Islet amyloid polypeptide (IAPP;amylin) influences the endocrine but not the exocrine rat pancreas.

The effect of synthetic rat amylin (10,100,1000 pmol/l) on glucose (10 mmol/) and arginine (10 mmol/l) -stimulated islet hormone release from the isolated perfused rat pancreas and on amylase release from isolated pancreatic acini was investigated. Amylin stimulated the insulin release during the first (+76%) and the second secretion period (+42%) at 1 nmol/l. The first phase of the glucagon release was inhibited concentration dependently by amylin and completely suppressed during the second phase. Amylin diminished the somatostatin release in a concentration dependent manner. This effect was more pronounced at the first than the second secretion period (1 nmol amylin: 1 phase: -60%, 2.phase: -22%). Amylin was without any effect on basal and CCK stimulated amylase release from isolated rat pancreatic acini. Our data suggest amylin, a secretory product of pancreatic B-cells, as a peptide with approximately strong paracrine effects within the Langerhans islet. Therefore, amylin might be involved in the regulation of glucose homeostasis.     

Dose-response for inhibition by amylin of cholecystokinin-stimulated secretion of amylase and lipase in rats

BACKGROUND AND AIMS: The neuroendocrine hormone amylin, cosecreted with insulin from pancreatic beta-cells in response to nutrient ingestion, has several physiologic actions to limit the rate of nutrient uptake, including the slowing of gastric emptying. METHODS: To investigate whether amylin might modulate digestive enzyme secretion from the exocrine pancreas, anesthetized Sprague Dawley rats were cannulated via the pancreatic duct and the secretory response (flow, amylase and lipase) to cholecystokinin (1 microg s.c.) was measured in the absence and in the presence of 0.1, 0.3 and 1 microg s.c. doses of amylin. RESULTS: Amylin alone did not affect pancreatic secretion, but it dose-dependently inhibited cholecystokinin-stimulated amylase secretion by up to 58% and lipase secretion by up to 67%. The ED50's for these responses were 0.21 microg+/-0.18 log and 0.11 microg+/-0.05 log, respectively, doses that result in excursions of plasma amylin concentration that are within the reported physiological range. Amylin did not evoke cell signalling in the Ar42j model of pancreatic acinar cells, and responses to amylin were not observed in either Ar42j cells or isolated pancreatic acini in a microphysiometer indicating that the effect of amylin was indirect. CONCLUSIONS: Inhibition of stimulated pancreatic enzyme secretion is likely to be a physiological, extrapancreatic, action of amylin. Amylinergic mechanisms modulating both gastric emptying and pancreatic enzyme secretion may thus match, respectively, the appearance of substrate and enzymes in the gut lumen.     

Cosecretion of amylin and insulin from isolated rat pancreas

Amylin, a 37 amino acid C-terminal amidated peptide is an integral part of secretory granules of pancreatic beta-cells. Utilizing a specific radioimmunoassay system we demonstrate in the present study a cosecretion of amylin and insulin from the isolated rat pancreas. The secretion pattern of both peptides during glucose or glucose plus arginine stimulation is identical. The molar ratio of amylin amounts to 10% of that of insulin. The biological significance of amylin is still unknown, but a paracrine/endocrine role in glucose homeostasis is speculated.     

Alterations of pancreatic juice amylase by glucocorticoid levels in the rat

By use of isoelectrofocusing, three isoenzymes with pIs of 8.40, 8.55, and 8.65 were characterized in the amylase fraction of rat pancreatic juice. Enzyme secretion in rat exocrine pancreas is affected by glucocorticoid levels; adrenalectomy led to a significant decrease in protein secretion which was more pronounced in the amylase fraction, in which the isoenzymes with pI 8.55 and 8.65 disappeared. Substitution therapy with hydrocortisone (25 mg/kg/day, for 6 days) restored exocrine pancreatic secretion to almost normal levels. Administration of hydrocortisone to control rats led to structural alterations in enzymes secreted, splitting the amylase isoenzymes with pI 8.40; this was confirmed by crossed immunoelectrophoresis. It is concluded that glucocorticoid levels play an important role in the maintenance of function of exocrine pancreas and it is suggested that, although hydrocortisone fulfills the objective of restoring enzyme secretion diminished by adrenalectomy, it is possible that intensive treatment could have undesirable effects on the structure of enzymes and could involve pancreatic disfunctionality.     

The effect of oxyntomodulin (Glucagon-37) and glucagon on exocrine pancreatic secretion in the conscious rat

The inhibitory effect of glucagon on exocrine pancreas has been the subject of controversial reports. On the other hand, oxyntomodulin (bioactive enteroglucagon or glucagon-37), a 37 amino acid peptide isolated from porcine lower intestine, has been shown to be 10–20 times more potent than glucagon in inhibiting gastric acid secretion in the rat. In view of this, the effect of glucagon and oxyntomodulin on basal and caerulein-stimulated pancreatic secretion has been studied, during re-introduction of pancreatic juice into duodenum, in the conscious rat provided with pancreatic and duodenal fistulas. A depression of pancreatic function was observed with both peptides on the three parameters studied: (volume of juice secreted, bicarbonate and protein output), either under basal conditions or during stimulation by caerulein. In all the experimental conditions used, oxyntomodulin was ca. ten times more potent than glucagon in its inhibitory effect. The fact that oxyntomodulin, as what is observed in the stomach, is one order of magnitude more potent than glucagon in inhibiting pancreatic secretion suggests that the biological mechanisms by which the peptides of the glucagon-family act on exocrine pancreas are similar, or related to that present at the gastric level.     

Inhibitory effect of pancreastatin on pancreatic exocrine secretion in the conscious rat

The effect of newly discovered pancreastatin on pancreatic secretion stimulated by a diversion of bile-pancreatic juice (BPJ) from the intestine was examined in the conscious rat. Exogenous pancreastatin infusion (20, 100 and 200 pmol/kg.h) inhibited pancreatic protein and fluid outputs during BPJ diversion in a dose-dependent manner. Pancreastatin did not affect plasma cholecystokinin (CCK) concentrations. Pancreastatin (100 pmol/kg.h) inhibited CCK-stimulated pancreatic secretion, but did not inhibit secretin-stimulated pancreatic secretion. Pancreastatin alone, however, did not affect basal pancreatic secretion. In contrast, pancreastatin (10(-10)-10(-7)M) did not suppress CCK-stimulated amylase release from isolated rat pancreatic acini. These results indicate that pancreastatin has an inhibitory action on exocrine function of the pancreas. This action may not be mediated by direct mechanisms and nor via an inhibition of CCK release. It is suggested that pancreastatin may play a role in the regulation of the intestinal phase of exocrine pancreatic secretion.     

Effects of gamma-aminobutyric acid on secretagogue-induced exocrine secretion of isolated, perfused rat pancreas

Because GABA and its related enzymes have been determined in beta-cells of pancreas islets, effects of GABA on pancreatic exocrine secretion were investigated in the isolated, perfused rat pancreas. GABA, given intra-arterially at concentrations of 3, 10, 30, and 100 microM, did not exert any influence on spontaneous or secretin (12 pM)-induced pancreatic exocrine secretion. However, GABA further elevated CCK (10 pM)-, gastrin-releasing peptide (100 pM)-, or electrical field stimulation-induced pancreatic secretions of fluid and amylase dose dependently. The GABA (30 microM)-enhanced CCK-induced pancreatic secretions were completely blocked by bicuculline (10 microM), a GABA(A) receptor antagonist, but were not affected by saclofen (10 microM), a GABA(B) receptor antagonist. The enhancing effects of GABA (30 microM) on CCK-induced pancreatic secretions were not changed by tetrodotoxin (1 microM) but were partially reduced by cyclo-(7-aminoheptanonyl-Phe-D-Trp-Lys-Thr[BZL]) (10 nM), a somatostatin antagonist. In conclusion, GABA enhances pancreatic exocrine secretion induced by secretagogues, which predominantly induce enzyme secretion, via GABA(A) receptors in the rat pancreas. The enhancing effect of GABA is partially mediated by inhibition of islet somatostatin release.     

Interactions between bile and pancreatic juice diversions on cholecystokinin release and pancreas in conscious rats

Pancreatic exocrine secretion in the conscious rat is regulated by proteases secreted by the pancreas, and cholecystokinin (CCK) is known to be involved in its mechanism. It has also been reported that the absence of either pancreatic juice or bile in the duodenum could stimulate pancreatic secretion. Therefore, differences in CCK release responding to the exclusion of bile, pancreatic juice (PJ), or both bile and pancreatic juice (BPJ) from the intestine were examined by using a bioassay for cholecystokinin. Plasma CCK levels were increased by all three treatments compared with the basal value, the order of their effects being BPJ greater than PJ greater than bile diversion, and CCK concentrations produced by BPJ diversion were much greater than can be explained as simply summed effect of exclusions of bile and PJ. Pancreatic exocrine secretions were significantly increased by PJ and BPJ diversions, but the effect of bile diversion on the pancreas was not statistically significant. An additional infusion of CR-1409 (0.1 mg/rat), one of CCK receptor antagonists, inhibited exocrine function stimulated by BPJ diversion. We conclude (i) BPJ diversion is the strongest endogenous stimulant on CCK release; (ii) the potentiation between bile and PJ diversions is induced on CCK release; (iii) pancreatic protein secretion during BPJ diversion is mainly modulated by CCK.     

Selective amylin inhibition of the glucagon response to arginine is extrinsic to the pancreas

Amylin, a peptide hormone from pancreatic beta-cells, is reported to inhibit insulin secretion in vitro and in vivo and to inhibit nutrient-stimulated glucagon secretion in vivo. However, it has been reported not to affect arginine-stimulated glucagon secretion in vitro. To resolve if the latter resulted from inactive peptide (a problem in the early literature), those experiments were repeated here with well-characterized peptide and found to be valid. In isolated perfused rat pancreas preparations, coperfusion with 1 nM amylin had no effect on arginine-, carbachol-, or vasoactive intestinal peptide-stimulated glucagon secretion. Amylin also had no effect on glucagon output stimulated by decreasing glucose concentration from 11 to 3.2 mM or on glucagon suppression caused by increasing glucose from 3.2 to 7 mM. Amylin at 100 nM had no effect in isolated islets in which glucagon secretion was stimulated by exposure to 10 mM arginine, even though glucagon secretion in the same preparation was inhibited by somatostatin. In anesthetized rats, amylin coinfusion had no effect on glucagon secretion stimulated by insulin-induced hypoglycemia. To reconcile reports of glucagon inhibition with the absence of effect in the experiments just described, anesthetized rats coinfused with rat amylin or with saline were exposed sequentially to intravenous L-arginine (during a euglycemic clamp) and then to hypoglycemia. Amylin inhibited arginine-induced, but not hypoglycemia-induced, glucagon secretion in the same animal. In conclusion, we newly identify a selective glucagonostatic effect of amylin that appears to be extrinsic to the isolated pancreas and may be centrally mediated.     

Effect of potato inhibitor of proteolytic enzymes on activity and morphology of the rat pancreas.

The effect of the inhibitor of proteolytic enzymes present in potatoes on morphology and activity of the rat pancreas was investigated administering the inhibitor with drinking water in doses of 50 and 100 mg to two groups of rats for 20 days. On the 21st day the exocrine activity of the pancreas was evaluated by the method of duodenal perfusion after previous hormonal stimulation of pancreatic secretion (secretin and cholecystokinin-pancreozymin 1 U CHR/100 g body weight), while morphology of the organ was assessed by histological methods. It was found that the inhibitor exerts a trophic effect on the rat pancreas, causing hypertrophy of acinar cells and raising the exocrine activity of the gland. The higher dose of the inhibitor had a more pronounced trophic effect.     

Responses of the exocrine pancreatic secretion to spontaneous feeding in rats with bile-pancreatic juice diversion

The regulatory response of the exocrine pancreas was examined in rats under unanesthetized and unrestrained conditions. The previous study demonstrated that the pancreatic protease secretion increased 2-fold after spontaneous feeding of a low protein diet in chronically bile-pancreatic cannulated rats (normal rats) whose bile-pancreatic juice (BPJ) was returned to the duodenum. In the present study, we observed the response of the exocrine pancreatic secretion to spontaneous feeding of a low protein diet in rats with chronic diversion of BPJ from the proximal small intestine for 6 days (bypass rat) whose diverted BPJ was returned to the upper ileum. During BPJ diversion, the dry weight and the protein content of the pancreas were increased 2-fold, compared with normal rats. Also, the levels of trypsinogen and chymotrypsinogen in the pancreas were increased several times, but amylase was decreased. The basal secretion of enzymes after a 24-hr fast was enhanced in bypass rats in proportion to the pancreatic enzyme contents. After spontaneous feeding of 8% casein fat-free diet, the increases in the pancreatic secretion of bypass rats were much smaller than those of normal rats. In contrast, the increase of BPJ flow of bypass rats after feeding was greater than that of normal rats. These findings represent that the chronic diversion of BPJ exerts hypergrowth of pancreas and hypersecretion of proteases in the fasting state, and less sensitivity of pancreatic enzyme secretion to dietary feeding.     

Nonparallel secretion of enzymes by the rabbit pancreas

Since nonparallel secretion of enzymes by the exocrine pancreas has been demonstrated with several experimental models, we were interested in verifying a recent claim that enzyme secretion remained strictly proportional (parallel) upon stimulation of the in vivo rabbit pancreas. Pancreatic juice was collected by extraduodenal cannulation of the pancreatic duct, in two different protocols. In the first protocol the administration of pentobarbital induces a mild anesthesia. Under this condition, amylase and chymotrypsin secretion remained parallel after cholecystokinin stimulation. In a second protocol, a deeper and constant anesthesia was attained with Fluothane resulting in a lower basal protein output than in the first protocol. Pancreatic secretion was collected under intravenous secretin perfusion (4.5 clinical units X kg-1 X h-1). After stabilization and basal collection periods, pancreatic secretion was stimulated with an i.v. bolus injection of either cholecystokinin (2 Ivy dog units/kg), caerulein (0.1 micrograms/kg), or carbachol (6 micrograms/kg). Upon stimulation of the pancreas, protein output increased an average of 30-fold and there was a concomitant 20-25% decrease in the ratio of the specific activities of amylase to chymotrypsin which resulted from a greater increase in the specific activity of chymotrypsin in pancreatic juice after stimulation of secretion. Thus, under appropriate conditions, nonparallel secretion of enzymes by the exocrine pancreas can be demonstrated in yet another experimental model. Furthermore, the proportion of amylase and chymotrypsin activities in pancreatic juice are once more shown to be dependent, up to a threshold, upon the rate of protein output by this exocrine gland.     

Immunohistochemical colocalization of type II angiotensin receptors with somatostatin in rat pancreas

Earlier studies indicate that binding sites of type II angiotensin (AT2) receptors are detected all over the pancreas, as well as in the pancreatic exocrine cell line AR4-2J. However, lack of corresponding functional AT2 receptor responses can be detected in the exocrine pancreas. The aim of present study is to determine the protein expression of AT2 receptors in the pancreas by probing with an AT2 receptor-specific antibody, and to examine the role of AT2 receptors in the regulation of pancreatic endocrine hormone release. In Western protein analysis of adult rat tissues, expression of AT2 receptor-immunoreactive bands of 56, 68, and 78 kDa was detected in the adrenal, kidney, liver, salivary glands, and pancreas. In adult rat pancreas, strong immunoreactivity was detected on cells that were located at the outer region of Langerhans islets. Immunohistochemical studies indicated that AT2 receptors colocalized with somatostatin-producing cells in the endocrine pancreas. Consistent with the findings in adult pancreas, abundant expression of AT2 receptors was also detected in immortalized rat pancreatic endocrinal cells lines RIN-m and RIN-14B. To examine the role of AT2 receptors on somatostatin secretion in the pancreas, angiotensin-stimulated somatostatin release from pancreatic RIN-14B cells was studied by an enzyme immunoassay in the absence or presence of various subtype-selective angiotensin analogues. There was a basal release of somatostatin from RIN-14B cells at a rate of 8.72 +/- 4.21 ng/10(6) cells (n = 7). Angiotensin II (1 nM-10 microM) stimulated a biphasic somatostatin release in a dose-dependent manner with an apparent EC50 value of 49.3 +/- 25.9 nM (n = 5), and reached maximal release at 1 microM angiotensin II (982 +/- 147.34% over basal secretion; n = 5). Moreover, the AT2 receptor-selective angiotensin analogue, CGP42112, was 1000 times more potent than the AT1 receptor-selective angiotensin analogue, losartan, in inhibiting angiotensin II-stimulated somatostatin release. These results suggest that angiotensin may modulate pancreatic hormone release via regulation of somatostatin secretion.     

Inhibition of gastric and pancreatic secretions by cerebroventricular injections of gastrin-releasing peptide and bombesin in rats

It has been suggested that mammalian gastrin-releasing peptide (GRP) and bombesin (BBS) might inhibit gastric secretion by a central nervous system action. The present investigations were intended to define the gastric effect and to look for an effect on the exocrine pancreas. Wistar male rats were provided with a chronic cannula allowing cerebroventricular injections in the 3rd ventricle, and with chronic gastric and/or pancreatic fistulas allowing the collection of gastric and/or pancreatic secretions in conscious animals. Both basal secretions were studied. Gastric secretion was stimulated with a 75 mg/kg s.c. injection of 2-deoxyglucose (2-dGlc). The dose range of bombesin was 0.01–1 μg (6–600 pmol) and GRP was 0.01–10 μg/rat (3.5 pmol to 3.5 nmol). A significant dose related decrease of basal gastric secretion was observed with the two peptides. The gastric acid response to 2-dGlc was inhibited by both peptides in a dose-related fashion and the reduction of gastric acid output mainly resulted from a decrease in the volume of gastric juice. The exocrine pancreatic secretion was also decreased by 30–55% after GRP but the BBS inhibitory effect was poorly dose-related. No significant difference was found after removal of gastric secretion, indicating that most of the pancreatic inhibition was independent of gastric secretion.     

Inhibitory effect of rat amylin on the insulin responses to glucose and arginine in the perfused rat pancreas

Amylin, a 37-amino acid polypeptide, is the main component of amyloid deposits in the islets of Langerhans, and has been identified in the B-cell secretory granules. We have investigated the effect of rat amylin on the insulin and glucagon release by the isolated, perfused rat pancreas. Amylin infusion at 750 nM, markedly reduced unstimulated insulin release (ca. 50%, P less than 0.025), whereas it did not modify glucagon output. At the same concentration, amylin also blocked the insulin response to 9 mM glucose (ca. 80%, P less than 0.025) without affecting the suppressor effect of glucose on glucagon release. The inhibitory effect of amylin on glucose-induced insulin secretion was confirmed by lowering the amylin concentration (500 nM) and increasing the glucose stimulus (11 mM); again, no effect of amylin on glucagon release was observed. Finally, amylin, at 500 nM, reduced the insulin response to 3.5 mM arginine (ca. 40%, P less than 0.025) without modifying the secretion of glucagon elicited by this amino acid. It can be concluded that, in the rat pancreas, the inhibitory effect of homologous amylin on unstimulated insulin secretion, as well as on the insulin responses to metabolic substrates (glucose and arginine), favours the concept of this novel peptide as a potential diabetogenic agent.     

Amylin secretion from the perfused pancreas: dissociation from insulin and abnormal elevation in insulin-resistant diabetic rats

Amylin has been co-secreted from pancreatic islet beta-cells in constant proportion with insulin in some studies. We measured basal and glucose-stimulated amylin and insulin secretion from isolated perfused pancreases of normal and diabetic fatty Zucker rats. Glucose concentrations in the perfusion buffer were increased then decreased in small steps to mimic physiologic changes occurring after a meal. The absolute rate of amylin secretion and the molar ratio of amylin to insulin secreted from diabetic pancreases increased dramatically when infused glucose concentrations fell. Similar changes also occurred in normal pancreases, although the absolute change in amylin secretion was smaller. These studies provide the first evidence that (i) there is a mechanism within the pancreas whereby independent secretion of amylin and insulin can occur; (ii) the molar ratio of amylin to insulin secreted from both normal and diabetic pancreases can vary over a wide range; and (iii) there are important differences in the kinetics of amylin and insulin secretion or their coupling to stimulation by glucose between the isolated pancreases of normal rats and those with genetically transmitted insulin resistance and diabetes mellitus.     

Vasoactive intestinal polypeptide (VIP) in the pig pancreas: role of VIPergic nerves in control of fluid and bicarbonate secretion

Vasoactive intestinal polypeptide (VIP) in the pig pancreas is localized to nerves, many of which travel along the pancreatic ducts. VIP stimulates pancreatic fluid and bicarbonate secretion like secretin. Electrical vagal stimulation in the pig causes an atropine-resistant profuse secretion of bicarbonate-rich pancreatic juice. In an isolated perfused preparation of the pig pancreas with intact vagal nerve supply, electrical vagal stimulation caused an atropine-resistant release of VIP, which accurately parallelled the exocrine secretion of juice and bicarbonate. Perfusion of the pancreas with a potent VIP-antiserum inhibited the effect of vagal stimulation on the exocrine secretion. It is concluded, that VIP is responsible for (at least part of) the neurally controlled fluid and bicarbonate secretion from the pig pancreas.     

Glucocorticoids effects on exocrine pancreatic secretion in caerulein-induced acute pancreatitis in the rat.

The present work reports on exocrine pancreatic secretion in control rats, adrenalectomized rats and hydrocortisone-treated (10 mg/Kg/d) rats during 7 days, under normal conditions and after induction of acute pancreatitis with caerulein (20 micrograms/Kg) by 4 subcutaneous injections at hourly intervals. Pancreatic secretion was seen to be affected by the procedure of adrenalectomy, which led to a marked reduction in the secretion of proteins and amylase with respect to control values. This was probably due to the decrease occurring in the zymogen granules in the acinar cells of the exocrine pancreas, a phenomenon which also led to a decrease in pancreatic weight observed in these animals. Treatment with hydrocortisone induced a decrease in the secretion of proteins and amylase, as well as an increase in pancreatic weight. This agrees with the accepted hypothesis that large amounts glucocorticoids stimulate the synthesis and storage of proteins in the exocrine pancreas, reducing the secretory phase. The administration of high doses of caerulein under these conditions led to acute pancreatitis in the three groups of animals. This was paralleled by a dramatic decrease in protein and amylase secretion and by severe interstitial edema of the pancreas and by increases in serum amylase values. In the case of the animals treated previously with hydrocortisone, the latter were tripled with respect to the control animals. The conclusion is offered that since the storage of enzyme proteins is governed by glucocorticoids, which furthermore increase the sensitivity of the acinar cells to stimulation by secretagogues, the administration of these substances during the development of pancreatic lesions such as acute pancreatitis is highly compromising to the organism.     

Protective effect of long term high fiber diet consumption on rat exocrine pancreatic function after chronic ethanol intake

The effects of ethanol administration on exocrine pancreas have been widely studied, but little is known about the effect of dietary fiber in combination with chronic ethanol on exocrine pancreatic function. The aim of this work was to examine the chronic effects of a high fiber diet, ethanol ingestion, and a combination of both on the function of the rat exocrine pancreas. Four groups of rats were fed for six months the following diets: 1.- NW: standard laboratory diet; 2.- FW: high fiber diet (15% cellulose); 3.- NE: standard laboratory diet and 20% ethanol in the drinking water; and 4.- FE: high fiber diet and 20% ethanol. Cholecystokinin (CCK) and acetylcholine (Ach) effects on amylase release and intracellular calcium mobilization in pancreatic acini were studied. In rats fed a 20% ethanol (NE), both the basal amylase release and the basal [Ca(2+)](i) were significantly increased; nonetheless, CCK and Ach-induced amylase release were significantly reduced compared with control rats. Ach- but not CCK-stimulated [Ca(2+)](i) increase in NE rats was significantly decreased compared with NW. In rats fed a combination of ethanol and a high fiber diet (FE) all the parameters under study were not significantly affected compared to control rats (NW). In conclusion, high fiber consumption does not alter the function of the exocrine pancreas. However, it ameliorates the deleterious effect of chronic ethanol consumption on pancreatic amylase secretion and, at least partially, reverses the ethanol-induced alterations on [Ca(2+)](i) in the rat exocrine pancreas.     

Role of cholecystokinin in mediating GRP-stimulated gastric, biliary and pancreatic functions in man.

To explore the mechanisms of gastrin-releasing peptide (GRP)-induced gut functions in man, we investigated the effect on gallbladder contraction, exocrine pancreatic secretion and gastric acid secretion of a recently developed CCK receptor antagonist, loxiglumide, on GRP-stimulated effects in six healthy human subjects. Intravenous infusion of graded doses of synthetic human GRP (1-27 pmol/kg per h) caused significant and dose-dependent increases in pancreatic enzyme and gastric acid secretions and in gallbladder contraction. Intravenous administration of loxiglumide (10 mg/kg per h) abolished GRP-stimulated gallbladder contraction, augmented gastric acid secretion, but did not affect exocrine pancreatic secretion. The results suggest that endogenously released CCK is (1) responsible for GRP-stimulated gallbladder contraction, and (2) involved in regulating gastric acid secretion. The results further suggest that GRP-stimulated pancreatic secretion is not mediated by CCK, but has a direct response of GRP on the exocrine pancreas.