Regulation of protein phosphorylation in pancreatic acini by cyclic AMP-mediated secretagogues: interaction with carbamylcholine

The effects on protein phosphorylation in mouse pancreatic acini of cyclic AMP-mediated secretagogues and the Ca2+-mediated agonist carbamylcholine were compared. Under the conditions adopted for the study of protein phosphorylation, carbamylcholine (3 microM) stimulated amylase release from pancreatic acini 6-fold, whereas vasoactive intestinal polypeptide (VIP) (100 nM) and the cyclic AMP analogue 8-bromo-cyclic AMP (1 mM) caused little or no increase in secretion. However, VIP and 8-bromo-cyclic AMP, when added in combination with carbamylcholine, potentiated the stimulation of amylase release to 170-180% of that caused by carbamylcholine alone. As assessed by two-dimensional gel electrophoresis, VIP reproduced four of the ten changes in protein phosphorylation elicited by carbamylcholine, these changes being the increased phosphorylation of one soluble protein and the decreased phosphorylation of three soluble proteins. VIP enhanced the carbamylcholine-induced changes in phosphorylation for three proteins. In addition, VIP increased the phosphorylation of a unique protein of Mr 52,000 and pI 5.66 which was not affected by carbamylcholine. All of the effects on protein phosphorylation exerted by VIP in the presence or absence of carbamylcholine were mimicked by 8-bromo-cyclic AMP. Secretin also reproduced most of the changes in protein phosphorylation caused by VIP, although concentrations of secretin of at least 100-fold higher were required to elicit a maximal response. It is concluded that cyclic AMP-mediated secretagogues alter the phosphorylation of a unique protein as well as of several pancreatic proteins affected by carbamylcholine. Moreover, these effects appear to be mediated primarily by VIP-preferring receptors and may be involved in the synergistic action of VIP to promote carbamylcholine-induced amylase release.     

Potentiating role of cyclic AMP in pancreatic enzyme secretion, demonstrated by means of forskolin

The role of cyclic AMP in the regulation of enzyme secretion by the rabbit pancreas has been investigated by means of forskolin, an activator of the catalytic subunit of adenylate cyclase. Forskolin increases the cyclic AMP level in isolated pancreatic acini in a dose-dependent way. Basal amylase release, however, remains unchanged. Forskolin potentiates the increase in amylase release induced by the C-terminal octapeptide of cholecystokinin (CCK-8). Potentiation is already apparent at hormone concentrations which are only marginally effective in stimulating amylase secretion. CCK-8 alone does not raise the cellular cAMP level, but it potentiates the forskolin-induced increase. In relative terms, potentiation is higher with decreasing concentration of forskolin. These results indicate that cAMP alone does not play a direct role in CCK-stimulated pancreatic enzyme secretion in the rabbit, but it potentiates enzyme secretion already stimulated through a cAMP-independent process.     

Pertussis toxin stimulates cholecystokinin-induced cyclic AMP formation but is without effect on secretagogue-induced calcium mobilization in exocrine pancreas

The role of a pertussis toxin sensitive GTP-binding protein in mediating between cholecystokinin receptors and phosphatidylinositol 4,5-bisphosphate phosphodiesterase as well as in preventing cholecystokinin from increasing cellular cyclic AMP has been investigated using dispersed acini from rabbit pancreas. Pertussis toxin pretreatment (500 ng/ml, 2 h) did not affect cholecystokinin(octapeptide) (CCK-8)-induced increases in cytosolic free Ca2+ as judged from changes in fluorescence obtained from quin2-loaded acini. Although pretreatment with pertussis toxin was also without effect on resting acinar cell cyclic AMP levels, adenylate cyclase activity was increased, since inhibition of cyclic AMP phosphodiesterase activity by isobutylmethylxanthine (IBMX) resulted in an additional increase in cyclic AMP levels in toxin-treated acini, indicating that acinar cell adenylate cyclase activity is under some tonic inhibitory control by the pertussis toxin-sensitive inhibitory GTP-binding protein (Gi) of the adenylate cyclase system. CCK-8 gave an increase in cyclic AMP levels in both control (1.6-fold) and toxin-treated (2.3-fold) acini, leading to cyclic AMP levels in the toxin-treated acini 2-times as high as those in control acini. In the presence of IBMX, the cyclic AMP response to CCK-8 was again markedly enhanced in acini pretreated with the toxin (3.2- vs. 1.8-fold), resulting in cAMP levels in the toxin-treated acini 3.7-times those in the absence of IBMX, 2.5-times those in control acini in the presence of IBMX and 7.0-times those in control acini in the absence of IBMX. Neither the pretreatment with pertussis toxin, nor the presence of IBMX alone, nor the combination had an effect on basal amylase secretion. However, all three treatments potentiated the stimulatory effect of CCK-8 on amylase secretion and the amount of potentiation was proportional to the cyclic AMP levels reached. Our findings suggest that in the intact pancreatic acinar cell Gi inhibition of the catalytic subunit of the adenylate cyclase may largely be responsible for preventing cholecystokinin from increasing cellular cyclic AMP. They moreover show that cyclic AMP is a modulatory agent in rabbit pancreatic enzyme secretion, not able to stimulate secretion itself, but potentiating effects mediated by the phosphatidylinositol-calcium pathway.     

Stoichiometry of GTP hydrolysis in a poly(U)-dependent cell-free translation system. Determination of GTP/peptide bond ratios during codon-specific elongation and misreading

Pancreatic secretory factor (PSF), a 17.5-kDa protein purified from the venom of Gila monster (Heloderma suspectum), stimulated amylase secretion from dispersed rat pancreatic acini more efficiently than CCK-8, bombesin, carbachol and secretin, and without increasing 45Ca2+ efflux and cyclic AMP levels. The secretory action was dependent on the presence of extracellular calcium and was additive to the secretion induced by agents acting via cyclic AMP or via Ca2+ efflux.     

Evidence against cyclic GMP as a mediator of the actions of secretagogues on amylase release from guinea-pig pancreas

In dispersed acini from guinea-pig pancrease several pancreatic secretagogues increased calcium outflux, cyclic GMP and amylase secretion, whereas nitroprusside and hydroxylamide increased cyclic GMP but did not increase calcium outflux or amylase secretion and did not alter the action of secretagogues on calcium outflux or amylase secretion. Secretin and vasoactive intestinal peptide increased cyclic AMP and increased secretion but did not alter cyclic GMP. Nitroprusside and hydroxylamine did not alter cyclic AMP or the action of secretin or vasoactive intestinal peptide on cyclic AMP and enzyme secretion. Agents that increased cyclic GMP also caused release of the nucleotide into the extracellular medium; however, this release did not correlate with secretion of amylase into the extracellular medium. 8-Bromo cyclic AMP as well as 8-bromo cyclic GMP increased enzyme secretion and potentiated the increase in enzyme secretion caused by cholecystokinin or carbachol. The increase in amylase secretion caused by vasoactive intestinal peptide or secretin plus either of the cyclic nucleotide derivatives was the same as that caused by the peptide alone. These results indicate that cyclic GMP does not mediate the action of secretagogues on pancreatic enzyme secretion, that the release of cyclic GMP into the extracellular medium does not occur by exocytosis and that the increase in enzyme secretion caused by 8-bromo cyclic GMP results from its stability to mimic the action of endogenous cyclic AMP.     

PACAP-38, a novel peptide from ovine hypothalamus, is a potent modulator of amylase release from dispersed acini from rat pancreas.

Despite studies indicating the presence of specific pancreatic acinar receptors for PACAP-38, a peptide that was recently isolated from ovine hypothalamus, the actions of the new peptide on pancreatic enzyme secretion have not been examined. The present study demonstrates that in terms of cAMP production and amylase release from dispersed acini from rat pancreatic acini, PACAP-38 and an N-terminal fragment, PACAP-27, have the same potency and efficacy as vasoactive intestinal peptide (VIP). As with VIP, these actions are potentiated by adding an inhibitor of cyclic nucleotide phosphodiesterase, and combination of PACAP-38 with bombesin, CCK-8, carbachol or the calcium ionophore A23187 results in 2-fold augmentation of the secretory actions of these agents. Inhibition of PACAP-38-induced cAMP production and amylase release by two VIP-receptor antagonists indicates that the secretory effects of PACAP-38 are mediated by interaction with VIP receptors. PACAP-38, a new brain-gut peptide, may be a physiological modulator of pancreatic enzyme secretion.     

Stimulatory effects of Gila monster venom on rat pancreatic acini

The effects of Gila monster venom on dispersed rat pancreatic acini were compared with those of secretin and VIP. The efficacy of the venom in terms of amylase release was much higher (a 24-fold increase over basal secretion) than that of secretin (a 4-fold increase) and VIP (+ 40% only). On the other hand, cyclic AMP levels increased 12-fold with the venom, as compared to 18-fold with secretin and 16-fold with VIP. The venom, VIP and secretin all displaced 125I-VIP and the competition curve with the venom was steeper, suggesting that all VIP-recognizing receptors bound the venom with the same affinity. VIP receptors were, however, not responsible for the release of amylase provoked by the venom since VIP (and secretin) did not inhibit the secretory action of the venom. The venom exerted no effect on 45Ca efflux and its secretory effect did not depend on the presence of external calcium. Besides, the effect of CCK-8 on amylase release was additive with the effect of the venom. A first exposure to the venom induced a refractoriness to itself with respect to amylase release but not in terms of cyclic AMP increase. In conclusion, Gila monster venom may contain one component binding to VIP/secretin receptors with resulting cyclic AMP elevation. A second venom component may be responsible for the high secretory efficacy, without involving cyclic AMP or calcium efflux.     

Forskolin potentiates calcium-dependent amylase secretion from rat pancreatic acinar cells

The cellular and molecular effects of forskolin, a direct, nonhormonal activator of adenylate cyclase, were assessed on the enzyme secretory process in dispersed rat pancreatic acinar cells. Forskolin stimulated adenylate cyclase activity in the absence of guanyl nucleotide. It promoted a rapid and marked increase in cellular accumulation of cyclic AMP alone or in combination with vasoactive intestinal peptide (VIP) but was itself a weak pancreatic agonist and did not increase the secretory response to VIP or other cyclic AMP dependent agonists. Somatostatin was a partial antagonist of forskolin stimulated cyclic AMP synthesis and forskolin plus cholecystokinin-octapeptide (CCK-OP) induced amylase release. Forskolin potentiated amylase secretion in response to calcium-dependent agonists such as CCK-OP, carbachol and A-23187, but did not affect the ability of CCK-OP and (or) carbachol to mobilize 45Ca from isotope preloaded cells; forskolin alone did not stimulate 45Ca release. In calcium-poor media, the secretory response to forskolin and CCK-OP was reduced in a both absolute and relative manner. The data suggests that calcium plays the primary role as intracellular mediator of enzyme secretion and that the role of cyclic AMP may be to modulate the efficiency of calcium utilization.     

Action of cholera toxin on dispersed acini from rat pancreas. Post-receptor modulation involving cyclic AMP and calcium

In dispersed acini from rat pancreas, cholera toxin caused a significant increase in cellular cyclic AMP but little or no change in amylase secretion. The presence of a secretagogue that causes mobilization of cellular calcium (e.g., cholecystokinin, carbamylcholine, bombesin or ionophore A23187) caused a substantial increase in the effect of cholera toxin on enzyme secretion. Cholera toxin did not alter calcium transport or the changes in calcium transport caused by other secretagogues, and secretagogues that mobilize cellular calcium did not alter cellular cyclic AMP or the increase in cyclic AMP caused by cholera toxin. These results indicate that in dispersed acini from rat pancreas there is post-receptor modulation of the action of cholera toxin by secretagogues that mobilize cellular calcium and that this modulation is a major determinant of the effect of the toxin on enzyme secretion.     

Effect of AA861, a 5-lipoxygenase inhibitor,on amylase secretion from rat pancreatic acini

We have examined the effects of 2,3,5-trimethyl-6-(12-hydroxy-5,10-dodecadiynyl)-1,4-benzoquinone (AA861), a selective inhibitor of 5-lipoxygenase, on the action of cholecystokinin (CCK) and other secretagogues in the stimulation of amylase secretion from dispersed rat pancreatic acini. AA861 inhibited amylase secretion caused by CCK, carbamylcholine (carbachol), bombesin or calcium ionophore A23187 but failed to affect amylase secretion by vasoactive intestinal peptide or 12-O-tetradecanoyl-phorbol 13-acetate. Inhibition by AA861 of CCK or carbachol-induced amylase secretion was confined to the relatively lower concentrations of these secretagogues. AA861 did not inhibit receptor binding of CCK or alter the cellular calcium mobilization induced by CCK. In kinetic studies, AA861 was effective only on amylase secretion from pancreatic acini incubated with CCK for more than 5 min. Indomethacin, a known inhibitor of cyclooxygenase, did not affect the amylase secretion caused by all secretagogues used. These results indicate that the 5-lipoxygenase pathway of arachidonate metabolism may be involved in the actions of calcium-dependent secretagogues of amylase secretion in rat dispersed pancreatic acini, especially for sustaining stimulation of amylase secretion by CCK.     

Action of cholera toxin on dispersed acini from rat pancreas: Post-receptor modulation involving cyclic AMP and calcium

In dispersed acini from rat pancreas, cholera toxin caused a significant increase in cellular cyclic AMP but little or no change in amylase secretion. The presence of a secretagogue that causes mobilization of cellular calcium (e.g., cholecystokinin, carbamylcholine, bombesin or ionophore A23187) caused a substantial increase in the effect of cholera toxin on enzyme secretion. Cholera toxin did not alter calcium transport or the changes in calcium transport caused by other secretagogues, and secretagogues that mobilize cellular calcium did not alter cellular cyclic AMP or the increase in cyclic AMP caused by cholera toxin. These results indicate that in dispersed acini from rat pancreas there is post-receptor modulation of the action of cholera toxin by secretagogues that mobilize cellular calcium and that this modulation is a major determinant of the effect of the toxin on enzyme secretion.     

Phosphorylation of 3 particulate proteins in rat pancreatic acini in response to vasoactive intestinal peptide (VIP), secretin and cholecystokinin (CCK-8)

Rat pancreatic acini were preincubated with 0.4 mM 32Pi for 45 min at 37 degrees C, then exposed for 15 min to VIP, secretin or CCK-8. The incubation was terminated with a stop solution and a fraction rich in mitochondria and zymogen granules was separated from a microsome-rich fraction by differential centrifugation. After heating in the presence of SDS, beta-mercaptoethanol was added and the pattern of equivalent amounts of 32P-labelled proteins was examined by autoradiography of SDS-PAGE gels. VIP, secretin, and CCK-8 stimulated the phosphorylation of a Mr=33 K microsomal protein and that of two proteins of Mr=21 K and Mr=25 K mostly present in a fraction rich in mitochondria and zymogen granules. Stimulations were dose-dependent, the highest stimulant concentrations tested allowing 2- to 3-fold increases of phosphorylation over basal. When 1 nM CCK-8 was used simultaneously with 1 microM VIP, the cyclic AMP levels attained and the pattern of protein phosphorylation were similar to those obtained with VIP alone, and there was a potentiation of amylase secretion; when a supra-maximal 0.1 microM CCK-8 concentration was added, the VIP-induced elevation in cyclic AMP levels and the phosphorylation of the Mr=21 K and Mr=25 K proteins were partially antagonized, and no potentiation any more of secretion occurred. To conclude the in vitro phosphorylation of three particulate proteins (Mr=33 K, 25 K, and 21 K) was similarly increased in rat pancreatic acini in response to secretin and VIP (acting through cyclic AMP) and to CCK-8 (acting mostly through Ca2+).     

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.     

Secretin induces rapid increases in inositol trisphosphate, cytosolic Ca2+ and diacylglycerol as well as cyclic AMP in rat pancreatic acini.

Previous studies have shown that the dose-response relationship for secretin-stimulated cyclic AMP accumulation is different from that for secretin-stimulated enzyme secretion in the rat exocrine pancreas. Here we show that secretin concentrations of 10(-10) M and higher stimulated a rise in cyclic AMP levels, with maximum effect on cyclic AMP accumulation being achieved already with 10(-8) M-secretin. However, at this concentration of secretin, enzyme secretion rates were approximately half-maximal. Unexpectedly, at concentrations of secretin greater than 10(-8) M there was evidence suggestive of phosphatidylinositol bisphosphate hydrolysis with rapid increases in inositol trisphosphate, cytosolic free calcium and diacylglycerol content of rat pancreatic acini. Furthermore, there was a dose-response relationship among secretin concentration (in the range 10(-8) M-2 X 10(-6) M), increases in inositol trisphosphate and increases in cytosolic free calcium ([Ca2+]i). Contrary to what has been previously believed, these results clearly indicate that in rat pancreatic acini secretin not only stimulates cyclic AMP accumulation but also raises inositol trisphosphate, [Ca2+]i and diacylglycerol. Thus, two second messenger systems may play a role in the regulation of secretin-induced amylase release.     

对牛胰多肽抑制胰酶分泌作用的离体研究

为探讨胰多肽抑制胰酶分泌的机制,我们利用大鼠离体胰腺泡制备观察了牛胰多肽(BPP)在细胞受体水平对氨甲酰胆碱等促分泌物作用的影响。实验结果显示,BPP 对氨甲酰胆碱诱导的胰腺泡淀粉酶分泌具有抑制作用,并存在剂量反应关系。BPP0.1μmol/L 和0.2μmol/L,可分别使氨甲酰胆碱诱导淀粉酶分泌的效价降低3倍和10倍;BPP 还可抑制氨甲酰胆碱刺激胰腺泡释放~(45)Ca。以上结果提示,BPP 对胰腺泡的胆碱能 M 受体具有拮抗作用。此外,BPP 对促胰液素及其同类激动剂和氨甲酰胆碱协同作用诱导的胰腺泡淀粉酶分泌具有抑制作用,提示胰多肽在整体对促胰液素诱导的胰酶分泌的抑制,可能是通过拮抗胰腺泡细胞上的 M 受体而抑制了促胰液素和胆碱能刺激协同作用引起的胰酶分泌。     

The effects of γ-hexachlorocyclohexane on amylase secretion and inositol phospholipid metabolism in mouse pancreatic acini

Dispersed mouse and guinea-pig pancreatic acini were used to examine the effects of the inositol analogue, γ-hexachlorocyclohexane (lindane) on agonist-stimulated amylase secretion. Secretion from mouse acini in response to carbachol and cholecystokinin octapeptide (CCK-8) was reduced by lindane. Similarly, amylase release from guinea-pig acini stimulated by carbachol was abolished by lindane. These acini, however, still remained responsive to dibutyryl-cAMP with only a slightly diminished secretion to this agent. Inositol phospholipid synthesis and hydrolysis was stimulated in mouse acini by both carbachol and CCK-8. Although hydrolysis of these lipids in response to CCK-8 was reduced by only 18%, stimulation of inositol phospholipid synthesis by either agonist was abolished by lindane. Dose-response curves for inositol phospholipid synthesis stimulated by carbachol and CCK-8 in mouse acini were biphasic and superimposable with those of amylase secretion. In contrast, the dose-response curve for phosphoinositide hydrolysis was sigmoid and clearly separable from that of synthesis. Reducing the external Ca²⁺ concentration caused the dose-response curves for carbachol- and CCK-8-induced inositol phospholipid synthesis to be displaced to the right, as has been observed for amylase secretion. A23187 was also found to induce amylase secretion and inositol phospholipid synthesis, and both of these responses were inhibited by lindane. Amylase secretion and inositol phospholipid synthesis may, therefore, be closely related events in the exocrine pancreas. Lindane may provide a valuable tool with which to determine the role of inositol phospholipid metabolism in stimulus-response coupling.     

A synthetic peptide derivative that is a cholecystokinin receptor antagonist

So far, there are no known peptidic effective receptor antagonists of both peripheral and central effects of cholecystokinin (CCK). Here, we describe a synthetic peptide derivative of CCK, t-butyloxycarbonyl-Tyr(SO3-)-Met-Gly-D-Trp-Nle-Asp 2-phenylethyl ester 1 (where Nle is norleucine), which is a potent CCK receptor antagonist. In rat and guinea pig dispersed pancreatic acini, this peptide derivative did not alter amylase secretion, but was able to antagonize the stimulation caused by cholecystokinin-related agonists. It caused a parallel rightward shift in the dose-response curve for the stimulation of amylase secretion with half-maximal inhibition of CCK-8-stimulated amylase release at a concentration of about 0.1 microM. Compound 1 was able to inhibit the binding of labeled CCK-9 (the C-terminal nonapeptide of CCK) to rat and guinea pig pancreatic acini (IC50 = 5 X 10(-8) M) as well as to guinea pig cerebral cortical membranes (IC50 = 5 X 10(-7) M). These results indicate that Compound 1 is a potent competitive CCK receptor antagonist.     

Effects of synthetic human pancreastatin on pancreatic secretion and blood flow in rats and dogs.

Effects of synthetic human pancreastatin-52 and human pancreastatin-29 on pancreatic secretion and blood flow were examined in rats and dogs. Synthetic human pancreastatin-52 and human pancreastatin-29 were equally potent in suppressing the release of amylase stimulated by cholecystokinin in rats in vivo. However, neither human pancreastatin-52 nor human pancreastatin-29 altered basal and cholecystokinin-stimulated amylase release from isolated dispersed rat pancreatic acini. In studies in dogs, human pancreastatin-29 suppressed releases of amylase and protein stimulated by cholecystokinin, but did not alter pancreatic blood flow. These results suggest that the inhibitory effects of pancreastatin on pancreatic secretion do not involve a direct action on pancreatic acinar cells nor alteration of pancreatic blood flow. Pancreastatin probably is important in regulating exocrine pancreatic secretions as well as endocrine pancreatic secretions.     

Introduction of calcium chelators into isolated rat pancreatic acini inhibits amylase release in response to carbamylcholine

The Ca2+ chelators, EGTA and BAPTA, have been introduced into intact, isolated rat pancreatic acini using a hypotonic swelling method. This resulted in complete inhibition of amylase release, stimulated by carbamylcholine at a submaximal concentration and 82 - 85% inhibition at maximal concentrations. Acini swollen in the absence of Ca2+ chelators showed similar secretory responses to those of unswollen acini. Treatment of unswollen acini with chelators inhibited the maximum response to carbamylcholine by only 23%. The inhibitory effect of intracellular chelators was not due to ATP depletion or a lowering of the total cell Ca2+ content. Thus, these results provide the first direct demonstration that an increase in intracellular Ca2+ concentration is necessary for the stimulation of enzyme release from pancreatic acinar cells.     

Exogenous leptin inhibits the secretion of pancreatic juice via a duodenal CCK1-vagal-dependent mechanism in anaesthetized rats

Leptin originally described as product of the ob gene has been shown to be expressed in various tissues including the gastrointestinal tract. In this study, we investigated the influence of leptin on the secretion of pancreatic juice in biliary-pancreatic duct cannulated anaesthetised rats and in dispersed rat pancreatic acini in vitro. Exogenous leptin was given in boluses intravenously with or without CCK-8 (12 pmol kg(-1) body weight) in the presence or absence pharmacological CCK(1) receptor blockade, cervical vagotomy, and capsaicin pre-treatment. Administration of leptin (0.1, 1 and 10 microg kg(-1) body weight) did not affect the volume of bile and pancreatic juice while the protein and trypsin outputs were reduced in a dose-dependent manner. In the rats, leptin inhibited CCK-8 stimulated protein and trypsin outputs stronger than the basal pancreatic secretion. The inhibition by leptin was abolished by the pharmacological CCK(1) receptor blockade, cervical vagotomy, and capsaicin pre-treatment. In contrast, leptin did not affect basal and CCK-8-stimulated amylase release from the dispersed rat pancreatic acini in vitro. In conclusion, the results of the present study suggest that leptin does not act directly on the rat pancreatic acinar cells but inhibits the secretion of pancreatic enzymes acting indirectly via a neurohormonal CCK-vagal-dependent mechanism.