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Title: Observations on the metabolic role of the rumen epithelium
Author: Weekes, Timothy Edward Charles
Awarding Body: University of Aberdeen
Current Institution: University of Aberdeen
Date of Award: 1972
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Attempts were made to produce a viable suspension of rumen epithelial cells, using a variety of chemical, physical and enzymic treatments. Although treatment with a papain, cysteine and EDTA admixture resulted in a high yield of cells, the metabolic properties of these cells were abnormal, as judged by rates of oxygen uptake, lactate formation in vitro from added propionate and levels of enzyme activity. Optimum assay procedures were determined for the estimation of propionyl-coA synthetase, propionyl-coA, carboxylase, NADP-malate dehydroganase, lactate dehydrogenase, a spartate aminotransferase, alanine aminotransferase, b-hydroxybutyrate dehydrogenase, pyruvate carboxylase and phosphoenolphyruvate carboxykinase activities in the rumen mucose. The subcellular distribution of enzyme activities was estimated. A standard incubation procedure was developed to study the formation of loctate and pyruvate by ruman mucosa incubated in vitro with added propionate. Lactate end pyruvate formation was partially inhibited when high concentrations of propione to were present, but the concentration of propionate resulting in an inhibition varied between experiments. Lactate and pyruvate were also formed in the presence of valerate. Lactate and pyruvate were formed when rumen papillae were incubated with glucose, the presence of glucose and propionate resulting in a synergistic increase in lactate and pyruvate formation. Glucose was not synthesized by rumen papillae. The presence of ammonium chloride together with propionate inhibited lactate formation but stimulated pyruvate formation by rumen papillae. The activity of b-hydroxybutyrate dehydrogenase was greater using samples of mucosa bearing few papillae. Propionate metabolism was probably limited by the rate of propionate activation. The activity of propionyl-coA synthetase was insufficient to account for the rates of lactate and pyruvate formation in vitro. The effects of reproductive status on the sheep rumen mucosa was investigated in two studies using housed sheep. In the first study the weight of rumen mucosa rose linearly from 3 weeks ante partum to 6 weeks post partum. A similar increase was observed in the amount of crude protein, RNA and DNA in the rumen mucose, but the total amount of collagen in the rumen mucosa remained constant. A similar rise also took place in NADP-malato dehydrogenase activity per unit tissue weight. When this study was repeated, using ewes housed indoors and fed to appetite on a highly digestible diet, the food intake of the eves increased rapidly during early lactation. The dry matter and apparent nitrogen digestibilites of the diet were similar using pregnant ewes fed to appetite and post-weaning sheep fed a restricted amount of food, when lactating animals were used. The weight of rumen mucosa increased during lactation and declined after the lambs had been weaned, when the food intake of the ewes was restricted. The weight of rumen mucosa was closely correlated with the food intake of the ewes in the week preceding slaughter. Subcutaneous injections of L-thyroxine had very little effect on the daily food intake of ewes, or on the weight of rumen mucosa or the formation of lactate and pyruvate in vitro from added propionate. The effects of diets of dried grass, barley or maize on the rumon mucosa growing lambs were studied and the effects of including fish meal or urea as a source of supplementary nitrogen in a barley diet were compared. The rumen mucosa was heavier when concentrates were fed, this being associated with pathological changes and with a high concentration of DNA and more especially RNA in the rumen mocosa. Only very small amounts of lactate and pyruvate were formed in vitro by rumen mucosa taken from sheep fed on dried grass; no differences due to diet were found in animals fed on any of the concentrate diets. Glutamate dehydrogenase activity per unit tissue weight was greater in mucosa taken from sheep fed on concentrates rather than dried grass, and was also greater when fish meal rather than urea was used as a source of nitrogen in a concentrate ration. Glutamate dohydrogenase activity was located histochemically, activity being concentrated in the stratum granulosum. It is suggested that glutamate dehydrogenase activity in the rumen mucosa is involved in the process of keratinization. Lactate formation and glucose uptake were observed in vivo by the tissues drained by the portal bed in sheep when VFA solution were infused into the reticulorumen. The glucose uptake could account for a substantial part of the lactate formed. It is concluded that the conversion of propionate into lactate and pyruvate in the rumen mucosa is not a means of conserving substrates for hepatic gluconeogenesis, but may be a means of supplying reduced NADPH in the epithelial cells.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available