Galanin inhibits rat pancreatic amylase release via cholinergic suppression.

The effects of galanin on pancreatic exocrine function were examined using rat pancreatic tissues. In anesthetized rats, galanin (40 micrograms/kg/h) decreased amylase secretion stimulated by 2-deoxy glucose (5.8 +/- 0.1 vs. 3.1 +/- 0.1 times basal) and cholecystokinin octapeptide (21.5 +/- 0.6 vs. 16.8 +/- 0.5), while not inhibiting bethanechol-stimulated secretion. In dispersed acini, there was no effect of galanin alone (10(-8) to 10(-13) M) on amylase release, nor did galanin (10(-6) or 10(-8) M) coincubation affect amylase release stimulated by bethanechol (10(-3) to 10(-7) M) or CCK-8 (10(-8) to 10(-13) M). Using pancreatic lobules, coincubation with galanin (10(-6) M) suppressed 75 mM KCl-stimulated amylase secretion and ACh release (10.1 +/- 0.6% vs. 7.3 +/- 0.4%). Veratridine-stimulated (10(-4) M) amylase secretion and ACh release (12.4 +/- 1.7% vs. 8.5 +/- 0.7%) were similarly diminished.     

Effects of an inhibitor of myosin light chain kinase on amylase secretion from rat pancreatic acini

Ca(2+)/calmodulin-dependent protein (CaM) kinases play an important role in Ca(2+)-mediated secretory mechanisms. Previously, we demonstrated that a CaM kinase II inhibitor KN-62 had a small inhibitory effect on amylase secretion stimulated by CCK. In the present study, we investigated the effects of a myosin light chain kinase (MLCK) inhibitor on amylase secretion and Ca(2+) signaling in rat pancreatic acini. A specific inhibitor of MLCK, wortmannin, inhibited amylase secretion stimulated by CCK-8 (30 pM) in a concentration-dependent manner. Wortmannin (10 microM) had no effects on basal secretion but reduced amylase secretion stimulated by CCK-8 (30 pM) by 67 +/- 3%. Wortmannin inhibited amylase secretion stimulated by calcium ionophore (A23187) and phorbol ester (TPA). Wortmannin also inhibited amylase response to thapsigargin by 76 +/- 8% and to both thapsigargin and TPA by 52 +/- 10%. Ca(2+) oscillations evoked by CCK-8 (10 pM) were inhibited by wortmannin (10 microM). Wortmannin had a little inhibitory effect on an initial rise in [Ca(2+)](i), and abolished a subsequent sustained elevation of [Ca(2+)](i) evoked by 1 nM CCK-8. In conclusion, MLCK plays a crucial role in amylase secretion from pancreatic acini and regulates Ca(2+) entry from the extracellular space.     

Cyclic GMP inhibits protein kinase C-mediated secretion in rat pancreatic acini

Dibutyryl cyclic GMP (Bu2cGMP) inhibited agonist-induced secretion of amylase from isolated rat pancreatic acini. In contrast to previous studies, this inhibitory action was not confined to butyryl derivatives of cyclic GMP, since the membrane-permeant cyclic GMP analogues Bu2cGMP and cyclic 8-bromo-GMP (8-Br-cGMP) were equipotent (IC50 2 nM) in their inhibition of amylase secretion stimulated by cholecystokinin-(26-33)-octapeptide (CCK8): at extracellular concentrations up to 1 mM, cyclic GMP itself was devoid of inhibitory activity. Both Bu2cGMP and 8-Br-cGMP also potently inhibited secretion stimulated by 4 beta-phorbol 12-myristate 13-acetate (PMA) (IC50 6 nM), but only partially inhibited responses elicited by bethanechol or bombesin and were without effect on A23187-evoked secretion. Furthermore, agents that are known to raise intracellular cyclic GMP levels (MB22948 (2-o-propoxyphenyl-8-azapurin-6-one) or nitroprusside) or antagonize the actions of protein kinase C (4 alpha-PMA or staurosporine), also inhibited CCK8- or PMA-stimulated secretion but not secretion elicited by bombesin, bethanechol, or A23187. It is concluded from these and other observations reported here that protein kinase C is the major intracellular mediator of amylase secretion stimulated by CCK8 and that this pathway may be regulated by cyclic GMP at a step that follows protein kinase C activation.     

1,2-Diacylglycerol, protein kinase C, and pancreatic enzyme secretion

To determine the role of 1,2-diacylglycerol (1,2-DAG) and protein kinase C in pancreatic enzyme secretion, we measured the effect of various pancreatic secretagogues on the cellular mass of 1,2-DAG and amylase release in dispersed pancreatic acini from the guinea pig. In addition, we measured the effect of a recently described protein kinase C inhibitor 1-(5-isoquinolinesulfonyl)-2-methylpiperazine (H-7) (Hidaka, H., Inagaki, M., Kawamoto, S., and Sasaki, Y. (1984) Biochemistry 23, 5036-5041), on secretagogue-stimulated amylase release from the acini. Cholecystokinin-octapeptide (CCK-OP), cholecystokinintetrapeptide, and carbachol each increased 1,2-DAG 2-3-fold but the increases occurred only with concentrations of these secretagogues that were supramaximal for amylase release and that had an inhibitory effect on stimulated amylase release. Supramaximal concentrations of bombesin stimulated only a small increase in 1,2-DAG and did not cause inhibition of stimulated amylase release. When the action of carbachol was terminated with atropine or CCK-OP with dibutyryl cyclic GMP, stimulated amylase release ceased immediately but cellular 1,2-DAG required at least 15 min to return to the basal level. Increasing cytosolic free Ca2+ with the Ca2+ ionophore, A23187, in Ca2+-containing incubation media augmented amylase release stimulated by 4 beta-phorbol 12-myristate 13-acetate but inhibited amylase release stimulated by CCK-OP, carbachol, and bombesin without decreasing the cellular content of 1,2-DAG. H-7 inhibited protein kinase C activity in a pancreatic homogenate but augmented amylase release from acini stimulated by either CCK-OP, carbachol, or 4 beta-phorbol 12-myristate 13-acetate. These findings indicate that 1,2-DAG and protein kinase C do not have a stimulatory role in pancreatic stimulus-secretion coupling but may have an inhibitory one.     

Protein malnutrition and response of pancreatic acinar cells to stimulation by cholecystokinin

Pancreatic lobules were isolated from 2 groups of male Wistar rats after 23 days of diet. A control group (C) fed on a 20% protein diet (16% gluten + 4% casein) and an experimental group (E) on a 5% protein diet (4% gluten + 1% casein). After isolation, lobules were preincubated 10 min with 10 muCi [3H]-leucine, washed, then incubate within Krebs Ringer bicarbonate Hepes. Basal secretion, then stimulated secretion (50 pM of cholecystokinin (CCK] of radioactive and non-radioactive protein and amylase outputs were measured. During basal secretion, in (E) group, lobules secreted more proteins than (C) one, the same outputs of amylase and radioactive protein were observed in both groups. The stimulated secretion by CCK increased the outputs of non-radioactive protein and amylase of lobules (T) (2-3 fold), but was without effect on lobule (E) outputs. Therefore, a low-protein diet involved a decrease of CCK sensibility on acinar cells, this fact might be mediated by a decreasing number and/or affinity of their CCK receptors.     

Effects of potent bombesin antagonist on exocrine pancreatic secretion in rats.

Recent synthesis of specific, potent bombesin receptor antagonists allows examination of the role of bombesin-like peptides in physiological processes in vivo. We characterized effects of [D-Phe6]bombesin(6-13)-methyl-ester (BME) on pancreatic enzyme secretion stimulated by the C-terminal decapeptide of gastrin releasing peptide (GRP-10), food intake, and diversion of bile-pancreatic juice in rats. In isolated pancreatic acini, BME had no agonistic effects on amylase secretion but competitively inhibited responses to GRP-10, yielding a pA2 value of 8.89 +/- 0.19. In conscious rats with gastric, jugular vein, bile-pancreatic, and duodenal cannulas, basal enzyme secretion (bile-pancreatic juice recirculated) was not affected by the antagonist. Maximal amylase response to GRP-10 (0.5 nmol/kg/h) was inhibited dose dependently by BME, reaching 97% inhibition at a dose of 400 nmol/kg/h. The dose response curve of amylase secretion stimulated by GRP-10 was shifted to the right by 40 nmol/kg/h BME, but maximal amylase response was unaltered, suggesting competitive inhibition in vivo. Liquid food intake and bile-pancreatic juice diversion caused substantial increases in amylase secretion; neither response was altered during administration of 400 pmol/kg/h BME. These results demonstrate that BME is a potent, competitive antagonist of pancreatic responses to bombesin-like peptides in vitro and in vivo. Lack of effect of BME on basal pancreatic secretion or responses to liquid food intake or diversion of bile-pancreatic juice in rats suggests that endogenous bombesin-like peptides do not act either directly or indirectly to mediate these responses.     

Effects of sodium ions and monensin on amylase secretion from rat parotid cells

The role of sodium ions in amylase secretion from rat parotid cells was studied using various Na+-free media and monensin. In a sucrose medium, amylase secretion was not stimulated by isoproterenol but was significantly stimulated by dibutyryl cAMP. In choline chloride and LiCl media, both isoproterenol and dibutyryl cAMP clearly evoked amylase release. Monensin itself elicited amylase secretion slightly, but significantly inhibited the secretion stimulated by isoproterenol or dibutyryl cAMP. The inhibitory effect of monensin was detectable even in choline chloride, LiCl and KCl media. These results indicate that sodium ions are not essential for amylase secretion from rat parotid cells and that the inhibitory effect of monensin is independent of influx of sodium ions or efflux of potassium ions.     

Interactions of intracellular mediators of amylase secretion in permeabilized pancreatic acini.

Mouse pancreatic acini were permeabilized with streptolysin O to investigate amylase secretion stimulated by various intracellular mediators and the kinetics of secretion as a function of temperature. Amylase secretion was temperature dependent in that the initial rate of Ca2(+)-stimulated secretion increased with increasing temperature. In addition, there was no enhancement of Ca2(+)-stimulated secretion by GTP[gamma S] at 14 degrees C, while enhancement was maximal at 30 degrees C. GTP[gamma S]-mediated enhancement of secretion at a given temperature was mostly due to sustained secretion with a small increase in secretory rate. At 30 degrees C Ca2(+)-stimulated secretion was also enhanced by cAMP and phorbol ester (TPA) to similar extents as by GTP[gamma S]. The maximally effective concentration of cAMP was 1-10 microM in the presence of 0.1 mM isobutylmethylxanthine. The enhancements of Ca2(+)-stimulated amylase secretion by all combinations of cAMP (100 microM plus 0.1 mM isobutylmethylxanthine), TPA (1 microM), and GTP[gamma S] (30 microM) were fully additive. In Ca2(+)-free buffer, cAMP, TPA or GTP[gamma S] individually had no effect on amylase secretion. Together, TPA and GTP[gamma S] stimulated Ca2(+)-independent secretion, which was 187 +/- 38% of basal. Cyclic AMP together with TPA and GTP[gamma S] in the absence of Ca2+ stimulated 329 +/- 30% of basal secretion. Ca2(+)-stimulated amylase secretion was decreased about 50% by metabolic inhibition, while the enhancement by cAMP, TPA or GTP[gamma S] was totally blocked by metabolic inhibitors. These data demonstrate that amylase secretion in the acinar cell is mediated by multiple intracellular pathways which act in parallel and probably converge at a distal step in the exocytotic process.     

Effects of GP2 expression on secretion and endocytosis in pancreatic AR4-2J cells

GP2 is the major membrane protein present in secretory granules of the exocrine pancreas. GP2's function is unknown, but a role in digestive enzyme packaging or secretion from secretory granules has been proposed. In addition, GP2 has been proposed to influence endocytosis and membrane recycling following stimulated secretion. Adenovirus-mediated GP2 overexpression in the rat pancreatic cell line AR4-2J was used to study its impact on digestive enzyme secretion and membrane recycling. Immunoelectron microscopy showed that GP2 and amylase co-localized in secretory granules in infected AR4-2J cells. CCK-8 stimulation resulted in a fourfold increase in amylase secretion with or without GP2 expression. GP2 expression also did not influence endocytosis following CCK-8 stimulation. Thus, GP2 expression in AR4-2J cells does not affect amylase packaging in secretory granules or stimulated secretion. GP2 expression also does not influence membrane recycling in response to stimulated stimulation in AR4-2J cells.     

The effects of ammonia on pancreatic enzyme secretion in vivo and in vitro.

BACKGROUND: Recent studies clearly demonstrate that Helicobacter pylori (H. pylori) infection of the stomach causes persistent elevation of ammonia (NH3) in gastric juice leading to hypergastrinemia and enhanced pancreatic enzyme secretion. METHODS: The aim of this study is to evaluate the influence of NH4OH on plasma gastrin level and exocrine pancreatic secretion in vivo in conscious dogs equipped with chronic pancreatic fistulas and on secretory activity of in vitro isolated acini obtained from the rat pancreas by collagenase digestion. The effects of NH4OH on amylase release from pancreatic acini were compared with those produced by simple alkalization of these acini with NaOH. RESULTS: NH4OH given intraduodenally (i.d.) in increasing concentrations (0.5, 1.0, 2.0, 4.0, or 8.0 mM/L) resulted in an increase of pancreatic protein output, reaching respectively 9%, 10%, 19%, 16% and 17% of caerulein maximum in these animals and in a marked increase in plasma gastrin level. NH4OH (8 x 0 mM/L, i.d.) given during intravenous (i.v.) infusion of secretin (50 pmol/kg-h) and cholecystokinin (50 pmol/kg-h) reduced the HCO3 and protein outputs by 35% and 37% respectively, as compared to control obtained with infusion of secretin plus cholecystokinin alone. When pancreatic secretion was stimulated by ordinary feeding the same amount of NH4OH administered i.d. decreased the HCO3- and protein responses by 78% and 47% respectively, and had no significant effect on postprandial plasma gastrin. In isolated pancreatic acini, increasing concentrations of NH4OH (10(-7)-10(-4) M) produced a concentration-dependent stimulation of amylase release, reaching about 43% of caerulein-induced maximum. When various concentrations of NH4OH were added to submaximal concentration of caerulein (10(-12) M) or urecholine (10(-5) M), the enzyme secretion was reduced at a dose 10(-5) M of NH4OH by 38% or 40%, respectively. Simple alkalization with NaOH of the incubation medium up to pH 8.5 markedly stimulated basal amylase secretion from isolated pancreatic acini, whereas the secretory response of these acini to pancreatic secretagogues was significantly diminished by about 30%. LDH release into the incubation medium was not significantly changed in all tests indicating that NH4OH did not produce any apparent damage of pancreatic acini and this was confirmed by histological examination of these acini. CONCLUSIONS: 1. NH4OH affects basal and stimulated pancreatic secretion. 2. The excessive release of gastrin may be responsible for the stimulation of basal pancreatic enzyme secretion in conscious animals, and 3. The inhibitory effects of NH4OH on stimulated secretion might be mediated, at least in part, by its direct action on the isolated pancreatic acini possibly due to the alkalization of these acini.     

Role of free cytosolic calcium in secretagogue-stimulated amylase release from dispersed acini from guinea pig pancreas

To determine the role of free cytosolic calcium ([Ca+2]i) in stimulated enzyme secretion from exocrine pancreas, we determined the effects of various pancreatic secretagogues on [Ca+2]i and amylase release in dispersed acini from the guinea pig pancreas. Cholecystokinin-octapeptide (CCK-OP), carbachol, and bombesin, but not vasoactive intestinal peptide, stimulated rapid increases in [Ca+2]i from 100 to 600-800 nM that were independent of extracellular calcium. The increases in [Ca+2]i were transient (lasting less than 5 min) and correlated with an initial rapid phase of amylase release. After 5 min, secretagogue-stimulated amylase release occurred at basal [Ca+2]i. Carbachol pretreatment of the acini abolished the effects of CCK-OP and bombesin on [Ca+2]i and the initial rapid phase of amylase release. 4 beta-phorbol 12-myristate 13-acetate (PMA) had no effect on [Ca+2]i but stimulated an increase in amylase release. The addition of CCK-OP or A23187 to PMA-stimulated acini caused an increase in [Ca+2]i and PMA-stimulated amylase release only during the first 5 min after addition of these agents. These results indicate that CCK-OP, carbachol, and bombesin release calcium from an intracellular pool, resulting in a transient increase in [Ca+2]i and that this increase in [Ca+2]i mediates enzyme secretion during the first few minutes of incubation. The results with PMA suggest that secretagogue-stimulated secretion not mediated by increased [Ca+2]i (sustained secretion) is mediated by 1,2-diacylglycerol.     

Calcium concentration and amylase secretion in guinea pig pancreatic acini: interactions between carbachol, cholecystokinin octapeptide and the phorbol ester, 12-O-tetradecanoylphorbol 13-acetate

The effects of the phorbol ester, 12-O-tetradecanoylphorbol 13-acetate (TPA) on amylase secretion and cytoplasmic free calcium concentration ([Ca2+]i) were investigated in dispersed guinea pig pancreatic acini. Carbachol evoked dose-dependent increases in amylase secretion and [Ca2+]i with half-maximal responses at 2.5 and 5 microM, respectively. Carbachol-induced calcium transients could be blocked by atropine. In the presence of a maximal effective dose of carbachol, cholecystokinin octapeptide caused no further increase in [Ca2+]i, suggesting that both agonists act on the same pool of trigger calcium. TPA (10(-9)-10(-6) M) stimulated amylase secretion with no change in [Ca2+]i. Maximum amylase secretion occurred at 0.5 microM TPA. Preincubation of acini in the presence of TPA resulted in a time- and dose-dependent inhibition (IC50 = 30 nM) of the carbachol-induced rise in [Ca2+]i, the maximal effect being observed within 3 min. The inactive phorbol ester, 4 alpha-phorbol 12,13-didecanoate was ineffective in inhibiting the carbachol-stimulated rise in [Ca2+]i. These findings suggest that, in addition to stimulating amylase secretion, probably through protein kinase C, TPA may also exert a negative feedback control over secretagogue-induced calcium transients.     

Stimulatory effect of PG-KII, an NK3 tachykinin receptor agonist, on isolated pancreatic acini: species-related differences

More information is needed on the physiological role of the tachykinins (TKs), especially neurokinin3-receptor (NK3) agonists, in the pancreas. In this paper we investigated and compared the effect of PG-KII (10(-9) to 10(-6) M), a natural NK3-receptor agonist, with that of the known secretagogues substance P (10(-9) to 10(-6)M), caerulein (10(-11) to 10(-8) M) and carbachol (10(-8) to 10(-5) M), on amylase secretion from dispersed pancreatic acini of the guinea pig and rat. PG-KII (10(-7) M) significantly increased basal amylase release from guinea pig pancreatic acini (from 5.4+/-0.9% to 11.3+/-0.5%, P < 0.05) but left basal release in the rat unchanged (6.5+/-0.5%). The stimulant effect of PG-KII on guinea pig acini was significantly reduced by the NK3-receptor antagonist, SR 142801 (5 x 10(-7) M), and left unchanged by the NK1-receptor antagonist, SR 140333 (5 x 10(-7) M). Conversely, substance P (10(-7) M) significantly stimulated amylase secretion from rat and guinea pig acini (12.6+/-0.6% and 12.1+/-0.7%, P < 0.05). This stimulated effect of substance P was antagonized by the NK1--receptor antagonist (5 x 10(-7) M), but not by the NK3-receptor antagonist (5 x 10(-7) M). The PG-KII- and substance P-evoked maximal responses were lower than those evoked by caerulein (10(-9) M) (guinea pig, 19.1+/-1.3%; rat, 1802+/-0.9%, P < 0.01) and carbachol (10(-5) M) (guinea pig, 23.3+/-1.2%; rat, 24.0+/-1.1%, P < 0.01). The inhibitors of phospholipase C U-73122 (10(-5) M), phospholipase A2 quinacrine (10(-5)M), and protein tyrosine kinase genistein (10(-4) M), partly but significantly inhibited PG-KII, as well as carbachol-stimulated amylase release. Coincubation of PG-KII 10(-7) M with submaximal doses of caerulein (10(-11) to 10(-10) M) and carbachol (10(-7) to 10(-6) M) had an additive effect on amylase release. Pre-incubation with PG-KII (10(-7) M) for 30 min significantly reduced the subsequent amylase response to PG-KII, whereas pre-incubation with caerulein 10(-10) M or carbachol 10(-6) M did not. These findings suggest that PG-KII directly contributes to pancreatic exocrine secretion by interacting with acinar NK3 receptors of the guinea pig but not of the rat. PG-KII signal transduction involves the intracellular phospholipase C, phospholipase A2 and protein tyrosine kinase pathways. The NK3 receptor system cooperates with the other known secretagogues in regulating guinea pig exocrine pancreatic secretion and undergoes rapid homologous desensitization.     

Role of GRPergic neurons in secretin-evoked exocrine secretion in isolated rat pancreas

Effects of intrapancreatic gastrin-releasing peptide (GRP)-containing neurons on secretin-induced pancreatic secretion were investigated in the totally isolated perfused rat pancreas. Electrical field stimulation (EFS) increased secretin (12 pM)-induced pancreatic secretions of fluid and amylase. EFS induced a twofold increase in GRP concentration in portal effluent, which was completely inhibited by tetrodotoxin but not modified by atropine. An anti-GRP antiserum inhibited the EFS-enhanced secretin-induced secretions of fluid and amylase by 12 and 43%, respectively, whereas a simultaneous infusion of the antiserum and atropine completely abolished them. Exogenous GRP dose-dependently increased the secretin-induced pancreatic secretion with an additive effect on fluid secretion and a potentiating effect on amylase secretion, which was not affected by atropine. In conclusion, excitation by EFS of GRPergic neurons in the isolated rat pancreas results in the release of GRP, which exerts an additive effect on fluid secretion and a potentiating effect on amylase secretion stimulated by secretin. The release and action of GRP in the rat pancreas are independent of cholinergic tone.     

GTPγs对柴胡皂甙(I)刺激胰腺腺泡酶分泌的影响

为了解柴胡皂甙(I)[SA(I)]刺激大鼠胰腺腺泡酶分泌的信号传导通路,研究了GTPγs对SA(I)剌激通透腺泡细胞酶分泌的影响.用SLO通透细胞的同时,加入GTPγs在15min期间能诱发酶分泌,10'mol·L-1GTPγs有最大促泌效应.GTPγs浓度依赖性的增强SA(I)促酶分泌作用,l0-7 mol·L-1 GTPγs导致10-5mol·L-1 SA(I)刺激酶分泌量增加到1.6倍.用SLO预通透腺泡10min后,加入GTPγs使SA(I)刺激酶分泌的量-效曲线左移,SA(I)的EC50从2 0×10-5mol·L-1减小到1 0×10-5mol·L-1.以上结果提示,SA(I)活化受体偶联的G蛋白包括在其刺激酶分泌的信号传导通路中.     

The effect of calcium and cyclic AMP on amylase release in digitonin-permeabilized parotid gland cells

Rat parotid cells were permeabilized with digitonin to examine their secretory dynamics. Cells were isolated by a modification of the method previously described by Hootman [1985). J. Biol. Chem. 260, 4186-4194) in which alpha-chymotrypsin was included. The final preparation consisted of approx. 40-60% single cells. The cells were 85-90% viable by trypan blue exclusion and secreted amylase when stimulated with isoproterenol. Digitonin (2 or 5 microM) was sufficient for permeabilization while 2 microM digitonin was somewhat more effective in maintaining cell integrity as indicated by lactate dehydrogenase release. Digitonin had minimal effects on intracellular granules in the whole cell and was, thus, relatively selective. The response of digitonin-permeabilized cells to calcium (without secretagogues) in the incubation medium was monitored by amylase release. For a wide range of applied free calcium concentrations (1 X 10(-7) M to 10(-4) M) a statistically significant increase in amylase secretion was observed. Control cells did not release amylase to a similar extent without secretagogue. Cyclic AMP (50 microM) significantly enhanced amylase secretion from digitonin-treated cells at all concentrations of free calcium tested. Neither calcium nor cyclic AMP alone was sufficient to stimulate maximal amylase release. Our results provide direct evidence for a model in which calcium and cyclic AMP work on separate pathways as interacting regulators of exocytosis.     

Stimulatory effects of human pancreatic polypeptide on rat pancreatic acini

The effect of human pancreatic polypeptide (HPP) on rat pancreatic acini has been studied. It was found that HPP stimulated amylase and lipase release from the acini. The secretory response of acini to HPP was dose-dependent in a sigmoidal fashion. Between 10(-9) M and 10(-8) M concentration of HPP there was a slow increase of enzyme release to about 40-60% over basal release. At concentrations of HPP above 10(-8) M there was a rapid increase of enzyme release, amounting to 4-6 times over basal release at 10(-6) M concentration of HPP. The potency of HPP compared to other secretagogues at 10(-7) M concentration was 45% of CCK, 60% of carbachol and 75% of secretin. HPP did not inhibit the effect of CCK, secretin and carbachol on amylase release. The amylase release stimulated by HPP was accompanied by an increase in 45Ca2+ efflux. Atropine or dibutyryl cyclic GMP did not influence the effect of HPP. It is concluded that HPP stimulates the release of enzymes from rat pancreatic acini and that Ca2+ may be a mediator for this secretion.     

BAY-K-8644-stimulated amylase secretion from pancreatic acinar cells

Pancreatic acinar cells do not contain depolarization-sensitive calcium channels. Nonetheless, in the current study, the calcium channel activator, BAY-K-8644, was found to stimulate a time- and concentration-dependent increase in the spontaneous release of amylase. Secretion was dependent on the presence of extracellular calcium in the incubation medium. Racemic BAY-K-8644 and (or) its S(-)optical isomer did not enhance the secretory response to either carbachol or cholecystokinin octapeptide; however, when co-applied with either phorbol ester, vasoactive intestinal peptide, or forskolin, they potentiated amylase secretion. Nifedipine and the R(+)isomer of BAY-K-8644, which are both calcium channel antagonists, did not alter basal or forskolin-stimulated amylase secretion, and [3H]nitrendipine did not bind to acinar cell membranes. Neither atropine nor dibutyryl cGMP, inhibitors of cholinergic and cholecystokininergic receptors, respectively, affected BAY-K-8644-induced amylase secretion. While BAY-K-8644 stimulated concentration-dependent cGMP synthesis in acinar cells, it had no effect on basal or forskolin-stimulated cAMP formation. The data suggest that BAY-K-8644 may bind to acinar cell sites that are not functional calcium channel proteins but are coupled nevertheless to the secretory response, and that calcium channel antagonists do not bind to these sites. The mechanism of the secretagogue action of BAY-K-8644 remains to be elucidated.     

Reversible acetaldehyde inhibition of A23187-stimulated amylase secretion from isolated rat pancreatic acini

The Ca2+ ionophore, A23187, stimulated amylase secretion from isolated rat pancreatic acini in a dose-dependent manner with a maximal effect at 6 microM. Acetaldehyde, a metabolite of ethanol, caused a reduction in the magnitude of ionophore-stimulated secretion with no evidence of competitive inhibition. Furthermore, 6 microM ionophore-stimulated amylase secretion was dose-dependently inhibited by acetaldehyde. This inhibitory effect of acetaldehyde, however, was reversible on washing and reincubating acetaldehyde-treated acini. These results suggest that acetaldehyde reversibly inhibits intracellular components mediating stimulated secretion and this inhibition requires a continuous chemical interaction between acetaldehyde and intracellular component(s) regulating stimulated enzyme secretion.     

Phorbol ester attenuates cholecystokinin-stimulated amylase release in pancreatic acini of rats

12-O-tetradecanoylphorbol 13-acetate (TPA) and cholecystokinin octapeptide stimulate amylase secretion in dispersed pancreatic acini, presumably acting via the activation of protein kinase C. In this study, we examined TPA pretreatment on the subsequent response of rat pancreatic acini to secretagogues. Acini exposed to TPA (3 X 10(-7) M) at 37 degrees C reduced the subsequent amylase secretion as stimulated by cholecystokinin octapeptide and carbachol, but not by A23187 or VIP. The optimal effect was obtained after 5 min of preincubation with TPA. Longer incubation did not result in greater attenuation. The degree of attenuation was dependent on the concentration of TPA used in the pretreatment. Maximal effect was seen at TPA concentrations of 10(-7) M and higher. Preincubation with TPA resulted in alterations of the dose response of pancreatic acini to cholecystokinin octapeptide. A decrease in amylase secretion was obtained at optimal and suboptimal but not at supraoptimal concentrations of cholecystokinin octapeptide. The peak response to cholecystokinin octapeptide, furthermore, was shifted almost 1 log unit to the right, suggesting a decrease in cholecystokinin binding of the acini following TPA treatment. Binding studies demonstrated a reduction in the specific binding of 125I-labelled cholecystokinin octapeptide to acini following TPA treatment. Analysis of binding data revealed a decrease in affinity and binding capacity of the high-affinity component. No significant change in the binding capacity was detected with the low-affinity component, but a great increase in its affinity was observed. This suggests that the attenuation effect by TPA on the cholecystokinin octapeptide response in rat pancreatic acini in vitro is at the receptor level.