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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.Hypothesis: Complete abdominal vagotomy abolishes diurnal variations in gene expression and transport function of PEPT1.Methods: Twenty-four rats maintained in a 12-h light/dark room [6AM-6PM] underwent abdominal vagotomy; 24 other rats were controls. Four weeks later, mucosal levels of mRNA and protein were measured at 9AM, 3PM, 9PM, and 3AM (n = 6 each) by quantitative real-time PCR and Western blots, respectively; transporter-mediated uptake of dipeptide (Gly-Sar) was measured by the everted-sleeve technique.Results: Diurnal variation in mRNA, as in controls, was retained post-vagotomy in duodenum and jejunum (peak at 3PM, p < 0.05) but not in ileum. Diurnal variations in expression of protein and Gly-Sar uptake, however, were absent post-vagotomy (p > 0.3). Similar to controls, maximal uptake was in jejunum after vagotomy (V (max), nmol/cm/min: jejunum vs. duodenum and ileum; 163 vs. 88 and 71 at 3AM; p < 0.04); K (m) remained unchanged.Conclusions: Vagal innervation appears to mediate in part diurnal variations in protein expression and transport function of PEPT1, but not diurnal variation in mRNA expression of PEPT1. [ABSTRACT FROM AUTHOR]

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. 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 9 AM, 3 PM, 9 PM, and 3 AM (n =6 each) by real time RT-PCR and Western blotting, respectively, in rats maintained in a 12-h light/dark room [light 6 AM to 6 PM]; transporter-mediated uptake of dipeptide (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 3 PM, P <0.05), but not in ileum; maximal uptake was in jejunum. Vmax (nmol/cm/min) was greater at 3 PM and 9 PM compared with 9 AM (3 PM versus 9 AM: 104 versus 62 in duodenum, and 185 versus 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 9 PM and 3 AM. Conclusion: Gene expression and transport function of PEPT1 vary diurnally in duodenum and jejunum in temporal association with nocturnal feeding of rats. [Copyright &y& Elsevier]

Background: Protein absorption occurs as di- and tri-peptides via H(+)/peptide co-transporter-1 (PepT1).Aim: The aim of this study is to identify mechanisms of ileal adaptation after massive proximal enterectomy.Hypothesis: Ileal adaptation in uptake of peptides is mediated through upregulation of PepT1 gene expression.Study Design: Rats underwent 70% jejunoileal resection. Total mucosal cellular levels of messenger RNA (mRNA) and protein and transporter-mediated uptake per centimeter of the di-peptide glycyl-sarcosine (Gly-Sar) were compared in remnant ileum 1 and 4 weeks postoperatively to control and to 1-week sham laparotomy rats. Histomorphology, food consumption, and weights of rats were monitored.Results: After 70% resection, although mRNA per cell for PepT1 decreased at 1 week (p = 0.002), expression of mRNA at 4 weeks and protein at 1 and 4 weeks in remnant ileum were unchanged (p > 0.1). Ileal Gly-Sar uptake (V (max)-nanomoles per centimeter per minute, i.e., number of transporters per centimeter) increased at 1 and 4 weeks compared to control and 1-week sham (p < 0.05 each); K (m) (i.e., transporter function) was unchanged. Villous heights (millimeters) in remnant ileum increased at 1- and 4-week time points over controls (0.45 and 0.57 vs 0.21, resp; p < 0.001).Conclusions: Ileal adaptation to proximal resection for peptide absorption occurs through cellular proliferation (hyperplasia) and not through cellular upregulation of PepT1 mRNA or protein per enterocyte. [ABSTRACT FROM AUTHOR]

Introduction: Traditional models of intestinal glucose absorption confine GLUT2 to the basolateral membrane. Evidence suggests that GLUT2 is translocated to the apical membrane when the enterocyte is exposed to high luminal glucose concentrations. Hypothesis: GLUT2 translocates to the apical membrane by a PKC signaling mechanism dependent on activity of SGLT1 and the cellular cytostructure. Methods: Transporter-mediated glucose uptake was studied in rat jejunum using everted sleeves under seven conditions: Control, SGLT1 inhibition (phlorizin), GLUT2 inhibition (phloretin), both SGLT1 and GLUT2 inhibition, PKC inhibition (calphostin C or chelerythrine), and disruption of cellular cytostructure (nocodazole). Each condition was tested in iso-osmotic solutions of 1, 20, or 50 mM glucose for 1 or 5 min incubations (n = 6 rats each). Results: Control rats exhibited a saturable pattern of uptake at both durations of incubation. Phlorizin (P ≤ 0.006 each) inhibited markedly and phloretin (P ≤ 0.01 each) inhibited partially glucose uptake in all concentrations and time. Phloretin and phlorizin together completely inhibited uptake (P = 0.004 each). Calphostin C, chelerythrine, and nocodazole had little effect on glucose uptake at either 1 or 5 min. Inhibition of SGLT1 led to near complete cessation of transporter-mediated glucose uptake, while GLUT2 inhibition led to partial inhibition, suggesting some constitutive expression of GLUT2 in the apical membrane. Disruption of PKC signaling or cytoskeletal integrity partially inhibited transporter-mediated glucose uptake only in 1 mM glucose, suggesting a non-specific effect. Conclusions: Under these conditions, it does not appear that GLUT2 is translocated to the apical membrane on the cellular cytostructure in response to PKC signaling. [ABSTRACT FROM AUTHOR]