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Biochemical and Molecular Actions of Nutrients

ATB⁰/ASCT2 Expression in Residual Rabbit Bowel Is Decreased after Massive Enterectomy and Is Restored by Growth Hormone Treatment^1,2

Nelly E. Avissar³, Thomas R. Ziegler^*, Liana Toia, Liang Gu^*, Edward C. Ray, Jorge Berlanga-Acosta and Harry C. Sax

Department of Surgery, University of Rochester Medical Center, Rochester, NY; ^* Department of Medicine, Emory University School of Medicine, Atlanta, GA; and Center for Genetic Engineering and Biotechnology (CIGB), Havana, Cuba

³To whom correspondence should be addressed. E-mail: nelly_avissar{at}urmc.rochester.edu.

Two weeks after 70% enterectomy, glutamine (Gln) transport is downregulated in rabbit residual bowel due to a decrease in system B⁰ activity. Providing epidermal growth factor (EGF) and growth hormone (GH) restores Gln transport by increasing systems A and B^0,+ activities. We hypothesized that changes in Na⁺-dependent broad-spectrum neutral amino acid transporter (ATB⁰/ASCT2) protein and mRNA expression correlate with system B⁰ activity. New Zealand White rabbits underwent 70% jejunoileal resection or no resection. Resected rabbits immediately received parenteral EGF, GH, both, or neither agent for 2 wk. Tissues harvested from jejunum, ileum, and colon were subjected to Western and Northern blot analyses for ATB⁰/ASCT2 protein and mRNA. In all tissues, ATB⁰/ASCT2 mRNA was reduced by 50% in resected rabbits compared with nonresected controls. Similar reductions in protein amount occurred in the ileum and cecum. None of the growth factor treatments restored ATB⁰/ASCT2 protein, but GH treatment increased ATB⁰/ASCT2 mRNA abundance 250% in the residual ileum. Because changes in the ATB⁰/ASCT2 protein amount paralleled those in the system B⁰ activity in this model, it is likely that this is the protein responsible for this transport system. The increase in mRNA abundance in rabbits treated with GH for 2 wk may be a harbinger of subsequent increases in transporter protein and activity. Unlike reported upregulation of transporters in human colon after small bowel resection, ATB⁰/ASCT2 protein and mRNA expression in rabbit colon are decreased, suggesting different regulatory pathways.

KEY WORDS: • small bowel resection • ATB⁰/ASCT2 • rabbits • epidermal growth factor • growth hormone

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