Graduate Thesis Or Dissertation
 

Digesta passage rates in the rat

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  • The movements of digestion markers in the gut of the rat were investigated and the results of the investigation are reported in two manuscripts. The objective of the first study was to determine the influence of particle size of dietary wheat bran, chosen as a representative insoluble fiber, on the mean retention time (MRT) of digesta in the rat. The study design included a control group to detect the influence of particle size of digestion marker on the observed retention times. Additionally, a comparison was made between bran and the soluble fiber pectin. Both the soluble cobalt EDTA (Co EDTA) and insoluble chromium mordanted bran (CrMB), of two size ranges were administered to 4 groups of rats fed a semi-purified diet supplemented with wheat bran or pectin (10% dilution). Bran size and particulate marker size were large/large, large/small, small/small and pectin/small for the 4 groups. Mean retention times for CrMB were significantly longer in the pectin than the bran supplemented groups. Differences were not significantly different within the bran supplemented group. No significant differences were found between the rate of passage of CrMB and Co EDTA in any group. The second study was designed to identify pooling of markers in the rat gut. A mathematical model was developed as a system of equations which predicted the marker distribution along the gut following dosing. The model assumed that two pools, the stomach and cecum, were kinetically recognizable in the rat. The predicted distribution of CrMB and Co EDTA was compared to in vivo distribution at 4 h intervals by sequential termination and dissection of the animals. The smaller particle bran had a longer MRT in the cecum and a shorter MRT in the proximal colon. Total MRT to the mid-colon was similar in all bran supplemented groups. Pectin fed animals had significantly enlarged gut organs which explained the slower movement of marker in these animals. The cecum was found to delay the transit of marker from the small intestine to the proximal colon as much as 2.1 h. This delay resulted in the gut appearing as a single pool overall and therefore led the model to overpredict the initial rate of appearance of marker distal to the cecum. A streamlined system was developed to digest the fecal samples in preparation for atomic absorption spectroscopy, the method used to quantify digestion marker recovery. The development of the method is discussed and supporting data are presented on the reproducibility and limits of the method.
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