Bile-pancreatic Juice Diversion Research Articles

Intestinal Fat Suppresses Protein-Induced Exocrine Pancreatic Secretion in Chronically Bile-Pancreatic Juice-Diverted Rats

Abstract. Previously, we showed that the increase in pancreatic enzyme secretion was lower after feeding a casein diet containing fat than that after feeding a fat-free casein diet in chronically bile-pancreatic juice (BPJ)-diverted rats. In the present study, we determined whether the suppressive effects of fats on flow volume of BPJ and pancreatic enzyme secretion depend on delaying gastric emptying and examined the characteristics of the suppression with intraduodenal instillation of soybean oil or lecithin in BPJ-diverted rats. The study was conducted as three separate experiments using conscious rats with chronic BPJ diversion by means of a common bile-pancreatic duct catheter. The flow volume of BPJ and the secretion of pancreatic amylase and trypsin were determined after intraduodenal instillation of the test solution. Exocrine pancreatic secretion was strongly stimulated by administration of guanidinated casein hydrolysate (HGC, 150 mg/ml) in chronic BPJ-diverted rats. However, pancreatic secretion after administration of an emulsion containing HGC with either soybean oil (100 mg/ml) or mixed fat (50 mg/ml soybean oil + 50 mg/ml lecithin) was much lower than that after administration of HGC alone. In contrast, administration of the soybean oil emulsion without HGC resulted in a small, but significant increase in the volume of BPJ. The suppressive effects of soybean oil (100 mg/ml) on the increases in the BPJ flow and enzyme secretion were similar to those of sodium taurocholate (10 mg/ml), and there was no additive effect of soybean oil on taurocholate suppression. In conclusion, duodenally instilled soybean oil suppressed increases in flow volume of BPJ and pancreatic enzyme secretion induced by HGC in chronic BPJ-diverted rats, showing that the suppressive effect of the fat does not depend on delaying gastric emptying.

DISCREPANCY BETWEEN PANCREATIC PROTEIN SECRETION AND CCK RELEASE IN RESPONSE TO BILE-PANCREATIC JUICE DIVERSION IN THE HYPERTROPHIED RAT PANCREAS INDUCED BY SYNTHETIC TRYPSIN INHIBITOR

Pancreatic exocrine secretion in conscious rats is mainly regulated by protease activities in the proximal intestine (luminal feedback regulation).1 Decrease in protease activities by ingestion of trypsin inhibitors (TI)s or diversion of bile-pancreatic juice (BPJ) stimulates pancreatic secretion2 and produces pancreatic hypertrophy via CCK release. Since CCK releasing factor, LCRF was purified from rat intestine,3 we determined whether the levels of LCRF, CCK, and protein secretion were synchronized to one another. Changes in pancreatic secretion, plasma CCK levels, and luminal LCRF contents produced by 2- and 4-h BPJ diversion, were determined in rats with 7-day TI treatment, and compared with controls. A diet containing 0.1% synthetic TI (ONO-3402) and a standard diet (CE-2) were fed in Wistar male rats for 7 days. After 7 day-treatment, the pancreatic wet weight was significantly higher in TI treated rats than the controls. For the experiments, on the third day of the feeding, rats were prepared with cannulas draining BPJ separately, and with a duodenal cannula and with an external jugular vein cannula. On the 7th day of the feeding, after 90 min of basal secretion with returning BPJ, BPJ were diverted. Changes in pancreatic secretions of fluid and protein were determined. After 2- and 4-h BPJ diversion, rats were sacrificed. Samples of 3-4 ml of blood were withdrawn through the venous cannula to measure plasma CCK concentrations. The proximal quarter of the small intestine was removed to measure LCRF content. The levels of LCRF and CCK were parallel (Fig. 1). Pancreatic protein secretion was higher in rats treated with TI than in controls throughout the experimental period. The plasma CCK and luminal LCRF content 4-h after BPJD was significantly lower in rats treated with TI than in controls. The hypertrophied pancreas may require a smaller dose of CCK to increase protein secretion.FIGURE 1: Changes in plasma CCK concentrations, LCRF content, and pancreatic protein secretion after 4-h BPJ diversion. *significantly different from the control values. TI; trypsin inhibitor. The numbers in the parentheses are the number of animals.

Attempt to establish a chronic model to study the influence of bile and pancreatic juice diversion on pancreas feedback regulation in conscious pigs

The diversion of pancreatic juice and bile stimulates pancreatic exocrine secretion but the mechanism behind this process is still not clear. The present study investigates the influence of long lasting (10 h) bile diversion or pancreatic juice and bile diversion on the pancreatic secretion in conscious pigs. The experiments were performed on 4 weaned piglets, which had a catheter inserted to the accessory pancreatic duct and bile duct and two cannulas to the duodenum. The depletion of bile alone or both bile and pancreatic juice (PJ) resulted in an increased preprandial pancreatic juice outflow, as compared to controls. Bile diversion increased the pancreatic response to feeding. PJ volume, protein outflow, and trypsin activity values were significantly higher in bile diverted pigs than in control pigs during the prandial and postprandial periods. While in pancreatic juice and bile diverted piglets the PJ protein outflow and trypsin activity slightly increased in response to feeding, their values were lower than those of the control piglets. In conclusion, both pancreatic juice and bile present in the small intestine play an important role in the regulation of the pancreatic juice secretion. (c) 2007 Elsevier B.V. All fights reserved. (Less)

Ghrelin acts on the dorsal vagal complex to stimulate pancreatic protein secretion

Ghrelin receptors are present in the central nervous system. We hypothesized that ghrelin released from the stomach acts as an endocrine substance and stimulates brain stem vagovagal circuitry to evoke pancreatic secretion. In an in vivo anesthetized rat model, an intravenous infusion of ghrelin at doses of 5, 10, and 25 nmol increased pancreatic protein secretion from a basal level of 125 +/- 6 to 186 +/- 8, 295 +/- 12, and 356 +/- 11 mg/h, respectively. Pretreatment with atropine or hexamethonium or an acute vagotomy, but not a perivagal application of capsaicin, completely abolished pancreatic protein secretion responses to ghrelin. In conscious rats, an intravenous infusion of ghrelin at a dose of 10 nmol resulted in a 2.2-fold increase in pancreatic protein secretion over basal volume. Selective ablation of the area postrema abolished pancreatic protein secretion stimulated by intravenous infusion of ghrelin but did not alter the increase in pancreatic protein secretion evoked by diversion of bile-pancreatic juice. Immunohistochemical staining showed a marked increase in the number of c-Fos-expressing neurons in the area postrema, nucleus of the solitary tract, and dorsal motor nucleus of the vagus after an intravenous infusion of ghrelin in sham-lesioned rats; selective ablation of the area postrema eliminated this increase. In conclusion, ghrelin stimulates pancreatic secretion via a vagal cholinergic efferent pathway. Circulating ghrelin gains access to the brain stem vagovagal circuitry via the area postrema, which represents the primary target on which peripheral ghrelin may act as an endocrine substance to stimulate pancreatic secretion.

Melatonin and its precursor, L-tryptophan: influence on pancreatic amylase secretion in vivo and in vitro.

Melatonin, considered as a main pineal product, may be also synthetized in the gastrointestinal tract from L-tryptophan. Melatonin has been recently shown to affect insulin release and its receptors have been characterized in the pancreas however, the effects of melatonin on the pancreatic enzyme secretion have not been examined. The aim of this study was to investigate the effects of melatonin or L-tryptophan on amylase secretion in vivo in anaesthetized rats with pancreato-biliary fistulas, and in vitro using isolated pancreatic acini. Melatonin (1, 5 or 25 mg/kg) or L-tryptophan (10, 50 or 250 mg/kg) given to the rats as a intraperitoneal (i.p.) bolus injection produced significant and dose-dependent increases in pancreatic amylase secretion under basal conditions or following stimulation of enzyme secretion by diversion of bile-pancreatic juice. This was accompanied by a dose-dependent rise in melatonin plasma level. Stimulation of pancreatic enzyme secretion caused by melatonin or L-tryptophan was completely abolished by vagotomy, deactivation of sensory nerves with capsaicin or pretreatment with CCK1 receptor antagonists (tarazepide or L-364,718). Pretreatment with luzindole, an antagonist of melatonin MT(2) receptor failed to affect melatonin- or L-tryptophan-induced amylase secretion. Administration of melatonin (1, 5 or 25 mg/kg i.p.) or L-tryptophan (10, 50 or 250 mg/kg i.p.) to the rats resulted in the dose-dependent increase of cholecystokinin (CCK) plasma immunoreactivity. Enzyme secretion from isolated pancreatic acini was not significantly affected by melatonin or L-tryptophan used at doses of 10(-8) -10(-5) M. We conclude that exogenous melatonin, as well as that produced endogenously from L-tryptophan, stimulates pancreatic enzyme secretion in vivo while increasing CCK release. Stimulatory effect of melatonin or L-tryptophan on the exocrine pancreas involves vagal sensory nerves and the CCK release by these substances.

Inhibitory Effect of Somatostatin on Cholecystokinin Release Is Independent of Luminal Cholecystokinin-Releasing Factor Content in Conscious Rats

Exclusion of bile-pancreatic juice from the intestine increases pancreatic secretion via cholecystokinin (CCK) release in conscious rats. Luminal CCK-releasing factor (LCRF), purified from rat intestinal secretions, is an intraluminal regulator of CCK secretion during bile-pancreatic juice diversion. Because somatostatin is a potent inhibitor of CCK release and pancreatic secretion, the inhibitory effect of somatostatin on LCRF was examined. Rats were prepared with bile and pancreatic cannulae and two duodenal cannulae and with an external jugular vein cannula. The experiments were conducted without anesthesia. After 1.5-hour basal collection of pancreatic juice with bile-pancreatic juice return, bile-pancreatic juice was diverted for 2 hours, during which time somatostatin (2, 10 nmol/kg/h) was infused intravenously. The rats were killed before and 1 and 2 hours after bile-pancreatic juice diversion. To examine the effect of luminal somatostatin, 50 or 200 nmol/kg/h of somatostatin was infused into the duodenum. The plasma CCK and luminal content of LCRF were measured by specific radioimmunoassays. Bile-pancreatic juice diversion significantly increased pancreatic secretion, plasma CCK, and LCRF levels. Intravenous infusion of somatostatin inhibited CCK release and pancreatic secretion, but not LCRF content. Luminal administration of somatostatin did not show any effect. Inhibitory effect of circulating somatostatin on CCK release and pancreatic secretion is independent of LCRF content.

Oral administration of a synthetic trypsin inhibitor increases pancreatic duct function in CCK-A receptor-deficient rats.

The effects of oral administration of a synthetic trypsin inhibitor on bicarbonate secretion were examined in cholecystokinin A (CCK-A) receptor-deficient (OLETF) rats and compared with Wistar rats. Rats were fed chow containing 0.1% trypsin inhibitor for 7 days. Rats were prepared with cannulae draining bile and pancreatic juice separately and with duodenal and extrajugular vein cannulae after 3-day trypsin inhibitor ingestion. Then the animals were maintained in Bollman cages, and the experiments were conducted 4 days after surgery. After 1.5 h of basal secretion with bile-pancreatic juice return, bile-pancreatic juice was diverted for 2 h. The responses of bicarbonate secretion to bile-pancreatic juice diversion were significantly enhanced in rats treated with trypsin inhibitor compared with those given a control diet, whereas responses of fluid and protein secretion were not affected in OLETF rats. The response of protein secretion, but not those of fluid or bicarbonate secretion, was enhanced in Wistar rats by treatment with trypsin inhibitor. Carbonic anhydrase II gene expression was increased by 7-day treatment with trypsin inhibitor only in OLETF rats, and not in Wistar rats.

Intestinal fat suppresses protein-induced exocrine pancreatic secretion in chronically bile-pancreatic juice-diverted rats.

Previously, we showed that the increase in pancreatic enzyme secretion was lower after feeding a casein diet containing fat than that after feeding a fat-free casein diet in chronically bile-pancreatic juice (BPJ)-diverted rats. In the present study, we determined whether the suppressive effects of fats on flow volume of BPJ and pancreatic enzyme secretion depend on delaying gastric emptying and examined the characteristics of the suppression with intraduodenal instillation of soybean oil or lecithin in BPJ-diverted rats. The study was conducted as three separate experiments using conscious rats with chronic BPJ diversion by means of a common bile-pancreatic duct catheter. The flow volume of BPJ and the secretion of pancreatic amylase and trypsin were determined after intraduodenal instillation of the test solution. Exocrine pancreatic secretion was strongly stimulated by administration of guanidinated casein hydrolysate (HGC, 150 mg/ml) in chronic BPJ-diverted rats. However, pancreatic secretion after administration of an emulsion containing HGC with either soybean oil (100 mg/ml) or mixed fat (50 mg/ml soybean oil + 50 mg/ml lecithin) was much lower than that after administration of HGC alone. In contrast, administration of the soybean oil emulsion without HGC resulted in a small, but significant increase in the volume of BPJ. The suppressive effects of soybean oil (100 mg/ml) on the increases in the BPJ flow and enzyme secretion were similar to those of sodium taurocholate (10 mg/ml), and there was no additive effect of soybean oil on taurocholate suppression. In conclusion, duodenally instilled soybean oil suppressed increases in flow volume of BPJ and pancreatic enzyme secretion induced by HGC in chronic BPJ-diverted rats, showing that the suppressive effect of the fat does not depend on delaying gastric emptying.

Inhibitory effect of central calcitonin-gene related peptide (CGRP) on pancreatic secretion in conscious rats.

The inhibitory effect of central administration of calcitonin-gene related peptide (CGRP) on pancreatic secretion stimulated by bile-pancreatic juice diversion was determined in conscious rats. Rats were prepared with separate cannulae for draining bile and pancreatic juice and with a duodenal cannula and an extrajugular vein cannula. In addition, another cannula was stereotactically implanted into the left lateral cerebral ventricle. Rats were placed in restraint cages and experiments were conducted 4 d after the operation without anesthesia. An injection of CGRP (1 nmol/10 microl) into the left lateral cerebral ventricle (i.c.v.) inhibited pancreatic secretion as well as cholecystokinin (CCK) release induced by bile-pancreatic juice diversion. Intravenous infusion of alpha- and beta-adrenergic receptor antagonist, phentolamine and propranolol did not reverse the inhibition of pancreatic secretion. Intravenous infusion of CGRP did not affect pancreatic secretion or plasma CCK concentrations. The inhibitory action of central CGRP (i. c.v.) on pancreatic secretion and CCK release stimulated by bile-pancreatic juice diversion is partially mediated by an alpha-adrenergic mechanism, although its precise mechanism has not been elucidated.

Electrical physiological evidence for highand low-affinity vagal CCK-A receptors.

We have demonstrated that under physiological conditions CCK acts through vagal high-affinity CCK-A receptors to mediate pancreatic secretion. In this study, we evaluated the vagal afferent response to endogenous CCK in rats and defined the CCK-receptor affinity states and the vagal-receptive field responsive to CCK stimulation using electrophysiological studies. Experiments were performed on anesthetized rats prepared with bile-pancreatic fistula. Plasma CCK levels were elevated by diverting bile-pancreatic juice (BPJ). The single-unit discharge of sensory neurons supplying the gastrointestinal tract was recorded from the nodose ganglia. All units studied were either silent or they had a very low resting discharge frequency. Thirty-two single units were studied extensively; seven were shown to be stimulated by diversion of BPJ (2.6 +/- 2 impulses/min at basal to 40 +/- 12 impulses/min after diversion). Acute subdiaphragmatic vagotomy or perivagal capsaicin treatment abolished the response. The CCK-A-receptor antagonist CR-1409, but not the CCK-B antagonist L-365260, blocked the vagal response to endogenous CCK stimulation. Infusion of the low-affinity CCK-receptor antagonist CCK-JMV-180 completely blocked the vagal afferent response to the diversion of BPJ in three of seven rats tested but had no effect on the response in the remaining four. In a separate study, we demonstrated that gastric, celiac, or hepatic branch vagotomy abolished the response in different subgroups of neurons. In conclusion, under physiological conditions, CCK acts on both high- and low-affinity CCK-A receptors present on distinct vagal afferent fibers. The vagal CCK-receptor field includes the regions innervated by the gastric, celiac, and hepatic vagal branches. This study provides electrophysiological evidence that vagal CCK receptors are present on the vagal gastric, celiac, and hepatic branches and may occur in high- and low-affinity states.

Effect of deramciclane, a new 5-HT receptor antagonist, on cholecystokinin-induced changes in rat gastrointestinal function

Recent studies suggested that serotonin receptors may be involved in modulating the actions of cholecystokinin (CCK) in the gastrointestinal tract. The present work was designed to compare the effects of deramciclane, a recently developed serotonin-2 (5-HT 2A/2C) receptor antagonist, and lorglumide, a CCK A receptor antagonist, on exogenous and endogenous CCK-induced pancreatic enzyme secretion and pancreatic growth, as well as on the emptying of the stomach and the gallbladder. Pancreatic secretory function was tested while CCK release was evoked by diversion of bile-pancreatic juice in rats. Adaptive growth of the pancreas was induced by chronic intragastric administration of camostate, a potent synthetic trypsin inhibitor in rats. Gastric emptying of a noncaloric test meal was investigated in response to intraduodenal intralipid infusion, also in rats. In fasted mice, gallbladder emptying was examined in response to intragastric egg yolk administration. In rats, diversion of bile-pancreatic juice from the duodenum stimulated pancreatic amylase secretion. This action was blocked by deramciclane and by lorglumide. Pancreatic hypertrophy and hyperplasia induced by chronic camostate administration was also suppressed by both the serotonin- and the CCK-receptor antagonists. Intraduodenal administration of intralipid induced a significant delay in gastric emptying. This effect was inhibited by both deramciclane and lorglumide in rats. In mice, intragastric administration of egg yolk elicited an accelerated release of bile from the gallbladder. Prior treatment with either deramciclane or lorglumide abolished this response. Lorglumide was able to inhibit the functional responses elicited by exogenous CCK administration in both pancreas, stomach and gallbladder, while deramciclane was not effective under such circumstances. Our data show that deramciclane inhibited the effects of CCK on pancreatic, gastric and gallbladder function when its endogenous release was stimulated, but did not alter the effects of exogenously administered peptide. These results suggest that serotonin, primarily via 5-HT 2A receptors, may modulate CCK-mediated gastrointestinal functions in rats.

Atropine-resistant secretion of a putative luminal CCK-releasing peptide in conscious rats.

The changes in levels of the newly discovered luminal CCK-releasing factor (LCRF) in the small intestinal lumen before and after bile-pancreatic juice diversion in conscious rats were examined by a specific RIA. Moreover, we also examined whether LCRF secretion was under cholinergic control. Anti-LCRF antiserum was raised in rabbits, and a sensitive RIA was established. The localization of LCRF was examined by immunohistochemistry. The luminal content of LCRF was significantly increased by bile-pancreatic juice diversion, during which luminal trypsin activity was eliminated. The increase in luminal LCRF content was not inhibited by intravenous infusion of atropine. The changes in plasma levels of CCK and pancreatic secretion were similar to those in luminal LCRF contents. LCRF immunostaining was observed in villus tip enterocytes of the small intestine and was most prominent in the duodenal portion. These results support our original hypothesis that LCRF may be released spontaneously into the small intestinal lumen from the villus tip enterocytes and its intraluminal degradation by proteases regulates CCK release. Furthermore, LCRF release was not subject to cholinergic regulation.

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.

Guanidinated casein hydrolysate stimulates pancreatic secretagogue release by direct action to the intestine in rats.

Previously, we observed that pancreatic exocrine secretion was strongly enhanced after duodenal administration of guanidinated casein peptic hydrolysate (HGC) in rats with chronic bile-pancreatic juice (BPJ) diversion. Using a perifusion system of isolated dispersed rat intestinal mucosal cells, we investigated whether this phenomenon depends on a direct effect of protein on the intestine to release pancreatic secretagogues, such as cholecystokinin (CCK). Amylase release from isolated pancreatic acini was used as an assay to measure CCK or other pancreatic secretagogues in the effluents. Mucosal effluent with HGC stimulated amylase release from acini with or without soybean trypsin inhibitor (SBTI). Perifused effluent with low-concentrated SBTI did not stimulate amylase release. These results indicate that HGC stimulates release of pancreatic secretagogue from the intestinal mucosal cells independent of remaining trypsin activity in the isolated mucosa. Effluents with intact casein, its peptic digest, and homoarginine, which is a unique amino acid contained in HGC, were unable to stimulate amylase release from acini. Effluent with a high concentration of SBTI, which is rich in arginine residues, stimulated amylase release, but not with the same tryptic inhibitory effect of lima bean trypsin inhibitor, which is poor in arginine residues. These findings suggest that guanidyl residues in protein structure are responsible for release of pancreatic secretagogues from isolated intestinal mucosal cells. Finally, the increment of amylase release from pancreatic acini in response to the perifused effluent with HGC was eliminated in acini treated with a potent CCK antagonist, FK480. We conclude that in rats with BPJ diversion, HGC stimulates CCK release from the intestine by direct action on intestinal mucosa.

Incidence of apoptosis in the pancreas of young and old rats

We reported previously that the pancreatic protein responses to the high dose of cholecystokinin (CCK) or bile–pancreatic juice diversion were impaired in old rats of both sexes, whereas the basal secretion was comparable to that in young animals. To examine the mechanism of the attenuated response in old rats, we examined the incidence of apoptosis of the pancreatic acinar cells and the plasma CCK concentrations produced by bile–pancreatic juice diversion, which is a potent endogenous stimulator of pancreatic secretion, in young (4–8 months old) and old (25–29 months old) rats of both sexes. Apoptosis was examined by electron microscopic examination and the nick end-labeling method for detecting cells with DNA strand breaks. The plasma CCK level was determined by RIA with OAL-656 antibody. The incidence of nick end-labeling-positive cells (apoptotic index) was slightly higher in old rats of both sexes. Apoptosis coincided with the acinar cell loss in old male rats, in which apoptotic index was much greater than that in young animals. The plasma CCK levels produced by bile–pancreatic juice diversion were lower in old than in young male rats, whereas no age difference was observed in females. The basal plasma CCK levels were comparable regardless of age and sex. The pancreatic wet weights were higher in old than in young rats of both sexes. These observations suggested that although impaired CCK functions in old male rats might have some role in the increase in apoptosis in the pancreas, the increase in apoptosis could not fully explain the attenuated pancreatic response in old rats.

Regulation of cholecystokinin release and transcription in a rat without gene expression of cholecystokinin-A receptor.

An Otsuka Long-Evans Tokushima Fatty (OLETF) rat does not possess cholecystokinin (CKK)-A receptor gene expression because of a genetic abnormality. We examined the CCK release and its transcription in OLETF rats in comparison with control (Long-Evans-Tokushima-LETO) rats. Animals at 5-6 and 24-25 weeks of age were used. The level of CCK mRNA and CCK concentration in the small intestinal mucosa, and the level of CCK-A receptor mRNA in the pancreas were examined. To examine CCK release, rats were prepared with external bile and pancreatic fistulae. The basal plasma levels of CCK and those at 2 h after bile-pancreatic juice diversion were measured by radioimmunoassay. The levels of CCK mRNA, and tissue CCK concentration increased significantly with age in both strains, but the values in OLETF rats were significantly lower than those in LETO rats. The CCK-A receptor mRNA level also increased with age in LETO rats. The plasma CCK concentration was significantly increased by bile-pancreatic juice diversion regardless of age and strain; however, the level of plasma CCK in OLETF rats at 24-25 weeks of age was significantly lower than that of LETO rats. It is suggested that the long-term defect of CCK-A receptor may decrease CCK release and transcription.

Changes in messenger RNA of pancreatic enzymes and intestinal cholecystokinin after a 7-day bile-pancreatic juice diversion from the proximal small intestine in rats.

We have previously demonstrated the bile-pancreatic juice (BPJ)-independent stimulation of pancreatic enzyme secretion in chronic BPJ-diverted rats. Pancreatic and intestinal adaptation to 7-day BPJ diversion was next examined. Pancreatic enzyme mRNA and cholecystokinin mRNA in the jejunal mucosa were measured in rats with BPJ diverted into the ileum (PBD rats) in comparison with the figures for rats with BPJ returned to the duodenum (normal rats) or laparotomized (Intact) rats under well-nourished conditions. Amylase mRNA in the pancreas was lower and trypsinogen plus chymotrypsinogen mRNA was higher in the PBD rats than in the intact rats. The change in pancreatic mRNA was similar to that in the specific activities of the enzymes after a chronic BPJ diversion. This finding suggests that these pancreatic enzymes were regulated by the mRNA level. The portal concentration of cholecystokinin in the postabsorptive period (exogenously non-stimulated status) was 4-fold higher in the PBD group than in the normal and intact groups. Cholecystokinin mRNA in the jejunal mucosa of PBD rats was somewhat higher than that of intact rats. These results suggest that intestinal cholecystokinin was predominantly increased at the translational or later stage by chronic BPJ diversion.

CK-independent increases in pancreatic secretion induced by dietary protein in chronic BPJ-diverted rats.

Previously, we demonstrated that, in rats with chronic bile-pancreatic juice (BPJ) diversion, pancreatic enzyme secretion was increased after feeding animals a 25% casein fat-free diet. We determined whether cholecystokinin (CCK) or the cholinergic pathway is associated with the response of pancreatic secretion after protein ingestion in the diverted rats, using a potent CCK antagonist, MK-329 or FK-480, and a cholinergic blocker, atropine. Secretion rates of chymotrypsin and trypsin in the fasting state were very high 7 days after a BPJ diversion, and the hypersecretion of the proteases was markedly reduced with an injection of MK-329, FK-480, or atropine and was further reduced by combined injection of FK-480 and atropine. The lowered secretion of the proteases in CCK-antagonized rats was increased after oral feeding of a protein diet and after a duodenal instillation of some protein sources, especially hydrolysate of guanidinated casein (HGC). The CCK-independent increases by HGC instillation are completely depressed by atropine. In rats treated with only atropine, the lowered secretion tended to be increased by a duodenal instillation of HGC. Increases in secretion after an administration of the protein source in CCK-antagonized rats were not affected by bestatin, an inhibitor of brush-border peptidases. We conclude that the stimulatory effects of dietary protein on the pancreatic enzyme secretion partially do not depend on CCK in chronic BPJ-diverted rats and that the CCK-independent increase is atropine sensitive.

Pancreatic secretion stimulated by CCK is not mediated by capsaicin-sensitive vagal afferent pathway in awake rats.

A capsaicin-sensitive vagal afferent pathway was reported to mediate the effect of endogenous cholecystokinin (CCK) on pancreatic secretion in anesthetized rats. Because neural blockade affects pancreatic secretion much less in awake than in anesthetized rats, the effect of capsaicin ablation of vagal afferent pathways on pancreatic secretion stimulated by endogenous CCK was examined in awake rats. During surgery, abdominal vagal trunks were exposed, and 0.1 ml of capsaicin (10 mg/ml) was applied to the vagal trunks. Ablation of the vagal afferent pathway was assessed by the ability of intraperitoneal cholecystokinin octapeptide (CCK-8) to suppress food intake and inhibit gastric emptying. Endogenous CCK release was stimulated by diversion of bile pancreatic juice from the intestine and by intraduodenal infusion of casein. Pancreatic protein and fluid secretion were significantly increased by both treatments, and the responses were unaffected by capsaicin. Intraperitoneal CCK-8 markedly inhibited food intake and gastric emptying, and both effects were significantly attenuated in capsaicin-treated rats, indicating that capsaicin treatment successfully ablated vagal afferent fibers. It is concluded that CCK-stimulated pancreatic secretion in rats is not mediated by a vagal afferent pathway.

Lack of Response to Dietary Protein in Pancreatic Secretion by Chronic Deprivation of Jejunal Chyme in Rats

Exocrine pancreatic secretion is regulated by luminal factors, bile-pancreatic juice (BPJ), and food chyme. The effects of 10 days' chronic deprivation of luminal chyme on the stimulation of exocrine pancreatic secretion by dietary protein were examined in rats with or without BPJ in the jejunum. The jejunum was deprived of ingested food by preparing a whole-jejunum blind loop. The BPJ was diverted by a common bile-pancreatic duct catheter and was returned to the upper jejunum (with BPJ) or ileum (without BPJ). In rats with the ingested food and BPJ in the jejunum (control), secretion rates in terms of volume, protein, amylase, and trypsin increased more than twofold from the rates in the fasting state after a jejunal injection of peptic hydrolysate of casein. In contrast, the secretions were not increased by the protein injection in the rats deprived of jejunal chyme with or without BPJ in the jejunum. Even in the chyme-deprived group the protein and trypsin secretion of the fasting state was significantly higher in BPJ-diverted rats than in rats with BPJ. These results showed that chronic deprivation of the jejunal chyme impaired responses of the exocrine pancreas to dietary protein but not the hypersecretions of the pancreas by BPJ diversion.