Effects of enteral infusion of nutrients on canine intestinal motor-patterns

Fat digestion modulates gastrointestinal sensations induced by gastric distention and duodenal lipid in humans

BACKGROUND AND AIMS

It is unclear whether fat digestion is required for the induction of gastrointestinal sensations and whether different fats have different effects. We investigated the effect of fat digestion and of medium-chain triglycerides (MCTs; C < 12) and long-chain triglycerides (LCTs; C > 16) on gastrointestinal sensations.

METHODS

In a double-blind study, 15 healthy subjects were studied on 5 occasions during which LCT or MCT emulsions (2 kcal/min), with or without 120 mg tetrahydrolipstatin (THL, lipase inhibitor), or sucrose polyester (SPE, nondigestible fat) were infused intraduodenally in randomized order. After 30 minutes, the proximal stomach was distended in 1 mm Hg steps/min. Intensity of gastrointestinal sensations (on a 0-10 visual analog scale), plasma cholecystokinin (CCK) levels, and gastric volumes were assessed throughout.

RESULTS

LCT and MCT increased gastric volume at baseline pressure compared with SPE, and LCT more than MCT. THL entirely abolished this effect (volumes [mL]: LCT, 213 +/- 19; LCT-THL, 39 +/- 3; MCT, 155 +/- 12; MCT-THL, 43 +/- 5; SPE, 44 +/- 5). Only LCT increased plasma CCK levels (pmol/L per 30 minutes: LCT, 21 +/- 2; LCT-THL, 9 +/- 1; MCT, 9 +/- 1; MCT-THL, 11 +/- 1; SPE, 9 +/- 1). During distentions, intragastric volumes were greater during infusion of LCT and MCT than during the respective THL conditions or SPE, but plasma CCK levels did not change. The intensity of sensations increased (hunger decreased) more with LCT than with MCT. During infusion of THL or SPE, the effects were smaller than during LCT or MCT.

CONCLUSIONS

Fat digestion is required for the modulation of gastrointestinal sensations during gastric distention. The effects of fat depend on the fatty acid chain length and are not entirely explained by release of CCK.

Composition of enteral diets and meals providing optimal absorption rates of nutrients in mini pigs

BACKGROUND

Commercial enteral diets differ widely in nutrient composition. It is unknown whether the nutrient composition of the diets influences intestinal absorption.

OBJECTIVE

The objective of this study was to investigate the effects of different enteral diets providing 60% of energy as carbohydrate, protein, or fat or 33.3% of energy from each nutrient on intestinal absorption in mini pigs.

DESIGN

Kinetics of nutrient absorption were determined by perfusing a 150-cm jejunal segment. The kinetics of absorption were used to determine optimal relations between the absorption and recovery of each nutrient. From these data, the optimal nutrient composition of the diets providing complete absorption of the macronutrients in the shortest intestinal length was evaluated. Absorption of nutrients was further determined after oral administration of 4 corresponding meals.

RESULTS

With all enteral diets, the absorption of nutrients displayed saturation kinetics. Absorption rates of carbohydrate were significantly larger than those of fat and protein. Consequently, the amounts of nutrients remaining unabsorbed per unit length of jejunum differed among the macronutrients. After administration of various test meals, the length of the small intestine required for complete absorption of the nutrients depended on the composition of the meals. The shortest intestinal length for complete absorption was needed for a diet providing 48% of energy as carbohydrate, 23% as protein, and 29% as fat. This composition closely matched the nutritional requirements.

CONCLUSION

The nutrient composition of diets can optimize intestinal absorption. This may be especially important in patients with malabsorption or short-bowel syndrome.

Absorption of nutrients is only slightly reduced by supplementing enteral formulas with viscous fiber in miniature pigs

Viscous polysaccharides reduce intestinal absorption of glucose and diminish postprandial hyperglycemia. However, it is unknown whether viscous fiber also inhibits absorption of nutrients under conditions of enteric feeding. Therefore, we measured the absorption rates of nutrients in miniature pigs by perfusing a 150-cm length of jejunum with 8.37 kJ/min of the three following enteral diets: an isoosmotic oligomeric diet (1670 kJ/L), a hyperosmotic oligomeric diet and an isoosmotic polymeric diet (both 3350 kJ/L). The diets were supplemented with guar gum from 0 to 4.4 g/L. With the three guar-free diets, the mean absorption rate of energy was 5.2 +/- 0.32 kJ/min, corresponding to 62% of the energy infused. Absorption rates of carbohydrate, protein, fat and energy linearly declined as concentrations of guar or the logarithm of chyme viscosity increased. Due to modulations in viscosity, the inhibitory effects of guar were significantly different among the three diets. With the isoosmotic and hyperosmotic oligomeric and the polymeric diets, the addition of 1 g guar/L diminished the absorption of energy by 9.7, 6. 6 and 3.7%, respectively. The strong inhibitory effect on nutrient absorption with the isoosmotic oligomeric diet was caused by an increase in chyme viscosity due to water absorption. With the hyperosmotic oligomeric and the polymeric diets, the chyme viscosity and thus inhibitory effects on absorption were diminished by water secretion and the concomitant infusion of pancreatic enzymes. Results indicate that the addition of small amounts of guar gum to enteral diets of high energy density exerts only small effects on absorption of nutrients.

Reserve capacities of the small intestine for absorption of energy

Previous in vitro studies showed that the small intestine has reserve capacities for absorption of nutrients. However, the size of the reserve capacity is controversial. Therefore, we measured the intestinal capacity for absorption of energy in relation to the postprandial gastric delivery of energy into the gut. In minipigs, a 150-cm length of jejunum was perfused (1-8 kcal/min) with four nutrient solutions containing 60% of energy as carbohydrate, protein, and fat, respectively, or containing 33.3% of each nutrient. In separate experiments, gastric delivery of energy to the jejunum was measured after oral administration of four meals with the same nutrient composition as the perfusion solutions. With all nutrient solutions, intestinal absorption of energy demonstrated saturation kinetics. The jejunal capacity for absorption of energy ranged from 0.66 to 0.94 kcal . m-1 . min-1. Despite large differences in nutrient composition of the four meals, equal amounts of energy (1.3 +/- 0.41 kcal/min) were delivered from the stomach to the jejunum. The absorption rates of energy after meals ranged from 0.40 to 0.58 kcal . m-1 . min-1. Therefore, only 58.8 +/- 2.7% of the jejunal capacity for absorption of energy was used. Additionally, the length of small intestine that would have been required for complete absorption was 42.9 +/- 3.7% of the total length. Results indicate that the feedback control of gastric emptying provides at least two types of intestinal reserve capacities: a reserve in absorption (1.7 fold) and a reserve in intestinal length (2.4 fold).

Canine small bowel motor patterns and contractions are not neurally regulated during enteric nutrient infusion

The aims of this study were to determine the effects of duodenal and jejunoileal nutrient infusions on small intestinal motor patterns and intestinal contractions in neurally intact and neurally isolated small bowel. Fifteen dogs were prepared with duodenal and jejunal infusion and manometry catheters and a diverting jejunal cannula. Ten of the dogs underwent in situ neural isolation of the jejunoileum. A mixed nutrient meal (0.5 kcal/ml) was infused into the duodenum or jejunum at 3 ml/min for 5 h. Control experiments involved infusion of a balanced salt solution. Manometric data collected on-line to a microcomputer were analyzed for direction, distance, and velocity of spread of single pressure waves (SPW) and clustered contractions. Isolated duodenal and jejunoileal nutrient infusions inhibited the fasting motor pattern in neurally intact and neurally isolated small bowel. Motor activity (motility index) increased slightly during nutrient infusion within groups, but there were few differences between groups. Neither neural isolation nor nutrient infusion had a consistent effect on spread of SPW or migration of clustered contractions. Isolated duodenal and jejunoileal nutrient infusions in the dog inhibit fasting motor patterns and increase motor activity slightly but have little effect on characteristics of individual and clustered contractions. Extrinsic innervation to the jejunoileum or intrinsic neural continuity of the jejunum with the duodenum had little effect on single or grouped contractions. Although the changes in motor activity demonstrated in this study appear small, alterations in intestinal transit and absorption may still occur and may be of importance physiologically.

Duodenojejunal motility after oral and enteral nutrition in humans: a comparative study

BACKGROUND

Small bowel motility during enteral nutrition (EN) remains poorly known. Our aim was to compare, in six healthy volunteers, the duodenojejunal motor patterns after a 750-kcal meal either ingested or infused intraduodenally at two different infusion rates: 2 kcal/min for 6 hours (6-hour EN) or 1 kcal/min for 12 hours (12-hour EN).

METHODS

In each volunteer, the three manometric studies were carried out in a random order with an interval of > or = 1 week between each recording. Number of phase III (PIIIs), their characteristics, number of waves (NW), and area under the curve (AUC) were determined.

RESULTS

PIIIs were interrupted by each type of nutrition in every volunteer. In five of six during 6-hour EN and in six of six during 12-hour EN, the first PIII returned before the end of EN. The mean duration of the fed pattern was similar in the three studies. During the interruption of PIIIs after oral meal, duodenojejunal motility was characterized by uninterrupted random contractions. By contrast, in four of six during the 6-hour EN and in five of six during 12-hour EN, it was organized as regular short bursts of contractions separated by motor quiescence. In all studies during the disruption of PIIIs, NW and AUC values decreased progressively with time and were higher at the jejunum level than in the duodenum (p < .001). However, at each level of recording, NW and AUC values were similar in the three types of feeding. After the return of PIIIs, the number, duration, and propagation velocity of PIIIs, NW, and AUC values were similar in the three studies.

CONCLUSIONS

EN interrupts PIIIs, but, in most cases, PIIIs reappear before the end of EN. During the interruption of PIIIs, the organization of the contractions is qualitatively different from the fed pattern observed after oral feeding. For the same caloric value of the meal, the quantitative duodenojejunal motor response is not affected by the infusion rate, and the more important jejunal, rather than duodenal motor response found after an oral meal, is observed during EN. During EN, after the return of PIIIs, despite the persistence of a nutrient infusion into the duodenum, the small bowel motor patterns are not qualitatively or quantitatively different from those recorded in fasting subjects.

Effects of enteral feedback inhibition on motility, luminal flow, and absorption of nutrients in proximal gut of minipigs

We wanted to clarify whether the postprandial intestinal feedback control activated by nutrients in the distal gut exerts different effects on motility, transit of digesta, and absorption of nutrients in the proximal gut. Additionally, interrelationships among motility, transit, and absorption were to be elucidated because these relationships have only been investigated in the fasted state. In five minipigs, a 150-cm segment of the proximal jejunum was isolated by two cannulas. Motility of the jejunal segment was recorded by multiple strain gauges and analyzed by computerized methods. Markers (Cr- and Cu-EDTA) were used for the measurement of the flow rate, transit time, and absorption of nutrients. After a meal, the test segment was perfused with 2 kcal/min of an elemental diet over a period of 90 min. A feedback inhibition was activated by infusion of nutrients into the midgut at rates of 1-4 kcal/min. Saline was infused as control. With increasing energy loads infused into the midgut, the motility index and the length of contraction waves decreased, whereas the incidence of stationary contractions increased, ie, the motility changed from a propulsive to a segmenting pattern. These modulations of motility were associated with a linear decrease in the flow rate and a linear increase in transit time. Flow and transit were linearly correlated with each other. Additionally, the reduction in flow rate and the delay in luminal transit were associated with a linear increase in the absorption of nutrients. However, the increase in absorption induced by the feedback mechanism was small (7.3-13.4%) compared to the marked inhibition of the motility parameters (54-64%), the flow rate (59%), and the delay of transit (5.8-fold). Feedback control primarily modulated motor patterns and luminal flow, whereas the small increase in absorption was only a side effect due to the longer contact time of the nutrients with the mucosa.

Modulation of the migrating myoelectric complexes by cholecystokinin and gastrin in the gastrointestinal tract of chickens

Several mammalian avian species, including the chicken, show migrating myoelectric complexes (MMC) both in unfed and fed states. In these species, postprandial hormones seem to modulate but not to disrupt the MMC. To gain more information in this modulatory role, we evaluated the role of cholecystokinin (CCK) vs gastrin on the regulation of intestinal motility in chickens. Birds were implanted with eight electrodes for electromyography in the stomach, duodenum, jejunum, and ileum. In feed-deprived animals, CCK infusion (10(-12) mol/kg per min x 3 h) did not disrupt the MMC but induced changes in the MMC pattern similar to those induced by a meal. Infusion of CCK in fed animals induced dose-dependent effects: CCK infused at 10(-11) and 3 x 10(-11) mol/kg per min x 2 h, progressively elongated the MMC and slowed the speed of propagation of Phase 3. Furthermore, CCK infused at 10(-10) mol/kg per min x 2 h disrupted the MMC but a Phase 3 appeared just after the end of the infusion. By contrast, chicken gastrin (10(-10) mol/kg per min x 2 h) did not modify the MMC pattern. In conclusion, CCK influence on the intestinal motility of chickens ranges from the modulation of the MMC to total disruption, depending on the dose. Moreover, this study suggests that the mechanism of action of CCK could be similar in both mammalian and avian small intestines.

Effects of enteral infusion of hypertonic saline and nutrients on canine jejunal motor patterns

The aim of the study was to clarify the effects of hypertonic solutions on jejunal motility. The study focused on differential effects of hypertonic saline and nutrients. Motility of the canine proximal jejunum was recorded with closely spaced strain-gauge transducers. During fasting, hyperosmotic solutions (up to 1520 mosmol/liter) of saline or nutrients (1 kcal/ml) were infused into the proximal jejunum (0.5-1.5 ml/min) up to 6 hr. The hyperosmotic solutions stimulated jejunal motility. With both increasing osmolarity of saline or increasing energy load of nutrients, jejunal motility linearly declined. The reduction of motility was associated with a change in motor pattern from a propulsive to a more segmenting one. Hypertonic glucose evoked a significantly smaller level of motor activity compared with both saline (at given osmolarities) and an elemental diet (at given energy loads). Motility parameters were not different between glucose and maltose, although osmolarity of maltose was less than half (760 vs 1520 mosmol/liter). In contrast, a mixture of glucose-fructose exerted a smaller inhibition of jejunal motility than glucose. The hypertonic solutions of saline or nutrients were tolerated over 2 hr; with hypertonic saline retrograde power contractions with or without vomiting occurred, whereas with hypertonic nutrients vomiting was preceded by strong inhibition of jejunal motility. Three conclusions can be derived from the present results: (1) The behavior of jejunal motility suggested that the motor activity was the result of both a local stimulation and an inhibitory feedback mechanism. (2) The different degree of inhibition between glucose and saline indicated that the nutrient itself played a major role in the inhibitory feedback regulation, whereas osmolarity was of minor importance. (3) Comparisons between different nutrients suggested a linkage between inhibitory control of motility and the absorptive capacity of the gut for the single nutrient.