Hydrogen sensing properties of protective-layer-coated single-walled carbon nanotubes with palladium nanoparticle decoration.

Protective-layer-coated single-walled carbon nanotubes (SWNTs) with palladium nanoparticle decoration (Pd-SiO(2)-SWNTs) were fabricated and their sensing properties for hydrogen (H(2)) were investigated. SWNTs were coated with a 3-4 nm thick SiO(2) layer by pulsed laser deposition and subsequently decorated with Pd nanoparticles by electron beam evaporation. Even though the SWNTs were completely surrounded by a protective layer, Pd-SiO(2)-SWNTs responded to H(2) down to a concentration of 1 part per million. Compared with the Pd nanoparticle-decorated SWNTs without a protective layer (Pd-SWNTs), Pd-SiO(2)-SWNTs exhibited highly stable sensor responses with variations of less than 20%; Pd-SWNTs showed a variation of 80%. The density of the Pd-SWNTs significantly decreased after the sensing test, while that of the Pd-SiO(2)-SWNTs with the netlike structure remained unchanged. The hydrogen sensing mechanism of the Pd-SiO(2)-SWNTs was attributed to the chemical gating effect on the SWNTs due to dipole layer formation by hydrogen atoms trapped at the Pd-SiO(2) interface. Moreover, the relationship between H(2) concentration and sensor response can be described by the Langmuir isotherm for dissociative adsorption.

Secretin-induced exocrine secretion in perfused pancreas isolated from diabetic rats.

Exocrine secretory function in response to 10 pM to 10 nM synthetic secretin was evaluated in perfused pancreas isolated from control, streptozocin-induced diabetic (STZ-D), alloxan-induced diabetic (ALX-D), and insulin-treated STZ-D rats. In STZ-D rats, the basal rate of pancreatic juice flow was significantly increased (10.3 +/- 1.0 microliters/20 min) compared with control rats (4.4 +/- 0.2 microliters/20 min). The basal rate of amylase output as well as pancreatic amylase content were significantly decreased to less than 5% of control values. The basal rates of protein and trypsinogen outputs were similar in both groups. In both control and diabetic rats, secretin caused a dose-dependent increase in exocrine secretion. Secretin (10 pM to 10 nM) induced 1.1- to 11.7-fold increases in exocrine secretion in STZ-D rats. These increases were significantly lower than the 2.1- to 20.8-fold increases in control rats. Furthermore, there was no significant increase in exocrine secretion from STZ-D rats in response to 10 pM secretin, although this concentration of secretin caused a significant increase in control rats. Secretin-induced exocrine secretion in ALX-D rats was similar to that in STZ-D rats. In insulin-treated STZ-D rats, the basal rates of pancreatic secretion were not significantly different from those of control rats. These results suggest that insulin resistance in this patient was due to a circulating factor of low molecular weight that uncoupled insulin stimulation of glucose transport from receptor binding and phosphorylation. The factor appears to increase the binding activity of the alpha-subunit of the insulin receptor without affecting the kinase activity of the beta-subunit.

Increased beta-cell secretory responsiveness to ceruletide and TPA in streptozocin-induced mildly diabetic rats.

We examined the effects of various stimuli on immunoreactive insulin (IRI) and glucagon (IRG) release from perfused pancreases isolated from control and streptozocin-induced diabetic (STZ-D) rats. Diabetes was induced by injecting 30 mg/kg STZ into rats fasted for 16-18 h 12-17 days before our experiments. Glucose (11.1 mM) caused a distinct biphasic pattern of IRI release from the control pancreas, whereas the first phase was marginal and the second phase was absent in the diabetic pancreas. Arginine (20 mM)-induced IRI release was similar in both groups, whereas IRG release was greater in the control rats than in the diabetic rats. Thus, this model of STZ-D simulates a certain class of non-insulin-dependent diabetes mellitus (NIDDM). In these diabetic animals, the cholecystokinin (CCK) analogue ceruletide (620 pM) caused a significantly greater increase in IRI release in the presence of 5.6 mM glucose than in the control rats, but ceruletide caused a similar IRG release in both groups. Because CCK and ceruletide stimulate phosphoinositide turnover in pancreatic islets, we examined the effects of carbachol and phorbol ester TPA on IRI release in the presence of 5.6 mM glucose. Carbachol (10 microM), which is thought to generate similar second messengers as ceruletide, induced greater IRI release in diabetic than in control rats. TPA (100 nM) caused a significantly greater increase in IRI release from the diabetic than the control pancreas. Our results demonstrate that the insulin-releasing mechanism involved in protein kinase C activation is enhanced in this model of NIDDM.(ABSTRACT TRUNCATED AT 250 WORDS)

Mechanisms of insulin-induced insulin-receptor downregulation. Decrease of receptor biosynthesis and mRNA levels.

The influence of insulin on the downregulation of its receptor was studied in AR42J cultured pancreatic acinar cells, a cell line that has been demonstrated to be metabolically responsive to insulin. Downregulation induced by insulin was time and dose dependent. After a 20-h incubation with 1 microM insulin, Scatchard analysis revealed approximately 80% loss of insulin receptors. Studies of receptor half-life indicated that treatment with insulin accelerated the degradation of both the alpha- and beta-subunits of the insulin receptor by 30-60%. In addition, biosynthetic-labeling studies indicated that insulin inhibited the biosynthesis of the insulin-receptor precursor by greater than 30%. This decreased biosynthesis of the precursor was associated with decreased production of mature receptor subunits. Poly(A)+ RNA was extracted from control cells and cells treated for 24 h with 100 nM insulin. Slot blots and Northern transfers revealed that insulin induced an approximately 50% decrease in insulin-receptor mRNA levels. Therefore, these studies indicate that insulin may diminish the concentration of its receptors in target cells by at least two mechanisms: acceleration of receptor degradation and inhibition of receptor biosynthesis at the level of mRNA.

Insulin and other stimulants have nonparallel translational effects on protein synthesis.

Isolated pancreatic acini from streptozocin-induced diabetic rats were used to study the role of insulin on the synthesis of specific cellular proteins. When acini were incubated with 0-100 nM insulin for 2 h and then pulsed with [35S]methionine, a dose-dependent increase in [35S]methionine incorporation into total cellular proteins was observed. When acinar cell lysates were subjected to gel electrophoresis, 12 major newly synthesized protein bands were resolved. Insulin (100 nM) increased the incorporation of [35S]methionine into all bands but with significantly different rates, varying from 84 to 216% of control. Next, specific antibodies to amylase, trypsin, ribonuclease, myosin, and lactate dehydrogenase (LDH) were used to evaluate the biosynthesis of known proteins. Insulin stimulated labeled amino acid incorporation into amylase by 148% over control. Insulin stimulated the synthesis of trypsinogen to a similar degree, but ribonuclease synthesis showed a significantly smaller increase of 53% over control. Insulin stimulated myosin and LDH synthesis by 169 and 184%, respectively. A differential pattern of protein synthesis was also observed when acini were treated with two other stimulators of protein synthesis, cholecystokinin and hemin. Both of these stimulators had a reduced effect on ribonuclease synthesis compared with amylase and trypsinogen synthesis but failed to increase myosin synthesis. When the RNAs extracted from control acini and acini treated with 100 nM insulin were translated in vitro, the proteins synthesized were quantitatively similar. This study therefore indicates that insulin has translational effects on acinar protein synthesis, and these effects are nonparallel for various specific acinar cell proteins.

Regulation of insulin-receptor mRNA levels by glucocorticoids.

We found with IM-9 human cultured lymphocytes, that the glucocorticoid dexamethasone increased insulin-receptor mRNA levels. This increase correlated in a time- and dose-dependent manner with the increase in the biosynthesis of the insulin-receptor precursor. In addition, in AR42J cultured rat pancreatic acinar cells, dexamethasone increased insulin-receptor mRNA levels. These studies suggest, therefore, that an increase in mRNA levels is an early step in the regulation of the insulin receptor by glucocorticoids in several cell types.

Shc phosphotyrosine-binding domain dominantly interacts with epidermal growth factor receptors and mediates Ras activation in intact cells.

The adaptor protein Shc contains a phosphotyrosine binding (PTB) domain and a Src homology 2 (SH2) domain, both of which are known to interact with phosphorylated tyrosines. We have shown previously that tyrosine 1148 of the activated epidermal growth factor (EGF) receptor is a major binding site for Shc while tyrosine 1173 is a secondary binding site in intact cells. In the present study, we investigated the interaction between the PTB and SH2 domains of Shc and the activated human EGF receptor. Mutant 52-kDa Shc with an arginine-to-lysine substitution at residue 175 in the PTB domain (Shc R175K) or 397 in the SH2 domain (Shc R397K) was coexpressed in Chinese hamster ovary cells overexpressing the wild-type or mutant EGF receptors that retained only one of the autophosphorylation sites at tyrosine 1148 (QM1148) or 1173 (QM1173). Shc R397K was coprecipitated with the QM1148 and QM1173 receptors, was tyrosine-phosphorylated, and associated with Grb2 and Sos. In contrast, coprecipitation of Shc R175K with the mutant receptors was barely detectable. In cells expressing the QM1173 receptor, Shc R175K was tyrosine-phosphorylated and associated with Grb2, while association of Sos was barely detectable. In cells expressing the QM1148 receptor, tyrosine phosphorylation of Shc R175K was markedly reduced. When both Shc R175K and 46-kDa Shc R397K were coexpressed with the mutant receptors, p46 Shc R397K was dominantly tyrosine-phosphorylated. In cells expressing the wild-type receptor, Shc R397K, but not Shc R175K, translocated to the membrane in an EGF-dependent manner. In addition, Ras activity stimulated by the immunoprecipitates of Shc R397K was significantly higher than that by the immunoprecipitates of Shc R175K. The present results indicate that tyrosine 1148 of the activated EGF receptor mainly interacts with the Shc PTB domain in intact cells. Tyrosine 1173 interacts with both the PTB and SH2 domains, although the interaction with the PTB domain is dominant. In addition, Shc bound to the activated EGF receptor via the PTB domain dominantly interacts with Grb2-Sos complex and plays a major role in the Ras-signaling pathway.

Regulating insulin-receptor-gene expression by differentiation and hormones.

Insulin regulates cell function by first binding to the insulin receptor (IR) localized on the cell surface. With the cloning of IR cDNA and the IR-gene promoter, the regulation of the IR gene during differentiation and by various hormones can be studied. Muscle is a major target tissue for insulin action. BC3H1 cells, a mouse muscle cell line in culture, are a model cell type for studying insulin action. Differentiation in these cells results in a 5- to 10-fold increase in IR binding and a 5- to 10-fold increase in IR content. Studies of IR mRNA by Northern and slot-blot analyses reveal a 10-fold increase in IR mRNA after differentiation. These studies indicate that there is a selective increase in IR-gene expression during muscle differentiation. A similar increase in IR-gene expression is observed for the IR during pancreatic acinar cell differentiation. Glucocorticoids increase IR content in several target tissues. Studies in cultured IM-9 lymphocytes indicate that glucocorticoids induce a 5-fold increase in IR mRNA levels. Studies of IR mRNA half-life indicate that glucocorticoids do not alter IR mRNA stability. When the transcription of the IR is measured by elongation assays, glucocorticoids directly stimulate IR transcription 5- to 10-fold. The effect is detectable within 30 min of glucocorticoid treatment and is maximal within 2 h. Therefore, these studies demonstrate that the IR gene is under the direct regulation of glucocorticoids. Insulin downregulates the IR in various target tissues. Prior studies indicate that this downregulation was partly because of accelerated IR degradation. Studying AR42J pancreatic acinar cells, we also found that insulin accelerates IR degradation. Moreover, in these cells, insulin decreases IR biosynthesis by approximately 50%. Studies of IR mRNA indicate there is a concomitant decrease in IR mRNA levels after insulin treatment. Thus, insulin decreases IR-gene expression. The genomic structure of the IR promoter has been elucidated. Primer extension and nuclease S1 analysis indicate that IR mRNA has multiple start sites. The promoter fragment was ligated to a promoterless "reporter" plasmid containing the bacterial gene chloramphenicol acetyltransferase (CAT). When this plasmid is transfected into cultured cells, CAT activity is detected, indicating promoter activity. Various portions of a genomic fragment were ligated to a promoter to study glucocorticoid regulation of the IR promoter. These studies indicate that IR-gene expression is regulated by differentiation and hormonal agents.(ABSTRACT TRUNCATED AT 400 WORDS)

Effects of C-terminal fragments of cholecystokinin on exocrine and endocrine secretion from isolated perfused rat pancreas.

The ability of various C-terminal fragments of cholecystokinin (CCK) to increase pancreatic exocrine and endocrine secretion was examined in the isolated perfused rat pancreas. CCK octapeptide (CCK-8) induced biphasic dose-response curves for stimulation of pancreatic juice and amylase secretion. Maximal pancreatic juice and amylase output were obtained with 100 pM CCK-8. Concentrations of CCK-8 that caused pancreatic exocrine secretion also increased insulin release in the presence of 8.3 mM glucose. The tetrapeptide of CCK also simultaneously stimulated both exocrine and endocrine secretion, but was about 100,000 times less potent than CCK-8. By contrast both deca- and tetradecapeptide of CCK at a concentration of 100 pM stimulated secretion of pancreatic juice and amylase, and elicited insulin release comparably to CCK-8. The complete CCK-8 sequence was required as deamidated CCK-8 was without effects on exocrine and endocrine pancreatic secretion at a concentration of 100 pM. The present observations suggest that the structural requirements for CCK-induced insulin secretion are the same as those for CCK-induced exocrine secretions, and that the amino acids in position 5-8 and the amidated residue on the C-terminus are required for physiological activity of CCK on both the exocrine and endocrine pancreas. It is concluded that C-terminal fragments of CCK with eight or more amino acid residues are potent potentiators of insulin release as well as pancreatic exocrine stimulants.

Dibutyryl guanosine 3',5'-monophosphate inhibits cholecystokinin potentiation of insulin release in the isolated perfused rat pancreas.

(Bu)2cGMP is known to act as a specific competitive inhibitor for gastrin and cholecystokinin (CCK) peptides. We have examined the effects of (Bu)2cGMP on CCK octapeptide (CCK-8) stimulation of insulin release in the isolated perfused pancreas and compared them with those on protein output. Addition of (Bu)2cGMP after a 20-min perfusion with 100 pM CCK-8 resulted in two distinctly different phases of insulin suppression. There was a sharp initial decline in insulin release for 3 min, followed by transient recovery toward the control level for 5 min, and then a small decline until termination of (Bu)2cGMP infusion. (Bu)2cGMP produced a concentration-dependent inhibition of both phases of insulin decrement. (Bu)2cGMP also produced a concentration-dependent inhibition of protein output. Addition of 1 mM (Bu)2cGMP rapidly and completely abolished CCK-8-stimulated protein output. Since CCK is released by meal intake and exogenous CCK stimulates insulin release and augments glucose-induced insulin release, it is possible that endogenous CCK plays an important role in the enteroinsular axis. The present findings of blockade of CCK-8-induced insulin release by selective antagonist of the action of CCK provide evidence for CCK as a mediator in the enteroinsular axis.

Differential control of cellular gene expression by diffusible and non-diffusible EGF.

Cell gene expression is affected by both the kind and mode of growth factor stimulation (diffusive vs. non-diffusive). Epidermal growth factor (EGF) was pattern-immobilized on a polystyrene plate. Although the growth of the rat phaeochromocytoma cell line PC12 is stimulated by diffusible EGF, and differentiation is stimulated by diffusible nerve growth factor (NGF), immobilized (non-diffusible) EGF stimulated PC12 differentiation. The immobilized EGF caused a long-lasting stimulation of the intracellular signal protein mitogen-associated protein MAP kinase (MAPK, also known as ERK) and p38 (a subfamily of the MAPK superfamily) in cells, as did diffusible NGF. The switching between growth stimulation and differentiation is considered to be due to the duration of the stimulus. The function of the biosignal conjugate was regulated using conjugation methodology.

Enhancement of the mitogenic effect by artificial juxtacrine stimulation using immobilized EGF.

Mouse epidermal growth factor (EGF) was covalently conjugated with the water-soluble polymer, poly(acrylic acid) (EGF-PAA), or with the water-insoluble polymer, surface-hydrolyzed poly(methyl methacrylate) (EGF-PMMA). Immobilized EGF (EGF-PMMA) stimulated DNA synthesis in Chinese hamster ovary cells overexpressing EGF receptors in amounts that were 5 to 10% of those of free EGF required for comparable effects. In addition, the maximal mitogenic effect of EGF-PMMA was greater than that of unconjugated EGF or EGF-PAA. EGF, EGF-PAA, and EGF-PMMA induced the autophosphorylation of EGF receptors and the stimulation of mitogen-activated protein kinase. However, whereas the onset of these effects was delayed with EGF-PMMA, they persisted for much longer than those of EGF and EGF-PAA. Unlike EGF and EGF-PAA, EGF-PMMA was not associated with cells after their removal from culture and did not induce receptor internalization. Culturing cells with PMMA-immobilized EGF thus represents a model system for studying "juxtacrine" stimulation of cells by membrane-bound growth factors.

Pancreatic endocrine function in cirrhotic rats.

Pancreatic endocrine function in liver cirrhosis was examined in rats both in vivo and in vitro. Experimental liver cirrhosis was induced by subcutaneous injections of 50% carbon tetrachloride in a dose of 2 mL/kg body weight twice a week for 16 weeks. Control rats received a similar dose of olive oil during the same period. In cirrhotic rats, immunoreactive insulin contents in the pancreas were significantly lower, whereas immunoreactive glucagon contents were about threefold higher than those of control rats. In the first part of this study, insulin and glucagon concentrations in both jugular and portal venous blood at basal conditions and after oral glucose loading were simultaneously determined in vivo. Peripheral insulin levels, both before and after glucose loading, were higher, whereas portal insulin concentrations were lower in cirrhotic rats than in the control rats. In contrast, glucagon levels in both the peripheral and portal veins were significantly higher in cirrhotic rats than in control rats. In the second part, isolated perfused pancreata were prepared from cirrhotic and control rats to further characterize the endocrine function of cirrhotic rat pancreas. Insulin secretion in response to 16.7 mmol/L glucose and 100 pmol/L cholecystokinin-octapeptide both were 40% lower in cirrhotic rats than in controls. In contrast, there was no significant difference in arginine-stimulated insulin release between the two groups. However, glucagon secretion in response to 20 mmol/L arginine was 40% higher in cirrhotic rats. If sensitivity is defined as the hormone release proportional to the pancreatic contents, then A and B cells in the cirrhotic rats had normal sensitivity to both glucose and cholecystokinin-octapeptide.(ABSTRACT TRUNCATED AT 250 WORDS)

Oral glucose ingestion stimulates cholecystokinin release in normal subjects and patients with non-insulin-dependent diabetes mellitus.

The role of glucose in the regulation of plasma cholecystokinin (CCK) level was investigated in healthy control subjects and patients with non-insulin-dependent diabetes mellitus (NIDDM). Plasma CCK concentration was determined by a specific and sensitive bioassay and by a highly sensitive and reliable double-antibody radioimmunoassay using OAL-656 as an antiserum. In control subjects, ingestion of Trelan G-75 (1,200 mOsm/L,225 mL), which is equivalent to 75 g glucose as metabolic products, caused a rapid and significant increase in plasma CCK bioactivity from 1.3 +/- 0.2 to a peak of 5.8 +/- 0.6 pmol/L and immunoreactive CCK concentration from 1.2 +/- 0.1 to 4.6 +/- 0.6 pmol/L. Ingestion of 75 g glucose in 225 mL water (33.3% solution) increased plasma CCK bioactivity to a similar degree to that observed following Trelan G-75 (peak response, 4.5 +/- 0.4 pmol/L). The same volume of 0.9% NaCl solution or water failed to increase plasma CCK concentration. A smaller dose of glucose (50 b/150 mL water) increased plasma CCK concentration, although the peak level (3.0 +/- 0.5 pmol/L) was less than that observed following 75 g glucose. In patients with NIDDM, Trelan G-75 ingestion increased CCK concentration, but the peak level was lower, albeit insignificantly, than that of normal subjects. When the maximal increment of plasma CCK above the basal value was compared between control and NIDDM subjects, the differences were statistically significant (NIDDM, 3.6 +/- 0.1 pmol/L; control, 5.0 +/- 0.4; P < .01). However, integrated CCK responses to Trelan G-75 in NIDDM (165.8 +/- 15.5 pmol/120 min) were not significantly different from those in control subjects (189.8 +/- 15.9 pmol/120 min). Peak CCK bioactivity occurred within 10 to 30 minutes of ingestion, preceding the increase in glucose and insulin. These results suggest a possible effect of CCK on insulin release in humans, and that the CCK secretory response to glucose in well-controlled diabetic patients is not significantly altered.

Exocrine and endocrine pancreatic function in rats treated with alpha-glucosidase inhibitor (acarbose).

Pancreatic exocrine and endocrine secretory dynamics were studied in the isolated perfused pancreata of rats fed a normal diet or a diet supplemented with the alpha-glucosidase inhibitor, acarbose (150 mg/100 g food). After 10 days, the body weight of acarbose-treated rats was slightly lower than that of the control rats despite a larger food intake. Pancreatic amylase levels were significantly decreased, trypsinogen levels were significantly increased, and lipase levels were unaltered in the treated group compared with the controls. Basal and caerulein-stimulated flow rates of pancreatic juice as well as basal amylase output were similar in both groups, whereas caerulein-stimulated amylase output was significantly lower in the acarbose-treated group. Secretory responsiveness of amylase in the treated group was, however, about twice as high as that in the control group when related to pancreatic amylase content. Insulin release in response to either glucose or cerulein was similar in both groups. These findings indicate that treatment with acarbose may alter pancreatic enzyme content without changing the secretory responsiveness of either the exocrine or endocrine pancreas.

Involvement of endogenous cholecystokinin in the development of acute pancreatitis induced by closed duodenal loop.

Involvement of endogenous cholecystokinin (CCK) in the development of acute pancreatitis induced in rats by closed duodenal loop (CDL) was examined, and the effects of the potent and specific CCK receptor antagonist loxiglumide on this model of acute pancreatitis were evaluated. Plasma CCK bioactivity was markedly elevated 3 and 6 h after onset of acute pancreatitis. A single subcutaneous injection of 50 mg/kg body wt of loxiglumide 30 min before the induction of acute pancreatitis completely eliminated the hypercholecystokinemia. Loxiglumide given 3 h after the induction of acute pancreatitis suppressed plasma CCK bioactivity, which had risen up to 30-fold over basal value (0 h) at 3 h, to nearly the basal level. Loxiglumide pretreatment, in addition, significantly prevented the rise in serum amylase and lipase activity, as well as the increase in ascitic volume. It also ameliorated histological alterations of hemorrhagic and necrotizing pancreatitis. Reduction of plasma CCK bioactivity by loxiglumide after the onset of pancreatitis slowed the rate of progression of pancreatitis. However, pancreatic wet weight and cellular infiltration were not significantly influenced by loxiglumide treatment. These observations suggest that endogenous CCK is not involved in the initiation of acute hemorrhagic and necrotizing pancreatitis induced by CDL, but is involved in the development of pancreatitis in this model.

Effect of synthetic protease inhibitor camostate on pancreatic exocrine function in rats.

Pancreatic exocrine function in rats given synthetic protease inhibitor camostate (200 mg/kg body weight) perorally once daily for 10 days was investigated. Pancreatic wet weight was significantly increased in the camostate-treated rats. The increase in pancreatic weight was associated with pronounced hypertrophy and moderate hyperplasia. Total amylase, trypsin, and lipase contents in the pancreas were also increased in the camostate-treated group compared with the control rats. Secretory patterns of pancreatic juice and amylase in response to caerulein were similar in both groups, whereas the dose-response curve for pancreatic juice secretion in the camostate-treated rats was shifted tenfold toward higher concentrations of caerulein. Basal and caerulein-stimulated flow rates of pancreatic juice were significantly greater in the camostate-treated rats than the control rats, although both groups showed a threefold increase over basal secretion in response to maximal stimulation. Amylase outputs in basal state and in response to submaximal doses of caerulein were significantly lower, whereas those to maximal and supramaximal doses were significantly greater in the camostate-treated animals than that in the control rats. These results indicate that treatment with camostate induces pancreatic hypertrophy and hyperplasia, and that the secretory function of the hypertrophied pancreas is quantitatively but not qualitatively altered.

Effect of ethanol on pancreatic exocrine secretion in rats.

The effect of ethanol on pancreatic exocrine secretion was studied in isolated rat pancreatic acini. Ethanol caused a dose-dependent stimulation of amylase release, and a twofold increase of amylase release was observed with 600 mM ethanol. Ethanol inhibited cholecystokinin octapeptide (CCK-8)- and carbamylcholine-stimulated amylase release and similarly inhibited binding of [125I]CCK-8 and [N-methyl-3H]scopolamine to isolated rat pancreatic acini in a dose-dependent manner. The inhibitory effect of ethanol was fully reversible with respect to CCK-8-induced amylase release. On the other hand, ethanol potentiated secretin- and vasoactive intestinal peptide (VIP)-stimulated amylase release. Ethanol induced a small but significant increase in Ca2+ efflux, whereas CCK-8 induced an immediate and large increase, but ethanol significantly inhibited CCK-8-stimulated Ca2+ efflux. The present study clearly demonstrates the dual effects of ethanol on pancreatic exocrine function: stimulation and inhibition. We suggest that mobilization of intracellular Ca2+ may be involved in the mechanism of ethanol's action on isolated rat pancreatic acini.

The protective effect of the trypsin inhibitor urinastatin on cerulein-induced acute pancreatitis in rats.

We examined the protective effects of the trypsin inhibitor, urinastatin, extracted from human urine in experimental acute pancreatitis in conscious rats. Acute pancreatitis was induced by four subcutaneous injections of 20 micrograms/kg body weight of cerulein at hourly intervals. Urinastatin at a dose of 50,000 U/kg body weight/6.5 h was given by continuous i.v. infusion beginning 0.5 h before the first cerulein injection and continuing until 3 h after the last one, for a total of 6.5 h. Urinastatin significantly reduced serum levels of amylase, lipase, and anionic trypsin(ogen) but did not affect pancreatic wet weight or protein or enzyme content. Urinastatin also significantly reduced the degree of acinar cell vacuolization, interstitial edema, and cellular infiltration. These results suggest that urinastatin does not block the induction of acute pancreatitis by cerulein but does substantially reduce its severity.

Synthesis and secretion of rat pancreatic proteins by Xenopus laevis oocytes.

An in vivo translation system, the Xenopus laevis oocyte, was employed to study the synthesis and secretion of pancreatic proteins. RNA was purified from normal and diabetic rat pancreas and normal rat liver by use of guanidine isothiocyanate lysis and cesium chloride gradient centrifugation. The presence of functional mRNA was documented by translation in a reticulocyte lysate that yielded precursors of all major secretory proteins, i.e., slightly higher Mr than proteins synthesized in situ by pancreatic acini. Mature X. laevis oocytes were then microinjected with either total RNA or purified mRNA. When oocytes were subsequently incubated with 35S-methionine, pancreatic secretory proteins or hepatic albumin could be immunoprecipitated from oocyte lysate with specific polyclonal antibodies against amylase, trypsin, ribonuclease, and albumin. Amylase was shown to be enzymatically active. Moreover, oocytes released pancreatic secretory proteins into the medium when injected with pancreatic RNA in a time-dependent manner. Only the mature form of amylase was secreted and secretion was not regulated by secretagogues. When a comparison was made after injection of RNA from diabetic pancreas known to contain altered amounts of individual mRNAs, there was a decrease in amylase and an increase in trypsinogen synthesis in oocytes that was comparable to the results of cell free translation. The oocyte expression system, therefore, should be useful not only for studies of protein synthesis but also for processing and secretion.