Browsing by Subject "Pancreas"

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Influence of selenium on pancreatic carcinogenesis and the role of the selenoproteins cytosolic and mitochondrial thioredoxin reductase in the pancreas
(2007) Aichler, Michaela; Graeve, Lutz
Pancreatic ductal adenocarcinoma (PDA) is one of the most aggressive cancers in humans. It is the fourth leading cause of cancer related deaths in Germany and in the United States. Most PDA occurs sporadically, but there are also approximately 5-10% of patients with a family history of pancreatic cancer. The high mortality of PDA is attributed to a lack of early detection methods and poor efficacy in therapies for advanced disease. As an alternative, preventive strategies in individuals with familial pancreatic carcinoma should be considered. Several epidemiological studies showed an inverse correlation between selenium-intake and mortality of certain types of cancer and particularly in gastrointestinal cancers. To this end, in the first part of this study, the influence of selenium as a preventive nutritional additive was investigated in a genetically defined pancreatic cancer mouse model, the EL-TGFatg/+;p53+/- mouse strain. As a major finding, the differentiation grade of the pancreatic carcinomas was heavily influenced by the selenium status. In the selenium-deficient group there were more non-differentiated pancreatic carcinomas than in the selenium-adequate group, which highlighted the implication of selenium or selenoproteins in tumour differentiation. Unexpectedly, however, there was no protective effect of selenium on total or pancreatic tumour latency. Within the selenoproteins, the thioredoxin reductases are strong candidates which may influence cell death and differentiation in pancreatic carcinogenesis. Their function is generally associated with tumour proliferation and also linked to the activation of the tumour suppressor p53. Consequently, the role of the thioredoxin reductases in the pancreas was studied in the second part of this thesis. The enzymatic activity of cytosolic (TXNRD1) and mitochondrial (TXNRD2) thioredoxin reductase in the pancreas and other organs was determined in relation to the selenium-status. TXNRD1 activity in the pancreas was moderate and decreased under selenium deficiency. TXNRD2, instead, showed very high pancreatic activity in relation to other organs and its activity was even increased under selenium-deficiency emphasising its special role in this organ. To further investigate the function of Txnrd1 and Txnrd2 in the pancreas, tissue-specific knockout mice were created and characterized. The Txnrd1 knockout mice did not show an overt phenotype. Interestingly although, pancreatic acinus cells in one year old mice showed a disturbed rough endoplasmic reticulum and alterations in serum amylase and lipase. These mice also had an impaired glucose tolerance. The pancreas of Txnrd2 knockout mice showed severe chronic pancreatitis and pancreatic atrophy at the end of an observation period of one year. The progressive pathogenic process started with mild pancreatitis, developing spontaneously at an age of four weeks. The chronic stage was characterized by the formation of different types of acinar-to-ductal metaplastic lesions, which could be classified in part as early precursor lesions of pancreatic carcinomas. The endocrine pancreas was not affected. The pancreas-specific Txnrd2 knockout mouse strain is the first genetically modified mouse model spontaneously developing acute and chronic pancreatitis. This strain constitutes a unique and powerful tool to model pancreatic pathogenesis, especially the yet unresolved process of transformation from inflammatory to malignant disease.
The exocrine pancreatic secretion in pigs and its hormonal regulation as influenced by carbohydrates and fats given per os or infused intraduodenally
(2000) Jakob, Stefan; Mosenthin, Rainer
In the present study the influence of carbohydrates in the form of potato fibre (NSP) and of different fats on the exocrine pancreatic secretion and on the regulative hormonal mechanisms was investigated. When feeding a diet supplemented with 2 potato fibre all measured parameters, e.g. volume of pancreatic secretion, protein output and total trypsin, lipase and alpha-amylase activities increased in pancreatic juice. Simultaneously there was a trend towards a decrease in plasma concentration of CCK. After the intraduodenal infusion of medium chain triglycerol (mct: glyceroltricaprylat), long chain triglycerol (lct: glyceroltristearat) or vegetable oils (olive oil or coconut oil) in all treatments a prandial peak was found as a direct reaction on feed intake for volume of secretion, total protein and colipase contents as well as the total activities of trypsin and lipase. After application of mct the secretion course occured in two phases. In phase 1 a parallel prandial increase in volume of secretion, total protein and colipse content as well as total activities of trypsin and lipase was found. For the same parameters in the second phase 60 min postprandially much lower values were observed compared to the preprandial values. The courses of the curves differed for total lipase activities. The diurnal course of plasma levels of CKK and PYY was not influenced. After coconut oil treatment the course of volume secretion was characterized by 2 phases. After a prandial peak in phase 1 the values decreased by 100 below the preprandial starting values. After the application of olive oil the specific lipase activity was elevated five times. In case of coconut oil there was only a prandial increase by 2.5. It is suggested that the exocrine pancreas responds differently in its secretion to different fat sources. Adaptation is probably regulated through a feedback-mechanism whereas CCK and PYY are of minor importance. Probably other hormones as e.g. secretin have a regulative