SOMATROPIN-INDUCED PROTEIN ANABOLISM IN HINDQUARTERS AND PORTAL-DRAINED VISCERA OF GROWING PIGS

Authors: BUSH, J - BAYLOR COLLEGE OF MED; Burrin, Douglas - Doug; SURYAWAN, A - BAYLOR COLLEGE OF MED; O'CONNOR, P - BAYLOR COLLEGE OF MED; NGUYEN, H - BAYLOR COLLEGE OF MED; REEDS, P - UNIV OF ILLINOIS; Steele, Norman; VAN GOUDOEVER, J - BAYLOR COLLEGE OF MED; DAVIS, T - BAYLOR COLLEGE OF MED

Submitted to: American Journal of Physiology - Endocrinology and Metabolism
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/4/2002
Publication Date: 2/1/2003
Citation: Bush,J.A., Burrin,D.G., Suryawan,A., O'Connor,P.M., Nguyen,H.V., Reeds,P.J., Steele,N.C., Van Goudoever,J.B., Davis,T.A. 2003. American Journal of Physiology - Endocrinology and Metabolism. 284(2):E302-E312.

Interpretive Summary: Researchers are studying the effects of somatotropin in animal models to learn how doctors might be able to use growth hormone to help people with various maladies. Most somatotropin studies conducted so far have involved mature animals. Some of these studies have suggested that somatotropin increases protein synthesis in skeletal muscle, although results have been conflicting. Little is known about the effect of growth hormone on protein metabolism in the gut. We gave young, growing pigs somatotropin for a week, using a double stable isotope labeling method. We measured the flux of amino acids, which are the building blocks of protein, across the hindlimb, which is mostly muscle, and the portal-drained viscera (PDV), meaning primarily the gut, while the pigs were being fed. Somatotropin increased protein synthesis in both the hindlimb and PDV, with no change in protein breakdown. The effects were different on a whole-body basis: the rest of the tissues showed decreased protein breakdown, and no change in protein synthesis. Therefore, the effects seem to be tissue-specific. These findings may have human ramifications. For example, if we were to extrapolate, we might guess that growth hormone might be able to help a child with a serious intestinal disease, such as short-gut syndrome. Based on what we found in growing pigs, whose gut is similar to that of growing children, growth hormone might increase the protein mass in a child's gut. If the gut protein mass increased, so would the absorptive area, so the gut could get more nutrients and help sustain the child. More work needs to be done in this area to build on these promising findings.

Technical Abstract: 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 micro g(.)kg(-1)(.)d(-1)) for 7 d were infused intravenously with NaH(13)CO3 and [(2)H5]phenylalanine and enterally with [1-(13)C]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.