PubMed · 4103696
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A Hodgkinson, M Peacock, B E Nordin, C A Pegg, J M Stowers, W Michie. 1971-07-03. Asymptomatic hyperparathyroidism.. https://doi.org/10.1016/s0140-6736(71)90042-0
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The effects of the oxidant tert-butylhydroperoxide (t-buOOH) on carbachol-stimulated pancreatic secretion in the vascularly perfused rat pancreas have been studied in parallel with [Ca2+]i signalling and amylase output in perifused rat pancreatic acinar cells. Perfusion of the pancreas with t-buOOH (0.1-1 mM) caused a rapid and irreversible inhibition of carbachol-stimulated (3x10-7 M) amylase and fluid secretion. Pre-perfusion of the pancreas with vitamin C and dithiothreitol or a cocktail of GSH and GSH-precursor amino acids provided only marginal protection against the deleterious effects of t-buOOH, even though GSH levels were elevated significantly. In perifused pancreatic acini, repetitive [Ca2+]i spikes evoked by carbachol (3x10-7 M) were sustained for 40 min. t-buOOH (1 mM) acutely increased the amplitude and duration of Ca2+ spikes, then attenuated Ca2+ spiking and subsequently caused a marked and sustained rise in [Ca2+]i. t-buOOH-induced alterations in carbachol-stimulated [Ca2+]i signalling and amylase release in perifused pancreatic acini were prevented by vitamin C. Although vitamin C restored impaired Ca2+ signalling and maintained amylase output in pancreatic acini, it seems likely that oxidative stress inhibits fluid secretion irreversibly in the intact pancreas, resulting in a loss of amylase output. Thus, perturbations in [Ca2+]i signalling may not fully explain the secretory block caused by oxidative stress in acute pancreatitis.
Misfolding or unfolding of polypeptides can occur as a consequence of environmental stress and spontaneous mutation. The abundance of general chaperones and proteases suggests that cells distinguish between proteins that can be refolded and "hopeless" cases fated to enter the proteolytic pathway. The mechanisms controlling this key metabolic decision are not well understood. We show here that the widely conserved heat shock protein DegP (HtrA) has both general molecular chaperone and proteolytic activities. The chaperone function dominates at low temperatures, while the proteolytic activity is present at elevated temperatures. These results show that a single cellular factor can switch between two key pathways, controlling protein stability and turnover. Implications of this finding for intracellular protein metabolism are discussed.
The role of intrapancreatic neurons in the action of cholecystokinin (CCK) on pancreatic exocrine secretion of the totally isolated, perfused rat pancreas was investigated. Intrapancreatic neurons were activated by applying electrical field stimulation (EFS) to the isolated pancreas for 45 min. When applying EFS, spontaneous pancreatic secretions of fluid and amylase increased until the second 15-min period of EFS and then decreased during the third 15-min period. Atropine (2 microM) notably reduced the EFS-evoked pancreatic secretions of fluid and amylase. The CCK-induced (10 pM) pancreatic secretions of fluid and amylase elevated further in the first 15-min period of EFS and then gradually resumed to the levels observed during application of CCK alone in the third 15-min period of EFS. However, the CCK-induced pancreatic secretions remained elevated even in the third 15-min period of EFS when an action of endogenous somatostatin was inhibited by cyclo-(7-aminoheptanonyl-Phe-d-Trp-Lys-Thr[BZL]) (10 nM) or pertussis toxin (200 ng/ml). EFS further elevated spontaneous exocrine secretion by the cysteamine-treated (300 mg/kg) pancreas, but this was markedly reduced, to normal levels, by infusing somatostatin (100 pM). EFS increased the numbers of immunoreactive somatostatin cells in the Langerhans' islets. The results indicate that intrapancreatic neuronal activation influences CCK-induced pancreatic secretions in a dual-phase pattern in the rat: an increase during the early phase and a decrease during the late phase. Endogenous somatostatin released from the islets appears to inhibit the enhancing effect of neuronal activation on CCK-induced pancreatic secretion. Of the intrapancreatic neurons, the cholinergic ones appear to predominate in EFS's effects on CCK-induced pancreatic secretion.