Luminal ATP stimulates fluid and HCO3- secretion in guinea-pig pancreatic duct

1. The location of purinoceptors in the pancreatic duct and their role in regulating ductal secretion have been investigated by applying ATP and UTP to basolateral and luminal surfaces of pancreatic ducts isolated from the guinea-pig pancreas. 2. Changes in intracellular Ca2+ concentration were measured by microfluorometry in microperfused interlobular duct segments. Fluid and HCO3- secretion were estimated by monitoring luminal pH and luminal volume in sealed duct segments microinjected with BCECF-dextran. 3. Both ATP and UTP (1 microM) caused biphasic increases in intracellular Ca2+ concentration in pancreatic duct cells when applied to either the basolateral or luminal membrane. 4. Luminal application of both ATP and UTP evoked fluid and HCO3- secretion. The maximum response to 1 microM ATP or UTP was about 75 % of that evoked by secretin. By contrast, basolateral application of ATP or UTP inhibited spontaneous secretion by 52 % and 73 %, respectively, and secretin-evoked secretion by 41 % and 38 %, respectively. 5. The data suggest that luminal nucleotides may act in an autocrine or paracrine fashion to enhance ductal secretion while basolateral nucleotides, perhaps released from nerve terminals, may have an inhibitory effect. The fact that both apical and basolateral purinoceptors elevate intracellular Ca2+, but that they have opposite effects on secretion, suggests that additional signalling pathways are involved.

Carcinogenicity of heterocyclic amines for the pancreatic duct epithelium in hamsters

Effects of eight heterocyclic amines (HCAs) on pancreatic duct carcinogenesis were investigated in a rapid production model in hamsters. N-Nitrosobis(2-oxopropyl)amine (BOP) was given to effect initiation, followed by augmentation pressure consisting of four daily i.p. injections of 500 mg/kg DL-ethionine, a choline-deficient (CD) diet, a single i.p. injection of 800 mg/kg L-methionine and a s.c. injection of 20 mg/kg BOP. After two cycles of augmentation pressure, the HCAs 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP), 2-amino-3,8-dimethylimidazo[4,5-f]quinoxaline (MeIQx), 2-amino-3-methylimidazo[4,5-f]quinoline (IQ), 3-amino-1,4-dimethyl-5H-pyrido[4,3-b]indole (Trp-P-1), 3-amino-1-methyl-5H-pyrido[4,3-b]indole (Trp-P-2), 2-amino-9H-pyrido[2,3-b]indole (AalphaC), 2-amino-3-methyl-9H-pyrido[2,3-b]indole (MeAalphaC) or 2-amino-3,4,8-trimethylimidazo[4,5-f]quinoxaline [4,8-DiMeIQx) were administered in the diet for 50 or 70 days. The numbers of pancreatic ductal hyperplasias (H) and a total lesions including, atypical hyperplasia (AH), carcinomas in situ (CIS) and invasive carcinomas, were increased in hamsters given the diet containing 0.02% Trp-P-1 for 50 days. This result was confirmed and extended by the finding of increased numbers of invasive carcinomas in hamsters given 0.02% Trp-P-1 for 70 days. The number and incidence of invasive carcinomas were also elevated in hamsters given the diet containing 0.06% 4,8-DiMeIQx for 50 days. These results suggest a possible involvement of Trp-P-1 and 4,8-DiMeIQx in pancreatic duct carcinogenesis.

Arginine vasopressin inhibits fluid secretion in guinea pig pancreatic duct cells

The effects of arginine vasopressin (AVP) on pancreatic ductal secretion were studied in guinea pigs. In the isolated vascularly perfused pancreas, AVP reduced secretin-stimulated fluid secretion and increased the vascular resistance when the perfusion rate was held constant. In the isolated interlobular duct segments, AVP inhibited secretin-stimulated fluid secretion, indicating the direct inhibitory action of AVP on the duct cells. AVP affected neither the basal nor the secretin-induced cAMP productions, suggesting that AVP inhibits the fluid secretion at a point distal to the production of cAMP. AVP increased intracellular Ca(2+) concentration ([Ca(2+)](i)) in the absence of extracellular Ca(2+). When [Ca(2+)](i) was elevated by the application of thapsigargin, AVP caused a rapid decrease in [Ca(2+)](i). AVP seems to activate both Ca(2+) release from intracellular stores and Ca(2+) efflux across the plasma membrane, but its relation to the inhibition of fluid secretion remains to be clarified. It is concluded that AVP directly inhibits secretin-stimulated ductal fluid secretion in the guinea pig pancreas.

Defective regulation of gap junctional coupling in cystic fibrosis pancreatic duct cells

The cystic fibrosis (CF) gene encodes a cAMP-gated Cl- channel (cystic fibrosis transmembrane conductance regulator [CFTR]) that mediates fluid transport across the luminal surfaces of a variety of epithelial cells. We have previously shown that gap junctional communication and Cl- secretion were concurrently regulated by cAMP in cells expressing CFTR. To determine whether intercellular communication and CFTR-dependent secretion are related, we have compared gap junctional coupling in a human pancreatic cell line harboring the DeltaF508 mutation in CFTR and in the same cell line in which the defect was corrected by transfection with wild-type CFTR. Both cell lines expressed connexin45 (Cx45), as evidenced by RT-PCR, immunocytochemistry, and dual patch-clamp recording. Exposure to agents that elevate intracellular cAMP or specifically activate protein kinase A evoked Cl- currents and markedly increased junctional conductance of CFTR-expressing pairs, but not in the parental cells. The latter effect, which was caused by an increase in single-channel activity but not in unitary conductance of Cx45 channels, was not prevented by exposing CFTR-expressing cells to a Cl- channel blocker. We conclude that expression of functional CFTR restored the cAMP-dependent regulation of junctional conductance in CF cells. Direct intercellular communication coordinates multicellular activity in tissues that are major targets of CF manifestations. Consequently, defective regulation of gap junction channels may contribute to the altered functions of tissues affected in CF.

Role of transforming growth factor-beta in growth and injury response of the pancreatic duct epithelium in vitro

Chronic pancreatitis is characterized by increased levels of expression of transforming growth factor-beta (TGF-beta), particularly in and around the ducts. To examine the consequences of elevated exposure to TGF-beta on the pancreatic duct epithelium, we cultured segments of the main bovine pancreatic duct in the presence of increasing doses of TGF-beta. We also studied the effect of TGF-beta on epithelial injury, produced in this model by exposure to a bile acid. The extent of proliferation, migration, and epithelial damage was measured morphometrically on sections stained with hematoxylin and eosin. Proliferation and apoptosis were qualitatively determined by means of immunohistochemical analysis. In this model of duct cell culture, TGF-beta stimulated cell migration in areas of the explants where the native basement membrane of the duct epithelium was absent. In segments where the native basement membrane remained intact, proliferation was inhibited and apoptosis induced. When the explants were exposed to bile acid, extensive epithelial injury was observed. TGF-beta exposure at high doses (1 nmol/L protected epithelial integrity, but cellular morphology was altered and the process of apoptosis appeared to be increased. Our results suggest that increased periductal levels ot TGF-beta in the setting of pancreatic injury may be intended to promote repair of acute epithelial damage but may have detrimental long-term effects.

Electron microscopic study of intercalated duct cells in the chicken pancreatic islet and effects of tolbutamide administration

Intercalated duct cells are present in the alpha and beta islets of chicken. The intercalated duct cells adhere to each other via intercellular junctional complexes at the apical side, projecting many microvilli and a few cilia into the lumen. They also extend slender cytoplasmic processes between the islet endocrine cells. These intercalated cells appear to have a stellate form, and to wrap their cytoplasm around endocrine cells. Administration of tolbutamide led to increased electron density in the cytoplasm of intercalated duct cells. Lysosomes are present in these cells in various numbers and sizes and tend to increase with time after administration of tolbutamide. These observations suggested that the intercalated ducts not only pass through the islet, but also play a role in supplying islet cells.

Stimulation of HCO3- secretion across cystic fibrosis pancreatic duct cells by extracellular ATP

Previous studies have demonstrated that extracellular ATP is able to activate Ca2+-dependent Cl- channels which may be important in circumventing the defective cAMP-dependent pancreatic ductal HCO3- secretion in cystic fibrosis (CF). The present study further investigated the effect of extracellular ATP on the stimulation of HCO3- secretion across CF pancreatic duct cells (CFPAC-1). Cells were grown in culture plate inserts which enabled the access of a pH microelectrode to the apical compartment. Changes in apical pH upon stimulation by extracellular ATP, as an indication of HCO3- secretion, were measured. ATP induced a rapid increase in apical pH, which reached a plateau with an averaged pH unit of 0.3 higher than that measured in unstimulated cells. The effect of ATP was concentration dependent. The ATP-induced change in pH could be blocked by apical addition of Cl- channel blockers, indicating that activation of apical Cl- channel is vital for HCO3- secretion by the pancreatic duct cells. Together with the previous finding, the present study suggests that HCO3- secretion may be stimulated in CF pancreatic duct cells by extracellular ATP via a cAMP-independent pathway.

Effect of reg protein on rat pancreatic ductal cells

The pancreatic regenerating gene (reg I) is expressed in the exocrine pancreas and is involved in islet regeneration. Reg I protein has been shown to be mitogenic to beta- and ductal cell lines, but not mature islets. In this study, we tested the effect of two isolates of reg I on primary cultures of ductal cells. Rat pancreatic ductal cells were isolated by collagenase digestion and isolated colonies were maintained in culture. The cells were proven to be ductal in origin by their morphology and by immunofluorescent staining with epithelial markers. Reg I was isolated from human pancreatic extracts or from the rat acinar cell line AR42J by sequential ammonium sulfate precipitation and acid precipitation. Cells were cultured with doses of reg I for 72 h, pulsed with 10 microM bromodeoxyuridine (BrdU) for 2 h. After fixation, nuclei were double-stained with propidium iodide and BrdU monoclonal antibody. The percentages of nuclei positive for BrdU were calculated from at least five colonies per group. A 10-nM concentration of human reg I increased BrdU incorporation by 2.3-fold over controls, rat reg I increased it by 1.4-fold (p < 0.05). When compared to their effects on the ductal cell line ARIP, both human and rat reg I were 100 times more potent on the primary cultures of ductal cells. We conclude that human and rat reg I proteins are mitogenic to primary cultures of ductal cells. Although principally a product of the acinar cell, reg I appears to be a stimulus of ductal cell growth and, in this fashion, may modulate the expansion of the pancreatic ductal population during islet regeneration.

Ion-transport properties of cultured bovine pancreatic duct epithelial cells

Primary cultures of bovine pancreatic duct epithelial cells grown on permeable supports exhibit electrogenic transepithelial ion transport. The short-circuit current (I(sc)) generated by unstimulated duct cell monolayers and the increase in I(sc) elicited by increased levels of cyclic adenosine monophosphate (cAMP) were greater in monolayers bathed by bicarbonate-containing solution compared with monolayers bathed by nominally bicarbonate-free solution. An inhibitor of epithelial sodium channels (amiloride, 10 microM) had no effect on I(sc), whereas a Cl- channel blocker, N-phenylanthranilic acid (DPC; 1 mM), reduced the forskolin-stimulated I(sc) by approximately 50% in the absence or presence of bicarbonate. Bumetanide (an inhibitor of Na+,K+,2Cl- cotransport activity; 10 microM) reduced forskolin-stimulated I(sc) by 49 +/- 6% in bicarbonate-free bathing solution and by only 18 +/- 1% in bicarbonate-containing solution. Measurements of unidirectional 36Cl- flux across short-circuited ductal monolayers in a bicarbonate-containing solution revealed that net Cl- secretion accounted for the I(sc) during secretin stimulation. However, the basal I(sc) and the I(sc) measured during exposure to secretin plus bumetanide were significantly greater than net Cl- flux. The permeability coefficient for [14C]acetate (a surrogate tracer for bicarbonate) measured in the secretory direction was approximately 1.5-fold greater than the permeability coefficient measured in the absorptive direction, indicating net secretion. These results suggest that primary cultures of bovine pancreatic duct epithelial cells secrete both Cl- and HCO3-.

beta-Adrenergic regulation of ion transport in pancreatic ducts: patch-clamp study of isolated rat pancreatic ducts

BACKGROUND & AIMS

In the intact pancreas, bicarbonate secretion is thought to be controlled by a number of regulators, including adrenergic agonists. The aim of this study was to investigate the effects of adrenergic agonists on pancreatic ducts, which are the site of bicarbonate secretion.

METHODS

Small intralobular ducts were isolated from rat pancreas and studied in vitro by the whole-cell patch clamp technique. Cell membrane voltages and currents were indicators of cellular ion transport. In some ducts, intracellular Ca2+ activity was measured by fluorescence optical methods.

RESULTS

Unstimulated duct cells had a membrane voltage (Vm) of about -50 mV. Isoproterenol had a concentration-dependent effect on Vm; at 10(-7) mol/L, it depolarized Vm by 20-25 mV and the cell conductance increased by 100 nanosiemens. These effects were a result of opening of luminal Cl- channels. Phenylephrine had much smaller effects. At comparable concentrations, it depolarized Vm by a few millivolts. Neither agonist had significant effects on intracellular Ca2+.

CONCLUSIONS

This study provides the first direct evidence that adrenergic stimulation, namely, that of beta-adrenoceptors, controls ion transport in pancreatic ducts. Similar to secretin, isoproterenol stimulation leads to opening of luminal Cl- channels, and HCO3- enters the lumen in exchange for Cl-.

Different purinergic receptors lead to intracellular calcium increases in pancreatic ducts

Extracellular adenosine 5'-triphosphate (ATP) has been described to act as a regulator in many cells and tissues, including epithelia, and in the gastrointestinal tract ATP is one of the substances involved in non-cholinergic non-adrenergic control. However, very little is known about the effect of ATP on pancreatic ducts, which normally secrete bicarbonate-rich fluid in response to secretin. Hence, the aim of our present study was to test the effect of ATP and other nucleotides on intracellular Ca2+ activity ([Ca2+]i) of pancreatic ducts, and thereby get information about purinergic receptors that might play a role in the regulation of pancreatic bicarbonate transport. Native intralobular ducts were obtained from rat pancreas and [Ca2+]i in 10-20 cells was measured using the fura-2 method. ATP (10(-4) mol/l) evoked a characteristic biphasic Ca2+ transient in duct cells. Nucleotides, used to classify the P2 receptors, acted with the following potency on the peak Ca2+ in many ducts: uridine 5'-triphosphate (UTP) >/= ATP >inosine 5'-triphosphate >/= 2-methylthio-ATP > beta,gamma-methyl-ATP > adenosine. However, although the peak [Ca2+]i responses to ATP and UTP were similar, the plateau [Ca2+]i was nearly doubled with UTP. Moreover, in about one-third of the ducts studied, UTP had no effect on cell Ca2+, while the response to ATP was normal. In further experiments we found that removal of extracellular Mg2+ increased the peak [Ca2+]i evoked in response to ATP. 2'&3'-O-(4-benzoylbenzoyl) ATP (BzATP) evoked a monophasic and slower increase in [Ca2+]i, which was inhibited by removal of extracellular Ca2+, or by addition of 4,4'-diisothiocyanatostilbene-2, 2'-disulphonic acid (DIDS). Taken together, our data indicate that there are two types of purinergic receptors on pancreatic ducts through which ATP can act. These are pharmacologically known as P2U and P2Z receptors and may correspond to P2Y2 and P2X7 receptors.

Sphincter of Oddi manometry. Paradoxical response to secretin but not to CCK in alcoholic patients with no pancreatic disease

CONCLUSION

In chronic alcohol abusers with no pancreatic disease, secretin was found to induce a paradoxical spasmodic response in the sphincter of Oddi (SO) instead of the relaxation observed in controls. Cerulein, on the contrary, had a normal relaxing effect on the SO.

BACKGROUND

We previously reported SO dyskinesia in cases of chronic pancreatitis. Here we investigated whether chronic alcohol consumption may have contributed to the genesis of this dyskinesia.

METHODS

SO and main pancreatic duct pressures were recorded endoscopically with a dual electronic pressure sensor in 27 chronic alcohol abusers and compared with the values obtained in 15 normal controls. These pressures were recorded both in the basal state and after applying hormonal stimulation by injecting either secretin (1 CU/kg) or cerulein (75 ng/kg).

RESULTS

Cerulein relaxed the SO in both the controls and the chronic alcohol abusers, whereas it transiently enhanced the main pancreatic duct (MPD) pressure. Secretin induced a wave of MPD hyperpressure (+15.4 +/- 3.0 mm Hg) in both groups of subjects, but in the alcoholic group, instead of relaxing SO, it significantly enhanced the amplitude of phasic contractions (+32.6 +/- 8.4 mm Hg). The SO basal pressure was also paradoxically enhanced by secretin in the alcoholic patients (28.8 +/- 8.2 vs 10.1 +/- 2.4 mm Hg).

Pathophysiologic studies of experimental chronic pancreatitis in rats induced by injection of zein-oleic acid-linoleic acid solution into the pancreatic duct

An experimental model of chronic pancreatitis was induced by a retrograde injection of a viscous solution consisting of zein-oleic acid-linoleic acid (0.05 ml/100 g body weight) into the rat pancreatic duct. Histologic and biochemical changes were investigated over a period of 6 months after induction of this model. The treated rats gained weight, but pancreatic weight decreased with time. Histologically, the widening of acinar lumen and cellular vacuolization occurred within 24 h at the parenchyma neighboring the small ducts filled with the injected solution. Degenerative parenchyma, interstitial edema, and inflammatory cell infiltration were pronounced 1 week later. Thereafter, duct-like tubular complex formation progressed, and the exocrine tissue exhibited marked atrophy of the gland with irregular fibrosis and fat replacement over a period of 6 months. Pancreatic contents of protein, amylase, DNA, and RNA markedly decreased, as did pancreatic weight, whereas hydroxyproline content increased. Oral administration of camostat did not affect pancreatic weight and contents of enzyme in this model. Urinary para-aminobenzoic acid (PABA) excretion in the BT-PABA test decreased to 54% at 6 weeks and 22% at 6 months. Although three quarters of pancreatic immunoreactive insulin (IRI) content was lost after 6 months, overt diabetes did not occur. The results suggest that an obstructive mechanism in the small ducts plays an important role in the genesis and development of chronic pancreatitis.

Acute effects of bile acids on the pancreatic duct epithelium in vitro

BACKGROUND

Acute pancreatitis is associated with passage of gallstones, although the mechanism(s) linking the two processes remains undefined. Bile reflux into the pancreatic duct could play a role but the experimental conditions often employed to induce pancreatitis rarely develop clinically. Here we examined whether low concentrations of bile affect ductal electrophysiology as an indirect measure of ductal epithelial integrity and function in vitro.

METHODS

The main duct was dissected out of freshly harvested bovine pancreata, cut into 1- x 2-cm sections, placed in tissue culture for 48-72 h, then placed in Ussing chambers. Changes in tissue resistance (Rt) and short-circuit current (Isc) were monitored. The responses to forskolin and bile (taurodeoxycholic acid, TDCA) were examined separately and together.

RESULTS

Forskolin (10 microM) produced a decrease in the Isc without a significant change in Rt, suggesting a secretory response, followed by a return to baseline. TDCA caused a similarly reversible decrease in the Isc at low doses, but a persistent drop at higher concentrations. A concurrent drop in Rt was noted at all TDCA concentrations, the duration of which correlated with dosage and degree of histological damage. Prior exposure to low (0.5 mM) doses of TDCA significantly blunted the response to subsequent forskolin challenge.

CONCLUSIONS

Acute exposure to TDCA in vitro causes epithelial damage at levels lower than those normally used to induce experimental pancreatitis. At the lower concentrations, Rt returns to baseline rapidly, suggesting recovery (restitution) from epithelial damage but with a persistent loss of the response to forskolin. Reflux of minute amounts of bile into the pancreatic duct could play a significant role in the pathogenesis of gallstone pancreatitis by uncoupling the normal stimulus-secretion apparatus of the ductal system and breaking down the epithelial barrier.

Plasma levels of TNF and IL-6 following induction of acute pancreatitis and pentoxifylline treatment in rats

Activation of cytokine cascade is a decisive factor in determining the pathobiology of different inflammatory processes including acute pancreatitis. The purposes of this study were to determine the TNF and IL-6 levels after the induction of acute necrotizing pancreatitis, and to establish the effects of pentoxifylline on the cytokine production and the severity of pancreatitis. Acute necrotizing pancreatitis was induced by the retrograde injection of 200 microliters taurocholic acid into the pancreatic duct in male Wistar rats. TNF was titrated in a bioassay on cell line WEHI clone 164. IL-6 was measured via its proliferative action on the IL-6 dependent mouse hybridoma cell line B-9. Seven mg/kg pentoxifylline was administered intraperitoneally at the time of operation and/or 24 hours later. Rats were sacrificed, 48 or 72 hours after the operation. The TNF bioassay revealed high levels of TNF (36.6 +/- 6.0 U/ml) in the control group whereas levels decreased to zero in the pentoxifylline-treated group. The IL-6 bioassay likewise demonstrated high levels of IL-6 in the control group and markedly decreased levels in the pentoxifylline treated group (7083 +/- 2844 pg/ml, 6463 +/- 1307 pg/ml vs. 137.5 +/- 85.5 pg/ml, respectively, p < 0.05). The high mortality observed in the control group (43%) was sharply decreased by pentoxifylline administration to 11%. The data suggest that pentoxifylline is capable of modifying the cytokine production after 48 hours of induction of acute pancreatitis.

Glucose-specific regulation of aldose reductase in capan-1 human pancreatic duct cells In vitro

Impaired pancreatic duct secretion is frequently observed in insulin-dependent diabetes mellitus (IDDM), although the cellular mechanism(s) of dysfunction remains unknown. Studies in other tissues have suggested that a hyperglycemia-induced decrease in Na, K-ATPase activity could contribute to the metabolic complications of IDDM and that increased polyol metabolism is involved in this response. The present studies examined the effects of glucose on Na, K-ATPase activity and on expression and activity of aldose reductase (AR), a primary enzyme of polyol metabolism, in Capan-1 human pancreatic duct cells. Increasing medium glucose from 5.5 to 22 mM caused a 29% decrease in Na,K-ATPase activity. The decrease was corrected by 100 microM sorbinil, a specific AR inhibitor. Increasing glucose from 5.5 to 110 mM also resulted in concentration-dependent increases in AR mRNA and enzyme activity that could be resolved into two components, one that was glucose specific and observed at pathophysiological concentrations (< 55 mM) and a second that was osmotically induced at high concentrations (> 55 mM) and which was not glucose specific. The present study demonstrates that pathophysiological levels of glucose specifically activate polyol metabolism with a consequent decrease in Na,K-ATPase activity in pancreatic duct epithelial cells, and that this response to hyperglycemia could contribute to decreased pancreatic secretion observed in IDDM. This is the first report of AR regulation in the pancreatic duct epithelium.

Systemic treatment with epidermal growth factor in pigs induces ductal proliferations in the pancreas

BACKGROUND & AIMS

Epidermal growth factor (EGF), transforming growth factor alpha (TGF-alpha), and the EGF receptor are often overexpressed in chronic pancreatitis and in malignant pancreatic growth. Transgenic mice overexpressing TGF-alpha develop tissue changes in the pancrease resembling changes found in chronic pancreatitis. The effects of systemic treatment with EGF on the porcine pancrease were investigated in this study.

METHODS

Mature Goettingen minipigs were treated with solvent (n = 5), EGF (30 micrograms.kg-1.day-1; n = 6) for 4 weeks, or EGF (30 micrograms.kg-1.day-1; n = 5) for 5 weeks followed by 3 weeks of recovery. Pancreata were studied by routine histological examination and electron microscopy and were immunostained for proliferating cell nuclear antigen (PCNA).

RESULTS

In the EGF-treated animals, mainly larger interlobular ducts of the pancreas appeared to be considerably hyperplastic, with an increased number of nuclei that stained for PCNA. The epithelia of these ducts were increased in height, with accumulations of glycoconjugates in the columnar cells and in an increased number of goblet cells.

CONCLUSIONS

A new approach to experimentally induced hyperplastic changes of the excretory ducts of the pancreas is presented. Because ductal changes with glycoconjugate accumulations are common features of chronic pancreatitis and pancreatic cancer, the findings may be relevant to the pathogeneses of these conditions.

Clinical perspectives of a sonographic secretin test

The normal-sized pancreatic duct can be demonstrated today by sonography in about 90% of all persons examined. In healthy individuals intravenous bolus injection of secretin generally leads to a short-lasting distinct dilatation of Wirsung's duct being likewise visible on ultrasonography. Further investigations showed no or only a slight secretin-induced pancreatic duct dilatation in chronic pancreatitis, whereas patients with papillary or pancreatic duct stenosis had a marked and prolonged duct enlargement after stimulation. Different authors reported a high sensitivity and specificity of this sonographic secretin test in the diagnosis of chronic pancreatitis, even in early stages. In patients with pancreas divisum the secretin test result seems to be less uniform, a marked and prolonged duct enlargement after secretin stimulation, however, has been successfully used as a diagnostic criterion of accessory sphincter obstruction. Recently this test method has also been used to differentiate the etiology of cystic pancreatic lesions under observation by endoscopic ultrasonography. Since sonographic measurement of the pancreatic duct diameter before and after secretin stimulation is easy to perform with modern technical equipment, it could be a useful screening test for different diagnostic questions in pancreatic disease. Further investigations are needed for the evaluation of its reliability and standardization.

Ultrasonography-secretin test pattern after acute administration of octreotide in healthy persons and in patients with recurrent acute pancreatitis

The intravenous administration of octreotide stimulates sphincter of Oddi activity and impairs pancreatic flow into the duodenum. Postsecretin ultrasonography (US-S test) has revealed an increase in the caliber of the main pancreatic duct, which disappears in healthy persons approximately 10 minutes later as a result of the opening of the sphincter of Oddi and passage of stimulated fluids into the duodenum. We have assessed US-S test patterns after octreotide in healthy persons and in patients with recurrent acute pancreatitis. The study sample consisted of 16 participants: alcohol-abstinent, nonsmoking, healthy volunteers (four men, three women; mean age: 28 +/- 2.5 years) and nine patients with recurrent acute pancreatitis (six men, three women; mean age: 32.1 +/- 7.1 years). All participants underwent measurement of the main pancreatic duct at 1-min intervals for 60 min after secretin stimulation (1 IU/kg intravenous bolus). On a different day the same persons had repeated US-S tests 1 hour after administration of 0.1 mg octreotide intramuscularly. In both controls and patients with recurrent acute pancreatitis, octreotide administration induced an appreciable dilatation of the main pancreatic duct before secretin stimulation, and the caliber remained significantly increased throughout the duration of the test. These results suggest that a single administration of octreotide at the dose used (a) does not inhibit pancreatic secretion of basal and secretin-stimulated fluid within the first 60 min and (b) probably exerts an inhibitory effect on sphincter of Oddi relaxation. These findings warrant more intensive study given their therapeutic implications for acute pancreatic disease.

Mutagenicity of 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP) when activated by hamster pancreatic duct epithelial cells: a chemopreventive role for glutathione

We have shown a role for glutathione (GSH) in the detoxification of 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP) using mutagenicity in V79 cells as the end-point. Immortalized hamster pancreas duct epithelial cells (CK cells) were used to metabolize PhIP in this assay. Intracellular GSH concentrations were lowered by treatment with buthionine sulfoximine (BSO) and were raised by treatment with sodium sulfite. BSO treatment (10 mM, 4 h) reduced the GSH concentration in V79 cells from 18 +/- 1 to 6 +/- 1 nmol/mg protein, 4 h after treatment. The mutation frequency of PhIP in these V79 cells rose from 15 +/- 2 to 34 +/- 4 mutants/10(6) survivors in BSO-treated V79 cells. In a related experiment both CK and V79 cells were treated with sulfite. Sulfite treatment (2 mM, 4 h) produced a greater reduction in PhIP mutagenicity when the V79 cells were treated with sulfite (from 15 +/- 2 to 3 +/- 1 mutants/10(6) survivors) than when the CK cells were treated (from 15 +/- 2 to 7 +/- 2 mutants/10(6) survivors). These data show a relationship between intracellular GSH concentration and the mutagenicity of PhIP.

Angiotensin II receptor type I-regulated anion secretion in cystic fibrosis pancreatic duct cells

The beta-adrenergic (cAMP-dependent) regulation of Cl- conductance is defective in cystic fibrosis (CF). The present study explored alternative regulation of anion secretion in CF pancreatic ductal cells (CFPAC-1) by angiotensin II (AII) using the short-circuit current (ISC) technique. An increase in ISC could be induced in CFPAC-1 cells by basolateral or apical application of AII in a concentration-dependent manner (EC50 at 3 microm and 100 nm, respectively). Angiotensin receptor subtypes were identified using specific antagonists, losartan and PD123177, for AT1 and AT2 receptors, respectively. It was found that losartan (1 microm) could completely inhibit the AII-induced ISC, whereas, PD123177 exerted insignificant effect on the ISC, indicating predominant involvement of AT1 receptors. The presence of AT1 receptors in CFPAC-1 cells was also demonstrated by immunohistochemical studies using specific antibodies against AT1 receptors. Confocal microscopic study demonstrated a rise in intracellular Ca2+ upon stimulation by AII indicating a role of intracellular Ca2+ in mediating the AII response. Depletion of intracellular but not extracellular pool of Ca2+ diminished the AII-induced ISC. Treatment of the monolayers with a Cl- channel blocker, DIDS, markedly reduced the ISC, indicating that a large portion of the AII-activated ISC was Cl--dependent. AII-induced ISC was also observed in monolayers whose basolateral membranes had been permeabilized by nystatin, suggesting that the ISC was mediated by apical Cl- channels. Our study indicates an AT1-mediated Ca2+-dependent regulatory mechanism for anion secretion in CF pancreatic duct cells which may be important for the physiology and pathophysiology of the pancreas.

Effect of vascular endothelial growth factor on growth and differentiation of pancreatic ductal epithelium

Endocrine and exocrine pancreatic morphogenesis is known to occur from ductal epithelium, but the factors that regulate this process are unknown. Vascular endothelial growth factor (VEGF)/vascular permeability factor has recently been reported to affect fetal islet ontogenesis. VEGF is an angiogenic factor with a growth-promoting effect that is thought to be restricted to vascular endothelial cells. We demonstrated that VEGF is also a mitogen for adult rat pancreatic duct epithelial cells in primary culture. VEGF supplementation to a serum-free culture medium increased the 5-bromo-2'-deoxyuridine-pulse labeling index of ductal cells more than 2-fold. Immunohistochemical staining and protein blots revealed that pancreatic duct cells express fetal liver kinase-1 high-affinity receptors for VEGF. In pancreatic tissue, immunohistochemistry shows that VEGF peptide is expressed in normal pancreatic islet cells. In duct ligation-induced acute pancreatitis, numerous inflammatory leukocytes containing VEGF were seen to infiltrate between hyperplastic ducts. In the latter model, islet neogenesis has previously been observed. Our data indicate the possibility that VEGF plays a role in the paracrine regulation of ductal growth and differentiation in vivo, eg, in pancreatitis. In vitro, however, VEGF did not induce endocrine differentiation of ductal cells, indicating that it is not the only factor required for the activation of islet neogenesis.

Characterization of two distinct chloride channels in cultured dog pancreatic duct epithelial cells

Cl- secretion by pancreatic duct epithelial cells (PDEC) regulates cellular HCO3- secretion, an important component of the exocrine pancreas. In cystic fibrosis, for example, impaired function of the cystic fibrosis transmembrane conductance regulator (CFTR) Cl- channel results in decreased pancreatic secretion and secondary pancreatic insufficiency. Studies of ion transport by PDEC have been hindered by the lack of a practical in vitro model. We have successfully cultured nontransformed dog PDEC on Vitrogen-coated permeable membranes overlying a feeder layer of myofibroblasts and report the characterization of Cl- channels in these cells. Cl- conductance, assessed through efflux of 125I from PDEC, was stimulated by agents acting via adenosine 3',5'-cyclic monophosphate (cAMP) or cytosolic Ca2+. The Cl- conductances activated by cAMP and Ca2+ were distinct, since they were differentially inhibited by 4,4'-diisothiocyanostilbene-2,2'-disulfonic acid and, to a lesser extent, by 5-nitro-2-(3-phenylpropylamino)benzoic acid and diphenylamine-2 carboxylate. Patch-clamp studies confirmed the presence of Cl- channels activated by cAMP and Ca2+, with differential inhibition by 4,4'-diisothiocyanostilbene-2,2'-disulfonic acid. The presence of CFTR Cl- channels in PDEC was confirmed by immunoblotting. These cultured PDEC are an optimal model for studies of pancreatic duct secretion.