BACKGROUND Protein is absorbed primarily as di/tripeptides which are transported into the enterocyte exclusively by H+/peptide cotransporter 1 (PEPT1). Diurnal changes in expression and function of several other mucosal transporters occur in rat. HYPOTHESIS Diurnal variations in mRNA, protein, and transport function of PEPT1 occur in rat duodenum and jejunum but not in ileum. METHODS Mucosal levels of mRNA and protein were determined at 9AM, 3PM, 9PM, and 3AM (n=6 each) by real time RT-PCR and Western blotting, respectively, in rats maintained in a 12-h light/dark room [lights 6AM to 6PM]; transporter-mediated uptake of di-peptide (Gly-Sar) was also measured by everted sleeve technique. RESULTS mRNA transcripts of PEPT1 and Gly-Sar uptake varied diurnally in duodenum and jejunum (peak at 3PM, p<0.05) but not in ileum; maximal uptake was in jejunum. Vmax (nmol/cm/min) was greater at 3PM and 9PM compared to 9AM (3PM vs. 9AM: 104 vs. 62 in duodenum, and 185 vs. 101 in jejunum; p<0.03); Km was unchanged across time points or locations. Protein levels varied minimally in jejunum and ileum with peaks at 9PM and 3AM. CONCLUSION Gene expression and transport function of PEPT1 vary diurnally in duodenum and jejunum in temporal association with nocturnal feeding of rats.

INTRODUCTION The hexose transmembrane transporters SGLT1 and GLUT2 are present in low quantities in ileum where little glucose absorption occurs normally; however, glucose uptake in ileum is highly adaptable after small bowel resection. HYPOTHESIS Ileal adaptability for glucose absorption after jejunal resection is mediated predominately by upregulation of GLUT2. METHODS Rats underwent 70%, proximal-based jejunoileal resection. Transporter-mediated glucose uptake was measured in proximal and distal remnant ileum 1 and 4 wk postoperatively (n=6 rats, each) and in corresponding ileal segments in control and 1 wk sham laparotomy rats (n=6, each) without and with selective inhibitors of SGLT1 and GLUT2. In separate groups of rats (n=6, each), protein (Western blots), mRNA (RT-PCR), and villus height (histomorphology) were measured. RESULTS After 70% proximal intestinal resection, there was no dramatic change in protein or mRNA expression per cell of either SGLT1 or GLUT2, but median glucose uptake (nmol/cm/min) increased markedly from 52 (range, 28-63) in controls to 118 (range, 80-171) at 1 wk, and 203 (range, 93-248) at 4 wk (p≤0.04 each) correlating with change in villus height (p≤0.03). CONCLUSIONS Ileal adaptation for glucose transport occurs through cellular proliferation (hyperplasia) and not through cellular upregulation of glucose transporters.

BACKGROUND: Protein is absorbed predominantly as di/tripeptides via H + /peptide cotransporter-1 (PEPT1). We demonstrated previously diurnal variations in expression and function of duodenal and jejunal but not ileal PEPT1; neural regulation of this pattern is unexplored.