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Articles in PresS, published online ahead of print October 15, 2002
Am J Physiol Endocrinol Metab, 10.1152/ajpendo.00309.2002
Submitted on July 11, 2002
Accepted on October 4, 2002
1 Pediatrics, United States Department of Agriculture/Agricultural Research Service Children's Nutrition Research Center, Houston, TX, USA
2 Agricultural Research Service Growth Biology Laboratory, United States Department of Agriculture, Beltsville, MD, USA
* To whom correspondence should be addressed. E-mail: tdavis{at}bcm.tmc.edu.
To differentiate the effect of somatotropin (ST) treatment on protein metabolism in the hindquarter (HQ) and portal-drained viscera (PDV), growing swine (n=20) treated with ST (0 or 150 µg.kg-1.d-1) for 7 d were infused intravenously with NaH13CO3 and [2H5]phenylalanine and enterally with [1-13C]phenylalanine while in the fed state. Arterial, portal venous, and vena cava whole blood samples, breath samples, and blood flow measurements were obtained for determination of tissue and whole body phenylalanine kinetics under steady state conditions. In the fed state, ST treatment decreased whole body phenylalanine flux, oxidation, and protein degradation without altering protein synthesis, resulting in an improvement in whole body net protein balance. Blood flow to the HQ (+80%), but not the PDV, was increased with ST treatment. In the HQ and PDV, ST increased phenylalanine uptake (+44% and +23%, respectively) and protein synthesis (+43% and +41%, respectively), with no effect on protein degradation. In ST-treated and control pigs, phenylalanine was oxidized in the PDV (34-43% of enteral and arterial sources), but not the HQ. In both treatment groups, dietary (40%) rather than arterial (10%) extraction of phenylalanine predominated gut amino acid metabolism, while localized blood flow influenced HQ amino acid metabolism. The results indicate that ST increases protein anabolism in young, growing swine by increasing protein synthesis in the HQ and PDV, with no effect on protein degradation. Differing results between the whole body and the HQ and PDV suggest that the effect of ST treatment on protein metabolism is tissue specific.
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