Pancreozymin bioassay in man based on pancreatic enzyme secretion: potency of specific amino acids and other digestive products

L-valine is a powerful stimulator of GLP-1 secretion in rodents and stimulates secretion through ATP-sensitive potassium channels and voltage-gated calcium channels

BACKGROUND

We previously reported that, among all the naturally occurring amino acids, L-valine is the most powerful luminal stimulator of glucagon-like peptide 1 (GLP-1) release from the upper part of the rat small intestine. This makes L-valine an interesting target for nutritional-based modulation of GLP-1 secretion. However, the molecular mechanism of L-valine-induced secretion remains unknown.

METHODS

We aimed to investigate the effect of orally given L-valine in mice and to identify the molecular details of L-valine stimulated GLP-1 release using the isolated perfused rat small intestine and GLUTag cells. In addition, the effect of L-valine on hormone secretion from the distal intestine was investigated using a perfused rat colon.

RESULTS

Orally given L-valine (1 g/kg) increased plasma levels of active GLP-1 comparably to orally given glucose (2 g/kg) in male mice, supporting that L-valine is a powerful stimulator of GLP-1 release in vivo (P > 0.05). Luminal L-valine (50 mM) strongly stimulated GLP-1 release from the perfused rat small intestine (P < 0.0001), and inhibition of voltage-gated Ca2+-channels with nifedipine (10 μM) inhibited the GLP-1 response (P < 0.01). Depletion of luminal Na+ did not affect L-valine-induced GLP-1 secretion (P > 0.05), suggesting that co-transport of L-valine and Na+ is not important for the depolarization necessary to activate the voltage-gated Ca2+-channels. Administration of the KATP-channel opener diazoxide (250 μM) completely blocked the L-valine induced GLP-1 response (P < 0.05), suggesting that L-valine induced depolarization arises from metabolism and opening of KATP-channels. Similar to the perfused rat small intestine, L-valine tended to stimulate peptide tyrosine-tyrosine (PYY) and GLP-1 release from the perfused rat colon.

CONCLUSIONS

L-valine is a powerful stimulator of GLP-1 release in rodents. We propose that intracellular metabolism of L-valine leading to closure of KATP-channels and opening of voltage-gated Ca2+-channels are involved in L-valine induced GLP-1 secretion.

Exocrine pancreatic insufficiency and pancreatic exocrine replacement therapy in clinical practice

Exocrine pancreatic insufficiency (EPI) is a complex condition that disrupts normal digestion and absorption. Patients with EPI may suffer from mild to debilitating malabsorption with a constellation of symptoms that can have a significant effect on quality of life and nutrition status. Pancreatic enzyme replacement therapy (PERT) is effective and safe to treat EPI and is the standard of care for this condition. A wide variety and various forms of these products exist, as well as numerous guidelines and recommendations. Obtaining PERT for patients can oftentimes be cost prohibitive. Determining the presence and extent of EPI can be challenging and patient specific, making it difficult for practitioners. This narrative review will explore these issues, as well as several disease states potentially affected by EPI, and review current management strategies.

Assessment of exocrine pancreatic function in children and adolescents with direct and indirect testing

The exocrine pancreas plays an important role in digestion. Understanding of the physiology and regulation of exocrine function provides insight into disease processes and basis of functional testing. Specifically, exocrine pancreatic insufficiency (EPI) can cause maldigestion and thus a proper assessment of exocrine pancreatic function is important. There are indirect and direct methods for evaluating pancreatic function. Indirect methods are varied and include stool, serum, urine, and breath tests. Fecal elastase is a commonly used indirect test today. Direct methods involve stimulated release of pancreatic fluid that is collected from the duodenum and analyzed for enzyme activity. The most used direct test today is the endoscopic pancreatic function test. Indirect pancreatic function testing is limited in identifying cases of mild to moderate EPI, and as such in these cases, direct testing has higher sensitivity and specificity in diagnosing EPI. This review provides a comprehensive guide to indirect and direct pancreatic function tests as well as an in-depth look at exocrine pancreatic function including anatomy, physiology, and regulatory mechanisms.

Amino acids differ in their capacity to stimulate GLP-1 release from the perfused rat small intestine and stimulate secretion by different sensing mechanisms

The aim of this study was to explore individual amino acid-stimulated GLP-1 responses and the underlying stimulatory mechanisms, as well as to identify the amino acid-sensing receptors involved in amino acid-stimulated GLP-1 release. Experiments were primarily based on isolated perfused rat small intestines, which have intact epithelial polarization allowing discrimination between luminal and basolateral mechanisms as well as quantitative studies of intestinal absorption and hormone secretion. Expression analysis of amino acid sensors on isolated murine GLP-1 secreting L-cells was assessed by qPCR. We found that l-valine powerfully stimulated GLP-1 secretion but only from the luminal side (2.9-fold increase). When administered from the vascular side, l-arginine and the aromatic amino acids stimulated GLP-1 secretion equally (2.6- to 2.9-fold increases). Expression analysis revealed that Casr expression was enriched in murine GLP-1 secreting L-cells, whereas Gpr35, Gprc6a, Gpr142, Gpr93 (Lpar5), and the umami taste receptor subunits Tas1r3 and Tas1r1 were not. Consistently, activation of GPR35, GPR93, GPR142, and the umami taste receptor with specific agonists or allosteric modulators did not increase GLP-1 secretion (P > 0.05 for all experiments), whereas vascular inhibition of CaSR reduced GLP-1 secretion in response to luminal infusion of mixed amino acids. In conclusion, amino acids differ in their capacity to stimulate GLP-1 secretion. Some amino acids stimulated secretion only from the intestinal lumen, whereas other amino acids exclusively stimulated secretion from the vascular side, indicating that amino acid-stimulated GLP-1 secretion involves both apical and basolateral (postabsorptive) sensing mechanisms. Sensing of absorbed amino acids involves CaSR activation as vascular inhibition of CaSR markedly diminished amino acid stimulated GLP-1 release.NEW & NOTEWORTHY Using isolated perfused rat small intestines, we show that amino acids differ in their mechanisms and capacity of stimulating GLP-1 release. Furthermore, we demonstrate that sensing by GPR142, GPR35, GPR93, and the umami taste receptor (Tas1R1/Tas1R3) are not involved in amino acid stimulated GLP-1 release. In contrast to previous studies, this experimental model allows discrimination between the luminal and the vascular side of the intestine, which is essential when studying mechanisms of amino acid-stimulated GLP-1 secretion.

Administration of encapsulated L-tryptophan improves duodenal starch digestion and increases gastrointestinal hormones secretions in beef cattle

Objective

This study investigated the effects of oral administration of rumen-protected L-tryptophan (RPL-T) on duodenal starch digestion and gastrointestinal hormones (GIH) secretions using Hanwoo beef steers as the animal models.

Methods

Four steers (423±24 kg) fitted with ruminal and duodenal cannulas were employed in a crossover design replicated twice. Treatments were control (basal diet) and RPL-T (basal diet+191.1 mg/kg body weight [BW]) group. Blood and duodenal samples were collected to measure serum GIH levels and pancreatic α-amylase activity at day 0, 1, 3, and 5 (−30, 30, 90, 150, and 210 min) of the study. Samples from each segment of the gastrointestinal tract were collected via ruminal and duodenal cannulas and were used to determine soluble protein and the starch digestion rate at days 6 (−30, 180, 360, and 540 min) and 8 (−30, 90, 270, and 450 min) of the experiment.

Results

No significant difference in ruminal pH, NH₃-N, and total volatile fatty acid including the levels of acetate, propionate, butyrate, isobutyrate, valerate, isovalerate, and the acetate-to-propionate ratio was observed between groups (p>0.05). Crude protein uptake was higher and feces starch content was lower in RPL-T group than the control group (p<0.05). The D-glucose contents of feces in RPL-T group decreased at day 5 compared to those in the control group (p<0.05), however, no change was found at day 0, 1, or 3 compared to the control group (p>0.05). Serum cholecystokinin (CCK), melatonin, duodenal pancreatic α-amylase activity, and starch digestion were significantly higher in RPL-T group than the control group (p<0.05).

Conclusion

Taken together, oral administration of RPL-T at the rate of 191.1 mg/kg BW consistently increased CCK concentration, pancreatic α-amylase activity in duodenal fluids, and starch digestion rate in the small intestine and thus found to be beneficial.

Intravenous administration of L-tryptophan stimulates gastrointestinal hormones and melatonin secretions: study on beef cattle

This study aimed to determine the effective dose of intravenous administration of L-tryptophan (L-T) on gastrointestinal hormones (GIH) secretions and melatonin using Hanwoo cattle. Three steers (362 ± 23 kg) fitted with indwelling jugular vein catheters were assigned in a 3 × 3 Latin square design. Treatments were intravenous administration of saline (control), 28.9 mg L-T/kg body weight (BW; low) and 57.8 mg L-T/kg BW (high) L-T for 1 day with 7 days of adaptation. Samples were collected after adaptation period at -60, 0, 30, 60, 90, 120, 150, 180, 240, and 300 min of sampling day. The levels of serum cholecystokinin (CCK) and secretin were higher (p < 0.05) in the high L-T group than those in the other groups. Serum Melatonin (MEL) levels were increased upon L-T administration (p < 0.05) in the high L-T group. Taken together, the effective dose of L-T administration was defined at 57.8 mg L-T/kg BW in order to stimulate increase of GIH and MEL.

IV Hypertonic Glucose Stimulates the Exocrine Pancreas in Rat

BACKGROUND

Pancreatic atrophy and dysfunction resulting from parenteral nutrition (PN) may be explained by several mechanisms; one of the important factors is the nutrient in the circulation, which affects the pancreatic growth and secretion. The effect of nutrients on the pancreatic exocrine still has controversies. The aim of the present study is to better understand the effect of i.v. glucose on the exocrine pancreas stimulated by cholecystokinin during the parenterally fed condition.

METHODS

Two mixed solutions consisting of 30% and 50% glucose, respectively, were used. Thirty male Sprague-Dawley rats were randomly divided into 5 groups, including a control group; a freely fed group received cholecystokinin; 2 groups were infused with 30% and 50% glucose, and a group was infused with 50% glucose with cholecystokinin. The body weight and pancreatic contents were measured after 10 days.

RESULTS

The body weight in all groups was increased but lower than in the freely fed rats. I.v. glucose caused a decrease in the pancreatic weight, the amount of the pancreatic protein and DNA, and the level of amylase but elevated the level of trypsin in all treated groups. The enzymes were elevated after infusion of cholecystokinin with glucose, but they were lower than in freely fed animals with cholecystokinin. Compared with 30% glucose, 50% glucose elevated the level of amylase but did not affect the level of trypsin.

CONCLUSIONS

I.v. glucose results in atrophy of the exocrine pancreas, elevates the amylase in pancreas, but suppresses the stimulatory effect of cholecystokinin on the exocrine pancreas.

Effect of Oral Administration of Intact Casein on Gastrointestinal Hormone Secretion and Pancreatic α-Amylase Activity in Korean Native Steer

Three Korean native steers (779±24 kg) fitted with duodenal cannulas were used in a 3×3 Latin square design to investigate the influence of oral administration of soluble proteins, intact casein (IC) and acid hydrolyzed casein (AHC), on gastrointestinal hormone (GIH) secretion in the blood and pancreatic α-amylase activity in the duodenum. Oral treatment consisted of a basic diet (control), IC (C+100% protein), or AHC (C+80% amino acid, 20% peptide) for 21 d. Blood and duodenum samples were collected for measurement of serum GI hormones, and pancreatic α-amylase activity was determined at 900, 1030, 1330, 1630, and 1930 h after feeding on d 21 of treatment. The levels of serum cholecystokinin (CCK) and secretin in the IC treatment group were higher compared to the other treatment groups (p<0.05). In addition to the changes in CCK and secretin levels upon IC treatment, the pancreatic α-amylase activity in the duodenum was higher in the IC group compared to the control diet group (p<0.05). The response of serum ghrelin to IC and AHC treatment was in accordance with the response of serum secretin. The level of peptide fragments flowing in the duodenum was higher in the IC treatment group than the other treatment groups (p<0.05). In conclusion, this study demonstrated that an increase in duodenal CCK and secretin upon IC oral administration increased pancreatic α-amylase secretion. In addition, ghrelin may be associated with GI hormone secretion in Korean native steers.

Human Gastrointestinal Juices Intended for Use in In Vitro Digestion Models

The aim of this study was to characterise the individual human gastric and duodenal juices to be used in in vitro model digestion and to examine the storage stability of the enzymes. Gastroduodenal juices were aspirated, and individual variations in enzymatic activities as well as total volumes, pH, bile acids, protein and bilirubin concentrations were recorded. Individual pepsin activity in the gastric juice varied by a factor of 10, while individual total proteolytic activity in the duodenal juice varied by a factor of 5. The duodenal amylase activity varied from 0 to 52.6 U/ml, and the bile acid concentration varied from 0.9 to 4.5 mM. Pooled gastric and duodenal juices from 18 volunteers were characterised according to pepsin activity (26.7 U/ml), total proteolytic activity (14.8 U/ml), lipase activity (951.0 U/ml), amylase activity (26.8 U/ml) and bile acids (4.5 mM). Stability of the main enzymes in two frozen batches of either gastric or duodenal juice was studied for 6 months. Pepsin activity decreased rapidly and adjusting the pH of gastric juice to 4 did not protect the pepsin from degradation. Lipase activity remained stable for 4 months, however decreased rapidly thereafter even after the addition of protease inhibitors. Glycerol only marginally stabilised the survival of the enzymatic activities. These results of compositional variations in the individual gastrointestinal juices and the effect of storage conditions on enzyme activities are useful for the design of in vitro models enabling human digestive juices to simulate physiological digestion.

Control of pancreatic secretion in humans

Studies on the control of pancreatic secretion in humans of all ages have been a difficult task over the years because of patients' availability and ethic committee rules. Nevertheless, studies were performed and the objectives of this review are to summarize our knowledge on the development of secretory process in newborns, on the different phases of the pancreatic responses to a meal, on the pancreatic responses to the different components of the diet, on the mechanisms involved in the control of the pancreatic responses, and finally on the receptors involved in these controls.

GPR93 activation by protein hydrolysate induces CCK transcription and secretion in STC-1 cells

In the intestinal lumen, protein hydrolysate increases the transcription and release of cholecystokinin (CCK) from enteroendocrine cells of the duodenal-jejunal mucosa. Our recent discovery that a G protein-coupled receptor, GPR93, is activated by dietary protein hydrolysate causing induced intracellular calcium-mediated signaling events in intestinal epithelial cells raises a possibility that GPR93 might be involved in the protein hydrolysate induction of CCK expression and/or secretion. Using the enteroendocrine STC-1 cells as a model, the present study demonstrates that increasing expression of GPR93 amplifies the peptone induction of endogenous CCK mRNA levels. A similar increase in CCK transcription, indicated by the luciferase reporter activity driven by an 820-bp CCK promoter, is also observed in response to peptone at a dose as little as 6.25 mg/ml, but not to lysophosphatidic acid (LPA), an agonist of GPR93. We discovered that the upregulation of CCK transcription involves ERK1/2, PKA, and calmodulin-dependent protein kinase-mediated pathways. Additionally, GPR93 activation by peptone induces a response in CCK release at 15 min, which continues over a 2-h period. The cAMP level in STC-1 cells overexpressing GPR93 is induced at a greater extent by peptone than by LPA, suggesting a possible explanation of the different effects of peptone and LPA on CCK transcription and secretion. Our data indicate that GPR93 can contribute to the observed induction of CCK expression and secretion by peptone and provide evidence that G protein-coupled receptors can transduce dietary luminal signals.

An enteral therapy containing medium-chain triglycerides and hydrolyzed peptides reduces postprandial pain associated with chronic pancreatitis

BACKGROUND/AIM

Pain in patients with chronic pancreatitis is difficult to manage. We examined if an enteral formulation containing medium-chain triglycerides (MCT) and hydrolyzed peptides would (1) minimally stimulate the exocrine pancreas by blunting cholecystokinin release and (2) decrease pain in patients with chronic pancreatitis.

METHODS

In the first part of the study, on separate days, 6 healthy controls consumed a standard enteral formulation, an enteral formulation containing MCT and hydrolyzed peptides, and a high-fat meal. Baseline and postprandial plasma cholecystokinin (CCK) concentrations were analyzed. Subsequently, 8 patients with chronic pancreatitis were enrolled and instructed to complete a visual analog pain assessment for a baseline period of 2 weeks followed by three cans per day of the enteral formulation containing MCT and hydrolyzed peptides for 10 weeks.

RESULTS

Mean CCK levels for our control subjects were 0.46 +/- 0.29 pM at baseline, 10.75 +/- 0.45 pM in response to the high-fat meal, and 7.9 +/- 1.25 pM in response to the standard enteral formulation. Of note, CCK levels were 1.43 +/- 0.72 pM in response to the enteral supplement containing MCT and hydrolyzed peptides. In patients with chronic pancreatitis, the average improvement in pain scores from baseline to the conclusion of the study was 61.8% (p = 0.01). This corresponded to a clinical improvement in 6 of the 8 patients.

CONCLUSIONS

A complete enteral supplement containing MCT and hydrolyzed peptides minimally increases plasma CCK levels. This therapy may be effective in reducing postprandial pain associated with chronic pancreatitis.

Physiological mechanisms mediating aspartame-induced satiety

Aspartame has been previously shown to increase satiety. This study aimed to investigate a possible role for the satiety hormones cholecystokinin (CCK) and glucagon-like peptide-1 (GLP-1) in this effect. The effects of the constituents of aspartame, phenylalanine and aspartic acid, were also examined. Six subjects consumed an encapsulated preload consisting of either 400 mg aspartame, 176 mg aspartic acid+224 mg phenylalanine, or 400 mg corn flour (control), with 1.5 g paracetamol dissolved in 450 ml water to measure gastric emptying. A 1983-kJ liquid meal was consumed 60 min later. Plasma CCK, GLP-1, glucose-dependent insulinotropic polypeptide (GIP), glucose, and insulin were measured over 0-120 min. Gastric emptying was measured from 0 to 60 min. Plasma GLP-1 concentrations decreased following the liquid meal (60-120 min) after both the aspartame and amino acids preloads (control, 2096.9 pmol/l min; aspartame, 536.6 pmol/l min; amino acids, 861.8 pmol/l min; incremental area under the curve [AUC] 60-120 min, P<.05). Desire to eat was reduced from 60 to 120 min following the amino acids preload (control, -337.1 mm min; aspartame, -505.4 mm min; amino acids, -1497.1 mm min; incremental AUC 60-120 min, P<.05). However, gastric emptying rates, plasma CCK, GIP, insulin, and glucose concentrations were unaffected. There was a correlation between the increase in plasma phenylalanine and decrease in desire to eat after the liquid meal following the constituent amino acids (r=-.9774, P=.004). In conclusion, it is unlikely that aspartame increases satiety via CCK- or GLP-1-mediated mechanisms, but small changes in circulating phenylalanine concentrations may influence appetite.

Casein and whey exert different effects on plasma amino acid profiles, gastrointestinal hormone secretion and appetite

Protein, generally agreed to be the most satiating macronutrient, may differ in its effects on appetite depending on the protein source and variation in digestion and absorption. We investigated the effects of two milk protein types, casein and whey, on food intake and subjective ratings of hunger and fullness, and on postprandial metabolite and gastrointestinal hormone responses. Two studies were undertaken. The first study showed that energy intake from a buffet meal ad libitum was significantly less 90 min after a 1700 kJ liquid preload containing 48 g whey, compared with an equivalent casein preload (P<0.05). In the second study, the same whey preload led to a 28 % increase in postprandial plasma amino acid concentrations over 3 h compared with casein (incremental area under the curve (iAUC), P<0.05). Plasma cholecystokinin (CCK) was increased by 60 % (iAUC, P<0.005), glucagon-like peptide (GLP)-1 by 65 % (iAUC, P<0.05) and glucose-dependent insulinotropic polypeptide by 36 % (iAUC, P<0.01) following the whey preload compared with the casein. Gastric emptying was influenced by protein type as evidenced by differing plasma paracetamol profiles with the two preloads. Greater subjective satiety followed the whey test meal (P<0.05). These results implicate post-absorptive increases in plasma amino acids together with both CCK and GLP-1 as potential mediators of the increased satiety response to whey and emphasise the importance of considering the impact of protein type on the appetite response to a mixed meal.

The metabolic response to ingested glycine

BACKGROUND

The metabolic effects of dietary protein are complex. In persons with type 2 diabetes, protein ingestion results in little or no increase in plasma glucose concentrations but a stimulation of insulin and glucagon secretion. Furthermore, when protein is ingested with glucose, a synergistic effect on insulin secretion is observed. The most potent protein is gelatin, which consists of 30% glycine residues.

OBJECTIVE

The objective of the present study was to determine whether glycine per se stimulates insulin secretion or reduces the glucose response when ingested with glucose.

DESIGN

Nine healthy subjects were tested on 4 separate occasions. Plasma glucose, insulin, glucagon, and glycine concentrations were measured at various times during a 2-h period after the ingestion of 1 mmol glycine/kg lean body mass, 25 g glucose, 1 mmol glycine/kg lean body mass + 25 g glucose, or water only, given in random order.

RESULTS

Plasma concentrations of glycine and glucagon were elevated after the ingestion of glycine, as expected. The serum insulin concentration also was slightly elevated after the ingestion of glycine alone. When glycine was ingested with glucose, the plasma glucose area response was attenuated by > 50% compared with the response after the ingestion of glucose alone. The dynamics of the insulin response after the ingestion of glycine plus glucose were modestly different from those after the ingestion of glucose alone, but the area response was not significantly different.

CONCLUSION

The data are compatible with the hypothesis that oral glycine stimulates the secretion of a gut hormone that potentiates the effect of insulin on glucose removal from the circulation.

Advances in nutritional management of chronic pancreatitis

Nutrition has an important role in the management of chronic pancreatitis (CP), with two main goals for treatment of patients. The first goal is to provide optimal nutrition support and the second is to decrease pain by minimizing stimulation of the exocrine pancreas. Because cholecystokinin (CCK) stimulates secretion from the exocrine pancreas, one approach is to decrease CCK levels through modulation of diet. If postprandial pain is a limiting factor, alternative enteral therapies that minimally stimulate the pancreas may be beneficial. Nutritional counseling, antioxidants, and pancreatic enzymes may play a role in effective management of CP as well. In addition, because idiopathic CP is associated with cystic fibrosis gene mutations, therapies directed toward cystic fibrosis may also benefit these patients.

Pathophysiological role of cholecystokinin in humans

Cholecystokinin (CCK) is a major gastrointestinal hormone that plays an important role in stimulation of pancreatic secretion and gall-bladder contraction, regulation of gastrointestinal motility and induction of satiety. Ingestion of fat and protein induces significant increases in plasma CCK. Intraluminal mediators of CCK secretion, luminal CCK releasing factor and diazepam-binding inhibitor, were purified from rat intestinal secretion. These CCK-releasing factors (RF) are secreted tonically by the small intestine and stimulate CCK release. Another kind of CCK-RF named 'monitor peptide' was purified from the rat pancreatic juice that stimulates CCK secretion when introduced into rat intestine. Bile exclusion from the duodenum causes an increase in basal CCK and enhances stimulated plasma CCK release, and bile salt replacement reverses these effects. Thus, the CCK-RF are spontaneously secreted into the intestinal lumen in humans, while the CCK-producing cells are under constant suppression by intraduodenal bile acids. In acute pancreatitis, plasma CCK levels are high in patients with gallstone pancreatitis, but not in patients with pancreatitis from other causes, such as alcoholic and idiopathic pancreatitis. A transient disturbance of bile flow into the duodenum by stones or oedema of the pancreas together with impairment of pancreatic exocrine function might cause the increase in plasma CCK release in gallstone pancreatitis. Patients with chronic pancreatitis with mild to moderate impairment of exocrine function and abdominal pain, had significantly higher plasma CCK concentrations, whereas patients with pancreatic insufficiency had a significantly lower plasma CCK response to a test meal than the healthy subjects. The increased CCK may further aggravate pancreatitis and worsen the prognosis of pancreatitis by stimulating the injured pancreas, resulting in the vicious circle via endogenous CCK release. The CCK-A receptor antagonist might be therapeutically useful in acute pancreatitis by stopping the vicious circle.

Pancreatic supplements reduce symptomatic response of healthy subjects to a high fat meal

In a double-blind, crossover study, we determined whether microencapusulated pancreatic enzymes reduce postprandial symptoms experienced by healthy volunteers after ingestion of a high calorie, high fat meal. At 7 AM, 18 subjects ingested 185 g of cookies (1196 calories and 72 g of fat) with three pancrelipase capsules or a placebo. The severity of gastrointestinal symptoms and flatus passages were recorded for 15-17 hr, and end-alveolar samples were obtained hourly for 10 hr. Ingestion of pancreatic supplements was associated with a significant (P = 0.049) reduction in bloating over the entire recording period, and with significant reductions in bloating, gas, and fullness during the dinner to bedtime period. Pancreatic supplements had no significant effect on breath H2 or CH4 concentration. The finding that pancreatic supplements reduce postprandial symptoms in healthy subjects suggests that these supplements also might be beneficial in irritable bowel syndrome.

Regulation of the action of the novel cholecystokinin-releasing peptide diazepam binding inhibitor by inhibitory hormones and taurocholate

Diazepam binding inhibitor (DBI1-86) has recently been isolated in search for a cholecystokinin (CCK)-releasing peptide in the duodenum that is responsible for the feedback regulation of exocrine pancreatic secretion. Synthetic porcine DBI1-86 stimulates CCK release in vivo and in vitro from isolated intestinal mucosal cells. We postulated that DBI intraduodenally releases CCK in a paracrine fashion and might be the missing link in the feedback regulation of exocrine pancreatic secretion. Somatostatin, peptide YY (PYY) and taurocholate are known to inhibit feedback-stimulated CCK release in the rat. In this study, we investigated the effect of somatostatin, PYY and taurocholate on DBI-stimulated CCK secretion. Dispersed rat intestinal mucosal cells were prepared from the proximal small bowel and continuously perfused. The perfusate was collected and the release of CCK into the medium was measured. DBI1-86 dose-dependently stimulated CCK release, with a maximal effect at 10(-9) M. Somatostatin blocked the DBI-stimulated CCK release. Pretreatment of the cells with pertussis toxin fully reversed the inhibitory effect of somatostatin on DBI-stimulated CCK secretion, suggesting that somatostatin exerts its action by an inhibitory G-protein. In contrast, PYY (10(-6) M) and taurocholate (10(-6) M) did not affect DBI stimulated CCK levels, indicating that they act through different mechanisms to inhibit feedback-stimulated CCK release.

The potency of dietary amino acids in elevating plasma cholecystokinin immunoreactivity in cats is related to amino acid hydrophobicity

Incomplete agreement exists on the relative potency of amino acids in stimulating endocrine secretion of cholecystokinin (CCK). Species and methodological variations have been suggested to account for the apparent inconsistencies. In the present research, the CCK-releasing potency of dietary amino acids was evaluated in cats using plasma CCK-like immunoreactivity (CCK-LI) as an indicator of CCK secretion rather than pancreatic protein and enzyme secretion, as has been used in past research. Oral-gastric administrations of a casein-simulating amino acid mixture increased (P < 0.05) plasma CCK-LI but not to the extent of that observed for casein or sodium oleate. The response in plasma CCK-LI to administrations of 50 mM solutions of amino acids was significant (P < 0.05) for tryptophan, phenylalanine, leucine, and isoleucine and the response increased linearly (P < 0.01) with increasing amino side-chain hydrophobicity. Control administrations of water and saline also evoked elevation in plasma CCK-LI, but the responses were so transient that amino acid effects were not obscured. This was substantiated by the finding of a significant linear (P < 0.001) dose response to phenylalanine administration. Cholecystokinin-8, 33 and 58 were among the CCK molecular forms identified by HPLC in plasma after administrations of phenylalanine and water. The present findings indicate that lipophilic amino acids released during digestion account for at least part of the endocrine CCK response in cats to ingested protein. The greater CCK-releasing potency observed for intact protein relative to free amino acids may have been the result of a slow digestive release of amino acids, elaboration of peptide secretogogues or protection of protease-sensitive releasing factors.

Review article: the dietary management of Crohn's disease

Enteral feeding has been shown to be as effective as primary therapy for Crohn's disease, but it requires high patient motivation, may be unpalatable and is expensive. However, in adolescents with growth failure and when corticosteroid therapy is contra-indicated or has failed, it may become the treatment of choice. Furthermore, dietary therapy allows circumvention of the adverse side-effects of repeated courses of steroids. A number of different hypotheses have been proposed to explain the effect of enteral feeds but none has reached universal acceptance. Prospective trials suggest that the exclusion of whole protein is not necessary. Comparison of feeds with differing composition suggests that a low fat content increases efficacy and various explanations have been offered. The reduction of colonic bacterial load may also be important. Because symptoms of Crohn's disease may be provoked by eating, there is a risk of falsely attributing symptoms to specific foodstuffs. However, in many individuals foods can be identified which affect disease activity, and their exclusion leads to prolongation of disease remission. Dietetic supervision during food testing is important to avoid detrimental effects on nutrient and micronutrient intake.

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.

Effect of beer, yeast-fermented glucose, and ethanol on pancreatic enzyme secretion in healthy human subjects

The effect of beer, ethanol (4% v/v), and corresponding volumetric (water), caloric (glucose 5.76% w/v), and osmotic (glucose 11.5% w/v) control solutions on pancreatic enzyme output and release of gastrin and cholecystokinin (CCK) were studied in six healthy human subjects. As a simpler model of beer, yeast-fermented glucose solution (11.5% w/v) was also studied and compared with unfermented glucose (11.5% w/v). Among the control solutions, the two glucose solutions, but not water, significantly (P < 0.05) increased the 150-min integrated trypsin and amylase output over basal levels. Beer and fermented glucose caused a significantly higher increase in trypsin and amylase output compared to water or glucose. Ethanol (4% v/v) failed to stimulate pancreatic enzyme output. Fermented glucose and beer, but not the control solutions, significantly increased plasma gastrin levels above basal values. Isotonic and hypertonic glucose, beer, and fermented glucose significantly increased plasma levels of cholecystokinin (CCK), but the effect was significantly higher after hypertonic glucose than after isotonic glucose, beer, or fermented glucose. Ethanol and water had no effect on plasma levels of gastrin and CCK. We conclude that: (1) in the doses studied intragastric beer and fermented glucose but not ethanol (4% v/v) stimulate pancreatic enzyme output and release of gastrin and CCK; (2) the lack of effect of ethanol indicates that nonalcoholic ingredients of beer and fermented glucose are responsible for this stimulatory effect; and (3) CCK could be one of the major mediators of the stimulation of pancreatic enzyme output after ingestion of beer and fermented glucose.

Nutrients and cyclical interdigestive pancreatic enzyme secretion in humans

BACKGROUND AND AIMS

It is hypothesised that nutrients increase pancreatic enzyme secretion by converting cyclical interdigestive secretion to a non-cyclical pattern. This study tested the hypotheses that nutrients do not interrupt cycles and determined the relation of nutrients, calories, and osmotic load to the rate of pancreatic secretion.

METHODS

Twenty six healthy persons were intubated with oroduodenal and orogastric tubes. Each had one of four different solutions containing 12 to 36% of calories as protein, 24 to 48% as fat, and 40 to 64% as carbohydrate infused into the duodenum at 40, 90, or 160 kcal/h for 300 minutes. Nine g/l sodium chloride (290 mOsm) was added to 16 infusates; osmolality of the other 10 infusates was 24 to 98 mOsm. Pancreatic enzyme outputs were measured every 15 minutes and peaks of enzyme secretion were identified.

RESULTS

The number of enzyme peaks was similar for the different infusates and the proportion of nutrients in the infusates did not affect secretion of individual enzymes. The nadir, but not the peak of the cycles of enzyme outputs correlated with increasing the caloric load (r = 0.55, p < 0.003 for nadir:peak ratio). Increasing osmolality did not affect cycling but reduced (p < 0.001) enzyme output.

CONCLUSION

Nutrients entering the duodenum do not abolish cycles of enzyme secretion; instead they modulate cycles by increasing the nadir. Forty and 90 kcal infusions submaximally stimulate pancreatic secretion and might be used in patients with pancreatitis without producing pain; adding sodium chloride to solutions should increase this effect.

Effects of parenteral nutrients on gastrointestinal motility and secretion

BACKGROUND

The stimulation of gastrointestinal motility and secretion during nutrient digestion is generally divided into a cephalic, gastric and intestinal phase. Little is known about the effects of macronutrients on gastrointestinal function during the postabsorptive or circulatory phase of digestion.

METHODS

Review of studies investigating the effects of circulating macro-nutrients such as fat, amino acids and glucose on gastrointestinal motility and secretion.

RESULTS

Intravenous infusion of fat emulsions delays gastric emptying and interrupts the interdigestive intestinal motor pattern. Intravenous amino acids, administered in high doses, stimulate gastric acid secretion, pancreatic secretion, gallbladder contraction, and intestinal motility. Patients receiving total parental nutrition (TPN) have inert gallbladders and are at risk of developing gallbladder sludge and stones. Administering a proportion of the daily amino acid requirement by rapid intravenous infusion may prove useful in the prevention of sludge and stone formation during TPN by promoting gallbladder contraction. Intravenous infusion of glucose, already at physiological postprandial plasma levels, inhibits gastrointestinal motility and secretion. The inhibitory effect of glucose is dose-dependent, that is, more pronounced at higher plasma glucose levels. Recent studies have indicated that in patients with diabetes mellitus alterations in gastrointestinal function are related to the degree of hyperglycaemia.

CONCLUSIONS

Nutrients during the circulatory phase of digestion influence gastrointestinal motility and secretion. Knowledge of these effects is relevant for conditions with increased plasma levels of macro-nutrients such as in patients with diabetes mellitus or during total parenteral nutrition.

Effect of alpha 1-adrenergic blockade on canine ileal water, electrolyte, and glucose absorption

Meal ingestion stimulates an increase in small intestinal water and electrolyte absorption. Endogenous norepinephrine may at least partially mediate this meal-stimulated proabsorptive response. Luminally administered alpha 1-adrenergic agonists such as norepinephrine and phenylephrine cause significant small bowel absorption, which can be prevented by the selective alpha 1-adrenergic antagonist terazosin. This study tested two hypotheses: (1) a meal stimulates ileal water, electrolyte, and glucose absorption; and (2) meal-stimulated ileal absorption is mediated via alpha 1-adrenergic receptor activation. Absorption studies (N = 27) were performed on dogs with 25-cm ileal Thirty-Vella fistulas (TVF). Perfusion with [14C]PEG was used to calculate absorption of water, electrolytes, and glucose from the TVF. Three groups were randomly studied over 4 hr: (1) terazosin alone, (2) meal alone, and (3) terazosin plus meal. Terazosin (10(-4) M) was administered to the TVF in groups 1 and 3 following the first hour. A 480-kcal mixed canine meal was ingested at the end of the second hour in groups 2 and 3. Ileal water, electrolyte, and glucose absorption increased significantly in response to meal ingestion (P < 0.05). Luminal terazosin did not significantly alter basal or meal-stimulated ileal absorption. In conclusion, meal ingestion stimulates ileal absorption of water, electrolytes, and glucose. Neither basal nor meal-stimulated ileal absorption is altered by alpha 1-adrenergic receptor blockade. These data suggest that nonadrenergic neural pathways or humoral factors are the likely mediators of meal-induced intestinal absorption.

The role of gastrointestinal peptides on pancreatic secretion in response to different stimulants in conscious rats

Effects of intragastric food, intraduodenal amino acids, and intravenously administered bombesin and gastrin-releasing peptide (GRP) were examined in conscious rats with pancreatic fistula in terms of responses of exocrine pancreatic secretion, plasma levels gastrin, and cholecystokinin (CCK). Pancreatic juice and blood samples were collected at regular intervals before and after the stimuli. Intragastric food increased pancreatic secretion and plasma levels of gastrin and CCK. Intraduodenal infusion of amino acids had no effect on pancreatic secretion and plasma levels of gastrin and CCK. Intravenous infusion of bombesin at 1 microgram/kg/h induced significant increases in pancreatic volume and protein outputs, but had no effect on plasma levels of gastrin and CCK. Bombesin infusion at 10 micrograms/kg/h resulted in significant increases in pancreatic volume and protein outputs as well as plasma gastrin levels, but had no effect on plasma CCK levels. Intravenous infusion of GRP induced increases in pancreatic volume and protein outputs and plasma gastrin levels, but had no effect on CCK levels. Antrectomy resulted in significant decreases in basal levels of plasma gastrin. GRP-stimulated pancreatic volume and protein outputs were not significantly changed by antrectomy. In rats that underwent antrectomy, GRP infusion significantly increased pancreatic volume and protein outputs, but had no effect on plasma levels of gastrin and CCK. Food-stimulated pancreatic secretion and plasma levels of gastrointestinal peptides of rats were similar to other species, but amino acids, bombesin, or GRP may not be the stimulants for CCK release in rats. The stimuli that release CCK from duodenal mucosa probably varies among species.

Initial response and subsequent course of Crohn's disease treated with elemental diet or prednisolone

Elemental diet is as effective as corticosteroids in the treatment of previously untreated Crohn's disease. It is unclear whether a poor nutritional state is a prerequisite for efficacy of elemental diet, whether previously treated patients respond as well, or how duration of remission using elemental diet compares with corticosteroid induced remission. Forty two patients with active Crohn's disease were stratified for nutritional state and randomised to receive Vivonex TEN 2.1 l/day for four weeks, or 0.75 mg prednisolone/kg/day for two weeks and subsequent reducing doses. Nine of 22 (41%) patients assigned to nutritional treatment were intolerant of the diet. Thirty patients completed four weeks treatment. Disease activity decreased on elemental diet from mean (SEM) 4.8 (0.9) to 1.7 (0.6), p < 0.05, and on prednisolone from 5.3 (0.5) to 1.9 (0.6), p < 0.05. For each treatment, nourished and malnourished patients responded similarly. Patients with longstanding disease responded as well as newly diagnosed patients. The probability of maintaining remission at six months was 0.67 after prednisolone, 0.28 after elemental diet, and at one year was 0.35 after prednisolone and 0.09 after elemental diet, p < 0.05. When tolerated, elemental diet is as effective in the short term as prednisolone in newly and previously diagnosed Crohn's disease, and its benefit is independent of nutritional state. The subsequent relapse rate after elemental diet induced remission, however, is greater than after treatment with prednisolone.

Pancreatic polypeptide and exocrine pancreatic function in the elderly

The relationship between exocrine pancreatic function and plasma pancreatic polypeptide levels was studied in 14 normal elderly subjects and in ten elderly patients with exocrine pancreatic insufficiency determined by the para-amino-benzoic acid test. There was a decrease in the total pancreatic polypeptide response after a standard mixed meal in the group with pancreatic insufficiency (t = 2.753, p = 0.01). An increase above basal of less than 100% in plasma pancreatic polypeptide levels 30 min after a standard mixed meal is strongly associated with exocrine pancreatic insufficiency (Fisher's exact test, p = 0.005).

Small bowel origin and calorie dependence of a signal for meal-induced jejunal absorption

The ingestion of a meal stimulates the absorption of water and electrolytes from the small intestine independent of the cephalic or gastric phases of digestion. This study tested two hypotheses: (1) the jejunum is the origin of a postmeal proabsorptive signal and (2) the magnitude of the proabsorptive response is dependent on the caloric content of the meal stimulus. Twenty-five-centimeter proximal canine jejunal Thiry-Vella fistulas and feeding jejunostomies were constructed under general anesthesia. Jejunal absorption studies (n = 50) were performed by luminal perfusion of the Thiry-Vella fistula with 14C-polyethylene glycol (PEG) to calculate fluxes of water and electrolytes. Five groups were studied: (1) CONTROL: no meal, (2) 240 kcal oral meal, (3) 480 kcal oral meal, (4) 240 kcal jejunal meal, and (5) 480 kcal jejunal meal. Independent of the route of delivery (i.e., oral vs. jejunal), each meal stimulus significantly increased jejunal water and electrolyte absorption (p < 0.05). The magnitude of the proabsorptive response increased significantly as the calories delivered increased (p < 0.05). These data support the hypothesis that a proabsorptive signal responsible for meal-induced jejunal absorption originates from, or distal to the jejunum and suggest that intestinal chemoreceptors or osmoreceptors participate in the generation of the proabsorptive signal.

Induction of the fed pattern of human exocrine pancreatic secretion by nutrients: role of cholecystokinin and neurotensin

The aim of the present study was to assess the role of cholecystokinin and neurotensin in converting the cyclical interdigestive pattern of pancreatic secretion into the non-cyclical fed pattern. Six healthy male volunteers were studied on 4 separate days. During each experiment a mixed liquid meal or solutions of individual nutrients were perfused intraduodenally for 180 min at 2 ml/min. The mixed meal contained 4.3 g glucose, 2.0 g fractionated soya oil, and 1.7 g casein hydrolysate per 100 ml, which delivered a caloric load of 0.9 kcal/min into the duodenum. The isocaloric and isotonic solutions of individual nutrients contained 44.5 g glucose, 17.8 g fractionated soya oil, or 44.5 g hydrolysed serum bovine albumin per liter and delivered 0.36 kcal/min into the duodenum. Duodenal aspirates and blood samples were collected at regular intervals for determination of pancreatic enzyme outputs and plasma levels of cholecystokinin and neurotensin, respectively. The mixed meal converted the cyclical interdigestive secretory pattern into the noncyclical fed pattern whereas none of the three individual nutrients abolished the interdigestive pattern. Not only the mixed meal but also lipid and protein perfusion consistently stimulated cholecystokinin release. Integrated incremental cholecystokinin release amounted to 32.3 +/- 9.9 pg/ml x 180 min with the mixed meal, 23.2 +/- 6.5 with lipid perfusion (P < 0.05 versus mixed meal) and 13.4 +/- 3.8 with protein perfusion (P < 0.05 versus mixed meal). The carbohydrate solution did not significantly release cholecystokinin. None of the duodenal perfusates raised neurotensin plasma levels.(ABSTRACT TRUNCATED AT 250 WORDS)

Meal-stimulated canine jejunal ionic absorption. Effect of direct jejunal meal delivery and premeal intravenous hydration

The ingestion of a meal stimulates water and ion absorption from the small intestine. The administration of nutrient substances directly to the small bowel can cause dumping symptoms, with intraluminal fluid accumulation and relative systemic hypovolemia. This study compared the effect of oral versus direct jejunal meal delivery on jejunal water and ion absorption, with and without premeal intravenous saline infusion. Jejunal absorption studies (N = 40) were performed on dogs with 25 cm proximal jejunal Thiry-Vella fistulas and feeding jejunostomies. Luminal perfusion with [14C]PEG was used to calculate fluxes of water and electrolytes. Five groups were randomly studied: (1) intravenous 0.9% saline alone, (2) oral meal alone, (3) intravenous 0.9% saline plus oral meal, (4) jejunal meal alone, and (5) intravenous 0.9% saline plus jejunal meal. Hydration status was assessed hourly by measurement of hematocrit. Water and electrolyte absorption was significantly stimulated by both oral and jejunal meal delivery (P less than 0.01). Intravenous saline hydration significantly reduced the hematocrit (P less than 0.05) but did not alter the proabsorptive response to an oral or jejunal meal. In conclusion, a postprandial signal for proximal jejunal water and electrolyte absorption was stimulated equally by orally or jejunally administered nutrients and was not affected by premeal hydration. These data support the hypothesis that the proabsorptive signal that stimulates water and ion absorption is an enteroenteric phenomenon originating from the small intestine, without implicating pathophysiologic events such as hypovolemia or dumping.

Site-specific variations in basal and meal-stimulated intestinal absorption

The ingestion of a meal increases water and electrolyte absorption in the proximal jejunum. The purpose of these experiments was to elucidate any site-specific variations in intestinal absorption, comparing jejunum to ileum, in both the basal and the meal-stimulated states. Twenty-five-centimeter proximal jejunal and distal ileal Thirty-Vella fistulae were constructed in four dogs. Simultaneous jejunal and ileal absorption studies were performed using [14C]PEG to calculate net absorption of water and electrolytes. Two groups were studied: in Group 1 no meal was ingested, while in Group 2, the animals ingested a mixed meal. Each study consisted of a 1-hr basal period and a 3-hr experimental period. In the basal state ileal absorption significantly exceeded jejunal absorption (P less than 0.0001). The ingestion of mixed meal significantly increased water and electrolyte absorption in both the jejunum and the ileum, (P less than 0.001), with the magnitude of meal-stimulated ileal absorption significantly exceeding the magnitude of meal-stimulated jejunal absorption (P less than 0.001). These studies demonstrate distinct site specific variations in intestinal water and electrolyte absorption in both the basal and the meal-stimulated states.

Gallbladder emptying stimuli in obese and normal-weight subjects

Gallbladder stasis may be an important factor in the pathogenesis of cholesterol-gallstone formation in some individuals. We investigated gallbladder function in a group of nondieting, gallstone-free, healthy subjects with normal (22 +/- 1 kg/m2) and high (36 +/- 1 kg/m2) body mass indexes. Fasting gallbladder volume (28.2 +/- 4.4 ml) and residual volume after maximal emptying (8.4 +/- 2.3 ml) in high-body-mass index subjects were not significantly different from those of normal-body-mass index subjects (20.5 +/- 2.5 ml and 4.2 +/- 1.3 ml, respectively). The percentage of gallbladder emptying (71% +/- 5%) and the rate of gallbladder emptying (-1.9 +/- 0.3 x 10(-2) min-1) in high-body-mass index subjects in response to a maximal emptying stimulus was similar to the percentage of emptying (78% +/- 6%) and rate of emptying (-2.3 +/- 0.6 x 10(-2) min-1) in normal-body-mass index subjects. A liquid meal containing less than 1 gm fat, 14 gm protein and 6 gm carbohydrate resulted in both a decreased rate of gallbladder emptying and an increased residual gallbladder emptying and an increased residual gallbladder volume in both groups. The addition of 10 or 20 gm (but not 4 gm) of fat to the liquid meal restored gallbladder emptying to the maximal-stimulus level. These results demonstrate that gallbladder emptying in response to a single liquid meal stimulus is not altered in obesity and that dose-response relationships to fat are similar in obese and normal-weight individuals.(ABSTRACT TRUNCATED AT 250 WORDS)

Influence of meal composition on canine jejunal water and electrolyte absorption

The absorption of water and electrolytes from the proximal jejunal lumen increases immediately after a meal. This meal-induced jejunal absorption occurs in jejunal segments out of normal gastrointestinal continuity. This study was designed to characterize the jejunal absorptive response to a series of isovolumetric gavage-delivered stimuli. Twenty-five-centimeter canine proximal jejunal Thiry-Vella fistulas were constructed, and jejunal absorption studies (n = 66) were performed by luminal perfusion of the jejunal segments with an isotonic buffer containing 14C-labeled polyethylene glycol. Each study consisted of a 1-hour basal period, followed by a 3-hour experimental period. Nine groups were studied, each receiving one of the following isovolumetric stimuli delivered via the gavage route: water, 0.9% saline, mixed meal, protein, lipid, carbohydrate, and mannitol (150 mmol/L, 300 mmol/L, and 600 mmol/L). The water and 0.9% saline gavage groups showed no significant changes in integrated postprandial water and electrolyte absorption above basal. The isocaloric mixed meal, protein, lipid, carbohydrate, and mannitol groups all had significantly increased integrated postprandial jejunal water and electrolyte absorption above basal (P less than 0.05). These results indicate that a proabsorptive signal for meal-induced jejunal absorption originates from or distal to the stomach. Meal-induced jejunal absorption occurs in response to nutrients of diverse composition and is also responsive to nonnutritive solutes such as mannitol. These findings support a new role for gastric or intestinal chemo- or osmo-receptors in stimulating the neurohumoral mechanisms that mediate meal-induced jejunal absorption.

Meal-induced jejunal absorption requires intact neural pathways

A signal for meal-induced absorption originates from the small intestine and is transmitted to a luminally excluded segment of the proximal jejunum (Thiry-Vella [TV] fistula). Using intraluminal topical anesthesia with oxethazaine, this study assessed the role of intestinal neural pathways in basal and postprandial jejunal water and electrolyte absorption. Studies (n = 45) were performed on dogs with 25-cm proximal jejunal TV fistulae and feeding jejunostomies, using luminal perfusion with 14C-polyethylene glycol. The animals were randomized into five study groups: (1) jejunostomy oxethazaine alone, (2) jejunostomy water and jejunal meal, (3) jejunostomy oxethazaine and jejunal meal, (4) TV fistula water and jejunal meal, and (5) TV fistula oxethazaine and jejunal meal. The jejunal meal significantly increased TV fistula absorption, whereas oxethazaine significantly reduced basal absorption when administered via the TV fistula and postprandial absorption when administered via the jejunostomy (p less than 0.05). TV fistula oxethazaine did not diminish the magnitude of postprandial absorption. We conclude that intact intestinal neurotransmission is necessary for maintenance of the normal basal absorptive state of the proximal jejunum and for the generation of a normal meal-stimulated proabsorptive signal from the small intestine. A nonneural mechanism appears to be of predominant importance in transmitting the proabsorptive signal from the intact gastrointestinal tract to the TV fistula.

Further analysis of the short-term inhibition of food intake in humans by the dipeptide L-aspartyl-L-phenylalanine methyl ester (aspartame)

It was reported previously that the dipeptide sweetener aspartame suppresses food intake in humans by a postingestive action. The present study examined the hypothesis that this is due to an effect of phenylalanine, one of the primary breakdown products of aspartame (phenylalanine is a potent releaser of the so-called satiety hormone cholecystokinin, CCK). Capsulated aspartame (400 mg) administered to human volunteers reduced food intake by 15% (253 kcal) in a lunchtime test meal begun 1 hour later. However, neither phenylalanine (200 mg) nor the other constituent amino acid of aspartame, aspartic acid (200 mg), altered intake compared with placebo. Despite the large effect on food intake there were no treatment differences in pre- or postmeal ratings of motivation to eat. This suggests that aspartame may act to intensify the satiating effects of ingested food. Although high doses of phenylalanine reduce food intake, an individual action of phenylalanine cannot account for the potent anorexic effect of aspartame. In discussing alternative mechanisms it is noted that the amino acid sequence of aspartame (Asp-Phe) is the same as the C-terminal dipeptide of CCK. A direct action of aspartame at CCK receptors appears to be unlikely; however, aspartame might act as CCK releaser. Further studies are required to elucidate the mechanism of aspartame's anorexic action and perhaps to evaluate its therapeutic potential as an antiobesity agent.

Are diets associated with different rates of human interdigestive and postprandial pancreatic enzyme secretion?

To determine if diets are associated with different rates of interdigestive and postprandial enzyme secretion and how quickly enzyme secretion is modulated by nutrients, 27 healthy humans were randomly selected to follow one of five diets. The calorie proportions of carbohydrate, fat, and protein in each diet was assigned by a mixture design. After the subjects followed a diet for 2 weeks, they were intubated with an oroduodenal tube, and enzyme outputs were measured during the interdigestive period and after eating a meal identical to meals eaten during the previous 2 weeks. For the next 24 hours subjects either followed the same diet or a diet that contained the same amount of fat, but the percent of carbohydrate and protein was changed by 30%. Then interdigestive and postprandial pancreatic enzyme outputs were remeasured. After 2 weeks, diets containing the most carbohydrate (50%-80%) were associated with the lowest interdigestive and postprandial amylase and lipase (P less than 0.05) and trypsin outputs (P less than or equal to 0.05). In contrast, diets containing the most fat (40%) were associated with the highest interdigestive and postprandial outputs of amylase (P less than 0.05) and trypsin (P less than 0.05). Maintaining or altering diets for 24 hours did not change interdigestive pancreatic enzyme outputs, but postprandial amylase output was significantly increased (P less than 0.05) by increasing protein and decreasing carbohydrate content of the diets by 30% for 24 hours. We conclude that diets containing a high proportion of calories as carbohydrate for 2 weeks are associated with lower interdigestive and postprandial pancreatic secretion than diets that have a high fat content. In response to diets, changes in postprandial pancreatic enzyme secretion occur within 24 hours whereas changes in interdigestive secretion (no nutrients in the lumen) occur after 24 hours.

Hormones as regulators of pancreatic secretion in man

At the beginning of the century, Pavlov suggested that the pancreas was exclusively controlled by the nervous reflex mechanisms. In 1902, Bayliss & Starling published their experiments on secretin and claimed that the nervous regulation is 'superfluous and improbable'. In the following decades, especially after the discovery of CCK, it was generally held that exocrine pancreatic secretion is regulated mainly by hormones. The present summary clearly demonstrates the importance of the cholinergic system in regulating exocrine pancreatic secretion and the complexity of neurohormonal interactions. The question is no longer hormones or nerves, but rather a very complicated coordination of neural, hormonal and possible paracrine effects, resulting in the control of exocrine pancreatic activity. In this complex regulatory system, the cholinergic control is central with hormones such as CCK or secretion modulating the response.

Pancreatobiliary responses to an intragastric amino acid meal: comparison to albumin, dextrose, and a maximal cholecystokinin stimulus

Little is known about how gastric and pancreatobiliary responses differ after intake of elemental diets from responses to polymeric food. We therefore compared pancreatic and biliary secretions after gastric instillation of albumin (7 g%, with dextrose 21 g%) with an elemental diet in 6 healthy volunteers. The elemental diet contained amino acids (7 g%, with dextrose 21 g%) in the same molar composition as the albumin. Furthermore, we studied the effect of a pure intragastric dextrose solution (21 g%) on pancreatobiliary secretions, as glucose constitutes a major component of elemental diet formulas. The various pancreatobiliary responses were tested against a maximal i.v. cholecystokinin stimulus. The dextrose, amino acid, and albumin meals emptied at similar rates, and gastric emptying was completed within 3 h. Similar pancreatobiliary responses were observed after the albumin and amino acid meals, but response to both the amino acid and albumin meals was smaller than to the intravenous cholecystokinin stimulus. The glucose meal caused a marked and sustained stimulation of pancreatobiliary outputs, which did not differ significantly from the other test meals. However, lower cholecystokinin levels were observed after the glucose meal compared with distinct cholecystokinin release after the albumin and amino acid meals. We conclude first that there are no major differences in secretory responses between elemental (amino acid) and polymeric (protein) meals and second, that intragastric pure glucose meals strongly stimulate pancreatobiliary secretions. The marked pancreatic and biliary responses to intragastric dextrose cannot be fully explained on the basis of cholecystokinin release, suggesting that this response is probably mediated by neural mechanisms.

Action of amino acids on stomach, pancreas, and gallbladder in dogs

An intravenous infusion of a 3% solution of amino acids was given to 8 dogs, all with Heidenhain pouches and gastric fistulae. Four of these had duodenal cannulae opposite the pancreatic and 4 opposite the biliary ampulla. The usual basal 100 min spontaneous peaking of pancreatic juice volume and protein secretion was seen but peaks were abolished by the amino acid infusion and troughs were slightly elevated, but the total 90 min volume protein and bicarbonate outputs were not different from control. Gastric acid and pepsin secretions were augmented reaching a peak during the first hour with a subsequent decline. The 90 min acid and pepsin output was significantly higher than control. The gallbladder contracted during the first hour and remained thus until the infusion was terminated. This happened even when the duodenum was kept alkaline, but was abolished by ganglionic blockade. During intravenous amino acid infusion the patterns of gallbladder activity and pancreatic secretion resembled those of the post cibal rather than fasting state.

Responses of the pancreatic digestive enzyme secretion to various combinations of amino acids and cholecystokinin in chicks (Gallus domesticus)

1. Effect of amino acid administration on pancreatic secretion of digestive enzymes, amylase, trypsinogen and chymotrypsinogen was studied after wing vein injection of an amino acid (AAs) mixture (Thr, Lys, Phe, Leu, Ile, Glu, Val, His, and Met) or combinations of selected amino acids, i.e. Thr + Phe + Ile, Thr + Phe, Thr + Ile or Phe + Ile, in the presence of cholecystokinin (CCK) in chicks. 2. Time course changes of enzyme output were similar in all treatment groups having a peak within 10-30 min, except for Phe + Ile that resulted in delayed induction of the enzyme release as shown by significant increases in the last 20 min compared with those in the rest. 3. When increases in enzyme outputs for the first 30 min were compared, it was shown that the three enzyme responses brought about by the administration of the AAs mixture was almost entirely accounted for by the combined injection of Thr + Phe. 4. Neither Thr + Ile nor Phe + Ile was as effective as Thr + Phe in inducing the output of these pancreatic enzymes. 5. The present results suggest that Thr and Phe may have a specific regulatory role in the secretion of pancreatic digestive enzymes in chicks when administered simultaneously.