Lack of functionally active sweet taste receptors in the jejunum in vivo in the rat.

Background: When studied in enterocyte-like cell lines (Caco-2 and RIE cells), agonists and antagonists of the sweet taste receptor (STR) augment and decrease glucose uptake, respectively. We hypothesize that exposure to STR agonists and antagonists in vivo will augment glucose absorption in the rat.

Materials And Methods: About 30-cm segments of jejunum in anesthetized rats were perfused with iso-osmolar solutions containing 10, 35, and 100 mM glucose solutions (n = 6 rats, each group) with and without the STR agonist 2 mM acesulfame potassium and the STR inhibitor 10 μM U-73122 (inhibitor of the phospholipase C pathway).

Acute enterocyte adaptation to luminal glucose: a posttranslational mechanism for rapid apical recruitment of the transporter GLUT2.

Background: Glucose absorption postprandially increases markedly to levels far greater than possible by the classic glucose transporter sodium-glucose cotransporter 1 (SGLT1).

Hypothesis: Luminal concentrations of glucose >50 mM lead to rapid, phenotypic, non-genomic adaptations by the enterocyte to recruit another transporter, glucose transporter 2 (GLUT2), to the apical membrane to increase glucose absorption.

Methods: Isolated segments of jejunum were perfused in vivo with glucose-containing solutions in anesthetized rats.

Role of hydrogen sulfide as a gasotransmitter in modulating contractile activity of circular muscle of rat jejunum.

Aim: Our aim was to determine mechanisms of action of the gasotransmitter hydrogen sulfide (H(2)S) on contractile activity in circular muscle of rat jejunum.

Methods: Jejunal circular muscle strips were prepared to measure isometric contractions. Effects of sodium hydrosulfide (NaHS), a H(2)S donor, were evaluated on spontaneous contractile activity and after pre-contraction with bethanechol.

Mechanisms of glucose uptake in intestinal cell lines: role of GLUT2.

Background: GLUT2 is translocated to the apical membrane of enterocytes exposed to glucose concentrations >∼50 mM. Mechanisms of GLUT2-mediated glucose uptake in cell culture models of enterocytes have not been studied.

Aim: To explore mechanism(s) of glucose uptake in 3 enterocyte-like cell lines.

Peptide absorption after massive proximal small bowel resection: mechanisms of ileal adaptation.

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.

Differentiating passive from transporter-mediated uptake by PepT1: a comparison and evaluation of four methods.

Background: To quantify transmembrane transport of dipeptides by PepT1, passive uptake (non-PepT1 mediated) must be subtracted from total (measured) uptake. Three methods have been described to estimate passive uptake: perform experiments at cold temperatures, inhibit target dipeptide uptake with a greater concentration of a second dipeptide, or use modified Michaelis-Menten kinetics. We hypothesized that performing uptake experiments at pH 8.

Intestinal adaptation for oligopeptide absorption via PepT1 after massive (70%) mid-small bowel resection.

Introduction: Proteins are absorbed primarily as short peptides via peptide transporter 1 (PepT1).

Hypothesis: Intestinal adaptation for peptide absorption after massive mid-small intestinal resection occurs by increased expression of PepT1 in the remnant small intestine and colon.

Methods: Peptide uptake was measured in duodenum, jejunum, ileum, and colon using glycyl-sarcosine 1 week (n = 9) and 4 weeks (n = 11) after 70% mid-small bowel resection and in corresponding segments from unoperated rats (n = 12) and after transection and reanastomosis of jejunum and ileum (n = 8).

Mechanisms of action of the gasotransmitter hydrogen sulfide in modulating contractile activity of longitudinal muscle of rat ileum.

Aim: This study aims to determine mechanisms of action of the gasotransmitter hydrogen sulfide (H(2)S) on contractile activity in longitudinal muscle of rat ileum.

Methods: Ileal longitudinal muscle strips were prepared to measure isometric contractions. Effects of sodium hydrosulfide (NaHS), a donor of H(2)S, were evaluated on spontaneous contractile activity and after enhanced contractile activity with bethanechol.

Absence of evidence of translocation of GLUT2 to the apical membrane of enterocytes in everted intestinal sleeves.

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.

Age-related changes in functional NANC innervation with VIP and substance P in the jejunum of Lewis rats.

Age-related changes in non-adrenergic, non-cholinergic (NANC) neurotransmission might contribute to differences in gastrointestinal motility. Our aim was to determine age-related changes in functional innervation with vasoactive intestinal polypeptide (VIP) and substance P (Sub P) in rat jejunum. We hypothesized that maturation causes changes in neurotransmission with these two neuropeptides.

Role of vagal innervation in diurnal rhythm of intestinal peptide transporter 1 (PEPT1).

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.

Diurnal expression and function of peptide transporter 1 (PEPT1).

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.

Hexose transporter expression and function in mouse small intestine: role of diurnal rhythm.

Background: Expression and function of hexose transporters vary diurnally in rat small intestine; however, this subject remains unexplored in mice.

Aim: The aim of the study was to investigate the diurnal expression and function of hexose transporters SGLT1, GLUT2, and GLUT5 in mouse small bowel.

Methods: Twenty-four c57bl6 mice maintained in a 12-h light/dark room (6 AM: -6 PM: ) were sacrificed at 9 AM: , 3 PM: , 9 PM: , and 3 AM: (n = 6 each).

Coordinated, diurnal hexose transporter expression in rat small bowel: implications for small bowel resection.

Background: Hexose transporter mRNA and protein levels follow a diurnal rhythm in rat jejunum. Their coordinated expression and resultant function throughout the small bowel is not well understood. We hypothesized that hexose transporter levels and glucose absorption follow a coordinated, site-specific diurnal rhythm in rat duodenum and jejunum, but not in ileum.

Long-term effects of extrinsic denervation on VIP and substance P innervation in circular muscle of rat jejunum.

Intestinal denervation contributes to enteric motor dysfunction after small bowel transplantation (SBT). Our aim was to determine long-term effects of extrinsic denervation on function of nonadrenergic, noncholinergic innervation with substance P and vasoactive intestinal polypeptide (VIP). Contractile activity of jejunal circular muscle strips from six age-matched, naive control rats (NC) and eight rats 1 year after syngeneic SBT was studied in tissue chambers.

Role of VIP and substance P in NANC innervation in the longitudinal smooth muscle of the rat jejunum - influence of extrinsic denervation.

Background: This study was designed to determine changes in nonadrenergic, noncholinergic (NANC) neurotransmission mediated by Vasoactive Intestinal Polypeptide (VIP) and Substance P after small bowel transplantation (SBT).

Materials And Methods: Six groups of rats (n > or = 6 per group) were studied: naïve controls (NC); 1 wk after anesthesia/sham celiotomy (SC-1); 1 or 8 wk after jejunal and ileal transection/reanastomosis (TA-1, TA-8), or syngeneic, orthotopic SBT (SBT-1, SBT-8). Jejunal longitudinal muscle strips were studied under NANC-conditions for spontaneous contractile activity, response to exogenous VIP and Substance P, and electrical field stimulation (EFS).

Postprandial augmentation of absorption of water and electrolytes in jejunum is neurally modulated: implications for segmental small bowel transplantation.

Postprandial augmentation of absorption of water and electrolytes is believed to occur in the jejunum. Neural mechanisms of control, however, have not been studied in the in situ jejunum or in the transplanted bowel. The aim of this study was to determine if postprandial augmentation of absorption occurs in the in situ jejunum and to evaluate neural mechanisms controlling postprandial jejunal absorption.

The diurnal periodicity of hexose transporter mRNA and protein levels in the rat jejunum: role of vagal innervation.

Background: Protein and messenger RNA (mRNA) levels of the hexose transporters sodium-dependent glucose transporter-1, glucose transporter 2, and glucose transporter 5 follow a (daily) diurnal rhythm in rat jejunum. Because vagal innervation mediates the diurnal activity of other proteins in the rat small bowel, we hypothesized that the diurnal variation of mRNA and protein levels of these hexose transport proteins are mediated by vagal innervation.

Methods: Forty-eight rats kept in a strictly maintained, alternating 12-hour light-dark room underwent either sham laparotomy (n = 24) or bilateral total abdominal vagotomy (n = 24).

Inhibition by nitric oxide and nonadrenergic, noncholinergic (NANC) nerves is preserved in a canine model of extrinsic denervation: implications for small bowel transplantation.

Background: Small bowel transplantation (SBT) is complicated by changes in graft motility, especially in the early postoperative period. This dysmotility may be related in part to the extrinsic denervation necessitated by the procedure, but specific neurotransmitter response to SBT is incompletely understood. The aim of this study was to evaluate the role of nitric oxide and nonadrenergic, noncholinergic (NANC) enteric neural input in the nonimmunologic etiology of the dysmotility seen after SBT.

Extrinsic denervation alters postprandial absorption of glucose and glutamine in the ileum: implications for small bowel transplantation.

In the postprandial period, augmentation of absorption of water, electrolytes, and taurocholate is believed to occur in the ileum. The role of extrinsic innervation in this postprandial augmentation has not been well studied and may be an important concept in small bowel transplantation. Our aim was to investigate extrinsic neural mechanisms mediating postprandial absorptive patterns.

Nitrergic mechanisms mediating inhibitory control of longitudinal smooth muscle contraction in mouse small intestine.

Studies using genetic manipulation to investigate mechanisms of control of physiologic function often necessitate mouse models. However, baseline functional analysis of murine small intestinal motility has not been well defined. Our aim was to define nitrergic mechanisms regulating mouse small intestinal longitudinal muscle.

Contractile activity of mouse small intestinal longitudinal smooth muscle.

Background: Interest in genomic modulation experimentally often necessitates use of mouse models.

Aim: To characterize and quantitate smooth muscle contractile activity of the mouse small intestine using in vitro techniques. Full-thickness jejunal and ileal muscle strips from mice were cut in the direction of longitudinal muscle, suspended in tissue baths (37 degrees C), and connected to force transducers.

Postprandial absorptive augmentation of water and electrolytes in the colon requires intraluminal glucose.

Postprandial absorptive augmentation of water and electrolytes occurs in the small intestine and colon. The role of intraluminal nutrients in this response is poorly understood. Our aim was to determine whether postprandial absorptive augmentation of water and electrolytes in the colon requires the presence of intraluminal glucose.

Role of extrinsic innervation in jejunal absorptive adaptation to subtotal small bowel resection: a model of segmental small bowel transplantation.

Segmental small bowel transplantation offers theoretic advantages over total jejunoileal transplantation, but the regional ability of the transplanted segment to adapt is unknown. Absorption was measured in an 80 cm jejunal segment via a triple-lumen perfusion technique. Separate experiments measuring absorption of four nutrients (glucose, glutamine, oleic acid, and taurocholic acid) were performed before and 2 and 12 weeks after operative intervention.