Effect of bile duct obstruction on pancreatic enzyme secretion and intestinal proteolytic enzyme activity in the rat

Gastrointestinal satiety signals II. Cholecystokinin

During a meal, ingested nutrients accumulate in the stomach, with a significant portion passing on to the small intestine. The gastrointestinal presence of ingested nutrients initiates a range of physiological responses that serve to facilitate the overall digestive process. Thus peptides and transmitters are released, and various neural elements are activated that coordinate gastrointestinal secretion and motility and can eventually lead to meal termination or satiety. Among the range of gastrointestinal peptides released by ingested nutrients is the brain/gut peptide CCK. CCK plays a variety of roles in coordinating gastrointestinal activity and has been demonstrated to be an important mediator for the control of meal size.

Cholecystokinin cells

Cholecystokinin (CCK) is an important hormonal regulator of the digestive process. CCK cells are concentrated in the proximal small intestine, and hormone is secreted into the blood upon the ingestion of food. The physiological actions of CCK include stimulation of pancreatic secretion and gallbladder contraction, regulation of gastric emptying, and induction of satiety. Therefore, in a highly coordinated manner, CCK regulates the ingestion, digestion, and absorption of nutrients. CCK is produced by two separate cell types: endocrine cells of the small intestine and various neurons in the gastrointestinal tract and central nervous system. Accordingly, CCK can function as either a hormone or a neuropeptide. This review focuses on the physiology of the CCK cell in the intestine and, in particular, on how the CCK cell is regulated to secrete its hormone product. The effects of ingested nutrients on the CCK cell and the intracellular messenger systems involved in controlling secretion are reviewed. A summary is provided of recent studies examining the electrophysiological properties of CCK cells and newly discovered proteins that act as releasing factors for CCK, which mediate feedback pathways critical for regulated secretion in the intact organism.

Purification, characterization and substrate specificity of rat pancreatic elastase II

A somatostatin-14-degrading activity has been purified to homogeneity from rat pure pancreatic juice. This proteinase was concentrated more than 350-fold in a four-step procedure including ion-exchange and gel filtration. The final preparation contained a single protein with a molecular weight (M(r)) of approx. 29,000, as determined by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. The determination of its NH2-terminal sequence led us to conclude that the purified proteinase corresponds to the rat pancreatic elastase II predicted from the cDNA clone isolated by MacDonald in 1982. This anionic proteinase exhibits an isoelectric point of 5.6 and does not contain any carbohydrate moieties in its structure. The proteinase is sensitive to the trypsin inhibitors soybean trypsin inhibitor and N alpha-tosyl-L-lysine-chloromethyl ketone and also to 3,4-dichloroisocoumarin, a general elastase inhibitor. The cleavage products obtained after hydrolysis of somatostatin-14 by the purified elastase, were separated by reversed phase high performance liquid chromatography and identified by amino-acid analysis. The primary hydrolysis was trypsin-like and consisted in an opening of the cyclic structure of somatostatin-14 after the Lys-9 residue leading to the formation of a Y-shaped peptide with the same amino-acid composition as the native peptide. The initial 'trypsin-like specificity' was not observed during the secondary hydrolysis of the Y-shaped peptide; indeed the proteinase seemed more specific for a certain motif in the native peptide rather than for a specific class of amino acid, this last kind of selectivity is commonly observed with trypsin and chymotrypsin. In order to establish that the proteinase possesses an extended recognition site on the substrate rather than a specificity for a class of amino acid, the substrate specificity of the rat pancreatic elastase II was investigated with a series of para-nitroanilide peptides. The proteinase exhibits a large specificity involving peptide chain of at least four amino acids with a preference for bulky residue in P1 or P2. The Km values of 89 microM and 1567 microM obtained for somatostatin-14 and Suc-Ala-Ala-Pro-Met-pNA, respectively, indicate that elastase II has a greater affinity for the natural substrate than for synthetics. This last observation along with the substrate specificity of the proteinase leads us to propose that elastase II could be specifically involved in the regulation of biological functions of somatostatin-14 in the gastrointestinal tract.

Pancreatic enlargement in obstructive jaundice. Effects of biliary stream diversion in humans

To verify the influence of obstructive jaundice on pancreatic growth, the anteroposterior width of the pancreas was measured by computed tomography in 30 cholangiocarcinoma patients excluded patients with distal bile duct tumor (jaundice group) and 74 control subjects. Follow-up examinations were performed on 12 patients with and without internal biliary drainage to elucidate the temporal relationship between pancreatic enlargement and the diversion of the obstructed biliary stream. Histologic analysis on autopsy samples from 13 control and 10 jaundice cases also was performed. Mean pancreatic head and body widths in the jaundice group were 2.93 +/- 0.3 cm and 2.01 +/- 0.3 cm, respectively. These values were significantly greater than those of the controls (2.13 +/- 0.3 cm and 1.49 +/- 0.3 cm, P < 0.01). The glandular widths returned to their normal sizes following internal biliary drainage. No changes were seen in patients who underwent external drainage alone. Histologic examination revealed that enlargement of the acinar cells or of the islet of Langerhans was often seen in the jaundiced patients. Therefore obstructive jaundice is thought to cause pancreatic growth through a trophic effect by interrupting biliary circulation.

Direct, concentration-dependent inhibition by taurocholate of pancreatic exocrine secretion and CCK release in conscious rats

In conscious rats, bile inhibits pancreatic secretion. The role of luminal taurocholate (TC), a major component of rat bile, in the regulation of pancreatic secretion was studied in conscious rats with external bile and pancreatic fistulae. On the fourth postoperative day, after the basal collection of bile and pancreatic juice (PJ) returned to the duodenum, graded doses of TC (0, 0.4, 4, 40 mM) containing 10 mM CaCl2 were infused into the duodenum instead of bile and PJ for 2 hr (1 ml/hr), with or without 1 mg/ml of porcine trypsin. Luminal trypsin activities were not affected by any dose of TC. The increases in pancreatic secretion in response to diversion of bile and PJ were progressively inhibited with increasing doses of infused TC from 0 mM to 4 mM both with and without trypsin infusion. The effects with 4 and 40 mM TC were not significantly different. Changes in plasma cholecystokinin concentrations roughly correlated with changes in protein output in rats without trypsin infusion. We concluded that TC directly inhibited pancreatic secretion independent of the luminal trypsin activity and that its inhibitory action was concentration dependent.

Two mechanisms of inhibition by bile on luminal feedback regulation of rat pancreas

BACKGROUND

Pancreatic exocrine secretion in conscious rats is regulated by luminal protease activities. A decrease in protease activities results in pancreatic hypersecretion (luminal feedback regulation). Although bile has been known to affect this regulation, the mechanism is not clear. In the present study, the effect of bile in the intestinal lumen on luminal feedback regulation was examined.

METHODS

Rats were prepared with separate cannulas for draining bile and pancreatic juice and with a duodenal cannula and an extrajugular vein cannula. Because the rate of enzyme secretion varies in individual rats, porcine trypsin was infused instead of pancreatic juice. Graded doses of porcine trypsin were infused with bile or Tris buffer containing 10 mmol/L CaCl2 instead of bile.

RESULTS

The trypsin activities in the proximal quarter of the small intestine were similar in rats infused with bile and with Tris buffer containing 10 mmol/L CaCl2 (without bile); however, increments of pancreatic secretions of fluid and protein were significantly higher in rats without bile infusion than in those with bile infusion. Infusion of calcium-free Tris buffer resulted in significantly lower trypsin activity.

CONCLUSIONS

The results indicate that bile has two inhibitory mechanisms on pancreatic secretion, one stabilizing luminal trypsin, the other independent of luminal trypsin activity.

Regulation of intestinal concentration of cholecystokinin by bile and/or pancreatic juice

Pancreatic exocrine secretion in conscious rats is regulated by intraluminal bile and/or pancreatic juice. Exclusion of bile and/or pancreatic juice from the intestinal lumen caused cholecystokinin (CCK) release and stimulated pancreatic secretion. CCK in the plasma is mainly derived from endocrine cells in the proximal small intestinal mucosa. We examined the changes in CCK concentrations in the intestinal mucosa and compared them to those of plasma CCK concentrations and the changes of luminal trypsin activities after bile and/or pancreatic juice diversion in conscious rats. Rats with bile and pancreatic fistulae were used. Each treatment of bile, pancreatic juice, and bile-pancreatic juice diversion decreased luminal trypsin activity and increased plasma and intestinal CCK concentrations. The potency of the stimulatory effect on plasma and intestinal CCK concentrations was bile-pancreatic juice diversion > pancreatic juice diversion > or = bile diversion. Neither plasma CCK concentration nor intestinal CCK concentration was in inverse proportion to trypsin activity. The plasma CCK concentration did not parallel intestinal CCK concentration. Intravenous infusion of CCK-8 (300 pmol/kg/hr) did not increase CCK concentration in the intestinal mucosa. It was proposed that bile and/or pancreatic juice in the intestinal lumen regulated CCK concentrations not only in the plasma but also in the intestinal mucosa.

Exocrine pancreatic function in obstructive jaundice rats: studies with isolated dispersed pancreatic acini

This study was conducted to investigate pancreatic exocrine function and pancreatic growth in rats with obstructive jaundice (OJ). OJ was produced in adult male Sprague-Dawley rats by bile duct ligation; control rats underwent laparotomy only. Induction of OJ was associated with significant hyperplasia and hypertrophy of the pancreas in rats as shown by increased DNA and RNA contents of pancreatic tissue. Factors associated with pancreatic growth in OJ rats were further examined in isolated dispersed pancreatic acini from OJ rats and the data were compared with those for control rats. Studies with isolated dispersed acini from OJ rats showed that pancreatic growth was accompanied by significant increases in total cellular amylase content; however, amylase release (percentage of initial) in response to cholecystokinin octapeptide was significantly decreased in OJ rats compared to control rats. Total amylase output in response to 100 pM cholecystokinin (CCK) was higher in the OJ group when compared to the control group (8.6 U/mg protein versus 6.4 U/mg protein), as calculated from the total amylase content and percentage of amylase released. Receptor binding data showed that the capacity of CCK receptors in OJ rats was significantly lower when it was compared with control. In addition, plasma levels of CCK were significantly elevated in OJ rats when compared to controls. These results suggest that obstructive jaundice induces pancreatic growth that is associated with alteration of exocrine pancreatic function. Abnormally high levels of stored amylase in pancreatic acini may be implicated in the development of pancreatitis as often seen in obstructive jaundice patients.

Role of bile acids in the control of pancreatic secretion and CCK release

In most species stimulated pancreatic enzyme secretion and CCK release are increased in the absence and inhibited in the presence of luminal bile acids. Changes in CCK release are almost unequivocal in all investigated species. With respect to enzyme secretion, physiological bile acid concentrations seem to be necessary to exert an inhibitory effect on stimulated enzyme output in humans. Bile acids administered in higher concentrations may enhance basal and stimulated pancreatic secretion. Furthermore, the chemical properties of different bile acids (i.e., hydroxylation, conjugation) seem to contribute to their stimulating effect on enzyme secretion as was observed in several species. The rank order of bile acids inhibiting stimulated enzyme secretion in humans is taurocholate greater than taurodeoxycholate greater than taurochenodeoxycholate. On the other hand, chenodeoxycholic acid exerts the strongest stimulating effect on secretion release, which may account for the stimulating effect of this bile acid on exocrine pancreatic secretion. The strongest candidate for the mediator role in bile-acid-induced changes of exocrine pancreatic secretion is CCK (at least in dogs and rats). The CCK cell may be influenced either directly or indirectly. In conclusion, bile acids modulate pancreatic enzyme secretion and CCK release. CCK is a major candidate for this regulatory role under physiological conditions.

Regulation of plasma cholecystokinin levels by bile and bile acids in the rat

To determine whether intraduodenal bile acids inhibit pancreatic secretion and cholecystokinin (CCK) release independent of pancreatic proteases, experiments were conducted in rats with bile and pancreatic juice chronically diverted to the ileum. Diversion of bile and pancreatic juice increased plasma CCK concentration to 19.1 +/- 4.0 pmol/L. Intraduodenal sodium taurocholate (78 mumol/h) reduced plasma CCK concentration to 6.6 +/- 1.5 pmol/L after 1 hour, but values increased to 17.3 +/- 2.3 pmol/L after 13.5 hours despite continued taurocholate infusion. Pancreatic protein secretion was also significantly but transiently inhibited by taurocholate. However, neither acute nor chronic intraduodenal bile infusion significantly reduced plasma CCK concentration compared with sodium bicarbonate infusion (13.4 +/- 1.9 pmol/L vs. 15.0 +/- 1.7 pmol/L, respectively). Chronic (13.5 hours) intraduodenal infusion of taurocholate plus pancreatic juice caused a sustained reduction of plasma CCK level to 3.1 +/- 0.5 pmol/L, which significantly increased to 9.4 +/- 1.1 pmol/L after cessation of taurocholate but with continued infusion of pancreatic juice. The results indicate that bile does not inhibit CCK release and that bile acids do not physiologically inhibit pancreatic secretion or CCK release independent of the presence of pancreatic proteases.

Effect of loxiglumide (CR-1505) on bombesin- and meal-stimulated plasma cholecystokinin in man

Cholecystokinin (CCK)-receptor antagonists have been reported to inhibit the effects of the hormone on the gastrointestinal tract. Their effect on plasma CCK levels in man has not been described. The present study in 5 normal subjects demonstrated that i.v. infusion of the potent, specific CCK-receptor antagonist loxiglumide (CR 1505) significantly augmented plasma CCK levels during infusion of bombesin (402 pM per 30 min) and after administration of a meal (1390 pM per 300 min) when compared to the bombesin- (192 pM per 30 min) and meal- (886 pM per 300 min) stimulated CCK responses during infusion of saline. The basal plasma CCK during saline infusion (0.1 pM per 40 min) was not significantly influenced by CR 1505 (-1.8 pM per 40 min). Thus, both enteral (meal) and parenteral (bombesin) stimulation of CCK secretion are augmented by CCK-receptor blockade.

Role of cholecystokinin in the regulation of pancreatic enzyme secretion in the rat

Whereas pancreatic exocrine secretion in the rat varies considerably depending on the condition under which a study is performed, it is of great importance to study pancreatic pathophysiology in vivo, while the rat is conscious. In recent years several studies were performed in the conscious rat with a cannulated pancreatic duct, and much progress was made in delineating the role of cholecystokinin (CCK) in the regulation of pancreatic enzyme secretion in more detail. This progress was mainly due to the development of specific and sensitive radioimmunoassays for CCK and the availability of specific CCK-receptor antagonists. In the rat it was shown that a negative feedback regulation mechanism of pancreatic enzyme and CCK secretion exists in which intraluminal trypsin and, to a lesser extent, bile acids and plasma CCK, plasma secretin, and the cholinergic system play important roles. Probably by interference with this feedback mechanism in the rat, casein is a stronger stimulant of plasma CCK release and pancreatic exocrine secretion than fat. Finally, CCK does not play an important role in bombesin-stimulated pancreatic enzyme secretion in the rat.

Luminal bile regulates cholecystokinin release in conscious rats

The effects of intraluminal bile on cholecystokinin release and pancreatic exocrine secretion were studied in conscious rats. Since it has been suggested that bile acid may influence pancreatic secretion indirectly by interacting with luminal protease activities, intraduodenal protease activities were eliminated by pancreatic juice diversion accompanied with simultaneous intraduodenal infusion of aprotinin. This treatment resulted in gradual increases in pancreatic juice flow, bicarbonate and protein outputs, and an increase in plasma cholecystokinin levels, reaching plateau levels 2 hr after the start of the treatment. When endogenous bile was excluded from the intestine, the pancreatic secretion and plasma cholecystokinin concentrations further increased. The intraduodenal infusion of sodium taurocholate during bile pancreatic juice diversion inhibited cholecystokinin release, while pancreatic protein output was only transiently decreased. The results indicate that bile in the duodenum directly regulates cholecystokinin release, probably through its major components, bile salts.

Influence of bile flow obstruction vs bile diversion on pancreatic secretion in the conscious rat

Changes in pancreatic exocrine functions were compared between conscious rats with bile duct ligation and bile diversion from the duodenum on the first, third, fifth, and seventh postoperative days. Body weight was significantly decreased with time in both groups. Basal secretions of fluid, bicarbonate, and protein remained unchanged throughout the experimental period in bile duct ligated rats, whereas in bile diverted rats, the basal bicarbonate secretion with returning of pancreatic juice to the duodenum increased on the third postoperative day, and the basal protein output significantly increased with time. Basal secretions with returning of pancreatic juice to the duodenum in both groups were higher than that in control (bile and pancreatic juice returned to the intestine) rats. Stepwise increases in fluid and bicarbonate outputs responding to the graded doses of secretin were observed in bile duct ligated rats on the first and third postoperative days, as has been observed in bile diverted rats. However, on the fifth and seventh postoperative days, stepwise responses to graded doses of secretin were no longer observed in bile duct ligated rats. The pancreatic response to cerulein was greater in bile diverted rats than in bile duct ligated rats. Plasma CCK concentration in 7-d bile duct ligated rats (4.7 pM) was significantly higher than that in 7-d bile diverted rats (1.6 pM), although the pancreatic wet weight, protein concentration, and total content were comparable for the two groups. It was suggested that the presence of bile in the duodenum is required to maintain normal pancreatic secretion, and that the removal of bile from the intestine has quite different effects, depending on whether the bile flow is obstructed or diverted.

Morphometric study of the rat exocrine pancreas after diversion of bile and pancreatic juice from the intestine

The effects of 6 h of diversion of bile and pancreatic juice from the intestine on the ultrastructure of rat pancreatic acinar cells were studied by morphometric procedures. After diversion the volume of zymogen granules decreased markedly, representing a reduction of 77%. The volume of autophagic vacuoles increased twofold after diversion. The volume of rough endoplasmic reticulum and Golgi apparatus was not different from that of control. It has been proved by electron microscopic morphometry that the degree of reduction of zymogen granules was similar to that after stimulation by exogenous cholecystokinin or introduction of trypsin inhibitor to the duodenum. This suggests that hypersecretion caused by diversion is due to failure of a negative feedback regulation normally induced by proteases found in pancreatic juice. An increased number of autophagic vacuoles suggests an increase of organelle turnover due to heightened secretory activity of acinar cells.

Effect of cholestyramine on plasma cholecystokinin and pancreatic polypeptide levels, and exocrine pancreatic secretion

The effect of acute and long-term administration of cholestyramine, a non-absorbable bile salt binding resin, on exocrine pancreatic secretion, plasma-cholecystokinin (CCK) and plasma-pancreatic polypeptide (PP) was investigated in 10 healthy volunteers. Oral ingestion of 12 g cholestyramine augmented the stimulatory effect of a liquid test meal on plasma-CCK (3.5-fold) and plasma-PP (2-fold). During prolonged treatment with 3 x 12 g cholestyramine daily for 4 weeks, the most pronounced increase in basal hormone levels was observed after 1 day, but progressively decreased during treatment and had normalized after 4 weeks. However, the stimulated plasma-CCK output was still significantly elevated after cessation of treatment, compared with pretreatment values. After acute and chronic cholestyramine administration only stimulated lipase secretion was elevated, whereas trypsin and amylase remained unchanged. It is suggested that removal of bile salts enhances CCK and thereby PP release and pancreatic lipase secretion.

Association of cholecystectomy with pancreatic growth and increased plasma levels of cholecystokinin in the Syrian golden hamster

This study examined the effect of cholecystectomy on plasma concentrations of cholecystokinin (CCK) and pancreatic growth. Seventy female Syrian golden hamsters were used in the investigation. Half the animals underwent cholecystectomy and half had a sham procedure. Following cholecystectomy, significant increases were observed in pancreatic weight (11-41%), total DNA content (8-16%), total protein content (9-19%), DNA synthesis rate (57-200%), and in random plasma CCK concentrations (12-81%) in comparison to the control group. There was no significant change in protein synthesis rate. We conclude that cholecystectomy may have a significant trophic effect on the pancreas and that this effect may be mediated by an increase in circulating levels of CCK.

A difference in stimulatory effects on pancreatic exocrine secretion between ursodeoxycholate and trypsin inhibitor in the rat

We previously reported that intraduodenally infused ursodeoxycholate produced hypersecretion of pancreas in bicarbonate and fluid secretion in the rabbit (Digestive Diseases and Sciences, 28:942, 1983). Since trypsin inhibitor stimulates pancreatic secretion in the rat whose pancreatic exocrine secretion is regulated by a luminal feedback mechanism, in the present study we examined the stimulatory effect of ursodeoxycholate in comparison to Trasylol in unanesthetized rats with both the presence and the absence of returning bile-pancreatic juice. Under the condition in which bile-pancreatic juice were continuously returned to the intestine, the intraduodenally infused ursodeoxycholate produced significant increases in juice flow and bicarbonate and protein outputs, while Trasylol significantly increased protein output only. After an 8- to 10-hr period of bile-pancreatic juice diversion, Trasylol no longer affected pancreatic secretion, whereas ursodeoxycholate still stimulated the bicarbonate output significantly. Trypsin activities in the proximal half of the small intestine were not decreased by the infusion of UDCA. The mechanism of stimulatory effect of ursodeoxycholate on pancreatic secretion is independent of luminal feedback regulation and appears to differ from that of trypsin inhibitor.

Effect of obstructive jaundice on amylase secretion in rat pancreatic acini

The effect of obstructive jaundice on pancreatic amylase secretion was studied in isolated pancreatic acini prepared from bile duct ligated rats (7 days postoperatively), sham operated rats being used as control. Obstructive jaundice caused increase in pancreatic wet weight, pancreatic protein content and pancreatic amylase content by 27.9%, 40.1% and 33.2%, respectively. In acini prepared from obstructive jaundice group, compared with acini from sham operation group, responsiveness to cholecystokinin (CCK) and carbachol was decreased when amylase release was expressed as the percentage of total amylase activity initially present in acini. However, sensitivity to both secretagogues was unchanged when expressed as the percentage of maximally stimulated amylase release. The dose-response curves to Ca2+ ionophore for amylase release were similarly shaped in both groups. These results suggested that a pancreatico-trophic effect, compared with altered responsiveness of pancreatic acini, should play a major role in hypersecretion in obstructive jaundice.

Influence of bile duct occlusion on the exocrine pancreas in rats

The exocrine pancreas was studied in the rat after both prolonged permanent and transient biliary obstruction. Double ligation, transection, and transposition of the distal end of the bile duct rendered the animal permanently jaundiced, whereas simple ligation led to a transient jaundice followed by restitution within 15-20 days. In permanent cholestasis pancreatic mass and protein, DNA, amylase, and trypsinogen content were increased. Transient cholestasis probably had only transient effects, since no significant changes in pancreatic mass, protein, DNA or enzymes could be found at 3-5 weeks after surgery. The results show that obstructive jaundice with absence of bile flow to the intestine causes enlargement of the pancreas due to parenchymatous hyperplasia and interstitial edema.

Effect of intraluminal bile on the feedback regulatory mechanism of pancreatic enzyme secretion in conscious rats

The effect of intraluminal bile on the well-known feedback regulatory mechanism of exocrine pancreatic secretion exerted by intraluminal trypsin was investigated in conscious rats with pancreatic, biliary and duodenal fistulae. The stimulated pancreatic enzyme secretion caused by diversion of bile-pancreatic juice from the intestine was apparently suppressed by intraduodenal reintroduction of pancreatic juice or bile-pancreatic juice, while it was slightly suppressed by intraduodenal reintroduction of bile. Although additional reintroduction of bile did not alter the already suppressed pancreatic enzyme secretion by the presence of pancreatic juice in the intestine, diversion of bile stimulated the suppressed pancreatic enzyme secretion by intraluminal bile-pancreatic juice. Infusion of sodium taurocholate into the duodenum with diversion of bile-pancreatic juice effectively inhibited pancreatic enzyme secretion. The inhibitory effect seemed to be dependent on the concentration of taurocholate infused into the duodenum. The results suggest that bile and bile acid have an important role in the feedback regulatory mechanism of pancreatic enzyme secretion, at least partly directly inhibiting the secretion.

Trophic effects on the pancreas of trypsin and bile salt deficiency in the small-intestinal lumen

The effect of trypsin inhibitor-containing diets was studied in rats, mice, and hamsters for 30 weeks. In rats, pancreatic weight, DNA, RNA, and protein increased in response to a diet of raw soya flour (containing trypsin inhibitor). In mice, pancreatic weight, DNA, RNA and protein content increased with the same diet. Only rats developed micro- and macro-nodules. In rats, longer treatment with raw soya flour resulted in further growth in the pancreas, with ultimate development of adenomas and carcinomas of the acinar pancreas. The pancreatic changes were reversible up to 6 months of feeding the raw soya diet, but thereafter became irreversible. Pancreatic growth, similar to that produced by trypsin inhibitor, was also produced by cholestyramine, perhaps as a result of its bile salt-binding properties. We conclude that removal of proteases and bile salts from the upper small intestine results in pancreatic growth, which may become neoplastic.

Exogenous and endogenous stimulations during different phases of pancreatic secretion in conscious rats

The effects of stepwise increasing doses of intravenous caerulein, secretin, urecholine and intraduodenal oleic acid were investigated in conscious rats. a) Basal water, bicarbonate, and protein secretion significantly augmented after diversion of pancreatic juice. On the basis of protein secretory pattern of basal secretion 3 stable stages have been recognised: 1. The most physiological basal stage during return of pancreatic juice. 2. The first, highly elevated plateau from the 4th to 7th 30-min period after diversion of pancreatic juice. 3. The second, delayed and less elevated plateau after 270 min. b) The following patterns of stimulated secretion were observed: 1. Caerulein stimulated protein and bicarbonate secretion during return of juice and the first plateau but it failed to elicit a significant response during the second, delayed plateau. 2. Secretin and urecholine showed similar protein responses during return of pancreatic juice but after diversion, they stimulated water and bicarbonate secretion only. 3. During the second plateau oleic acid stimulation resulted in a significant increase in water and bicarbonate secretion but no significant increase occured in protein output. The delayed inhibition of protein secretion, previously described in our laboratory, was unchanged. 4. Supramaximal doses of exogenous stimuli caused an inhibition in pancreatic secretion.

Inhibition of rat basal pancreatic secretion by intraduodenal bile

The effect on basal exocrine pancreatic secretion of diversion from and reintroduction into the duodenum of bile has been studied on conscious rats provided with pancreatic, biliary and duodenal fistulae. Diversion of bile from the intestine augmented protein output by 30%. After an eight-hour diversion recirculation of bile into the duodenum reduced pancreatic protein output by 30%; volume being not significantly modified. When either bile was diverted or the main bile duct was ligated, a similar inhibition of protein secretion was observed after intraduodenal injections of 20 mM solutions of taurocholate, taurochenodeoxycholate, chenodeoxycholate, and cholate, and of synthetic mixed micelles (bile salts, lecithin). Inhibitory action of bile salts on pancreatic secretion was seen equally whether or not the bile salts were in free or conjugated form or pancreatic juice returned to the intestine. We conclude that unlike man and the dog, bile as well as pancreatic juice inhibits the basal pancreatic exocrine secretion of the rat.