Effects of feeding, fasting, and caerulein treatment on ornithine decarboxylase in rat pancreas

Life with the pancreas: A personal experience

This review article has primary objective to summarize pancreatic research which has been done in our laboratory since 1965, the first year of the author's registration in the Ph.D. program at the University of Sherbrooke (Canada). It covers the following major topics of pancreatic physiology: controls of pancreatic adaptation to diet, control of pancreatic enzyme secretion, control of pancreatic enzyme synthesis, control of pancreatic growth, intracellular events stimulated during pancreatic growth, pancreas regeneration after pancreatitis and pancreatectomy, the pancreatic cholecystokinin receptor types 1 and 2, growth control and cell signaling in pancreatic cancer cells and finally, cystic fibrosis.

Polyamine biosynthesis is critical for growth and differentiation of the pancreas

The pancreas, in most studied vertebrates, is a compound organ with both exocrine and endocrine functions. The exocrine compartment makes and secretes digestive enzymes, while the endocrine compartment, organized into islets of Langerhans, produces hormones that regulate blood glucose. High concentrations of polyamines, which are aliphatic amines, are reported in exocrine and endocrine cells, with insulin-producing β cells showing the highest concentrations. We utilized zebrafish as a model organism, together with pharmacological inhibition or genetic manipulation, to determine how polyamine biosynthesis functions in pancreatic organogenesis. We identified that inhibition of polyamine biosynthesis reduces exocrine pancreas and β cell mass, and that these reductions are at the level of differentiation. Moreover, we demonstrate that inhibition of ornithine decarboxylase (ODC), the rate-limiting enzyme in polyamine biosynthesis, phenocopies inhibition or knockdown of the enzyme deoxyhypusine synthase (DHS). These data identify that the pancreatic requirement for polyamine biosynthesis is largely mediated through a requirement for spermidine for the downstream posttranslational modification of eIF5A by its enzymatic activator DHS, which in turn impacts mRNA translation. Altogether, we have uncovered a role for polyamine biosynthesis in pancreatic organogenesis and identified that it may be possible to exploit polyamine biosynthesis to manipulate pancreatic cell differentiation.

The role of the circadian clock system in nutrition and metabolism

Mammals have an endogenous timing system in the suprachiasmatic nuclei (SCN) of the hypothalamic region of the brain. This internal clock system is composed of an intracellular feedback loop that drives the expression of molecular components and their constitutive protein products to oscillate over a period of about 24 h (hence the term 'circadian'). These circadian oscillations bring about rhythmic changes in downstream molecular pathways and physiological processes such as those involved in nutrition and metabolism. It is now emerging that the molecular components of the clock system are also found within the cells of peripheral tissues, including the gastrointestinal tract, liver and pancreas. The present review examines their role in regulating nutritional and metabolic processes. In turn, metabolic status and feeding cycles are able to feed back onto the circadian clock in the SCN and in peripheral tissues. This feedback mechanism maintains the integrity and temporal coordination between various components of the circadian clock system. Thus, alterations in environmental cues could disrupt normal clock function, which may have profound effects on the health and well-being of an individual.

Effects of Freund's complete adjuvant on the diurnal rhythms of neuroendocrine processes and ornithine decarboxylase activity in various tissues of male rats

The aim of this study was to investigate the effects of Freund's complete adjuvant (FCA) on the diurnal rhythms of hormonal parameters in serum and ornithine decarboxylase (ODC) activity in various tissues of male rats. On days 1-2 after FCA, increase of ODC activity (used to evaluate the level of activation) was observed in the hypothalamus, pituitary gland, adrenal medulla, adrenal cortex, liver and lymphoid tissues, while the ODC activity in the kidney was reduced. This was accompanied by an increase in serum corticosterone. On days 3-4 after FCA, ODC activity remained elevated in the pituitary gland, liver and lymphoid tissues, while the ODC activity in the testes and pancreas was reduced; kidney ODC activity returned to baseline. This was associated with increased serum levels of prolactin (Prl) and luteinizing hormone, but decreased growth hormone, testosterone and insulin. The increase in ODC activity in the thymus, as well as the reduced ODC activity in the testes and kidney, can be obtained with paraffin. Furthermore, bromocryptine microcapsules (CBLA) reduced the FCA-induced increase of ODC activity in the pituitary gland, liver and lymphoid tissues (days 3-4) but did not affect the changes in other tissues. The increase in ODC activity in the pituitary gland, liver and lymphoid tissues is specific for FCA. A role for Prl in the induction of ODC in liver and lymphoid tissues is suggested by the fact that CBLA suppresses this enhancement.

Secretory activity and trophic effects of epidermal growth factor in the rat pancreas

This study was to investigate whether epidermal growth factor (EGF) may induce any long-term effect on pancreatic exocrine function in vivo as well to evaluate the chronic effects of EGF on pancreatic growth in rats. Rats were treated with EGF (10 micrograms/kg) for 5 or 7 days. EGF infused intravenously (2 micrograms/kg/h) in anaesthetized and pretreated rats for 5 or 7 days with EGF caused a slight decline flow rate after 1 h of EGF infusion compared to control values. In contrast, EGF evoked a increase in amylase secretion. This stimulatory effect was much larger in EGF-pretreated rats for 7 days, whereas the total protein output was unchanged. The trophic parameters which include pancreatic weight, total protein and total contents of DNA and RNA relative to body weight were not significantly different in any treated group. Only the pancreatic amylase content was increased significantly after 7 days of treatment with EGF. The present study fails to observe a stimulatory role of EGF on pancreatic growth in rats, but may participate in the regulation of pancreatic exocrine function in vivo.

Biochemical and morphological changes that characterise recovery from necrotising biliary pancreatitis in the opossum

The events that characterise recovery from severe biliary pancreatitis have not been defined. This study used a reversible model of necrotising pancreatitis, induced by obstructing the opossum common bile pancreatic duct (CBPD), to evaluate this phenomenon. The CBPD of opossums was obstructed with a balloon tipped catheter for five days and then decompressed by removal of the catheter. Recovery was evaluated 0-90 days after relief of obstruction. Serum bilirubin and amylase values rapidly declined, reaching control values 7-14 days after removal of the obstructing catheter. Pancreatic protein and amylase values were transiently increased shortly after relief of obstruction but returned to control values 21 days after decompression. Pancreatic ornithine decarboxylase activity and incorporation of [3H]-thymidine into DNA were transiently increased 14 days after duct decompression suggesting that regeneration occurs at approximately that time. Foci of pancreatic necrosis involved roughly 40% of the gland at time of decompression but these foci gradually disappeared and the gland resembled that of control animals 60 days after decompression. Evidence of fibrosis or collagen deposition in the pancreas was not noted at any time. These studies show that recovery after necrotising biliary pancreatitis occurs comparatively rapidly and the restitution ad integrum occurs. Recovery from necrotising acute pancreatitis in this model is not associated with the development of chronic pancreatitis.