animal and Dairy Science, Pennsylvania State University, University Park, Pennsylvania 16802
Somatotropin (ST) administration enhances
protein deposition in well-nourished, growing animals. To determine
whether the anabolic effect is due to an increase in protein synthesis
or a decrease in proteolysis, pair-fed, weight-matched (~20 kg)
growing swine were treated with porcine ST (150 µg · kg
1 · day
1,
n = 6) or diluent (n = 6) for 7 days. Whole body
leucine appearance (Ra), nonoxidative leucine disposal
(NOLD), urea production, and leucine oxidation, as well as tissue
protein synthesis (Ks), were determined in the fed
steady state using primed continuous infusions of
[13C]leucine,
[13C]bicarbonate, and
[15N2]urea. ST treatment increased
the efficiency with which the diet was used for growth. ST treatment
also increased plasma insulin-like growth factor I (+100%) and insulin
(+125%) concentrations and decreased plasma urea nitrogen
concentrations (
53%). ST-treated pigs had lower leucine
Ra (
33%), leucine oxidation (
63%), and urea
production (
70%). However, ST treatment altered neither NOLD
nor Ks in the longissimus dorsi, semitendinosus, or
gastrocnemius muscles, liver, or jejunum. The results suggest that in
the fed state, ST treatment of growing swine increases protein
deposition primarily through a suppression of protein degradation and
amino acid catabolism rather than a stimulation of protein synthesis.
protein synthesis; insulin-like growth factor I; insulin; growth hormone; muscle
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