Bovine pancreatic secretion in the first week of life: potential involvement of intestinal CCK receptors.

The aim of this study was to evaluate pancreatic juice secretion of calves in the first postnatal days, and determine a potential involvement of cholecystokinin (CCK) and intestinal CCK receptor in its regulation. Nine neonatal Friesian calves (five controls and four treated intraduodenally with FK480, a CCK-A receptor antagonist) were surgically fitted with a pancreatic duct catheter and a duodenal cannula before the first colostrum feeding. Collections of pancreatic juice and duodenal luminal pressure recordings were started early after recovery from anaesthesia and continued for 6 days. From day 2 or 3 of life, periodic fluctuations in pancreatic secretions were observed in concert with duodenal myoelectric motor complex (MMC) and variations in plasma pancreatic polypeptide (PP) concentrations. Intraduodenal administration of FK480 reduced pancreatic juice secretion while intravenous infusion of CCK had no effect. Immunocytochemistry indicated an association of mucosal CCK-A and -B receptors with neural components of the small intestine. In conclusion, periodic activity of the exocrine pancreas exists in neonatal calves soon after birth and local neural intestinal CCK-A receptors could be partly responsible for the modulation of neonatal calf pancreatic secretion.     

The role of luminal gastrin in the regulation of pancreatic juice secretion in preruminant calves

The effect of luminal gastrin on the secretion of pancreatic juice was studied in seven conscious preruminant calves employing luminal infusions of gastrin and cholecystokinin (CCK)-9 and pharmacological CCK1 and CCK2 receptor blocks with antagonists. The study was performed in the preprandial and prandial states. Pharmacological blocking of the CCK2 receptor, like that of the CCK1 receptor, resulted in reduction of pancreatic postprandial secretion and increased the duration of the prandial pattern of duodenal electrical activity. Exogenous luminal gastrin, like luminal CCK-9, enhanced the secretion of pancreatic juice proteins, though the overall effect of gastrin was weaker than that of CCK-9. The effect was inhibited by infusion of CCK2 but also by CCK1 receptor antagonist. In conclusion, duodenal luminal gastrin can stimulate exocrine pancreatic secretion by a mechanism that depends on CCK2 receptors in calves. Involvement of the CCK1 receptor in this mechanism needs further investigation. Prandial pancreatic secretory and duodenal motility cycles can be regulated by endogenous gastrin release.     

Role of cholecystokinin in the intestinal fat- and acid-induced inhibition of gastric secretion.

This study was designed to determine the role of cholecystokinin (CCK) in the inhibition of gastric HCl secretion by duodenal peptone, fat and acid in dogs with chronic gastric and pancreatic fistulas. Intraduodenal instillation of 5% peptone stimulated both gastric HCl secretion and pancreatic protein secretion and caused significant increments in plasma gastrin and CCK levels. L-364,718, a selective antagonist of CCK-A receptors, caused further increase in gastric HCl and plasma gastrin responses to duodenal peptone but reduced the pancreatic protein outputs in these tests by about 75%. L-365,260, an antagonist of type B receptors, reduced gastric acid by about 25% but failed to influence pancreatic response to duodenal peptone. Addition of 10% oleate or acidification of peptone to pH 3.0 profoundly inhibited acid secretion while significantly increasing the pancreatic protein secretion and plasma CCK levels. Administration of L-364,718 reversed the fall in gastric HCl secretion and significantly attenuated pancreatic protein secretion in tests with both peptone plus oleate and peptone plus acid. Exogenous CCK infused i.v. in a dose (25 pmol/kg per h) that raised plasma CCK to the level similar to that achieved by peptone meal plus fat resulted in similar inhibition of gastric acid response to that attained with fat and this effect was completely abolished by the pretreatment with L-364,718. We conclude that CCK released by intestinal peptone meal, containing fat or acid, exerts a tonic inhibitory influence on gastric acid secretion and gastrin release through the CCK-A receptors.     

Pancreatic secretory response to feeding in the calf: CCK-A receptors, but not CCK-B/gastrin receptors are involved

In bovine species, as in human, the pancreas predominantly expresses cholecystokinin-B (CCK-B)/gastrin receptors. However, the role of this receptor in the regulation of meal-stimulated pancreatic enzyme release has not been determined. In milk-fed calves, we previously described prandial patterns of exocrine pancreatic secretion and a long prefeeding phase was observed. The present study was aimed at determining both the role of external stimuli in the outset of the prefeeding phase and the implication of pancreatic CCK-A and CCK-B/gastrin receptors in the mediation of pancreatic response to feeding. The first objective was studied by suppressing external stimuli associated with food intake (unexpected meal) and the second by infusing highly specific and potent antagonists of CCK-A (SR 27897) and CCK-B/gastrin (PD 135158) receptors during the prandial period. When calves were given an unexpected meal, the long prefeeding increase in pancreatic secretion was absent. SR 27897 (but not PD 135158) inhibited the preprandial phase and greatly reduced postprandial pancreatic juice and enzyme outflows. The expectancy of a meal seemed to elicit an increased pancreatic response right before a meal and CCK-A receptors may mediate this information via neural pathways. The implication of CCK and CCK-A receptors in mediating the postfeeding pancreatic response was also demonstrated. The participation of CCK-B/gastrin receptors in this regulation was not demonstrated.     

Role of cholecystokinin in the intestinal phase of pancreatic circulation in dogs

The regulatory mechanisms of postprandial pancreatic hyperemia are not well characterized. The aim of this study is to clarify the role of cholecystokinin (CCK) in the intestinal phase of pancreatic circulation. Pancreatic, gastric, and intestinal blood flows were measured by ultrasound transit-time blood flowmeters in five conscious dogs. Pancreatic and gastric secretion and blood pressure were also monitored. Synthetic CCK octapeptide (CCK-8) or gastrin heptadecapeptide (gastrin-17) was infused intravenously, and milk was infused into the duodenum with or without loxiglumide, a specific CCK-A receptor antagonist. CCK-8 induced dose-related increases of pancreatic, but not gastric or intestinal, blood flow and protein secretion without affecting systemic blood pressure. Gastrin-17 did not affect pancreatic blood flow. An intraduodenal infusion of milk increased pancreatic and intestinal blood flows and pancreatic protein secretion. Loxiglumide completely inhibited pancreatic blood flow and protein responses to CCK-8 and milk but not the intestinal blood flow response. CCK is a potent and specific pancreatic vasodilator, with its effect mediated by CCK-A receptors. CCK plays an important role in the regulation of the intestinal phase of the pancreatic circulation in dogs.     

Intestinal Cholecystokinin Controls Glucose Production through a Neuronal Network

Cholecystokinin (CCK) is a peptide hormone that is released from the gut in response to nutrients such as lipids to lower food intake. Here we report that a primary increase of CCK-8, the biologically active form of CCK, in the duodenum lowers glucose production independent of changes in circulating insulin levels. Furthermore, we show that duodenal CCK-8 requires the activation of the gut CCK-A receptor and a gut-brain-liver neuronal axis to lower glucose production. Finally, duodenal CCK-8 fails to lower glucose production in the early onset of high-fat diet-induced insulin resistance. These findings reveal a role for gut CCK that lowers glucose production through a neuronal network and suggest that intestinal CCK resistance may contribute to hyperglycemia in response to high-fat feeding.     

Acid inhibition by intestinal nutrients mediated by CCK-A receptors but not plasma CCK

We examined the role of CCK-A receptors in acid inhibition by intestinal nutrients. Gastric acid and plasma CCK and gastrin levels were measured in rats with gastric and duodenal fistulas during intragastric 8% peptone and duodenal perfusion with saline, complete liquid diet (CLD; 20% carbohydrate, 6% fat, and 5% protein), and the individual components of CLD. Acid output was significantly inhibited (50-60%) by CLD, lipid, and dextrose. Plasma CCK was significantly increased by CLD (from 2.6 +/- 0.3 to 4.8 +/- 0.5 pM) and lipid (4.6 +/- 0.5 pM). CCK levels 50-fold higher (218 +/- 33 pM) were required to achieve similar acid inhibition by exogenous CCK-8 (10 nmol x kg(-1) x h(-1) iv). Intestinal soybean trypsin inhibitor elevated CCK (10.9 +/- 2.5 pM) without inhibiting acid secretion. The CCK-A antagonist MK-329 (1 mg/kg iv) reversed acid inhibition caused by CLD, lipid, and dextrose. Peptone-stimulated gastrin (21.7 +/- 1.9 pM) was significantly inhibited by CLD (14.5 +/- 3.6 pM), lipid (12.3 +/- 2.2 pM), and dextrose (11.9 +/- 1.5 pM). Lipid and carbohydrate inhibit acid secretion by activating CCK-A receptors but not by altering plasma CCK concentrations.     

Factors involved in the intestinal feedback regulation of pancreatic enzyme secretion in the rat.

Further studies on the feedback regulation of pancreatic enzyme secretion by trypsin were conducted in conscious rats, surgically prepared so that pancreatic juice could be collected or returned. Suppression of enzyme secretion by trypsin as well as its stimulation by SBTI occurred only in the upper part of the small intestine, where the hormone CCK is known to be released. Over a limited range, trypsin suppression of pancreatic secretion was proportional to the dose of trypsin. Higher concentrations had no further effect, suggesting "saturation" of the intestine. Trypsin which had its active center blocked by DFP did not suppress enzyme output. These results supported the concept that only trypsin (or chymotrypsin) with an exposed active center suppressed pancreatic enzyme secretion in the rat by somehow suppressing the release of CCK from the intestinal cell. Presumably CCK is released from the intestine following "removal" of trypsin from the intestine either by diverting the juice or by feeding SBTI which binds the enzyme. All of the evidence supported the view that the effect of trypsin or SBTI on pancreatic secretion was mediated at the intestinal level and not in the blood as has been suggested.     

CCK-A receptor activation induces fos expression in myenteric neurons of rat small intestine

Cholecystokinin (CCK), a hormone secreted from endocrine cells of the small intestine, participates in the control of motility and secretion in the gastrointestinal tract, and in the control of food intake. At least some of the effects of CCK on intestinal function appear to be mediated via activation of intrinsic neurons in the myenteric plexus. However, the distribution of CCK-responsive enteric neurons within the rat small intestine is not known. Neither has the role of CCK-A receptors in the activation of rat myenteric neurons been investigated. Therefore, to determine the distribution of CCK-responsive neurons in the small intestinal myenteric plexus we utilized immunohistochemical detection of Fos, the protein product of the immediate early gene c-fos, to identify neurons that were activated by exogenous CCK. We also monitored Fos expression in the dorsal hindbrain, and examined CCK-induced Fos expression in the presence or absence of a receptor antagonist for the type-A CCK receptor. We found that CCK significantly increased Fos expression in the hindbrain and in myenteric neurons of the duodenum and jejunum, but not the ileum. Neuronal Fos responsiveness in both brain and myenteric neurons was mediated by CCK-A receptors, as CCK-induced Fos expression was eliminated in rats pretreated with a CCK-A receptor antagonist. We conclude that CCK activates small intestinal myenteric neurons, via CCK-A receptors. Activation of these intrinsic intestinal neurons may participate in reflexes and behaviors that are mediated by CCK.     

Feedback control of pancreatic secretion in rats. Role of gastric acid secretion.

Pancreatic secretion in rats is regulated by feedback inhibition of cholecystokinin (CCK) release by proteases in the gut lumen, but little is known about the role of gastric acid in this regulation. This study, carried out on conscious rats with large gastric fistulas (GF) and pancreatic fistulas, shows that diversion of pancreatic juice results in the progressive stimulation of pancreatic secretion only in rats with the GF closed. When the GF was kept open, the diversion resulted in only small increment in pancreatic secretion and this was accompanied by progressive increase in gastric acid outputs. Similar amounts of HCl instilled into the duodenum in rats with the GF open fully reproduced the increase in pancreatic secretion observed after the diversion of pancreatic juice. Pretreatment with omeprazole (15 mumol/kg) to suppress gastric acid secretion or with L-364,718 (5 mumol/kg) to antagonize CCK receptors in the diverted state, resulted in the decline in pancreatic secretion similar to that observed after opening the GF. CCK given s.c. (20-320 pmol/kg) failed to cause any significant rise in the post-diversion pancreatic secretion in rats with the GF closed, but stimulated this secretion dose-dependently when the GF was open. Camostate (6-200 mg/kg) in rats with pancreatic juice returned to the duodenum caused dose-dependent increase in pancreatic secretion, but after opening the GF or after omeprazole this increase was reduced by about 75%. This study provides evidence that gastric acid plays a crucial role in the pancreatic response to diversion of pancreatic juice or inhibition of luminal proteases, and that factors that eliminate gastric acid secretion reduce this response.     

Mutual dependence of VIP/PACAP and CCK receptor signaling for a physiological role in duck exocrine pancreatic secretion

Unlike in rodents, CCK has not been established as a physiological regulator in avian exocrine pancreatic secretion. In the isolated duck pancreatic acini, 1 nM CCK was required for stimulation of amylase secretion, maximal effect being achieved at 10 nM; picomolar CCK was without effect. Vasoactive intestinal peptide (VIP)/pituitary adenylate cyclase activating peptide (PACAP) receptor (VPAC) agonists PACAP-38 and PACAP-27 (10(-12)-10(-7) M) alone had no effect, but made picomolar CCK effective. VPAC agonist VIP 10(-10)-10(-7) M stimulated amylase secretion marginally, but made CCK 10(-12)-10(-10) M effective also. PACAP-27 and VIP both shifted the maximal CCK concentration from 10(-8) to 10(-9) M. This sensitizing effect was mimicked by forskolin. CCK dose dependently induced intracellular Ca2+ concentration ([Ca2+]i) oscillations. PACAP-38 (1 nM), PACAP-27 (1 nM), VIP (10 nM), or forskolin (10 microM) alone did not stimulate [Ca2+]i increase, neither did they modulate CCK (1 nM)-induced oscillations; but when they were added to cells simultaneously exposed to subthreshold CCK (10 pM), calcium spikes emerged. Amylase secretion induced by the simultaneous presence of 10 pM CCK and VPAC agonists was completely blocked by removing extracellular calcium, but the protein kinase C inhibitor staurosporine (1 microM) was without effect. CCK (10 nM)-induced secretion was inhibited by CCK1 receptor antagonist FK480 (1 microM). Gastrin from 10(-12) to 10(-6) M did not stimulate amylase secretion nor did it (100 nM) induce [Ca2+]i increase. The above data suggest that duck pancreatic acini possess both CCK1 and VPAC receptors; simultaneous activation of both is required for each to play a physiological role.     

Secretion from acinar cells of the exocrine pancreas: role of enteropancreatic reflexes and cholecystokinin

Although the molecular machinery and mechanism of cell secretion in acinar cells of the exocrine pancreas is well documented and clear, only recently has the pharmacophysiology of pancreatic exocrine secretion come to light. Therefore, we focus in this article on the current understanding of the pharmacophysiology of pancreatic exocrine secretion. The pancreatic secretory response to ingestion of a meal is mediated via a complex interplay of neural, humoral and paracrine mediators. A major role in the control of the intestinal phase of pancreatic secretion is attributed to vago-vagal enteropancreatic reflexes. In the scheme of this control mechanism, afferents originating in the duodenal mucosa, and efferents mediating central input on the pancreatic ganglia, activate intrapancreatic postganglionic neurons. Experiments utilizing specific receptor antagonists demonstrate the involvement of both muscarinic M1 and M3 receptors expressed in pancreatic acinar cells. Cholecystokinin (CCK), originally implicated in the humoral secretion of pancreatic enzymes, through a direct action on acinar CCK receptors, is also essential to the enteropancreatic reflex mechanism. CCK stimulation of the exocrine pancreatic secretion through excitation of sensory afferents of the enteropancreatic reflexes, is a paracrine mode of CCK action, and is probably the only one in humans and the predominant one in rats. In dogs, however, CCK acts on the pancreas via both the humoral and a paracrine route. More recent experiments suggest further possible sites of CCK action. Additionally, at the brain stem, vago-vagal enteropancreatic reflexes may be modulated by input from higher brain centres, particularly the hypothalamic-cholinergic system in the tonic stimulation of preganglionic neurons of the dorsal motor nucleus of the vagus projecting into the pancreas.     

Attenuated satiation response to intestinal nutrients in rats that do not express CCK-A receptors.

Pharmacological experiments suggest that satiation associated with intestinal infusion of several nutrients is mediated by CCK-A receptors. Otsuka Long-Evans Tokushima Fatty, (OLETF), rats do not express CCK-A receptors and are insensitive to the satiation-producing effects of exogenous CCK. To further evaluate the role of CCK-A receptors in satiation by intestinal nutrient infusion, we examined intake of solid (pelleted rat chow) or liquid (12.5% glucose) food intake, following intestinal infusions of fats (oleic acid or fat emulsion), sugars (maltotriose or glucose), or peptone in OLETF rats and Long Evans Tokushima Otsuka control rats (LETO). Intestinal infusion of glucose or maltotriose reduced solid food intake more in LETO than in OLETF rats from 30 min through 4 h post infusion. Reduction of solid food intake by intestinal infusions of fat or peptone did not differ between OLETF and LETO rats during the first 30 min post infusion, but reduction of intake by these infusates was attenuated in OLETF rats over the ensuing 4h post infusion. Intestinal infusion of glucose, oleate, fat emulsion and peptone reduced 30-min intake of 12.5% glucose more in LETO than OLETF rats. Furthermore, pretreatment with the CCK-A receptor antagonist, devazepide, attenuated intestinal nutrient-induced reduction of food intake only in LETO, but not OLETF rats. Our results confirm pharmacological results, indicating that CCK-A receptors participate in satiation by nutrients that elevate plasma CCK concentrations, as well as by nutrients that do not stimulate secretion of endocrine CCK. In addition, our results indicate: 1) that OLETF rats have deficits in the satiation response to a variety of intestinal nutrient infusions; 2) that the temporal pattern for CCK-A receptor participation in satiation by intestinal nutrients is different during ingestion of liquid and solid foods and 3) that intestinal nutrients provide some satiation signals that are CCK-A receptor mediated and some that are not.     

Acceleration of ulcer healing by cholecystokinin (CCK): role of CCK-A receptors, somatostatin, nitric oxide and sensory nerves.

CCK exhibits a potent cytoprotective activity against acute gastric lesions, but its role in ulcer healing has been little examined. In this study we determined whether exogenous CCK or endogenously released CCK by camostate, an inhibitor of luminal proteases, or by the diversion of pancreatico-biliary secretion from the duodenum, could affect ulcer healing. In addition, the effects of antagonism of CCK-A receptors (by loxiglumide, LOX) or CCK-B receptors (by L-365,260), an inhibition of NO-synthase by N(G)-nitro-L-arginine (L-NNA), or sensory denervation by large neurotoxic dose of capsaicin on CCK-induced ulcer healing were examined. Gastric ulcers were produced by serosal application of acetic acid and animals were sacrificed 9 days after ulcer induction. The area of ulcers and blood flow at the ulcer area were determined. Plasma levels of gastrin and CCK and luminal somatostatin were measured by RIA and mucosal biopsy samples were taken for histological evaluation and measurement of DNA synthesis. CCK given s.c. reduced dose dependently the ulcer area; the threshold dose of CCK being 1 nmol/kg and the dose inhibiting this area by 50% being 5 nmol/kg. This healing effect of CCK was accompanied by a significant increase in the GBF at ulcer margin and the rise in luminal NO production, plasma gastrin level and DNA synthesis. Concurrent treatment with LOX, completely abolished the CCK-8-induced acceleration of the ulcer healing and the rise in the GBF at the ulcer margin, whereas L-365,260 remained without any influence. Treatment with camostate or diversion of pancreatic juice that raised plasma CCK level to that observed with administration of CCK-8, also accelerated ulcer healing and this effect was also attenuated by LOX but not by L-365,260. Inhibition of NO-synthase by L-NNA significantly delayed ulcer healing and reversed the CCK-8 induced acceleration of ulcer healing, hyperemia at the ulcer margin and luminal NO release, and these effects were restored by the addition to L-NNA of L-arginine but not D-arginine. Capsaicin denervation attenuated CCK-induced ulcer healing, and the accompanying rise in the GBF at the ulcer margin and decreased plasma gastrin and luminal release of somatostatin when compared to those in rats with intact sensory nerves. Detectable signals for CCK-A and B receptor mRNAs as well as for cNOS mRNA expression were recorded by RT-PCR in the vehicle control gastric mucosa. The expression of CCK-A receptor mRNA and cNOS mRNA was significantly increased in rats treated with CCK-8 and camostate, whereas CCK-B receptor mRNA remained unaffected. We conclude that CCK accelerates ulcer healing by the mechanism involving upregulation of specific CCK-A receptors, enhancement of somatostatin release, stimulation of sensory nerves and hyperemia in the ulcer area, possibly mediated by NO.     

Feedback regulation of pancreatic secretion by peptide YY

The present status of our understanding of the feedback regulation of pancreatic secretion by peptide YY (PYY) released from the distal intestine is reviewed. Exocrine pancreatic secretion is primarily controlled by the cephalic (the vagus nerve), gastric (acid and pepsin secretion, and nutrients delivered into the duodenum by gastric emptying), and intestinal (secretin and CCK) mechanisms. PYY acts on the multiple sites in the brain and gut, and inhibits pancreatic secretion by regulating these primary control mechanisms. The involvement of Y(1) and Y(2) receptors has been suggested in the regulation of pancreatic secretion. However, it remains to be studied which site of action or receptor subtype is physiologically most important for this regulation.     

Functional and molecular characterization of CCK receptors in the rat pancreatic acinar cell line AR 4-2J.

Competitive inhibition binding studies on membranes from the rat pancreatic AR 4-2J cell line revealed the predominance (80%) of low selectivity CCK receptors (KD of 1 nM and 4 nM for, respectively, CCK-8 and gastrin-17I (G-17I] over selective receptors (20% with a KD of 1 nM and 1 microM for, respectively, CCK-8 and G-17I). Amylase secretion was stimulated by low concentrations of CCK-8, G-17I and CCK-4. G-17I-induced amylase secretion was unaffected by 100 nM of the selective peripheral CCK-A receptor antagonist L-364,718, suggesting that amylase hypersecretion followed non-selective CCK receptor activation, a function normally assumed by selective CCK-A receptors in rat pancreatic acini. Direct ultraviolet irradiation of AR 4-2J cell membranes preloaded with 125I-BH-CCK-33 or 125I(Leu)G(2-17)I resulted in covalent cross-linking with, respectively, a 90 kDa protein and a 106 kDa protein, both distinct from the 81 kDa CCK binding species revealed in normal rat pancreatic membranes. Gpp[NH]p increased the dissociation rate of CCK-8 and G-17I from AR 4-2J cell membranes, indicating a coupling of receptors with guanyl nucleotide regulatory protein(s) G. [32P]ADP-ribosylation of AR 4-2J cell membranes allowed to detect the presence of two Gs alpha (the 50 kDa form predominating over the 45 kDa form) and one Gi alpha (41 kDa). However, Gi and Gs may not be involved in gastrin stimulation of amylase secretion, as Bordetella pertussis toxin and cholera toxin pretreatment of cells did not suppress G-17I-dependent amylase secretion.     

Elevation of plasma CCK concentration after intestinal administration of a pancreatic enzyme secretion-stimulating peptide purified from rat bile-pancreatic juice: analysis with N-terminal region specific radioimmunoassay

The rat plasma cholecystokinin (CCK) concentration was measured after intestinal administration of a peptide purified from rat bile-pancreatic juice, which has a stimulatory effect on pancreatic enzyme secretion. The plasma CCK concentration was measured by means of a radioimmunoassay using CCK-8 N-terminal specific antibody, OAL-656. In experimental rats with protease-free intestines, intraduodenal infusion of 10 micrograms of the purified peptide, which stimulates pancreatic enzyme secretion 2.0-2.5 fold, induced a significant increase in the plasma CCK level. Furthermore, after removal of CCK from the plasma by immunoabsorption with an OAL-656-bound Sepharose 4B column, the stimulatory effect of the plasma on pancreatic enzyme secretion was abolished when it was injected intravenously into recipient rats. It was concluded that this peptide stimulates the release of CCK in the intestine and that this is responsible at least in part for the pancreatic enzyme secretion-stimulating activity of the peptide.     

Guanidinated casein hydrolysate stimulation of cholecystokinin release via pancreatic enzyme- and cholinergic-independent mechanisms in rats.

We had demonstrated that a peptic hydrolysate of guanidinated casein that is made from casein by the conversion of lysine to homoarginine stimulated pancreatic exocrine secretion in rats with chronic bile-pancreatic juice (BPJ) diversion from the proximal small intestine. This modified protein also stimulated cholecystokinin (CCK) release from dispersed rat intestinal cells. In this study, we found that guanidinated casein hydrolysate stimulates CCK release in chronic BPJ-diverted rats with cholinergic control blocked by atropine. Intraduodenal guanidinated casein hydrolysate increased portal plasma CCK concentration and pancreatic secretion in atropine-treated BPJ-diverted rats. In contrast, the portal plasma CCK concentration was not increased by intact casein hydrolysate. We conclude that guanidinated casein hydrolysate directly stimulates CCK release from the intestine via some cholinergic-independent mechanism, and an increase of the pancreatic exocrine secretion is regulated by CCK released by guanidinated casein hydrolysate. A guanidyl residue is likely to be involved in this control.     

The importance of gastric secretion in the feedback control of interdigestive and postprandial pancreatic secretion in rats.

Previous studies demonstrated that pancreatic enzyme secretion in rats is stimulated by the diversion of pancreatic juice from the duodenum or by the inhibition of pancreatic proteinases in the intestinal lumen but little attention has been paid to the role of gastric secretion in this stimulation. This study, carried out on conscious rats with large gastric (GF) and pancreatic fistulas, confirms that diversion of pancreatic juice in rats with the GF closed results in the progressive stimulation of pancreatic secretion reaching the maximum similar to that induced by exogenous CCK. When the GF was kept open, the diversion resulted in only small increment in pancreatic secretion and this was accompanied by progressive increase in gastric acid outputs. Similar amounts of HCl (25-400 mumol/h) instilled intraduodenally (i.d.) in rats with the GF open fully reproduced the increase in pancreatic secretion observed after the diversion of pancreatic juice and this effect was completely abolished by the pretreatment with L-364,718, a specific CCK receptor antagonist. Pretreatment with omeprazole to suppress completely gastric acid secretion in the diverted state resulted in a decline in pancreatic secretion similar to that observed after opening the GF. Camostate given in graded doses (6-200 mg/kg) either i.d. or s.c. in rats with pancreatic juice returned to the duodenum caused a dose-dependent increase in pancreatic secretion, but after opening the GF or after omeprazole this increase was reduced by about 50% while after L-364,718 it was abolished. This study provides evidence that gastric secretion plays an important role in the pancreatic response to diversion of pancreatic juice or inhibition of luminal proteinases (but not to feeding) and the elimination of gastric acid reduces this response.