High fruit and vegetable intake correlates well with positive health outcomes and reduced rates of chronic diseases such as cardiovascular diseases, type 2 diabetes, cancers, neurological decline and metabolic diseases. Bioactive phytochemicals such as polyphenols, carotenoids, vitamins, minerals and others present in fruit and vegetables may be at least partly responsible for this effect. The precise mechanisms of action for several groups of compounds, and their potential impacts upon each sphere of health have not yet been fully elucidated. This work provides novel analysis of the total antioxidant capacity and total polyphenol content of 23 commercially available vegetable juices which are available on the UK market, utilising 6 biochemical assays, before and after in vitro digestion. Beetroot juice had the highest total antioxidant capacity and total polyphenol content regardless of the method of analysis, and both measures either increased or remained stable following in vitro digestion. A commercially available beetroot juice shot was selected as a viable method to increase bioactive phytochemical intake in the general population and its carbohydrate and phytochemical profiles were obtained by HPLC and GCMS analysis. The impact of consuming beetroot juice (70 mL) as part of a mixed meal or consuming beetroot juice alone (225 mL) on postprandial glucose and insulin responses was then assessed to investigate a potential role for these phytochemicals in the control of diseases featuring insulin resistance as a primary symptom, such as type 2 diabetes and metabolic syndrome. Consumption of 70 mL of beetroot juice as part of a mixed meal containing a total of 50g available carbohydrate resulted in a significant (P<0.05) reduction in postprandial insulin concentration at 15 minutes compared to a matched control meal. Consumption of 50g available carbohydrate as 225 mL beetroot juice resulted in a significant (P<0.05) lowering of blood glucose in the 0-30 minute segment of the glucose response and a significant (P<0.05) lowering of the insulin response in the corresponding 0-60 minute segment, compared to a matched control beverage. Insulin sensitivity was estimated using a mathematical model and non-significantly increased with the dose of beetroot juice. Phytochemicals in beetroot juice, namely betanin and its degradation products, alone or in combination with polyphenolic compounds, may improve the postprandial glycaemic state with relevance to diseases characterised by insulin resistance in a similar pattern to other investigated foods such as berries and cinnamon. Further research should aim to further quantify the effects of beetroot juice phytochemicals on postprandial insulinaemia using larger cohorts and diseased populations. Phytochemicals such as neobetanin should also be given in isolation to clarify the compounds responsible for the observed effects. The potential role of phytochemicals in potentiating endogenous nitrate conversion is also worthy of further investigation.

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Glutathione S-transferase (GST) is an important xenobiotic metabolising enzyme which has been extensively studied in the liver. In the first part of this study immunohistochemistry was used to identify the presence and histological localisation of different GST isoenzymes in various gastrointestinal tract tissues in the human in health and disease. GSTP was found throughout the gastrointestinal and biliary tract whilst the position and quantity of other isoenzymes varied locally. Increased expression of GSTP was observed in cholangiocarcinoma and colonic adenocarcinoma, but not hepatocellular carcinoma. In the pancreas GSTP was present in ductal and centroacinar cells, whilst GSTA was present in acinar cells. GSTM was universally present in the cells of islets of Langerhan, not demonstrating genetic polymorphism. In both chronic pancreatitis and pancreatic carcinoma increased expression of GSTP was demonstrated. Using affinity chromatography and high performance liquid chromatography GSTA, P and M were purified from human pancreatic tissue. A novel GST isoenzyme, which ran on SDS/PAGE, similar to GSTP, was identified, purified and confirmed by Western blot analysis to be a GSTA. Feeding rats exclusively on raw soya flour resulted in pancreatic hypertrophy and eventually carcinoma. Serial measurements of GST activity showed only a minor reduction with short term feeding which returned to normal with chronic administration contrary to what has been proposed (Ross & Barrowman, 1987). No selective change in GST isoenzymes was identified. A dominant cytoplasmic protein, shown both enzymatically and by Western blot analysis to be α-amylase fell dramatically with short term administration recovering only marginally with chronic administration.

In this thesis the <I>in vitro</I> ability of gallbladder epithelium to secrete hydrogen ions, the mechanism and regulation of the acidification process and its pathophysiological consequences to calcium salt solubility in bile, were studied. The human gallbladder epithelium was capable of secreting hydrogen ions, through a sodium/hydrogen apical exchange system (antiport) and its acidification ability was found reduced with inflammation. The normal bovine gallbladder epithelium was also capable of secreting hydrogen ions through a sodium/hydrogen apical exchange system that was ouabain and amiloride sensitive. Acidification was histamine dependent because it was stimulated by histamine and inhibited by H<SUB>1</SUB> and H<SUB>2</SUB> antagonists. Cholecystokinin augmented acidification but acetazolamide (carbonic anhydrase inhibitor) did not have any effect on acidification. Normal bovine gallbladder bile had striking similarities with human and bile acidification significantly improved calcium carbonate solubility but had no effect on calcium phosphate solubility. In addition the anatomical similarities of human and bovine gallbladders were confirmed by pathology studies. Primary gallbladder epithelial cell short-term cultures were developed to enable a closer study of the biological properties of the gallbladder epithelial cell. Acid production as well as the modulator effect of amiloride and histamine was visualised in gallbladder epithelial cell suspensions with the use of the fluorescent dye, acridine orange. In this thesis it was demonstrated that the gallbladder epithelium secretes hydrogen ions into the bile through a sodium-hydrogen apical antiport system and this may serve as a protective mechanism against calcium carbonate precipitation.

Current ideas of human gut immunity are derived heavily from animal studies; the few human studies have mainly addressed cellular aspects, and those on immunoglobulins and antibodies have used serum (or rarely jejunal aspirate) to investigate immune events at the gut level, assuming that these fluids are representative of the gut. The aims of this thesis were to develop, evaluate, and apply protocols for the study of gut secretions in man. Saliva was examined as a secretion in its own right, to investigate the relationship between systemic (serum) and mucosal antibodies, and as a potential mirror of immune events occurring more distally in the gut. Methods for the collection and processing of jejunal fluid, and intestinal fluid obtained via whole gut irrigation were then developed. Enzyme linked immunosorbent assay techniques were used to measure total immunoglobulin concentrations and antibody levels to three representative dietary protein antigens, in saliva, intestinal fluid, jejunal aspirate, and serum. Healthy subjects and groups of patients with a variety of gut diseases likely to have increased immunity were examined. There was great physiological variation in immunoglobulin concentrations and antibody levels in saliva, which were universally decreased by eating. In patients on a gluten-free or elemental diet, salivary antibody levels were maintained despite a lack of antigen stimulation. Neither saliva nor serum reflected immunity in gut lavage fluid, the only regularly observed relationship being a positive correlation between serum and saliva, especially after gut mucosal damage has occurred. Differences between control subjects and patients with coeliac disease were insufficient to allow the use of saliva as a diagnostic or clinical tool. Smoking strikingly influenced immunoglobulin concentrations, with a dose-dependent and reversible decrease in salivry IgA, and an increase in IgM. These alterations were not due to changes in the numbers of immunoglobulin-producing cells in the parotid gland. Smoking may also decrease IgA in lavage fluid.

Malnutrition is associated with an increased incidence of morbidity and mortality after surgical operations. The acute phase plasma protein response is believed to be an important mechanism in the repair and resolution of inflammation following operation. This study attempted to determine if the acute phase response is attenuated by malnutrition and thus a possible contributor to the observed increase in the incidence of complications after surgery. Four groups of patients were studied. Normally nourished patients with benign disease of the upper gastrointestinal tract, normally nourished patients with malignant disease of the oesophagus or stomach, malnourished patients with malignant disease of the oesophagus or stomach and malnourished patients with malignant disease of the oesophagus or stomach who had received intravenous nutrition for 7 days prior to operation. Firstly, nutritional indices of the patients were assessed. Then, in the in vivo study, the acute phase proteins C-reactive protein, alpha₁-antitrypsin, and alpha₁-acid glycoprotein were measured sequentially following radical surgery for upper gastrointestinal carcinoma in groups 2, 3 and 4. Finally liver biopsies from all 4 groups were incubated in vitro in the presence of interleukin-1 an acute phase stimulant and the production of C-reactive protein measured using an ELISA assay. The magnitude of the acute phase plasma protein response in vivo and in vitro was compared amongst the groups and correlations were sought between the magnitude of the acute phase plasma protein response in vivo and in vitro and the various nutritional indices. No influence of nutritional factors could be demonstrated in either arm of the study. This could be a genuine finding or the result of inadeguacy in the design of the study or the power of the study in relation to the number of patients studied. Further studies using methods to improve the preservation of the liver slices by shorter incubation and improved oxygenation are suggested.

Advances in gastrointestinal motility are hampered by current methodology. This thesis sought to evaluate novel methods for measurement of gastrointestinal motor physiology, including a) computerised analysis of gastric and small bowel motility and b) a non-invasive method of detection of gastrointestinal motor activity, termed Surface Vibration Analysis (SVA). SVA detects vibrational energy emanating from gastrointestinal contractions, using a transducer placed on the abdominal surface. The main objectives of this thesis were as follows: 1. Computerised analysis of gastrointestinal motility. Algorithms for peak detection, measurement of peak amplitude and duration, exclusion of artefact, identification of the individual phases of the Migrating Motor Complex (MMC) were constructed and validated against conventional manual analysis. This development was essential for the assessment of <i>objective 2</i>. 2. Comparison of SVA against intraluminal manometry. The SVA response was decreased during periods of motor quiescence (phase I of the MMC) as compared to motor activity (phases II & III of the MMC). This SVA response was increased by instillation of both gas and fluid in the upper gastrointestinal tract as compared to gas and fluid evacuation (<i>GFE</i>). There was no correlation between individual manometric contraction parameters and the SVA response. 3. Effects of intraluminal content on motility measurements. <i>GFE</i> reduced the duration and contraction amplitude of phase II of the MMC and increased the duration of phase I. Instillation of both gas and fluid had the converse effect. The parameters of phase III were unaffected. 4. Evaluation of SVA in chronic intestinal obstruction. SVA was applied to the detection of subacute intestinal obstruction in 46 patients and compared to 18 volunteers. On the basis of visual analysis of the SVA tracing, a positive diagnosis of subacute intestinal obstruction was made in 12 out of 14 patients subsequently proven to have adhesions at laparotomy.