Growth hormone and epidermal growth factor together enhance amino acid transport systems B 0,+ and A in remnant small intestine after massive enterectomy

Abstract

Background. Sodium-dependent brush-border nutrient transport is decreased 2 weeks after massive enterectomy. This down-regulation is ameliorated by a 1-week infusion of parenteral growth hormone (GH) and epidermal growth factor (EGF) started 1 week after resection. We hypothesize that glutamine (GLN) transport will be enhanced by earlier and longer growth factor infusion, with differential effects on the Na +-dependent GLN transport systems A, B 0,+, and B 0/ASCT2. Materials and methods. New Zealand White rabbits underwent 70% small bowel resection then immediately received parenteral EGF, GH, both EGF and GH, or neither for 2 weeks. Na +-dependent 3H-GLN uptake by jejunal and ileal brush-border membrane vesicles was measured and the contribution of systems A, B 0,+, and B 0 was then determined by competitive inhibition. Data were analyzed using one-way analysis of variance. Results. In nonresected animals, the relative contribution of the systems was similar in jejunum (A 9%, B 0,+ 20%, and B 0 71%) and ileum (A 13%, B 0,+ 27%, and B 0 60%). Na +-dependent GLN uptake was reduced by one half in resected untreated controls, primarily because of decreased B 0 activity. EGF or GH alone did not affect Na +-dependent GLN transport, but, as a combination, there was increased uptake in the residual ileum and jejunum by 144% and 150%, respectively, over resected controls ( P < 0.05). This was twice that achieved by delayed and shorter-duration combination treatment. This augmentation was a result of a 6.1–8.2-fold increase in system A as well as a 3.8–3.9-fold enhancement of system B 0,+ activity in remnant ileum and jejunum ( P < 0.01). Conclusions. Parenteral EGF and GH, given in combination for 2 weeks immediately after massive enterectomy, synergistically enhance GLN uptake by systems A and B 0,+.