Gastric emptying of solid food is most potently inhibited by carbohydrate in the canine distal ileum

The role of gastric function in control of food intake (and body weight) in relation to obesity, as well as pharmacological and surgical interventions

PURPOSE

The objectives of this review are to summarize the role of gastric motor functions in the development of satiation (defined broadly as postprandial fullness) and satiety (reduced appetite or postponing desire to eat after a meal) and their impact on weight change. The specific topics are the methods of measurement of gastric emptying and accommodation and their impact on food intake, satiation, and satiety. A second focus contrasts bariatric surgery to endoscopic gastroplasty that alter gastric emptying and incretin responses in markedly divergent manners.

BACKGROUND

The hormone, GLP-1, retards gastric emptying and increases gastric accommodation through vagally-mediated effects. Indeed, these effects provide the basis for the association of altered gastric emptying in the appetite and weight loss responses to pharmacological interventions particularly by those acting on receptors of incretin agonists such as liraglutide and the dual agonists, tirzepatide and cotadutide, all of which retard gastric emptying. In fact, retardation of gastric emptying and gastrointestinal adverse effects have been shown to contribute in part to the weight loss in response to this class of pharmacological agents.

SUMMARY

The motor functions of the stomach are relevant to postprandial fullness and to interventions aimed at weight loss in people with obesity.

Cooked rice- and wheat-based food structure influenced digestion kinetics and glycemic response in growing pigs

BACKGROUND

How starch-based food structure can impact the rate and extent of digestion in the small intestine and resulting glycemic response is not properly understood. One possible explanation is that food structure influences gastric digestion, which subsequently determines digestion kinetics in the small intestine and glucose absorption. However, this possibility has not been investigated in detail.

OBJECTIVES

Using growing pigs as a digestion model for adult humans, this study aimed to investigate how physical structure of starch-rich foods impacts small intestinal digestion and glycemic response.

METHODS

Male growing pigs (21.7 ± 1.8 kg, Large White × Landrace) were fed one of six cooked diets (250-g starch equivalent) with varying initial structures (rice grain, semolina porridge, wheat or rice couscous, or wheat or rice noodle). The glycemic response, small intestinal content particle size and hydrolyzed starch content, ileal starch digestibility, and portal vein plasma glucose were measured. Glycemic response was measured as plasma glucose collected from an in-dwelling jugular vein catheter for up to 390 min postprandial. Portal vein blood samples and small intestinal content were measured after sedation and euthanasia of the pigs at 30, 60, 120, or 240 min postprandial. Data were analyzed with a mixed-model ANOVA.

RESULTS

The plasma glucose Δmax_overall and iAUC_overall for couscous and porridge diets (smaller-sized diets) were higher than intact grain and noodle diets (larger-sized diets); 29.0 ± 3.2 vs. 21.7 ± 2.6 mg/dL and 5659 ± 727 vs. 2704 ± 521 mg/dL.min, for the smaller- and larger-sized diets, respectively (p < 0.05). Ileal starch digestibility was not significantly different between diets (p ≥ 0.05). The iAUC_overall was inversely related to the starch gastric emptying half-time of the diets (r = -0.90, p = 0.015).

CONCLUSIONS

Starch-based food structure affected the glycemic response and starch digestion kinetics in the small intestine of growing pigs.

Activation of gastrointestinal ileal brake response with dietary slowly digestible carbohydrates, with no observed effect on subjective appetite, in an acute randomized, double-blind, crossover trial

PURPOSE

To test the hypothesis that oral ingestion of slowly digestible carbohydrates (SDCs) that reach the ileum triggers the ileal brake as indicated by delayed gastric emptying, reduced glycemic response, and decreased subjective appetite.

METHODS

The study was a five-arm, randomized, double-blind, crossover trial with a 1-week washout period between treatments (n = 20; 9 females, 11 males). Five treatments consisted of three SDC ingredients [raw corn starch, isomaltooligosaccharide (IMO), sucromalt], and an IMO/sucromalt combination, shown in vitro to have slow and extended digestion profiles, and a rapidly digestible carbohydrate control (maltodextrin). Carbohydrates (26 g) were incorporated into yogurt [300 g total; carbohydrate (~ 77 g), fat (~ 0.2 g), and protein (~ 9 g)] with closely matched energy content (346 kcal) and viscosity (~ 30,000 cP). Outcomes were measured in a 4 h postprandial period.

RESULTS

Mean gastric half-emptying times were moderately though significantly increased for the raw corn starch and IMO treatments (P < 0.05), but they could be sub-divided into larger effect responder (n = 11) and non-responder groups (n = 9). Longer time for glycemic response to return to baseline was associated with increased gastric half-emptying time in an exploratory subset of data removing gastric half-emptying times > 3.5 h (P = 0.02). No significant differences in appetite ratings were observed.

CONCLUSION

SDCs caused slower gastric emptying rate through activation of the ileal brake, as closely matched semi-solid yogurts were used and only rate of carbohydrate digestion differed. Extending glycemic response through consumption of SDCs was associated with triggering the ileal brake.

TRIAL REGISTRATION

ClinicalTrials.gov NCT03630445, August 2018, retrospectively registered.

Structural breakdown of starch-based foods during gastric digestion and its link to glycemic response: In vivo and in vitro considerations

The digestion of starch-based foods in the small intestine as well as factors affecting their digestibility have been previously investigated and reviewed in detail. Starch digestibility has been studied both in vivo and in vitro, with increasing interest in the use of in vitro models. Although previous in vivo studies have indicated the effect of mastication and gastric digestion on the digestibility of solid starch-based foods, the physical breakdown of starch-based foods prior to small intestinal digestion is often less considered. Moreover, gastric digestion has received little attention in the attempt to understand the digestion of solid starch-based foods in the digestive tract. In this review, the physical breakdown of starch-based foods in the mouth and stomach, the quantification of these breakdown processes, and their links to physiological outcomes, such as gastric emptying and glycemic response, are discussed. In addition, the physical breakdown aspects related to gastric digestion that need to be considered when developing in vitro-in vivo correlation in starch digestion studies are discussed. The discussion demonstrates that physical breakdown prior to small intestinal digestion, especially during gastric digestion, should not be neglected in understanding the digestion of solid starch-based foods.

Traditional Malian Solid Foods Made from Sorghum and Millet Have Markedly Slower Gastric Emptying than Rice, Potato, or Pasta

From anecdotal evidence that traditional African sorghum and millet foods are filling and provide sustained energy, we hypothesized that gastric emptying rates of sorghum and millet foods are slow, particularly compared to non-traditional starchy foods (white rice, potato, wheat pasta). A human trial to study gastric emptying of staple foods eaten in Bamako, Mali was conducted using a carbon-13 (¹³C)-labelled octanoic acid breath test for gastric emptying, and subjective pre-test and satiety response questionnaires. Fourteen healthy volunteers in Bamako participated in a crossover design to test eight starchy staples. A second validation study was done one year later in Bamako with six volunteers to correct for endogenous ¹³C differences in the starches from different sources. In both trials, traditional sorghum and millet foods (thick porridges and millet couscous) had gastric half-emptying times about twice as long as rice, potato, or pasta (p < 0.0001). There were only minor changes due to the ¹³C correction. Pre-test assessment of millet couscous and rice ranked them as more filling and aligned well with postprandial hunger rankings, suggesting that a preconceived idea of rice being highly satiating may have influenced subjective satiety scoring. Traditional African sorghum and millet foods, whether viscous in the form of a thick porridge or as non-viscous couscous, had distinctly slow gastric emptying, in contrast to the faster emptying of non-traditional starchy foods, which are popular among West African urban consumers.

Duodenal and ileal glucose infusions differentially alter gastrointestinal peptides, appetite response, and food intake: a tube feeding study

Background: Activation of the ileal brake through the delivery of nutrients into the distal small intestine to promote satiety and suppress food intake provides a new target for weight loss. Evidence is limited, with support from naso-ileal lipid infusion studies.Objective: The objective of the study was to investigate whether glucose infused into the duodenum and ileum differentially alters appetite response, food intake, and secretion of satiety-related gastrointestinal peptides.Design: Fourteen healthy male participants were randomly assigned to a blinded 4-treatment crossover, with each treatment of single-day duration. On the day before the intervention (day 0), a 380-cm multilumen tube (1.75-mm diameter) with independent port access to the duodenum and ileum was inserted, and position was confirmed by X-ray. Subsequently (days 1-4), a standardized breakfast meal was followed midmorning by a 90-min infusion of isotonic glucose (15 g, 235 kJ) or saline to the duodenum or ileum. Appetite ratings were assessed with the use of visual analog scales (VASs), blood samples collected, and ad libitum energy intake (EI) measured at lunch, afternoon snack, and dinner.Results: Thirteen participants completed the 4 infusion days. There was a significant effect of nutrient infused and site (treatment × time, P < 0.05) such that glucose-to-ileum altered VAS-rated fullness, satisfaction, and thoughts of food compared with saline-to-ileum (Tukey's post hoc, P < 0.05); decreased ad libitum EI at lunch compared with glucose-to-duodenum [-22%, -988 ± 379 kJ (mean ± SEM), Tukey's post hoc, P < 0.05]; and increased glucagon-like peptide-1 (GLP-1) and peptide YY (PYY) compared with all other treatments (Tukey's post hoc, P < 0.05).Conclusions: Macronutrient delivery to the proximal and distal small intestine elicits different outcomes. Glucose infusion to the ileum increased GLP-1 and PYY secretion, suppressed aspects of VAS-rated appetite, and decreased ad libitum EI at a subsequent meal. Although glucose to the duodenum also suppressed appetite ratings, eating behavior was not altered. This trial was registered at www.anzctr.org.au as ACTRN12612000429853.

Lipids, CHOs, proteins: can all macronutrients put a 'brake' on eating?

The gastrointestinal (GI) tract and specifically the most distal part of the small intestine, the ileum, has become a renewed focus of interest for mechanisms targeting appetite suppression. The 'ileal brake' is stimulated when energy-containing nutrients are delivered beyond the duodenum and jejunum and into the ileum, and is named for the feedback loop which slows or 'brakes' gastric emptying and duodeno-jejunal motility. More recently it has been hypothesized that the ileal brake also promotes secretion of satiety-enhancing GI peptides and suppresses hunger, placing a 'brake' on food intake. Postprandial delivery of macronutrients to the ileum, other than unavailable carbohydrates (CHO) which bypass absorption in the small intestine en route to fermentation in the large bowel, is an uncommon event and hence this brake mechanism is rarely activated following a meal. However the ability to place a 'brake' on food intake through delivery of protected nutrients to the ileum is both intriguing and challenging. This review summarizes the current clinical and experimental evidence for activation of the ileal brake by the three food macronutrients, with emphasis on eating behavior and satiety as well as GI function. While clinical studies have shown that exposure of the ileum to lipids, CHOs and proteins may activate GI components of the ileal brake, such as decreased gut motility, gastric emptying and secretion of GI peptides, there is less evidence as yet to support a causal relationship between activation of the GI brake by these macronutrients and the suppression of food intake. The predominance of evidence for an ileal brake on eating comes from lipid studies, where direct lipid infusion into the ileum suppresses both hunger and food intake. Outcomes from oral feeding studies are less conclusive with no evidence that 'protected' lipids have been successfully delivered into the ileum in order to trigger the brake. Whether CHO or protein may induce the ileal brake and suppress food intake has to date been little investigated, although both clearly have GI mediated effects. This review provides an overview of the mechanisms and mediators of activation of the ileal brake and assesses whether it may play an important role in appetite suppression.

Ileal brake: a sensible food target for appetite control. A review

With the rising prevalence of obesity and related health problems increases, there is increased interest in the gastrointestinal system as a possible target for pharmacological or food-based approaches to weight management. Recent studies have shown that under normal physiological situations undigested nutrients can reach the ileum, and induce activation of the so-called "ileal brake", a combination of effects influencing digestive process and ingestive behaviour. The relevance of the ileal brake as a potential target for weight management is based on several findings: First, activation of the ileal brake has been shown to reduce food intake and increase satiety levels. Second, surgical procedures that increase exposure of the ileum to nutrients produce weight loss and improved glycaemic control. Third, the appetite-reducing effect of chronic ileal brake activation appears to be maintained over time. Together, this evidence suggests that activation of the ileal brake is an excellent long-term target to achieve sustainable reductions in food intake. This review addresses the role of the ileal brake in gut function, and considers the possible involvement of several peptide hormone mediators. Attention is given to the ability of macronutrients to activate the ileal brake, and particularly variation attributable to the physicochemical properties of fats. The emphasis is on implications of ileal brake stimulation on food intake and satiety, accompanied by evidence of effects on glycaemic control and weight loss.

Effect of food or antacid on pharmacokinetics and pharmacodynamics of febuxostat in healthy subjects

What is already known about this subject. Febuxostat is a novel nonpurine selective inhibitor of xanthine oxidase. What this study adds. This is the first manuscript to address the effect of food and antacid on the pharmacokinetics and/or pharmacodynamics of febuxostat. The study will determine whether the drug can be administered regardless of food or antacid. It will therefore influence how the drug should be administered.

AIMS

To evaluate the effects of food or antacid on the pharmacokinetics and/or pharmacodynamics of febuxostat.

METHODS

Four Phase I, two-period, crossover studies were performed in healthy male and female subjects. Subjects either received single 40-mg (n = 24), multiple 80-mg (n = 24) and single 120-mg (n = 20) doses of febuxostat in fasting and nonfasting conditions, or received single 80-mg (n = 24) doses alone or with antacid.

RESULTS

Food caused a decrease in C(max) (38-49%) and AUC (16-19%) of febuxostat at different dose levels following single or multiple oral dosing with febuxostat. However, a slightly greater percent decrease in serum uric acid concentrations (58% vs. 51%) after multiple dosing with 80 mg of febuxostat under nonfasting conditions was observed, which was statistically (P < 0.05) but not clinically significant. Antacid caused a decrease in C(max) (32%), but had no effect on AUC of febuxostat. Febuxostat was safe and well tolerated in all studies.

CONCLUSIONS

Even though food caused a decrease in the rate and extent of absorption of febuxostat, this decrease was not associated with a clinically significant change in febuxostat pharmacodynamic effect. Despite a decrease in the absorption rate of febuxostat, antacid had no effect on the extent of febuxostat absorption. Therefore, febuxostat can be administered regardless of food or antacid intake.

The pharmacokinetics of cinacalcet are unaffected following consumption of high- and low-fat meals

Cinacalcet HCl reduces iPTH, serum calcium, serum phosphorus, and the calcium-phosphorus product in patients with chronic kidney disease and secondary hyperparathyroidism who are receiving dialysis, and reduces elevated serum calcium associated with primary hyperparathyroidism and parathyroid carcinoma. Cinacalcet is administered orally, and thus concomitant administration with food may affect its bioavailability. The objective of this study was to examine the effect of fat and caloric intake on cinacalcet exposure. This phase 1, randomized, open-label, single-dose, 3-period, 3-treatment, 6-sequence crossover study enrolled 30 healthy subjects (19 men, 11 women) to receive a single oral dose of cinacalcet HCl (Sensipar/Mimpara; Amgen Inc. Thousand Oaks, CA) (90 mg) on 3 separate occasions: following a high-fat, high-caloric meal, a low-fat, low-caloric meal, and a 10-hour fast. Blood samples were obtained predose and up to 72 hours postdose for pharmacokinetic (AUCinfinity, Cmax) and safety evaluations. Twenty-nine subjects completed all the 3 treatment conditions. The mean (90% confidence intervals) AUCinfinity following high- and low-fat meals was increased by 68 (48 to 89)% and 50 (33 to 70)%, respectively, relative to fasting. The difference in mean AUCinfinity between high- and low-fat meals was small [12 (9.9-26)%]. The mean tmax of cinacalcet was prolonged in fasting subjects (6 h) in relation to high-fat (4 h) and low-fat (3.5 h) fed subjects. The mean t1/2beta was similar between treatment conditions. Adverse events (AE) were observed at a similar frequency across the treatment conditions [high fat (34%), low fat (23%), and fasting (31%)]; the type of AE did not differ among the treatment conditions. The most common treatment-related AEs were headache 6/30 (20%), nausea 5/30 (17%), and dyspepsia 4/30 (13%) subjects. Administration of cinacalcet with either high- or low-fat meals results in significant increases in exposure, relative to administration under fasting conditions. However, the small differences observed in exposure following the ingestion of the different types of meals suggest that although food has a significant effect, the type of food does not. The observed effect supports the labeling statement that cinacalcet be taken with food, or shortly after a meal.

Ileal brake: neuropeptidergic control of intestinal transit

Digestion and absorption of a meal are time-intensive processes. To optimize digestion and absorption, transit of the meal through the gastrointestinal tract is regulated by a complex integration of neuropeptidergic signals generated as the jejunal brake and ileal brake response to nutrients. Mediators involved in the slowing of transit responses include peptide YY (PYY), chemosensitive afferent neurons, intestinofugal nerves, noradrenergic nerves, myenteric serotonergic neurons, and opioid neurons. The activation of this circuitry modifies the peristaltic reflex to convert the intestinal motility pattern from propagative to segmenting. Fat is the most potent trigger of these transit control mechanisms. The integrated circuitry of gut peptides and neurons involved in transit control in response to nutrients is described in this review.

Measurement of gastrointestinal transit

An abnormality in transit is commonly considered to account for unexplained gastrointestinal (GI) symptoms. Since the symptoms of delayed transit overlap with those of accelerated transit, direct measurement of GI transit is needed to establish an accurate diagnosis. Similarly, since symptoms originating from one part of the gut may overlap with symptoms from another, localizing transit abnormality to one organ vs. another using direct measurement is an important part of diagnostic evaluations. Consequently, noninvasive tests of GI transit should be done early in the evaluation to guide therapy. We now have tools to measure transit accurately; results of transit tests often depend on the conditions selected for the test, so test results will match clinical expectations most closely when test conditions are selected to reproduce the circumstances for symptom production. This review describes the most commonly used methods for the measurement of GI transit including the gastric emptying test for some dyspeptic symptoms, small bowel transit test for dyspeptic symptoms and diarrhea, colonic transit test for constipation, and factors that influence the result of these studies. As we make progress in our understanding of the pathophysiology of transit disorders, the clinical usefulness of these diagnostic tests will be further enhanced.

Dilutions of low- vs. high-fat diets on intakes and gastric volumes in rats

Rats adapt to changes in dietary energy to maintain nearly constant energy intakes. This regulation indicates that animals sense and respond to nutrient content. We sought to determine whether this response was affected by the fat content of the diet. Our second goal was to determine how energy dilution affected intragastric volumes. Rats were randomized to high (18% w/w) and low fat (4.5% w/w) as the energy density of the diet was altered from 2.0 to 3.5 kcal/g. Average energy intake during 7-h feeds rose steeply (P<.01) when density was increased from 2.0 to 3.0 kcal/g, but modestly as density increased from 3.0 to 3.5 kcal/g. In other rats on 18% vs. 32% fat diets, energy intakes increased significantly (P<.01) as density of the diet was raised from 3.5 to 4.5 kcal/g. During diets at 2.0 and 2.5 kcal/g, animals on 18% fat ate fewer kilocalories than those on 4.5% fat; but over 3.0-4.5 kcal/g, energy intake was similar regardless of fat concentration (4.5-32%). Gastric contents after 7-h feeds increased with grams of food ingested similarly for high- and low-fat diets. We concluded that in rats: (a) compensation to energy dilution or concentration was inexact but (b) was about equal for high- vs. low-fat diets; thus, high fat was as well sensed as high carbohydrate; (c) compensations for energy densities were made despite varied gastric volumes; thus, rats learned to override the stimulus of gastric stretch and to sense energy via extra gastric mechanisms.

Drug, meal and formulation interactions influencing drug absorption after oral administration. Clinical implications

Drug-drug, drug-formulation and drug-meal interactions are of clinical concern for orally administered drugs that possess a narrow therapeutic index. This review presents the current status of information regarding interactions which may influence the gastrointestinal (GI) absorption of orally administered drugs. Absorption interactions have been classified on the basis of rate-limiting processes. These processes are put in the context of drug and formulation physicochemical properties and oral input influences on variable GI physiology. Interaction categorisation makes use of a biopharmaceutical classification system based on drug aqueous solubility and membrane permeability and their contributions towards absorption variability. Overlaying this classification it is important to be aware of the effect that the magnitudes of drug dosage and volume of fluid administration can have on interactions involving a solubility rate limits. GI regional differences in membrane permeability are fundamental to the rational development of extended release dosage forms as well as to predicting interaction effects on absorption from immediate release dosage forms. The effect of meals on the regional-dependent intestinal elimination of drugs and their involvement in drug absorption interactions is also discussed. Although the clinical significance of such interactions is certainly dependent on the narrowness of the drug therapeutic index, clinical aspects of absorption delays and therapeutic failures resulting from various interactions are also important.

Evaluation of solid phase radiolabels of dog food for gastric emptying

99mTc-Pertechnetate, 99mTc-mebrofenin, 99mTc-disofenin, 99mTc-sulfur colloid, and 99mTc-Dowex resin beads were evaluated for in vitro stability as a label for both dry extruded, and canned dog food for gastric emptying scintigraphy. A sample of each radiolabeled diet was added to water, gastric juice, intestinal juice, or gastric juice followed by intestinal juice for in vitro digestion. After a 3-hour digestion period, tubes were centrifuged and percentage solid phase retention (%SPR) was calculated. The experiment was repeated three times over a 14-day period to minimize day-to-day variation. For dry dog food, 99mTc-mebrofenin and 99mTc-disofenin had similar %SPR in water (96 and 93%, respectively) and gastric juice (>95% each) and were significantly higher than other labels. For canned dog food, mebrofenin had a 91% SPR for the water or gastric juice digestions, and 99mTc-Dowex had a %SPR of >99%. 99mTc-mebrofenin and 99mTc-Dowex were also tested in vivo, where 99mTc-Dowex had poor stability, and 99mTc-Mebrofenin had excellent stability. 99mTc-Mebrofenin is a suitable label for dog food for gastric emptying scintigraphy.

Effect of glucose supplementation on appetite and the pyloric motor response to intraduodenal glucose and lipid

The effects of different macronutrients on appetite and pyloric motility and the impact of short-term dietary glucose supplementation on these responses were evaluated. Ten males (aged 19-38 yr) received isocaloric (2.9 kcal/min) intraduodenal infusions of glucose and lipid while antropyloroduodenal motility and appetite were assessed by manometry and visual analog scales, respectively. Effects of each intraduodenal nutrient on appetite and motility were evaluated before and after 7 days of dietary supplementation with glucose (400 g daily). Initially, both nutrients caused a similar rise in pyloric tone, but intraduodenal lipid was a more potent stimulus of phasic pyloric motility (P = 0.05) and suppressed appetite more (P = 0.013) than intraduodenal glucose. After dietary glucose supplementation, the increase in pyloric tone during intraduodenal glucose was attenuated. Although intraduodenal lipid remained a more potent stimulant of phasic pyloric motility (P = 0.016), it no longer decreased appetite. We conclude that in healthy young males 1) intraduodenal infusion of lipid is a more potent stimulus of phasic pyloric motility and suppresses appetite more than intraduodenal glucose and 2) dietary glucose supplementation alters both the appetite suppressant effect of intraduodenal lipid and the pyloric motor response to intraduodenal glucose infusion.

Advances in nutrition and gastroenterology: summary of the 1997 A.S.P.E.N. Research Workshop

BACKGROUND

The 1997 A.S.P.E.N. Research Workshop was held at the annual meeting in San Francisco, on January 26, 1997. The workshop focused on advances in clinical and basic research involving the interface between nutrient and luminal gastroenterology.

METHODS

Presentations on the genetic regulation of gastrointestinal development, the molecular biology of small intestinal adaptation, the effect of nutrition support on intestinal mucosal mass, the relationship between nutrition and gastrointestinal motility, nutrient absorption, and gastrointestinal tract substrate metabolism were made by the preeminent leaders in the field.

RESULTS

The investigators presented an insightful analysis of each topic by reviewing data from their own laboratories and the published literature.

CONCLUSIONS

This workshop underscored the important interactions between nutrition and luminal gastroenterology at the basic science, metabolic/physiologic, and clinical levels. The integration of presentations from the different disciplines provided a unique interaction of information and ideas to advance our understanding of nutrition and gastrointestinal tract.

Intestinal transit and absorption of soy protein in dogs depend on load and degree of protein hydrolysis

Soy protein, in both intact and hydrolyzed forms, is widely used as the nitrogen source in infant and adult formulas. This protein is also consumed in vast quantities worldwide as soybean-based food products. Digestion is the rate-limiting step in the assimilation of proteins from the gut. As a result, intestinal transit must be slowed when a higher load of protein is available or when this nutrient is delivered in the intact rather than hydrolyzed form. However, little information is available on the effect of load and degree of hydrolysis of soy protein on intestinal transit and protein absorption. To test the hypothesis that inhibition of intestinal transit and protein absorption depend on the load of soy protein and the state of hydrolysis of this nutrient, we compared intestinal transit and protein absorption in dogs equipped with duodenal and midintestinal fistulas during intestinal perfusion with 0, 50, 100, or 200 g/L solutions of intact soy protein versus 0, 100, 200, 300, or 400 g/L solutions of hydrolyzed soy protein. We found that intestinal transit was slowed in a load-dependent fashion by intact (P < 0.001) and hydrolyzed (P < 0.05) soy protein. Soy protein inhibited intestinal transit more potently in the intact than hydrolyzed form (P < 0.05). A greater amount of protein was absorbed by the proximal half of the small intestine when soy protein was delivered in the hydrolyzed than intact form (P < 0.05), and the efficiency of protein absorption was maintained at a high and nearly constant level of 82.6 to 87.4% for intact soy protein and 89.0 to 92.3% for hydrolyzed soy protein. We conclude that in dogs intestinal transit and absorption of soy protein depend on the load and the degree of protein hydrolysis.

Gastric emptying of oil from solid and liquid meals. Effect of human pancreatic insufficiency

Digestion of fat in pancreatic insufficiency (PI) is strongly affected by how rapidly fat enters the duodenum. We postulated that: (1) oil empties faster in PI than in normals and (2) in both, it empties in a load-dependent fashion. We used a gamma camera to test these ideas by comparing gastric emptying of iodine-123 iodinated oil in normal and pancreatic-insufficient subjects after 15 g of free oil were ingested in a small spaghetti meal and 60 g of oil were ingested in a large spaghetti meal and in a milk emulsion. Indium-113m marked gastric emptying of water in the milk. In both groups after all meals, oil emptied fastest initially, slowing later; and oil emptied three to four times faster when 60 g vs 15 g were ingested. There were no significant differences between the groups of subjects with respect to gastric emptying of the spaghetti meals, but the pancreatic-insufficient subjects emptied both oil and water faster from the milk emulsion than did the normal subjects. The slower emptying of oil in the normal subjects was associated with significantly more layering of oil to the top of the intragastric milk emulsion.

Jejunal brake: inhibition of intestinal transit by fat in the proximal small intestine

Optimal absorption of fat requires adequate time of contact with the absorptive sites of the small intestine. In order to prevent steatorrhea, intestinal transit must be slowed in response to the fat that has emptied into the small intestine. Intestinal transit is known to be inhibited by fat in the ileum via the ileal brake. This response has suggested that the regulation of intestinal transit is a function of the distal small intestine. However, clinical observations suggest that the ileal brake is not the only control mechanism for intestinal transit. In short bowel patients with resection of the ileum, the proportion of fecal fat recovery remained constant even after the fat intake was increased threefold. In these patients, optimal fat absorption based on the slowing of intestinal transit must have been triggered by an inhibitory mechanism located outside of the distal small intestine. To test the hypothesis that fat in the proximal small intestine inhibited intestinal transit, we compared intestinal transit during perfusion of the proximal half of the small intestine with 0 (buffer only), 15, 30, or 60 mM oleate in dogs equipped with duodenal and mid-intestinal fistula. Intestinal transit across a 150-cm test segment (between fistulas) was measured by counting for the recovery of a radioactive marker in the output of the mid-intestinal fistula during the last 30 min of a 90-min perfusion. We found that oleate inhibited intestinal transit in a load-dependent fashion (P < 0.005). Specifically, while the mean cumulative recovery of the transit marker was 95.5% during buffer perfusion, the recovery decreased when 15 mM (64.3%), 30 mM o(54.7%), or 60 mM oleate (38.7%) was perfused into the proximal half of the small intestine. We conclude that fat in the proximal small intestine inhibits intestinal transit as the jejunal brake.

Delayed gastroduodenal emptying is an important mechanism for control of intestinal transit in short-gut syndrome

PURPOSE

To understand the relative importance of changes in ileal smooth muscle contractility versus alteration of intestinal flow rate as control mechanisms for regulating intestinal transit in a surgical model of short-gut syndrome.

METHODS

A model of short-gut syndrome was created by performing a 70% proximal small-bowel resection in dogs. Ten control and 6 animals with short-gut syndrome were instrumented with strain gauge transducers, steel collection cannulas, and a Silastic intraluminal infusion catheter in the midileum. Motor activity was analyzed by computer programs that determine frequency, amplitude, and propagation behavior of postprandial contractions. Perfusions of 14C-polyethylene glycol and bolus injection of 3H-polyethylene glycol were used to determine intestinal flow and transit rates. Total gastroduodenal emptying was determined using a 14C-polyethylene glycol-labelled meal.

RESULTS

Postprandial contraction frequency was decreased in animals with short-gut syndrome, but other significant changes in amplitude, mean area, and propagation behavior of postprandial ileal contractions were not seen. Gastroduodenal emptying and mean intestinal flow rates were markedly slower in animals with short-gut syndrome, as were intestinal transit rates.

CONCLUSIONS

In this model of short-gut syndrome, the major adaptive change is decreased intestinal flow rate, related to delayed gastroduodenal emptying. The spatial organization of ileal contractions does not change substantially aside from a change in frequency which can be accounted for by transection of the intestinal wall.

Detection of hepatitis D virus RNA in serum by a reverse transcription, polymerase chain reaction-based assay

We designed a reverse transcription, polymerase chain reaction-based assay for serum hepatitis D virus RNA. Amplified hepatitis D virus cDNA was revealed by ethidium bromide staining, followed by blotting onto a nylon membrane and hybridization with a 32phosphorus-labelled oligonucleotide, or by a DNA enzyme immunoassay (DEIA) using a double stranded DNA-specific monoclonal antibody. The absolute sensitivity was expressed as number of hepatitis D virus RNA molecules, using a serum of known viral RNA concentration. Three sets of primers were used, encompassing the base positions 66-686 (variable rod-stabilizing region), 701-962 (conserved, viroid-like domain) and 886-1,333 (portion of the open reading frame 5 encoding for the carboxyterminus of the hepatitis D antigen) of the viral genome. The lower detection limits, after amplification of the three RNA portions, as assessed by ethidium bromide staining, were 7.5 x 10(6), 7.5 x 10(4) and 7.5 x 10(2) molecules of hepatitis D virus RNA per assay, respectively. The region encompassing bases 886-1,333 was chosen for blotting and hybridization to a radiolabelled oligonucleotide probe or for a capture-based DNA enzyme immunoassay, where the microplate was coated with this same probe. The two procedures showed comparable sensitivity, i.e., about 10 molecules of viral RNA per assay. The specificity of the assay was further on a panel of both anti-hepatitis D-positive and -negative sera. Amplification of serum hepatitis D virus RNA by reverse transcription/polymerase chain reaction followed by detection of the amplified cDNA by DNA enzyme immunoassay is a promising and feasible routine assay for detecting low amounts of circulating virions.

Hepatitis delta virus RNA in serum of patients with chronic delta hepatitis

We studied 28 patients with chronic delta hepatitis for the presence of hepatitis delta virus (HDV) RNA in serum. The hot start polymerase chain reaction (PCR) method, in which the reaction begins at 60-80 degrees C, showed a higher sensitivity than conventional PCR reaction. Additionally, the presence of hepatitis B (HBV) and C virus (HCV) infections were determined by PCR. HDV RNA was detected in 26 patients (93%), HBV DNA in 22 (79%), and HCV RNA in only one. Detection of HDV RNA correlated very well with detection of hepatitis delta antigen by immunostaining in the liver. In six patients HDV RNA was detectable despite the absence of HBV DNA in serum, suggesting that high levels of HBV are not required for HDV replication. Of 29 control patients with chronic hepatitis B without antibody to HDV, none had detectable HDV RNA, while all had HBV DNA in serum. Detection of HDV RNA with PCR proved highly sensitive and specific, demonstrating that virtually all patients with chronic HDV infection had ongoing viral replication.

Disproportionate ileal digestion on canine food consumption. A possible model for satiety in pancreatic insufficiency

In animals, ileal sensors of nutrients signal satiety more potently than similar sensors in jejunum. We postulated that inadequate food intake and weight loss in human pancreatic insufficiency might arise by the displacement of digestion to ileum, where excessive release of digestive products would enhance satiety. To test this idea, we studied dogs prepared with pancreatic fistulas, which allowed reversible switching of pancreatic juice from entry at duodenum to entry at mid-small intestine. Dogs were studied in a crossover design over successive eight-day periods. Food consumption and body weight were measured while the dogs had continuous access to food. Diversion of pancreatic juice to mid-intestine significantly (P < 0.01) depressed food intake by an average of 28%. Diversion also significantly (P < 0.01) reduced body weight. The findings support the idea that insufficient food intake in human pancreatic insufficiency may result from stimulation of ileal satiety mechanisms.

Erythromycin accelerates solid emptying at the expense of gastric sieving

Erythromycin accelerates gastric emptying by inducing antral contractions similar to phase III of interdigestive MMC. These powerful contractions are capable of forcing coin-sized indigestibles out of the stomach. In contrast, fed motility is associated with submaximal contractions that fragment (trituration) and propel solids while retaining large (> 0.5 mm) pieces for further size reduction (gastric sieving). In this study, using dogs with duodenal fistulas, we tested the hypothesis that erythromycin-induced acceleration of gastric emptying resulted in the passage of inadequately triturated (> 0.05 mm) chunks of solids into the duodenum. We found that gastric emptying was accelerated by erythromycin (vs 0.15 M NaCl control, P < 0.05). However, the percentage of chyme collected in the > 0.5-mm fraction was much greater (P < 0.01) in the erythromycin-treated experiments (63 +/- 9%) than the controls (7 +/- 1%). Correspondingly, while a fine gruel was passed during controls, under erythromycin infusion, most of the solids were emptied as large chunks virtually unchanged from the swallowed pieces. We conclude that erythromycin accelerates gastric emptying at the expense of gastric sieving.

Sustained slowing effect of lentils on gastric emptying of solids in humans and dogs

The distal small intestine is an especially potent site for carbohydrate-triggered intestinal inhibition of gastric emptying of solids. Poorly digestible carbohydrates, such as lentils, may escape proximal absorption, travel over time to reach these inhibitory mechanisms, and slow the gastric emptying of a later meal. A slowing effect on gastric emptying may be associated with a lowering effect on postprandial glucose. The aims of this study were to determine (a) whether lentils (a poorly digestible carbohydrate) vs. bread (an easily digestible carbohydrate) eaten as a premeal (with equal amounts of carbohydrates) slow the gastric emptying of a second solid meal taken 4.0-4.5 hours later and (b) whether a slowing effect on the gastric emptying of the second meal is associated with a lower postprandial glucose response. We found that in 7 dogs and 10 humans, gastric emptying of the second meal was delayed after a lentil premeal compared with a bread premeal. However, there was no difference in the glucose response to the second meal under the two conditions.