Growth factors regulation of rabbit sodium-dependent neutral amino acid transporter ATB⁰ and oligopeptide transporter 1 mRNAs expression after enterectomy

Background: Sucessful intestinal adaptation after massive enterectomy is dependent on increased efficiency of nutrient transport. However, midgut resection (MGR) in rabbits induces an initial decrease in sodium-dependent brush border neutral amino acid transport, whereas parenteral epidermal growth factor (EGF) and growth hormone (GH) reverse this downregulation. We investigated intestinal amino acid transporter B⁰ (ATB⁰) and oligopeptide transporter 1 (PEPT 1) mRNA expression after resection and in response to EGF and/or GH. Methods: Rabbits underwent anesthesia alone (control) or proximal, midgut, and distal resections. Full-thickness intestine was harvested from all groups on postoperative day (POD) 7, and on POD 14 from control and MGR rabbits. A second group of MGR rabbits received EGF and/or GH for 7 days, beginning 7 days after resection. ATB⁰ and PEPT 1 mRNA levels were determined by Northern blot analysis. Results: In control animals, ileal ATB⁰ mRNA abundance was three times higher than jejunal mRNA, whereas PEPT 1 mRNA expression was similar. By 7 and 14 days after MGR, jejunal ATB⁰ mRNA abundance was decreased by 50% vs control jejunum. A 50% decrease in jejunal PEPT 1 message was delayed until 14 days after MGR. Treatment with EGF plus GH did not alter ATB⁰ mRNA expression but doubled PEPT 1 mRNA in the jejunum. Conclusion: The site of resection, time postresection, and growth factors treatment differentially influence ATB⁰ and PEPT 1 mRNA expression. Enhanced sodium-dependent brush border neutral amino acid transport with GH plus EGF administration is independent of increased ATB⁰ mRNA expression in rabbit small intestine after enterectomy.