Changes of lysosomal enzymes in pancreatic juice following hepatectomy in rats]

To explore the changes in the exocrine pancreas and the possible stimulation by gut hormones of secretion of lysosomal enzyme into the pancreatic juice, we measured the caerulein-stimulated amylase output, the cathepsin B output into the pancreatic juice and the pancreatic tissue amylase and cathepsin B contents, as well as the distribution of cathepsin B in acinar cells in both the regenerating (4 days) and recovery (8 days) stages after about 70% hepatectomy in rats. The amylase output increased significantly after hepatectomy. Cathepsin B was secreted into the pancreatic juice after stimulation by caerulein in both the control and hepatectomized groups. Four days after hepatectomy, the cathepsin B output was significantly greater than that of the control group, and redistribution of cathepsin B in acinar cells was noted. These changes in cathepsin B disappeared in the recovery stage (8 days) after hepatectomy. In addition, the pancreatic amylase content was significantly higher than in the control group, but the pancreatic cathepsin B content did not change significantly. These results suggest that caerulein stimulated the secretion of lysosomal enzyme into the pancreatic juice in the same way as digestive enzymes and that lysosomal enzymes in the pancreatic juice play an important physiological role. Furthermore, these results indicate the increased synthesis and secretion of amylase in and from acinar cells as well as the fragility of acinar cells.     

Non-parallel secretion of pancreatic amylase and trypsinogen following hepatectomy in rats.

To explore the changes in exocrine pancreatic function in the stages of active regeneration and recovery after hepatectomy, we measured the caerulein-stimulated amylase and trypsinogen output in anesthetized rats 4 days and 8 days after about 70% hepatectomy. Both 4 days and 8 days after hepatectomy, the amylase output was significantly greater than in the control groups. On the other hand, 4 days after hepatectomy, the trypsinogen output was almost the same as in the control groups, and 8 days after hepatectomy, it was significantly lower than in the control groups. Thus, the secretion of amylase and trypsinogen 8 days after hepatectomy was not parallel. The amylase content of the pancreas was significantly larger after hepatectomy than in the control groups, but the trypsinogen content was significantly smaller. These results indicate a non-parallel secretion of pancreatic digestive enzymes, as well as differences in the functions of the acinar cells after partial hepatectomy, and the important role of amylase in glucose metabolism after hepatectomy.     

Peptide Leukotriene Receptor Antagonist Diminishes Pancreatic Edema Formation in Rats with Cerulein-Induced Acute Pancreatitis

Background: This study was designed to evaluate the protective effect of a peptide leukotriene receptor antagonist, pranlukast hydrate, against pancreatic injuries during acute pancreatitis. Methods: Acute pancreatitis was induced in rats by intravenous infusion of a supramaximal dose of cerulein (5 μg/kg·h for 4 h). In this model marked hyperamylasemia, a significant increase in pancreatic water content, and a significant increase in pancreatic microvascular leakage of Evans blue dye were observed. Pancreatic subcellular redistribution of the lysosomal enzyme cathepsin B from the lysosomal fraction to the zymogen fraction was also observed. Results: Pretreatment with pranlukast hydrate at a dose of 10 mg/kg (twice, 8 and 4 h before cerulein infusion) significantly inhibited these pancreatic injuries, including hyperamylasemia, increased pancreatic microvascular permeability, and redistribution of cathepsin B in pancreatic acinar cells. Conclusions: These results suggest that peptide leukotrienes may be involved in the pathogenesis of acute pancreatitis in the early stage of the disease and that peptide leukotriene receptor antagonist might be of therapeutic value for treatment of acute pancreatitis.     

Activation of proteases in cerulein-induced pancreatitis

The activation of zymogen proteases and lysosomal enzyme cathepsin B in the pancreas was investigated in cerulein-induced pancreatitis in rats. Acute pancreatitis was induced by two intraperitoneal injections of 40 micrograms/kg of body weight of cerulein at intervals of 1 h. After the first cerulein injection, the active trypsin and elastase contents in the pancreas tissues significantly increased, and reached the highest level at 3 h after the first injection, followed by peaks at 5 h in the serum amylase and lipase levels and the pancreas wet weight. Cathepsin B contents in pancreas tissues showed a parallel increase with active zymogen enzymes during the first 3 h of pancreatitis. These findings may suggest that the intracellular activation of trypsinogen is an important step in the development of cerulein-induced acute pancreatitis and that cathepsin B plays a role in the activation of trypsinogen in pancreatic acinar cells.     

Cellular alterations of parotid gland of rats with acute pancreatitis induced by cerulein.

To explore the cellular and subcellular alterations of the parotid gland during acute pancreatitis, we examined the redistribution of lysosomal enzyme, cathepsin B, along with the discharge of the LDH and cathepsin B from parotid acini of rats with acute pancreatitis induced by a supramaximal dose of cerulein (5 micrograms/kg/h for 3.5 h). Both the serum amylase level and parotid-gland amylase content were increased significantly in rats with acute pancreatitis. The dry-/wet-wt ratio ratio was significantly lower than in the control. In vitro studies showed that discharge of LDH from the parotid acini and leakage of cathepsin B from lysosomes in the acini were significantly higher than in the control. In addition, there was redistribution of the cathepsin B (shifting from the lysosomal pellet to the zymogen pellet) in the parotid gland. These results indicate that in acute pancreatitis there is edema and accumulation of amylase in the parotid glands, along with increased cellular and lysosomal fragility. Thus, there seems to be a close relationship between the exocrine pancreas and the parotid glands. Gut hormones, such as cerulein, also appear to play an important role in the pathophysiology of the parotid glands.     

塞来昔布对大鼠胰腺腺泡细胞炎症损伤的作用

背景：急性胰腺炎（AP）的发病始于胰腺腺泡细胞内胰酶的激活,造成腺泡细胞损伤。环氧合酶-2（COX-2）和核因子-κB（NF．KB）在AP的炎症反应中起重要作用。目的：观察雨蛙肽和选择性COX-2抑制剂塞来昔布对离体大鼠胰腺腺泡细胞COX-2和NF—κB表达的影响．探讨塞来昔布对腺泡细胞炎症损伤的作用。方法：分离大鼠胰腺腺泡细胞,分为对照组、雨蛙肽组（1×10^-7mol／L）和塞来昔布干预组（100μmol／L,15min后加入雨蛙肽）,分别培养1、3、6、12h。测定腺泡细胞活力、淀粉酶分泌率和乳酸脱氢酶（LDH）漏出率,逆转录聚合酶链反应（RT-PCR）和免疫细胞化学染色检测COX-2、NF—κBmRNA和蛋白表达。结果：与对照组相比,雨蛙肽组各时间点腺泡细胞活力均显著降低,淀粉酶分泌率和LDH漏出率显著增高,COX-2和NF—κBmRNA表达量显著增高,蛋白表达阳性率亦增加（P〈0．05）。塞来昔布干预组各时间点腺泡细胞活力、淀粉酶分泌率和LDH漏出率均较雨蛙肽组显著改善（心O．05）,COX-2mRNA和蛋白表达显著降低（P〈0．05）,NF—κBmRNA和蛋白表达与雨蛙肽组无明显差异。结论：塞来昔布可抑制大鼠胰腺腺泡细胞中雨蛙肽刺激的COX-2活性,从而减轻细胞炎症损伤。     

The effect of chronic alcohol administration on cerulein-induced pancreatitis

Summary Alcohol consumption is associated with pancreatitis, but the mechanism underlying this injury remains unclear. Alcohol consumption has recently been shown to increase the fragility of both rat pancreatic lysosomes and zymogen granules in vitro, which may predispose to autodigestion via the intracellular activation of digestive enzymes by lysosomal enzymes. Cerulein-induced pancreatitis is also associated with lysosomal fragility. To determine the effect of alcohol consumption on this form of pancreatic injury, the severity of pancreatitis was compared in three groups of rats following iv cerulein infusion: rats fed alcohol in a liquid diet, pair-fed dextrose controls, and chow-fed controls. The histological severity of pancreatitis induced by supramaximal cerulein infusion was not found to be increased by prior alcohol consumption. Since alcohol did not appear to increase the severity of pancreatic injury induced by cerulein, we sought to define biochemical parameters that might precede obvious injury. The subcellular distribution of cathepsin B activity and markers of lysosomal fragility were compared in the same groups of experimental animals. Cerulein infusion led to a marked redistribution of cathepsin B activity from the lysosomal to the zymogen-granule-enriched fractions. For animals killed in the fed state, a redistribution of cathepsin B activity toward the zymogen-granule-enriched fraction was also demonstrated in alcohol-fed animals compared to their pair-fed controls. However, chronic alcohol administration did not influence the effect of cerulein on subcellular cathepsin B distribution or lysosomal fragility. In this rat study, administration of alcohol did not increase the effects of supramaximal doses of cerulein on the pancreas.     

Cytoprotective effects of prostaglandins and a new potent protease inhibitor in acute pancreatitis.

The redistribution of cathepsin B, a lysosomal enzyme, from the lysosomal pellet to the zymogen pellet in the subcellular fractionation, the colocalization of cathepsin B with digestive enzyme, and increased cellular, lysosomal, and mitochondrial fragility within acinar cells have been found during the early stages of caerulein-induced acute pancreatitis in rats. In the present study, the authors investigated the protective effects of prostaglandin E1 and E2, a combined therapy of these prostaglandins, and a new, synthetic, low molecular weight protease inhibitor, ONO3307, on the exocrine pancreas in this noninvasive model of experimental pancreatitis in vivo and in vitro. Prostaglandin E2, but not E1, prevented hyperamylasemia, congestion of amylase and trypsinogen in the acinar cells, redistribution of cathepsin B, and amylase and lactate dehydrogenase discharge from the dispersed acini. It also prevented cathepsin B leakage from the lysosomes and malate dehydrogenase leakage from the mitochondria in an almost dose-dependent manner, particularly at the dose of 100 micrograms/kg/hr continuous infusion. Furthermore, the combined therapy of prostaglandin E2 with ONO3307 strongly inhibited all the parameters tested in this study. This combination therapy seems to be the most effective against secretagogue-induced pancreatic injuries. These results indicate that cellular and subcellular organellar fragility seem to be closely involved in the pathogenesis of acute pancreatitis. Prostaglandin E2 seems to have important cytoprotective effects on the biologic membranes, such as a stabilizer of lysosomal or mitochondrial membranes. In addition, these findings also suggest the crucial roles of some unknown proteases in the etiology of acute pancreatitis, and indicate the clinical effectiveness of prostaglandins and this type of low molecular weight protease inhibitor for acute pancreatitis.     

Effect of alpha-glucosidase inhibitor on exocrine and endocrine pancreatic function in rats fed a high-carbohydrate diet consisting of sucrose or glucose

The effect of the alpha-glucosidase inhibitor acarbose on pancreatic exocrine and endocrine function was studied using the isolated perfused pancreata prepared from rats fed a normal (control diet) or an acarbose-containing sucrose- (ACS diet) or glucose-supplemented diet (ACG diet) for 10 days. Pancreatic amylase and insulin contents in rats fed the ACS diet were significantly decreased compared with those in rats with the control diet. Rats fed the ACG diet, however, had normal enzyme and hormone contents. Basal and cerulein-stimulated flow rates of pancreatic juice in rats with the ACS or ACG diet were similar to those in rats fed the control diet, suggesting that the pancreata from rats treated with acarbose have normal sensitivity and responsiveness to cerulein. On the other hand, cerulein-stimulated amylase output was significantly decreased in rats with the ACS diet, but was normal in rats with the ACG diet. Insulin secretion to both glucose and cerulein stimulation in rats fed the ACS diet was reduced by approximately 55% compared with the control rats. On the other hand, rats fed the ACG diet showed normal insulin secretion to glucose stimulation, although the insulin response to cerulein stimulation was reduced by 30%. These results suggest that the addition of acarbose to the sucrose-rich diet decreases the secretory responsiveness of amylase to cerulein stimulation and that of insulin to both glucose and cerulein stimulation. All these alterations, except the sensitivity of B cells to cerulein, can be normalized by replacing sucrose with glucose.     

Effect of urinary trypsin inhibitor on pancreatic cellular and lysosomal fragility in cerulein-induced acute pancreatitis in rats

We evaluated the protective effect and the mechanism of action of the trypsin inhibitor, urinastatin, extracted from human urine, in experimental acute pancreatitis induced by a supramaximal dose of cerulein (5 g/kg/hr for 3.5 hr). Urinastatin in a dose of 10,000 units/kg/hr was given by three different methods of continuous infusion: (1) 2 hr before and during cerulein infusion, (2) only during cerulein infusion, and (3) starting 1 hr after the beginning of cerulein infusion and continued for 3.5 hr. In protocol 1 and 2 urinastatin was significantly more protective than in 3. In protocol 1 urinastatin was very protective in all parameters tested (serum amylase level, pancreatic water and amylase content, distribution of lysosomal enzymes, cellular and lysosomal fragility). These results suggest that the administration of urinastatin before and during cerulein infusion may suppress the pathogenesis and evolution of pancreatitis by inhibiting the chain reaction of pancreatic enzyme activation closely related to redistribution of lysosomal enzyme and lysosomal fragility.     

Cerulein-induced acute pancreatitis in the rat

A study was made with different doses of cerulein (2, 4, 10 and 20 g/kg) administered subcutaneously to rats by four injections at intervals of 1 hr; the aim of this work was to study exocrine pancreatic secretion of the rat under cerulein-induced acute pancreatitis, analyzing enzyme and hydroelectrolyte secretion of pancreatic juice. A further aim was to study the relationship between the dose of cerulein and the plasma levels of peptides controlling hydroelectrolyte secretion of the pancreas, like secretin and vasoactive intestinal peptide (VIP). At the lowest dose schedule, the amounts of total protein and enzymes (amylase and trypsin) in pancreatic juice decreased significantly, plasma amylase increased, and the pancreas became edematous. Higher doses magnified these effects. By contrast, ductular function (flow and HCO ₃ ^– ) was well preserved in ceruleintreated rats, and this was probably due to the significant increase in plasma levels of immunoreactive secretin whereas VIP levels were unchanged. The secretin released by treatment with cerulein is able to palliate the lack of flow from acinar origin that is affected in the process of acute pancreatitis, being a beneficial response to the cerulein treatment.     

Proliferative response of different exocrine pancreatic cell types to hormonal stimuli. I. Effects of long-term cerulein administration.

The trophic effect on the exocrine pancreas of the cholecystokinin analogue cerulein was studied in a long-term experiment (20 or 160 micrograms/kg/24 h for 14 days) in mice by measuring changes in pancreatic weight and protein, amylase, and DNA content. Further, the selective cell growth stimulation exerted by various doses of cerulein (4, 20, 54, 160 micrograms/kg/24 h) on different exocrine pancreatic cell types was studied by continuous administration of 3H-thymidine. In the first experiment animals given 20 micrograms/kg/24 h of cerulein had increased pancreatic weight and amylase and protein content, whereas the animals given the higher dose had unchanged weight and a less pronounced increase in amylase and protein content. The pancreatic DNA content was unaffected in the 20-micrograms group but was clearly decreased by the higher dose. In the second experiment a statistically significant increase over controls was found in the fraction of labeled ductal cells when 20, 54, and 160 micrograms of cerulein was administered. However, in the acinar cell population an increase was measured only in the 160-micrograms group. A tendency to nadir in cell labeling was observed in both acinar and ductal cell groups at less stimulation. Labeling of centroacinar cells increased in all cerulein-treated groups. The results show that all cell types of the exocrine pancreas can be forced into proliferation by the cholecystokinin analogue used and that there is preferential cell growth stimulation in the ductal and centroacinar cell populations.     

Ultrasonography in the Evaluation of Extension,Activity, and Follow-up of Ulcerative Colitis

The trophic effect on the exocrine pancreas of the cholecystokinin analogue cerulein was studied in a long-term experiment (20 or 160 μg/kg/24 h for 14 days) in mice by measuring changes in pancreatic weight and protein, amylase, and DNA content. Further, the selective cell growth stimulation exerted by various doses of cerulein (4, 20, 54, 160 μg/kg/24 h) on different exocrine pancreatic cell types was studied by continuous administration of ³H-thymidine. In the first experiment animals given 20 μg/kg/24 h of cerulein had increased pancreatic weight and amylase and protein content, whereas the animals given the higher dose had unchanged weight and a less pronounced increase in amylase and protein content. The pancreatic DNA content was unaffected in the 20-μg group but was clearly decreased by the higher dose. In the second experiment a statistically significant increase over controls was found in the fraction of labeled ductal cells when 20, 54, and 160 μg of cerulein was administered. However, in the acinar cell population an increase was measured only in the 160-ug group. A tendency to nadir in cell labeling was observed in both acinar and ductal cell groups at less stimulation. Labeling of centroacinar cells increased in all cerulein-treated groups. The results show that all cell types of the exocrine pancreas can be forced into proliferation by the cholecystokinin analogue used and that there is preferential cell growth stimulation in the ductal and centroacinar cell populations.     

Water immersion stress induces heat shock protein 60 expression and protects against pancreatitis in rats

BACKGROUND & AIMS: Heat shock proteins (Hsps), induced by cell stress, are known to protect against cellular injury. Recent studies have indicated that Hsp60 expression, induced by exposure to water immersion stress, protects against pancreatitis induced by administration of supramaximal doses of cerulein in rats. However, the mechanisms responsible for this protection are not known. Methods: Rats were water-immersed for 3-12 hours. Pancreatitis was induced by cerulein administration. RESULTS: The results confirm that prior induction of Hsp60 expression by water-immersion stress significantly ameliorates the severity of cerulein-induced pancreatitis as judged by the markedly reduced degree of hyperamylasemia, pancreatic edema, and acinar cell necrosis. Water immersion also prevents the subcellular redistribution of cathepsin B from a lysosome-enriched fraction to a heavier, zymogen granule-enriched fraction that is known to occur in this model of pancreatitis. Intra-acinar cell activation of trypsinogen that occurs shortly after exposure to a supramaximally stimulating dose of cerulein both in vivo and in vitro is prevented by prior water-immersion stress and Hsp60 expression. The protection against pancreatitis that follows water-immersion stress is not caused by alterations of cholecystokinin receptors, because water immersion does not alter the typical biphasic amylase secretory response to stimulation with cerulein. CONCLUSIONS: Water-immersion stress induces Hsp60 expression, ameliorates cerulein-induced pancreatitis, and prevents intra-acinar cell activation of trypsinogen. We suggest that Hsp60 protects against cerulein-induced pancreatitis by preventing trypsinogen activation within acinar cells.     

Esterase inhibitors prevent lysosomal enzyme redistribution in two noninvasive models of experimental pancreatitis

Earlier studies have indicated that lysosomal enzymes such as cathepsin B become redistributed within pancreatic acinar cells during the early stages of both diet- and secretagogue-induced acute pancreatitis. As a result, cathepsin B and digestive zymogens became colocalized within large cytoplasmic vacuoles. As cathepsin B can activate trypsinogen, this colocalization could result in intracellular digestive enzyme activation. The present study investigates the protective effects of gabexate mesilate (FOY) and camostate (FOY 305) on both of these noninvasive models of experimental pancreatitis. These esterase inhibitors prevented the hyperamylasemia, pancreatic edema, and acinar cell vacuolization that characterize secretagogue-induced pancreatitis and the hyperamylasemia and mortality that characterize diet-induced pancreatitis. In addition, FOY and FOY 305 were found to significantly decrease the subcellular redistribution of cathepsin B that occurs in both models. These findings indicate that enzyme activity sensitive to inhibition by FOY and FOY 305 may be critical to the redistribution phenomenon that characterizes both of these models of pancreatitis.     

Effects of short-term pancreatic duct obstruction in rats.

The short-term effects of rat pancreatic duct obstruction were evaluated and compared with those recently reported to follow obstruction of the rabbit pancreatic duct. In both species pancreatic edema and hyperamylasemia are noted, and the lysosomal hydrolase cathepsin B is redistributed from the lysosome-enriched to the zymogen granule-enriched subcellular fraction. Theoretically, this redistribution phenomenon might lead to digestive enzyme activation because cathepsin B is known to be capable of activating trypsinogen. The hyperamylasemia and pancreatic edema (but not the cathepsin B redistribution) that follow rat pancreatic duct obstruction were increased by infusion of a submaximally stimulating dose of the cholecystokinin analogue cerulein. Administration of the cholecystokinin-receptor antagonist L-364,718 reduced the hyperamylasemia but did not alter the pancreatic edema or cathepsin B redistribution. These observations indicate that cholecystokinin may modulate some but not all of the effects of duct obstruction. Secretin administration increased the degree of pancreatic edema and had no demonstrable protective effect. The rat duct-obstruction model described in this report may prove particularly useful in future studies designed to clarify the early events underlying the development of acute pancreatitis.     

Exocrine pancreatic function in the early period after pancreatoduodenectomy and effects of preoperative pancreatic duct obstruction

Exocrine pancreatic function in the early period after pancreatoduodenectomy was investigated. The effects of preoperative pancreatic duct obstruction on exocrine pancreatic function were also investigated. The volume of pancreatic juice and its amylase activity were investigated in 39 patients who underwent pancreatoduodenectomy (including pylorus-preserving pancreatoduodenectomy). TheN-benzoyl-l-tyrosyl-p-aminobenzoic acid (BT-PABA) test was performed on 23 of 39 patients about 40 days after pancreatoduodenectomy. The exocrine pancreatic function was inhibited three to eight days after pancreatoduodenectomy (amylase activity: 23,700±4300 IU/day), and recovered on days 9–15 (48,000±8400 IU/day) in patients with a normal main pancreatic duct. In patients with pancreatic duct obstruction, the exocrine pancreatic function was almost eliminated (amylase activity: 440±260 IU/day) and BT-PABA test results were low (45±17%). In patients with narrowed pancreatic duct, amylase secretion was significantly inhibited even in patients with a normal number of acinar cells. There was a good positive correlation (Spearman's rank correlation coefficient,rs=0.715,P<0.01) between amylase secretion and BT-PABA test. Amylase secretion more than 10,000 IU/day is essential for a normal BT-PABA test and normal digestive function. The inhibited digestive function in patients with pancreatic duct obstruction may be due to the decreased number of acinar cells and the inhibition of exocrine pancreatic function.     

Glutathione and ATP levels,subcellular distribution of enzymes,and permeability of duct system in rabbit pancreas following intravenous administration of alcohol and cerulein

In order to reproduce what might occur during the initial phase in some cases of acute alcohol-induced pancreatitis, rabbits were infused with diluted ethanol and low-dose cerulein. The duct permeability was assessed by recovery of fluoresceinated dextran (molecular weight 19,500) in central venous blood following orthograde duct perfusion with this substance in the anesthetized animal. Serum ethanol, lipase, and amylase were measured; pancreatic duct morphology was examined by light microscopy and electron microscopy. ATP and glutathione were measured, as were amylase, trypsinogen/trypsin, cathepsin B, and DNA levels in differential centrifugates. As expected, acinar amylase and trypsinogen showed a significant decrease in the experimental group; cathepsin B activity was similarly diminished. Compared with the control group, the activity of serum amylase and lipase in the experimental group demonstrated a significant increase. However, no differences between saline-infused control animals and the treated group regarding pancreatic duct permeability, continuity of lumen-lining epithelium, ATP and glutathione levels, and the relative subcellular distribution of pancreatic digestive and lysosomal enzymes were observed. Thus, our findings do not support the relevance of some of the most common hypotheses on the pathophysiology of acute pancreatitis in its early stage for at least a certain subgroup of patients with acute alcohol-induced pancreatitis.Preliminary results of this study have been presented at the 1992 American Pancreatic Association Meeting in Chicago and have been published in abstract form (Pancreas 7:747, 1992).     

Serine protease inhibitor causes F-actin redistribution and inhibition of calcium-mediated secretion in pancreatic acini

BACKGROUND & AIMS: The present study was undertaken to evaluate the role of serine proteases in regulating digestive enzyme secretion in pancreatic acinar cells. METHODS: Isolated acini were stimulated by various secretagogues in the presence or absence of cell-permeant serine protease inhibitors 4-(2-aminoethyl)-benzenesulfonyl fluoride and N(alpha)-p-tosyl-L-phenylalanine chloromethyl ketone. F-actin distribution was studied after staining with rhodamine phalloidin. RESULTS: Both cell-permeant serine protease inhibitors blocked amylase secretion in response to secretagogues that use calcium as a second messenger (e.g., cerulein, carbamylcholine, and bombesin) but not to those that use adenosine 3',5'-cyclic monophosphate (cAMP) as a second messenger (e.g., secretin and vasoactive intestinal polypeptide). Incubation of the acini with these inhibitors also resulted in a dramatic redistribution of the F-actin cytoskeleton. This redistribution was energy dependent. Similar redistribution of F-actin from the apical to the basolateral region was also observed when acini were incubated with a supramaximally stimulating concentration of cerulein, which is known to inhibit secretion. CONCLUSIONS: These results suggest that a serine protease activity is essential for maintaining the normal apical F-actin distribution; its inhibition redistributes F-actin from the apical to the basolateral region and blocks secretion induced by secretagogues that act via calcium. cAMP reverses the F-actin redistribution and hence cAMP-mediated secretion is not affected.