Thesis (M. Sc.)--York University, 1999. Graduate Programme in Biology. / Typescript. Includes bibliographical references (leaves 82-92). Also available on the Internet. MODE OF ACCESS via web browser by entering the following URL: http://wwwlib.umi.com/cr/yorku/fullcit?pMQ56172.

Thesis (Ph.D.)--University of Adelaide, Dept. of Medicine, 1998. / Erratum is pasted onto back end-paper. Bibliography: leaves 164-207.

Thesis (M.S.)--Virginia Polytechnic Institute and State University, 1992. / Vita. Abstract. Includes bibliographical references. Also available via the Internet.

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GLP-2 is a potent intestinotrophic peptide that can increase mucosal growth, intestinal blood flow, and nutrient absorption when administered exogenously. We aimed to delineate the effects of endogenous GLP-2R signalling in conditions of nutrient deprivation and excess. Using a mouse with a targeted genetic deletion of the Glp2r gene (Glp2r-/-), we addressed the hypothesis that the known GLP-2R is required for intestinal adaptation to nutrient deprivation and excess. In Chapter 2, we demonstrate that Glp2r−/− mice fasted for 24 hours and re-fed for 24 hours failed to increase intestinal growth and jejunal crypt cell proliferation compared to littermate Glp2r+/+ mice. Administration of EGF to Glp2r−/− during the re-feeding period rescued this re-feeding defect. Wildtype mice re-fed for 30, 90, and 180 minutes following a 24 hour fast displayed increased jejunal mRNA levels of the ErbB ligands amphiregulin, epiregulin and HB-EGF. Treatment with the pan ErbB inhibitor CI-1033 inhibited induction of these ErbB ligands in jejunum of mice in association with prevention of crypt cell proliferation. Re-feeding also caused an increase in jejunal p-Akt levels and treatment with CI-1033 prevented increased p-Akt levels. Moreover, re-fed Glp2r−/− mice failed to increase ErbB ligands or p-Akt levels 90 minutes following re-feeding when compared to Glp2r+/+ littermates. Therefore, the GLP-2R is essential for re-feeding induced intestinal adaptation by activating the ErbB network and p-Akt to increase crypt cell proliferation. In Chapter 3, we show that the known GLP-2R is not required for intestinal adaptation to a perceived nutrient deprivation challenge (STZ-induced diabetes) or chronic nutrient excess (high-fat diet induced glucose intolerance). Although exogenous GLP-2 administration has been previously shown to stimulate glucagon secretion, glucose homeostasis was normal in STZ-diabetic and high fat fed Glp2r−/− mice. We also developed a third model of diabetes and glucose intolerance: ob/ob: Glp2r−/−. In the absence of GLP-2R signalling, ob/ob mice display improved oral but impaired intraperitoneal glucose tolerance, elevated fed and fasted glucose levels, increased circulating glucagon, decreased beta cell and increased alpha cell mass. Taken together, these results suggest that endogenous GLP-2R signalling is essential for intestinal and islet adaptation to conditions of nutrient deprivation and excess.

The vascularly and luminally perfused rat jejunum has been developed as a useful experimental model for the study of intestinal function. However there are discrepancies in the reported results on the fate of luminally absorbed glucose in different versions of this system. In the present work, the vascularly and luminally perfused rat jejunum in vitro was established and thorough investigation was made of the dissection procedure and other experimental variables thought to be important in the functioning of the model. Special attention was paid to the preparation of the erythrocytes for the vascular perfusion medium to ensure their ability to pass through the vascular bed and to deliver oxygen to the intestinal tissues. Measurements of the respiration of the perfused intestine were made routinely in view of the paucity of such observations in the literature. Glucose absorption, translocation and metabolism by the intestine were measured using recirculation and once-through perfusion modes and, in the latter system, analysis of these functions was followed using both enzymatic and radiochemical assay techniques. Glucose and water absorption was also studied using a lumen-only recirculation perfusion of rat jejunum in vivo. The experiments were performed over a wide range of luminal glucose concentrations and osmolarities, and using proprietary glucose-electrolyte solutions intended for use in the oral rehydration of patients. In consequence of this work, it has been possible for the first time to realise why literature reports on the fate of luminally absorbed glucose differ so widely, and the present results appear to give the most accurate record so far on the distribution of this glucose (in the absence of other metabolisable substrates, and using this particular experimental system). It is concluded that the vascularly and luminally perfused rat jejunum in vitro appears to be the best available preparation for the study of the absorptive, translocation and metabolic functions of the small intestine.

The bifidobacteria are among the microbial genera normally found in the gastrointestinal tract of pigs and other mammals. They are claimed to beneficially influence the health of the host by protecting against intestinal infections and have therefore been advocated and used as probiotics in man and animals. The purpose of this study was to investigate the bifidobacteria of the pig gut with a view to selecting strains suitable for probiosis. Bifidobacteria were isolated from the faeces of pigs by quantifying fermentation end-products and by assaying for the unique bifidobacterial enzyme fructose-6-phosphate phosphoketolase. Species identification was achieved by analysis of carbohydrate utilisation ability and isozyme mobility on polyacrylamide gels. A number of bifidobacteria of indeterminate species were found. Bifidobacterial isolates were further characterised to identify their resistance to heat and bile salts and sensitivity to oxygen. Certain indigestible carbohydrates have been proposed to selectively stimulate bifidobacteria in the hindgut when fed to animals. A range of these carbohydrates were screened for ability to support growth of the isolates in vitro using a microtitre plate assay. Bifidobacteria were screened for antagonistic activity against a number of intestinal pathogens and other bacteria likely to compete for the same ecological niche. A number of inhibitory strains were found. The inhibitory effect was due solely to the acidic end-products of bifidobacterial fermentation. A mixed flora fermenter simulation of the porcine ileum was used to study the effect of bifidobacterial and fructo-oligosaccharide supplementation on the survival of an enterotoxigenic Escherichia coli strain. Although the supplementation did not increase the rate of disappearance of the E. coli strain from the fermenter contents, an increase in acid production by the fermenter contents was noted. This may represent an advantageous consequence of bifidobacterial fermentation in vivo.

Postnatal growth of the small intestine can be divided into two separate but complementary mechanisms; mucosal growth and organ (cylindrical) growth. Mucosal growth, observed by increasing villus area and crypt length, is upregulated during weaning, compared to pre or post-weaned time frames. The dynamics of organ growth, mediated by the process of crypt fission, is unknown during this period of postnatal development. Keratinocyte Growth Factor (KGF) and Hepatocyte Growth Factor (HGF) are mesenchymally derived ligands which have been demonstrated to have trophic effects on the epithelium of the gastrointestinal tract in vitro and in vivo during embryonic development, repair/restitution and tumour progression. This study explores the hypothesis that small intestine organ growth occurs independently to that of mucosal growth and the mechanisms of growth are mediated by differential expression of either HGF or KGF within the pericryptal mesenchyme derived cells (fibroblasts). Alternatively, the corresponding receptors for these ligands, c-met and bek, may exhibit differential expression within the proliferative compartment of the crypts. The indices of mucosal and organ growth were compared at various ages during early postnatal life (suckling), then early, middle and late weaning through to adult animals. Microdissection techniques utilising whole tissue samples enabled microscopic evaluation of growth. The assessment of KGF, bek, HGF and c-met was also undertaken using immunohistochemistry on formalin fixed, paraffin processed sections of rat jejunum. The highest rate of organ growth occurred during weaning and was immediately preceded at day 14 (of age) by a peak in the incidence of branching crypts. KGF immunolabelling was observed within the mesenchymal cells at the tips of the villus from mid-weaning onwards but at no stage within pericryptal fibroblasts. Both KGF and bek were demonstrated within the crypt epithelium, with highest levels observed during weaning. Immunolabelling for HGF demonstrated an ubiquitous distribution within both epithelial and mesenchymal tissues at all ages, whilst the expression of c-met was in the crypt cell compartment was limited to the time of weaning. The use of an in vivo blockade technique utilising an anti-HGF (D9) antibody from age 7 to 14 days did not demonstrate any reduction of the indices of organ or mucosal growth. These results suggest that rate of organ and mucosal growth increase concurrently during weaning. The demonstration of both bek and c-met in the crypt cell population during this period suggests that KGF and HGF are potential mediators of organ or mucosal growth, despite only HGF being demonstrated in the pericryptal mesenchymal derived cells. Further, the expression of KGF and HGF at sites beyond the crypts suggest these ligands play a greater role in the development of the rat small intestine during postnatal growth. / thesis (MApSc(BiomedicalScience))--University of South Australia, 2005.