Background: Intestinal absorption of glutamine is the major source of exogenous glutamine for the increased glutamine metabolism in catabolic states. We previously observed that intestinal glutamine absorption and the glutamine transporter ASCT2 mRNA levels were up-regulated in sepsis. B0AT1, a Hartnup disorder-related gene, was recently identified as the gene for the predominant small intestinal mucosal glutamine transport System B. Regulation of B0AT1 is poorly understood. The purpose of the present in vivo study was to examine the regulation mechanism of B0AT1 by intra-abdominal abscess.
Methods: A total of 96 adult male Sprague-Dawley rats underwent sham surgery (sham), sham surgery plus sterile fecal-agar pellet (sterile), and sham surgery plus sterile fecal-agar pellet inoculated with E. coli (103) plus B. Fragilis (109) (abscess) in 6 separate experiments. Rats had access to water only after surgery, and were sacrificed at 6, 12 and 18 hours after surgery. Jejunum was harvested and processed. L-glutamine transport activity across brush border membrane vesicles, glutamine transporter B0AT1 mRNA and protein levels were measured. Data were means ± SD and analyzed by ANOVA (P<0.05).
Results: Mortality was 0 % in sham and sterile groups, and 15 % in abscess group. The glutamine transport activity was similar among the 3 groups at 6 hours, and was significantly higher in abscess group at 12 hours (2 fold increase, p<0.05) and at 18 hours (3 fold increase, p<0.05), compared to control group. Modest increase of glutamine transport activity in sterile group was observed (p>0.05). No significant change of B0AT1 protein levels was observed at 6 hours. The B0AT1 protein levels (whole cell protein and membrane protein) were significantly higher in abscess group at 12 hours (2.5 and 2.7 fold increase, p<0.05) and 18 hours (4.3 and 8.9 fold increase, p<0.01), compared to control group. There was modest increase of B0AT1 protein levels in sterile group (p>0.05). No significant change of B0AT1 mRNA levels was observed at 6 hours. Significant decrease of B0AT1 mRNA levels in both sterile and abscess groups was observed at 12 hours (4 and 9 fold decrease, P<0.01) and 18 hours treatments (2.5 and 3.5 fold decrease, p<0.05), compared to control group.
Conclusion: Intra-abdominal abscess stimulates intestinal glutamine absorption via a mechanism that involves an increase of cellular and membrane-bound glutamine transporters B0AT1 protein. This stimulation is independent of transporter mRNA levels, suggesting alteration of transporter B0AT1 protein stability.