Cholecystokinin release and biliopancreatic secretion in response to selective perfusion of the duodenal loop with aminoacids in man

L-phenylalanine Increased Gut Hormone Secretion through Calcium-Sensing Receptor in the Porcine Duodenum

Simple Summary

The proper modulation of feed intake not only meets the nutrient requirement for the maximum growth rate in pigs, but also avoids feed waste. A complete understanding of how dietary factors affect the appetite in pigs will provide a strategy to modulate the feed intake of pigs. L-phenylalanine (L-Phe) has been demonstrated to induce satiety through stimulating anorectic hormone secretion in rodents. However, whether L-Phe has similar effects in pigs is unknown. Here, we aimed to investigate how L-Phe affects gut hormone secretion, along with insight into the underlying mechanism in porcine duodenum by using an in vitro perfusion system. Results showed that 80 mM L-Phe triggered glucose-dependent insulinotropic peptide (GIP) and cholecystokinin (CCK) release, and also upregulated calcium-sensing receptor (CaSR) and its downstream molecules, such as protein kinase C (PKC) and inositol 1,4,5-triphosphate receptor (IP₃R) expression. However, these effects were attenuated by treatment with a CaSR antagonist. Our findings show that CaSR participates in Phe-induced hormone secretion in pig duodenum, indicating that CaSR may be a potential target in the food intake regulation of pigs.

Abstract

Luminal amino acids have a pivotal role in gut hormone secretion, and thereby modulate food intake and energy metabolism. However, the mechanisms by which amino acids exert this effect remains unknown. The purpose of this research was to investigate the response of L-phenylalanine (L-Phe) to gut hormone secretion and its underlying mechanisms by perfusing the pig duodenum. Eighty mM L-Phe and extracellular Ca²⁺ stimulated cholecystokinin (CCK) and glucose-dependent insulinotropic peptide (GIP) release, and upregulated the mRNA expression of the calcium-sensing receptor (CaSR), CCK, and GIP. Western blotting results showed that L-Phe also elevated the protein levels of CaSR, the inositol 1,4,5-triphosphate receptor (IP₃R), and protein kinase C (PKC). However, the CaSR inhibitor NPS 2143 reduced the mRNA expression of CaSR, CCK, and GIP, and the secretion of CCK and GIP, as well as the protein level of CaSR, IP₃R, and PKC. These results indicated that Phe stimulated gut secretion through a CaSR-mediated pathway and its downstream signaling molecules, PKC and IP₃R.

Branched-chain amino acids differently modulate catabolic and anabolic states in mammals: a pharmacological point of view

Substantial evidence has been accumulated suggesting that branched-chain amino acid (BCAA) supplementation or BCAA-rich diets have a positive effect on the regulation of body weight, muscle protein synthesis, glucose homeostasis, the ageing process and extend healthspan. Despite these beneficial effects, epidemiological studies have shown that BCAA plasma concentrations and BCAA metabolism are altered in several metabolic disorders, including type 2 diabetes mellitus and cardiovascular diseases. In this review article, we present an overview of the current literature on the different effects of BCAAs in health and disease. We also highlight the results showing the most promising therapeutic effects of dietary BCAA supplementation and discuss how BCAAs can trigger different and even opposite effects, depending on the catabolic and anabolic states of the organisms. Moreover, we consider the effects of BCAAs when metabolism is abnormal, in the presence of a mixture of different anabolic and catabolic signals. These unique pharmacodynamic properties may partially explain some of the markedly different effects found in BCAA supplementation studies. To predict accurately these effects, the overall catabolic/anabolic status of patients should be carefully considered. In wider terms, a correct modulation of metabolic disorders would make nutraceutical interventions with BCAAs more effective.

LINKED ARTICLES

This article is part of a themed section on Principles of Pharmacological Research of Nutraceuticals. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v174.11/issuetoc.

Ghrelin, CCK, GLP-1, and PYY(3-36): Secretory Controls and Physiological Roles in Eating and Glycemia in Health, Obesity, and After RYGB

The efficacy of Roux-en-Y gastric-bypass (RYGB) and other bariatric surgeries in the management of obesity and type 2 diabetes mellitus and novel developments in gastrointestinal (GI) endocrinology have renewed interest in the roles of GI hormones in the control of eating, meal-related glycemia, and obesity. Here we review the nutrient-sensing mechanisms that control the secretion of four of these hormones, ghrelin, cholecystokinin (CCK), glucagon-like peptide-1 (GLP-1), and peptide tyrosine tyrosine [PYY(3-36)], and their contributions to the controls of GI motor function, food intake, and meal-related increases in glycemia in healthy-weight and obese persons, as well as in RYGB patients. Their physiological roles as classical endocrine and as locally acting signals are discussed. Gastric emptying, the detection of specific digestive products by small intestinal enteroendocrine cells, and synergistic interactions among different GI loci all contribute to the secretion of ghrelin, CCK, GLP-1, and PYY(3-36). While CCK has been fully established as an endogenous endocrine control of eating in healthy-weight persons, the roles of all four hormones in eating in obese persons and following RYGB are uncertain. Similarly, only GLP-1 clearly contributes to the endocrine control of meal-related glycemia. It is likely that local signaling is involved in these hormones' actions, but methods to determine the physiological status of local signaling effects are lacking. Further research and fresh approaches are required to better understand ghrelin, CCK, GLP-1, and PYY(3-36) physiology; their roles in obesity and bariatric surgery; and their therapeutic potentials.

Effect of L-Tryptophan and L-Leucine on Gut Hormone Secretion, Appetite Feelings and Gastric Emptying Rates in Lean and Non-Diabetic Obese Participants: A Randomized, Double-Blind, Parallel-Group Trial

Background/Objectives

Gut hormones such as cholecystokinin (CCK) and glucagon-like peptide-1 (GLP-1) play a role as satiation factors. Strategies to enhance satiation peptide secretion could provide a therapeutic approach for obesity. Carbohydrates and lipids have been extensively investigated in relation to peptide release. In contrast, the role of proteins or amino acids is less clear. Our aim was to compare the effects of the amino acids L-tryptophan (L-trp) and L-leucine (L-leu) separately on gastric emptying and gut peptide secretion.

Participants/Methods

The study was conducted as a randomized (balanced), double-blind, parallel-group trial. A total of 10 lean and 10 non-diabetic obese participants were included. Participants received intragastric loads of L-trp (0.52 g and 1.56 g) and L-leu (1.56 g), dissolved in 300 mL tap water; 75 g glucose and 300 mL tap water served as control treatments.

Results

Results of the study are: i) L-trp at the higher dose stimulates CCK release (p = 0.0018), and induces a significant retardation in gastric emptying (p = 0.0033); ii) L-trp at the higher dose induced a small increase in GLP-1 secretion (p = 0.0257); iii) neither of the amino acids modulated subjective appetite feelings; and iv) the two amino acids did not alter insulin or glucose concentrations.

Conclusions

L-trp is a luminal regulator of CCK release with effects on gastric emptying, an effect that could be mediated by CCK. L-trp’s effect on GLP-1 secretion is only minor. At the doses given, the two amino acids did not affect subjective appetite feelings.

Trial Registration

ClinicalTrials.gov NCT02563847

Differential effects of L-tryptophan and L-leucine administration on brain resting state functional networks and plasma hormone levels

Depending on their protein content, single meals can rapidly influence the uptake of amino acids into the brain and thereby modify brain functions. The current study investigates the effects of two different amino acids on the human gut-brain system, using a multimodal approach, integrating physiological and neuroimaging data. In a randomized, placebo-controlled trial, L-tryptophan, L-leucine, glucose and water were administered directly into the gut of 20 healthy subjects. Functional MRI (fMRI) in a resting state paradigm (RS), combined with the assessment of insulin and glucose blood concentration, was performed before and after treatment. Independent component analysis with dual regression technique was applied to RS-fMRI data. Results were corrected for multiple comparisons. In comparison to glucose and water, L-tryptophan consistently modifies the connectivity of the cingulate cortex in the default mode network, of the insula in the saliency network and of the sensory cortex in the somatosensory network. L-leucine has lesser effects on these functional networks. L-tryptophan and L-leucine also modified plasma insulin concentration. Finally, significant correlations were found between brain modifications after L-tryptophan administration and insulin plasma levels. This study shows that acute L-tryptophan and L-leucine intake directly influence the brain networks underpinning the food-reward system and appetite regulation.

Effects of Intraduodenal Infusions of L-phenylalanine and L-glutamine on Antropyloroduodenal Motility and Plasma Cholecystokinin in Healthy Men

BACKGROUND/AIMS

Dietary proteins have potent eating-inhibitory and glucose-lowering effects, which may be mediated via effects of amino acids on gastrointestinal hormone and motor function, although little information is available. We have now evaluated the effects of L-phenylalanine (L-Phe) and L-glutamine (L-Gln) on antropyloroduodenal motility and plasma cholecystokinin (CCK) concen-trations.

METHODS

Two double-blind, 3-way cross-over studies were performed, each including 10 healthy, normal-weight men. We determined the antropyloroduodenal motor and plasma CCK responses to 90-minute intraduodenal infusions of L-Phe (study A) or L-Gln (study B), each at 0.15 kcal/min (total 13.5 kcal), or 0.45 kcal/min (total 40.5 kcal), or saline (control), in randomized fashion.

RESULTS

Intraduodenal L-Phe at 0.45 kcal/min, but not at 0.15 kcal/min, suppressed antral (P < 0.01), and stimulated phasic (P < 0.01), but not tonic, pyloric, or duodenal pressures, while L-Phe at both 0.15 kcal/min and 0.45 kcal/min stimulated plasma CCK. In contrast, L-Gln had no effect on antral, duodenal or pyloric pressures, or plasma CCK.

CONCLUSIONS

Intraduodenal infusions of L-Phe and L-Gln, in doses of 0.15 kcal/min and 0.45 kcal/min for 90 minutes, have different effects on antropyloroduodenal motility and CCK in normal-weight men. The modulation of antral and pyloric pressures and CCK may contribute to the eating-inhibitory effects of oral L-Phe, possibly through the slowing of gastric emptying.

Clinical management of post-pyloric enteral feeding in children

Post-pyloric feeding (PF) allows the administration of enteral nutrition beyond the pylorus, either into the duodenum or, ideally, into the jejunum. The main indications of PF are: upper gastrointestinal tract obstructions, pancreatic rest (e.g., acute pancreatitis), gastric dysmotility (e.g., critically ill patients and chronic intestinal pseudo-obstruction) or severe gastroesophageal reflux with risk of aspiration (e.g., neurological disability). Physiological and clinical evidence derives from adults, but can also be pertinent to children. This review will discuss the practical management and potential clinical applications of PF in pediatric patients. Some key studies pertaining to the physiological changes during PF will also be considered because they support the strategy of PF management.

Effect of intragastric or intraduodenal administration of a polymeric diet on gallbladder motility, small-bowel transit time, and hormone release

OBJECTIVE

During postpyloric tube feeding, GI intolerance is observed more frequently than during prepyloric feeding, possibly by evoking a stronger GI response.

METHODS

We investigated the effect of intragastric and intraduodenal administration of a polymeric diet (125 kcal/h) on gallbladder motility (by ultrasonography), duodeno-cecal transit time (by lactulose H2 breath test), and GI hormone release (including cholecystokinin, pancreatic polypeptide, and gastrin). Six healthy subjects (two male, four female; mean age 22 yr, range 18-27 yr) were studied on two separate occasions in random order during 6 h of continuous administration of the diet through either the gastric or duodenal port of a two-lumen tube.

RESULTS

Intraduodenal feeding resulted in a more rapid contraction of the gallbladder, from 32 +/- 4 to 23 +/- 4 cm3 at 10 min (p < 0.05), reaching a minimum of 6 +/- 1 cm3, in contrast to intragastric feeding (31 +/- 4 to 19 +/- 3 cm3 at 60 min, p < 0.05; minimum 14 +/- 1 cm3). The gallbladder remained contracted during the 6-h study period during both intraduodenal and intragastric feeding. Small-bowel transit time was significantly accelerated during intraduodenal compared with intragastric feeding (51 +/- 12 vs 81 +/- 9 min; p = 0.003). Plasma cholecystokinin secretion was significantly (p < 0.05) increased during intraduodenal compared with intragastric feeding (848 +/- 107 vs 279 +/- 89 pmol x L(-1) x 360 min). The same was true for pancreatic polypeptide secretion. However, gastrin release was significantly (p < 0.05) higher during intragastric feeding.

CONCLUSIONS

Intraduodenal feeding elicited a stronger GI response than intragastric feeding, as demonstrated by accelerated small-bowel transit time, more rapid and stronger gallbladder contractions, and increased cholecystokinin and pancreatic polypeptide release. Gastrin release, on the other hand, was stronger during intragastric feeding.

Postprandial biliary and pancreatic secretion during profound inhibition of gastric secretion in humans

This study assessed the effect of profound inhibition of gastric secretion by an H2 antagonist on postprandial gastric emptying of acid and chyme, and on bile acid and pancreatic enzyme secretion under physiological conditions in humans. Six subjects were studied before and while they were given famotidine (40 mg). This study combined a continuous intestinal perfusion technique using 14C-polyethylene glycol (14C-PEG) as duodenal recovery marker, with intermittent sampling of gastric content using PEG 4000 as meal marker. During the three hour study, the area under the curve for gastric acid output decreased from mean (SEM) 88.9 (7.6) mmol for those not receiving treatment, to 21.2 (2.7) mmol for subjects receiving famotidine (p < 0.01). The corresponding values for the rate of acid delivery into the duodenum decreased from 65.2 (11.9) to 16.6 (2.9) mmol (p < 0.05), and those for the rate of gastric emptying of chyme remained unchanged for the group receiving no treatment and during famotidine (1040 (200) v 985 (160) ml respectively, NS). Duodenal bile acid and trypsin output remained unchanged (area under the curve, 457 (128) v 373 (86) umol/kg and 5022 (565) v 5058 (400) IU/kg respectively, NS) receiving no treatment and during famotidine. It is concluded that profound inhibition of postprandial gastric acid secretion by anti-secretory drugs is not accompanied by changes in biliary and pancreatic secretion, mainly because the gastric emptying of chyme is unaffected.

Effect of chymotrypsin on human cholecystokinin release: use of clostripain in the validation of a new radioimmunoassay

We have developed and validated a new radioimmunoassay for cholecystokinin. In order to establish that the antiserum binds large and small forms of CCK to an equal extent, we used the microbial enzyme clostripain, which cleaves large forms of CCK yielding CCK 8. Cleavage by clostripain of synthetic and purified forms of CCK, and CCK extracted at from human jejunum and CCK in human plasma was found not to affect immunoactivity, indicating that the antiserum reacts similarly with all forms of CCK. There is controversy over whether intraduodenal trypsin inhibits release of CCK in man. We used our radioimmunoassay to investigate whether chymotrypsin, rather than trypsin, could be the major mediator of negative feedback control of CCK release. Six normal subjects received an intraduodenal infusion of L-phenylalanine and L-tryptophan on two occasions, with the addition of either 1 g/l bovine chymotrypsin or 1 g/l albumin. Plasma CCK concentrations rose in response to the amino acid infusion, but were not affected by the addition of chymotrypsin, indicating that this enzyme is not a mediator of CCK feedback regulation in man.

Role of the gastric phase in fat-induced gallbladder contraction and cholecystokinin secretion in humans

The present study was undertaken to investigate the role of the gastric phase of fat-induced gallbladder contraction and endogenous cholecystokinin (CCK) secretion in humans. Gallbladder emptying, measured by cholescintigraphy, and endogenous CCK secretion, measured by radioimmunoassay, were studied in healthy subjects after both intragastric and intra-intestinal administration of corn oil. In addition, patients with partial gastrectomy were investigated to study the effect of accelerated gastric emptying. In the healthy subjects, intragastric administration of fat resulted in a significantly (P less than 0.05) later increase in plasma CCK levels (20 +/- 2 min) compared to intraintestinal fat (5 +/- 1 min). Similarly, the onset of gallbladder emptying was significantly (P less than 0.05) delayed after intragastric fat (20 +/- 2 min) compared to intestinal fat (10 +/- 1 min). In the healthy subjects the integrated plasma CCK response to intragastric fat was significantly (P less than 0.005-P less than 0.01) reduced from 10 to 30 min. In the patients with partial gastrectomy the rise in plasma CCK (10 +/- 1 min) and the onset of gallbladder emptying (15 +/- 2 min) were in the same range after intra-intestinal and intragastric fat. No significant differences in plasma CCK levels, integrated CCK response or gallbladder emptying were found in the patients according to the site of fat application. It is concluded that endogenous CCK secretion and gallbladder emptying in response to intragastric fat are significantly delayed in healthy subjects but not in patients with partial gastrectomy, in whom gastric emptying is accelerated.(ABSTRACT TRUNCATED AT 250 WORDS)