Abstract
Two weeks after 70% enterectomy, glutamine (Gln) transport is downregulated in rabbit residual bowel due to a decrease in system B(0) 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 (ATB(0)/ASCT2) protein and mRNA expression correlate with system B(0) 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 ATB(0)/ASCT2 protein and mRNA. In all tissues, ATB(0)/ASCT2 mRNA was reduced by approximately 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 ATB(0)/ASCT2 protein, but GH treatment increased ATB(0)/ASCT2 mRNA abundance 250% in the residual ileum. Because changes in the ATB(0)/ASCT2 protein amount paralleled those in the system B(0) 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, ATB(0)/ASCT2 protein and mRNA expression in rabbit colon are decreased, suggesting different regulatory pathways.
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