Effect of ileal oleate on interdigestive intestinal motility of the dog

Importance of the enteric nervous system in the control of the migrating motility complex

The migrating motility complex (MMC), a cyclical phenomenon, represents rudimentary motility pattern in the gastrointestinal tract. The MMC is observed mostly in the stomach and gut of man and numerous animal species. It contains three or four phases, while its phase III is the most characteristic. The mechanisms controlling the pattern are unclear in part, although the neural control of the MMC seems crucial. The main goal of this article was to discuss the importance of intrinsic innervation of the gastrointestinal tract in MMC initiation, migration, and cessation to emphasize that various MMC-controlling mechanisms act through the enteric nervous system. Two main neural regions, central and peripheral, are able to initiate the MMC. However, central regulation of the MMC may require cooperation with the enteric nervous system. When central mechanisms are not active, the MMC can be initiated peripherally in any region of the small bowel. The enteric nervous system affects the MMC in response to the luminal stimuli which can contribute to the initiation and cessation of the cycle, and it may evoke irregular phasic contractions within the pattern. The hormonal regulators released from the endocrine cells may exert a modulatory effect upon the MMC mostly through the enteric nervous system. Their central action could also be considered. It can be concluded that the enteric nervous system is involved in the great majority of the MMC-controlling mechanisms.

Does the Ileal Brake Contribute to Delayed Gastric Emptying After Pancreatoduodenectomy?

Delayed gastric emptying (DGE) represents a significant cause for morbidity following pancreatoduodenectomy (PD). At a time when no specific and universally effective therapy exists to treat these patients, elucidating other potential (preventable or treatable) mechanisms for DGE is important. The aim of the manuscript was to test the hypothesis that ileal brake contributes to DGE in PD patients receiving jejunal tube feeding by systematically reviewing experimental and clinical literature. A series of clinically relevant questions were framed related to the potential role of the ileal brake in development of DGE post-PD and formed the basis of targeted literature searches. A comprehensive search of major reference databases from January 1980 to June 2015 was carried out which included human and animal studies. The ileal brake is a feedback loop neurally mediated by the vagus and sympatho-adrenergic pathways and hormonally by gut peptides including glucagon-like peptide-1, peptide YY (PYY), and neurotensin. The most potent stimulus for this inhibitory reflex is intra-ileal fat. There is evidence to indicate the role of an inhibitory reflex (on gastric emptying) mediated by PYY and CCK which, in turn, are stimulated by nutrient delivery into the distal small intestine providing indirect support to the role of ileal brake in post-PD DGE. The ileal brake is a likely factor contributing to DGE post-PD. While there has been no study to directly test this hypothesis, there is compelling indirect evidence to support it. Designing a trial that would answer such a question appears to be the most appropriate way forward.

A review of the physiology of the canine digestive tract related to the development ofin vitrosystems

Food and nutrition studies in animals and human beings often meet with technical difficulties and sometimes with ethical questions. An alternative to research in living animals is the dynamic multicompartmentalin vitromodel for the gastrointestinal tract described by Minekuset al.(1995) and Havenaar & Minekus (1996). The dynamic conditions that are simulated in this model are peristaltic movements, transit times, pH responses, secretion of enzymes and electrolytes and absorption of nutrients and water. To obtain data for anin vitromodel of the dog gastrointestinal tract, the literature was surveyed for physiological responses to different types of dog food. These included: values of enzyme activities, electrolyte concentrations, gastric emptying and intestinal transit times, pH values, secretion and composition of bile and absorption rates in different parts of the dog gastrointestinal tract. The review focuses on research carried out on healthy, adult dogs of 10–20 kg and on parameters related to the oral cavity, stomach and small intestine. This literature research gives sufficient data on the physiology of the canine digestive tract for the development of anin vitrodynamic model that adequately simulates the functions of the stomach and small intestine of the dog.

Excipient effects on gastrointestinal transit and drug absorption in beagle dogs

Previous work has shown that polyethylene glycol 400 (PEG 400) has an accelerating effect on gastrointestinal transit and a modulating influence on drug absorption in humans. The aim of this study was to assess the impact of various excipients, PEG 400, propylene glycol, d-alpha-tocopheryl-polyethylene glycol-1000 succinate (TPGS) and Labrasol on gastrointestinal transit and drug absorption in four beagle dogs using scintigraphy. Each dog received, on five separate occasions, water (control) or a dose of excipient equivalent to 1 g PEG 400, 2 g propylene glycol, 1 g TPGS or 2 g Labrasol dissolved in water and administered in the form of two capsules. The model drugs ampicillin (200mg) and antipyrine (100mg) were co-administered in the capsules. The capsule solutions were radiolabelled with technetium-99m to follow their transit using a dual-headed gamma camera, and blood samples were collected to determine drug pharmacokinetics. On a separate occasion, the drugs were dissolved in saline and given intravenously. The capsules rapidly disintegrated in the stomach liberating their liquid contents. The mean small intestinal transit times for the different treatments (control, PEG 400, propylene glycol, TPGS and Labarasol) were 183, 179, 195, 168 and 154 min, respectively. The corresponding mean absolute oral bioavailability figures were 36, 32, 39, 42 and 32% for ampicillin and 76, 74, 85, 73 and 74% for antipyrine, respectively. The transit and bioavailability data for the excipient treatments were not significantly different from the control. In summary, these excipients, at the doses administered, have limited influence on gastrointestinal transit and drug in beagle dogs.

The effect of ileal brake activators on the oral bioavailability of atenolol in man

A study was carried out in human volunteers to investigate whether ileal brake activators could alter the bioavailability of atenolol from the small intestine by slowing intestinal transit and thereby increasing the time available for absorption. Oleic acid and a monoglyceride were formulated into modified release capsules that were targeted to the small intestine. Atenolol was either dosed separately or incorporated into one of the capsules. Radiolabelled non-disintegrating tablets were dosed at the same time in order to determine the small intestinal transit time (SITT). Plasma concentrations of atenolol were determined by HPLC. The results showed that in some volunteers an increase in SITT did lead to an increase in the quantity of drug absorbed. However, drug absorption was related not only to the total time spent by the drug in the small intestine but other factors such as the proportion of such time spent at the ileocaecal junction. The study highlights the complexities of exploiting natural gastrointestinal processes to enhance the oral bioavailability of drugs.

Enterogastric brake in rats with segmental bowel resection: role of capsaicin-sensitive nerves

1. Unabsorbed nutrients in the distal gut inhibit upper gastrointestinal motility. 2. The aim of the present study was to investigate changes in gastric motility following segmental resections and to evaluate the role of capsaicin-sensitive afferent neurons that may be responsible for these changes. 3. Wistar albino rats of both sexes (200-250 g) were used. Under aseptic conditions and anaesthesia (100 mg/kg ketamine), a baby-feeding tube was placed distal to the resection in either the ileum or caecum for intraluminal perfusion of saline or 20 lipid. In one group of rats, capsaicin was perfused (0.6) for afferent denervation. One group of rats underwent jejunal and ileal resections with end-to-end anastomosis of the remaining segments and were cannulated distal to these anastomosis. Ten days after the surgery, the percentage gastric emptying of a solid meal was calculated. 4. Intra-ileal (18) and intracaecal (34) lipid perfusions delayed gastric emptying compared with groups perfused with saline (54 and 74, respectively; P< 0.001 and P< 0.01). The delay in gastric emptying by ileal perfusion was significantly greater than that following caecal perfusion (P< 0.05). With both resections, gastric emptying was delayed compared with sham groups (P< 0.05-0.01). Local administration of capsaicin abolished the inhibitory effect of lipid on gastric emptying in healthy intact rats and in the jejunal-resection group, whereas a partial reversal was seen in the ileal-resection group. 5. In conclusion, the present data demonstrate that in both healthy intact rat groups and in short bowel groups, capsaicin-sensitive extrinsic neurons participate in brake mechanisms of the distal gut.

Effects of abomasal infusion of long-chain fatty acids on intake, feeding behavior and milk production in dairy cows

Fat is often fed to dairy cows to increase the energy concentration of their diet; however, feeding fat often reduces dry matter intake (DMI), which limits its impact on metabolizable energy (ME) intake. To investigate the effects of postruminal fat infusion on intake, feeding behavior, and milk production of dairy cows at two stages of lactation (55 and 111 d postpartum), six Holstein x British Friesian cows were infused into the abomasum, with a mixture of rapeseed and sunflower oils supplying predominantly unsaturated long-chain fatty acids (LCFA). Dry matter intake was significantly depressed by oil infusion, but estimated ME intake was unchanged, and thus there was no effect of oil infusion on milk yield. There was no effect of stage of lactation on the DM or ME intake response to oil infusion. Milk fat concentration was increased by oil infusion in mid-lactation but not in early lactation, suggesting that the infused LCFA were utilized differently in early compared with midlactation. Cows spent an average of 654 min idling, 462 min ruminating, and 248 min eating during the last 22.8 h of each infusion. There were no significant effects of oil infusion or stage of lactation on the total time spent engaged in these activities. An assessment of the circadian pattern of feeding behavior suggested that the depression in DMI in response to oil infusion occurred after the 1630 and 2230 h feeding times. This may reflect differences in mechanisms regulating feed intake behavior and appetite during the day. Comparison of the results of the present study with the results of other trials involving postruminal fat infusion suggests that polyunsaturated nonesterified fatty acids have the most potent effect on DMI intake.

Does the site of intestinal delivery of oleic acid alter the ileal brake response?

Previous work has demonstrated that high doses of oleic acid can activate the ileal brake but the importance of site of delivery has yet to be investigated. The objective of this study was to use modified release capsules to release oleic acid in different regions of the intestine. When tested by in vitro dissolution in pH 6.8 phosphate buffer, one batch released the contents almost immediately, another after around 30 min and the last batch after around 60-70 min. The effect of oleic acid release site on the ileal brake was assessed by the measurement of transit time of radiolabelled non disintegrating tablets by gamma scintigraphy. The results demonstrated that the transit of tablets could be slowed down by oleic acid and therefore it appears the ileal brake can be activated along the entirety of the small intestine.

The effect of oleic acid on the human ileal brake and its implications for small intestinal transit of tablet formulations

PURPOSE

A human volunteer study was carried out to investigate whether activation of the ileal brake mechanism affects the transit of tablets through the small intestine.

METHODS

Oleic acid, which has previously been shown to activate the brake, was delivered to the small intestine in a modified release capsule at doses of 300 mg, 600 mg and 1200 mg. The effect of the oleic acid was determined by measuring the transit of two sets of radiolabelled tablets by gamma scintigraphy. One set of tablets was dosed with the capsule and the other one hour later.

RESULTS

The results show that in the majority of the volunteers small intestinal residence time was greater with the oleic acid than control. The effect was most pronounced in the tablets given concomitantly with the capsule and with the higher doses of oleic acid.

CONCLUSIONS

The ileal brake, activated by oleic acid, can slow the transit of tablets through the small intestine.

Is the pig a good animal model for studying the human ileal brake?

This study was designed to investigate the existence of an ileal brake mechanism in the pig model. The test substances used (oleic acid, deoxycholic acid, taurocholic acid) had all been previously shown to affect the ileal brake mechanism in other species including man. The substances were infused directly into the terminal ileum of surgically modified pigs, 45 min after the pigs had ingested a meal containing a drug marker. The marker used was sulfasalazine, which is cleaved to form a metabolite, sulfapyridine, when it reaches the colon. The subsequent HPLC analysis of collected blood samples allowed the appearance of sulfapyridine in the plasma and hence the arrival of sulfasalazine in the colon to be determined. Any differences in transit between control and test could be evaluated from a profile of plasma concentrations and corresponding values of AUC. The findings from this study show that the various substances did not affect transit of a test meal in the pig and suggest that it is not possible to use this pig model to make predictions about the human ileal brake.