Animal & Avian Sciences Theses and Dissertations
Permanent URI for this collectionhttp://hdl.handle.net/1903/2741
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Item ENERGY METABOLISM IN DEVELOPING CHICKEN LYMPHOCYTES DURING THE EMBRYONIC TO POSTHATCH TRANSITION(2007-07-26) Rudrappa, Shashidhara Govindareddy; Porter, Tom E; Humphrey, Brooke D; Animal Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)In chickens, the primary energy substrate is lipid during embryogenesis and carbohydrate after hatch. Accordingly, chicks adapt their metabolism to utilize glucose after hatch; however, little is known about metabolic adaptation in developing lymphocytes. Therefore, the objective of this dissertation was to examine metabolic adaptation in developing lymphocytes and the associated impact on their development. The first objective examined energy substrate utilization in bursacytes and thymocytes during the embryonic to posthatch transition. Glucose metabolism increased in both lymphocyte populations during the first two weeks posthatch due to increased glucose transporter-3 mRNA abundance, glucose uptake and hexokinase activity. Additionally, some of these metabolic markers were positively correlated with the serum glucose concentration. Glutamine metabolism increased in bursacytes only, and lipid metabolism was unaltered in both populations. Collectively, glucose is a preferred energy substrate for lymphocytes posthatch, and glucose utilization by developing lymphocytes may be related to the serum glucose concentration. The second objective determined the effect of glucose availability on thymocyte metabolism, energy status and survival. Embryonic thymic lobes were grown in culture in media containing varying glucose concentrations. Thymocyte glucose metabolism and mitochondria membrane potential were highest in 15 mM glucose and apoptosis was highest in 5mM glucose. Collectively, glucose availability regulates glucose metabolism in thymocytes, and these changes in glucose metabolism were related to thymocyte energy status and survival. The third objective determined the effect of glucose availability on T cell development. Thymocyte Interleukin-7Rα (IL-7Rα) mRNA abundance and CD4+ T cell numbers over the culture period were dependent upon glucose availability. Between 12 and 24 h, thymocyte IL-7Rα mRNA abundance increased in 5 mM increased 1.74-fold, while it decreased in 15 mM by 58.6%. CD4+ numbers decreased with time in 5 mM, whereas they increased with time in 15 mM. T cell receptor (TCR) β excision circles were higher in 15 mM compared to 5 mM at 12 h. Glucose availability alters TCR β rearrangement, IL-7Rα gene expression and CD4+ T cell development, which may influence naïve T cell generation. As thymocytes develop in a low glucose environment in ovo, this may be one factor that limits T cell development until hatch.Item Regulation of macronutrient metabolism by the gastrointestinal tract of ruminants(2006-07-28) El-Kadi, Samer Wassim; Bequette, Brian J; Animal Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)We set out to test the hypothesis that the gastrointestinal tract (GIT) of ruminant animals catabolizes amino acids (AAs) preferentially. We sought to determine whether this catabolism represents an obligate requirement, and whether this requirement stems from the need to generate energy or support other metabolic demands. The aim was to determine the composition of macronutrients (AAs, short chain fatty acids, and glucose) utilized by the GIT, and the influence of general and specific nutrient supplies on their routes of metabolism. Increasing protein supply to the small intestine did not alter the total amount of glucose removed by the GIT indicating, that glucose removal and therefore utilization is obligatory. In contrast, the net removal of AAs occurred at a constant proportion of arterial and luminal supplies. This translated to larger amounts of AAs removed from blood circulation, and from the lumen of the small intestine in response to increased small intestinal and blood supplies. In this respect, the net absorption of branched chain AAs was, unlike other essential AAs lower than 100%. Further, glutamate and glutamine net appearance across the whole GIT and small intestine was unaffected by protein supply. The disproportionate utilization of BCAA, glutamate, and glutamine as compared to other AAs suggested that their metabolism occurred toward specific metabolic requirements, possibly energy production. When Krebs cycle metabolism was investigated using individual AAs, glucose, and short chain fatty acids, leucine and valine did not contribute to the flux of Krebs cycle intermediates. Conversely, α-ketoglutarate flux originated mainly from glutamate, and to a lesser extent from glutamine. Though glucose was metabolized to pyruvate and lactate, glucose did not contribute to Krebs cycle intermediates. Overall, these results indicated that glutamate plays an important role in energy metabolism, and in insuring replenishment of Krebs cycle intermediates that leave the cycle via cataplerosis. Yet, the results raised new questions that ought to be addressed in future studies. The fate of glutamine carbon, the metabolic significance of leucine and valine deamination, and the role of glucose partial catabolism to lactate need to be investigated.