Simultaneous assessment of gastric emptying and secretion in rats by a novel computed tomography-based method

Purgative/laxative actions of Globularia alypum aqueous extract on gastrointestinal-physiological function and against loperamide-induced constipation coupled to oxidative stress and inflammation in rats

BACKGROUND

Chronic constipation is a gastrointestinal functional disorder which affects patient quality of life. Therefore, many studies were oriented to search herbal laxative agents. In this study, we investigated the effect of Globularia alypum L. leaves aqueous extract (GAAE) against loperamide (LOP)-produced constipation.

METHODS

Animals were given LOP (3 mg/kg, b.w., i.p.) and GAAE (100, 200, and 400 mg/kg, b.w., p.o.) or yohimbine (2 mg/kg, b.w., i.p.), simultaneously, for 1 week. Gastric-emptying test and intestinal transit were determined. Colon histology was examined, and oxidative status was evaluated using biochemical-colorimetric methods.

KEY RESULTS

GAAE ameliorates significantly gastric emptying (64% to 76.5%) and intestinal transit (66.65% to 84.73%). LOP negatively influenced defecation parameters and generated a stress situation. GAAE administration in contrast ameliorated those parameters and re-established oxidative balance.

CONCLUSION

GAAE showed a modest action against oxidative stress and decreased LOP effect and thereby can be considered a pharmacological agent in constipation.

Vagus nerve stimulation promotes gastric emptying by increasing pyloric opening measured with magnetic resonance imaging

BACKGROUND

Vagus nerve stimulation (VNS) is an emerging electroceutical therapy for remedying gastric disorders that are poorly managed by pharmacological treatments and/or dietary changes. Such therapy seems promising as the vagovagal neurocircuitry modulates the enteric nervous system to influence gastric functions.

METHODS

Here, the modulatory effects of left cervical VNS on gastric emptying in rats were quantified using a (i) feeding protocol in which the animal voluntarily consumed a postfast, gadolinium-labeled meal and (ii) a non-invasive imaging method to measure antral motility, pyloric activity and gastric emptying based on contrast-enhanced magnetic resonance imaging (MRI) and computer-assisted image processing pipelines.

KEY RESULTS

Vagus nerve stimulation significantly accelerated gastric emptying (sham vs VNS: 29.1% ± 1.5% vs 40.7% ± 3.9% of meal emptied per 4 hours), caused a greater relaxation of the pyloric sphincter (sham vs VNS: 1.5 ± 0.1 vs 2.6 ± 0.4 mm² cross-sectional area of lumen), and increased antral contraction amplitude (sham vs VNS: 23.3% ± 3.0% vs 32.5% ± 3.0% occlusion), peristaltic velocity (sham vs VNS: 0.50 ± 0.02 vs 0.67 ± 0.03 mm s^-1 ), but not its contraction frequency (sham vs VNS: 6.1 ± 0.2 vs 6.4 ± 0.2 contractions per minute, P = .22). The degree to which VNS relaxed the pylorus was positively correlated with gastric emptying rate (r = .5887, P < .001).

CONCLUSIONS & INFERENCES

The MRI protocol employed in this study is expected to enable advanced preclinical studies to understand stomach pathophysiology and its therapeutics. Results from this study suggest an electroceutical treatment approach for gastric emptying disorders using cervical VNS to control the degree of pyloric sphincter relaxation.

Contrast-Enhanced Magnetic Resonance Imaging of Gastric Emptying and Motility in Rats

The assessment of gastric emptying and motility in humans and animals typically requires radioactive imaging or invasive measurements. Here, we developed a robust strategy to image and characterize gastric emptying and motility in rats based on contrast-enhanced magnetic resonance imaging (MRI) and computer-assisted image processing. The animals were trained to naturally consume a gadolinium-labeled dietgel while bypassing any need for oral gavage. Following this test meal, the animals were scanned under low-dose anesthesia for high-resolution T1-weighted MRI in 7 Tesla, visualizing the time-varying distribution of the meal with greatly enhanced contrast against non-gastrointestinal (GI) tissues. Such contrast-enhanced images not only depicted the gastric anatomy, but also captured and quantified stomach emptying, intestinal filling, antral contraction, and intestinal absorption with fully automated image processing. Over four postingestion hours, the stomach emptied by 27%, largely attributed to the emptying of the forestomach rather than the corpus and the antrum, and most notable during the first 30 min. Stomach emptying was accompanied by intestinal filling for the first 2 h, whereas afterward intestinal absorption was observable as cumulative contrast enhancement in the renal medulla. The antral contraction was captured as a peristaltic wave propagating from the proximal to distal antrum. The frequency, velocity, and amplitude of the antral contraction were on average 6.34 ± 0.07 contractions per minute, 0.67 ± 0.01 mm/s, and 30.58 ± 1.03%, respectively. These results demonstrate an optimized MRI-based strategy to assess gastric emptying and motility in healthy rats, paving the way for using this technique to understand GI diseases, or test new therapeutics in rat models.The assessment of gastric emptying and motility in humans and animals typically requires radioactive imaging or invasive measurements. Here, we developed a robust strategy to image and characterize gastric emptying and motility in rats based on contrast-enhanced magnetic resonance imaging (MRI) and computer-assisted image processing. The animals were trained to naturally consume a gadolinium-labeled dietgel while bypassing any need for oral gavage. Following this test meal, the animals were scanned under low-dose anesthesia for high-resolution T1-weighted MRI in 7 Tesla, visualizing the time-varying distribution of the meal with greatly enhanced contrast against non-gastrointestinal (GI) tissues. Such contrast-enhanced images not only depicted the gastric anatomy, but also captured and quantified stomach emptying, intestinal filling, antral contraction, and intestinal absorption with fully automated image processing. Over four postingestion hours, the stomach emptied by 27%, largely attributed to the emptying of the forestomach rather than the corpus and the antrum, and most notable during the first 30 min. Stomach emptying was accompanied by intestinal filling for the first 2 h, whereas afterward intestinal absorption was observable as cumulative contrast enhancement in the renal medulla. The antral contraction was captured as a peristaltic wave propagating from the proximal to distal antrum. The frequency, velocity, and amplitude of the antral contraction were on average 6.34 ± 0.07 contractions per minute, 0.67 ± 0.01 mm/s, and 30.58 ± 1.03%, respectively. These results demonstrate an optimized MRI-based strategy to assess gastric emptying and motility in healthy rats, paving the way for using this technique to understand GI diseases, or test new therapeutics in rat models.

Expression and regulation of the neutral amino acid transporter B0AT1 in rat small intestine

Absorption of neutral amino acids across the luminal membrane of intestinal enterocytes is mediated by the broad neutral amino acid transporter B0AT1 (SLC6A19). Its intestinal expression depends on co-expression of the membrane-anchored peptidase angiotensin converting enzyme 2 (ACE2) and is additionally enhanced by aminopeptidase N (CD13). We investigated in this study the expression of B0AT1 and its auxiliary peptidases as well as its transport function along the rat small intestine. Additionally, we tested its possible short- and long-term regulation by dietary proteins and amino acids. We showed by immunofluorescence that B0AT1, ACE2 and CD13 co-localize on the luminal membrane of small intestinal villi and by Western blotting that their protein expression increases in distal direction. Furthermore, we observed an elevated transport activity of the neutral amino acid L-isoleucine during the nocturnal active phase compared to the inactive one. Gastric emptying was delayed by intragastric application of an amino acid cocktail but we observed no acute dietary regulation of B0AT1 protein expression and L-isoleucine transport. Investigation of the chronic dietary regulation of B0AT1, ACE2 and CD13 by different diets revealed an increased B0AT1 protein expression under amino acid-supplemented diet in the proximal section but not in the distal one and for ACE2 protein expression a reverse localization of the effect. Dietary regulation for CD13 protein expression was not as distinct as for the two other proteins. Ring uptake experiments showed a tendency for increased L-isoleucine uptake under amino acid-supplemented diet and in vivo L-isoleucine absorption was more efficient under high protein and amino acid-supplemented diet. Additionally, plasma levels of branched-chain amino acids were elevated under high protein and amino acid diet. Taken together, our experiments did not reveal an acute amino acid-induced regulation of B0AT1 but revealed a chronic dietary adaptation mainly restricted to the proximal segment of the small intestine.

A high-throughput assay for quantifying appetite and digestive dynamics

Food intake and digestion are vital functions, and their dysregulation is fundamental for many human diseases. Current methods do not support their dynamic quantification on large scales in unrestrained vertebrates. Here, we combine an infrared macroscope with fluorescently labeled food to quantify feeding behavior and intestinal nutrient metabolism with high temporal resolution, sensitivity, and throughput in naturally behaving zebrafish larvae. Using this method and rate-based modeling, we demonstrate that zebrafish larvae match nutrient intake to their bodily demand and that larvae adjust their digestion rate, according to the ingested meal size. Such adaptive feedback mechanisms make this model system amenable to identify potential chemical modulators. As proof of concept, we demonstrate that nicotine, l-lysine, ghrelin, and insulin have analogous impact on food intake as in mammals. Consequently, the method presented here will promote large-scale translational research of food intake and digestive function in a naturally behaving vertebrate.

In vivo ultrasound assessment of gastric emptying in newborn mice

OBJECTIVES

The aim of the present study was to develop an ultrasonographic approach to comparatively assess gastric emptying in newborn wild-type and guanosine triphosphate cyclohydrolase knockout hph-1 mice, because we previously reported gastroparesis early in life in this strain.

METHODS

Stomach transverse, anteroposterior, and longitudinal ultrasonographic measurements were obtained with a 40-MHz transducer in pups immediately after maternal separation and 4 hours later. A conventional equation was used and the predicted values validated by obtaining postmortem gastric content volume measurements. Wild-type and hph-1 mice gastric emptying rates were comparatively evaluated at 1 to 3 and 5 to 8 days of age, respectively.

RESULTS

The ultrasound equation closely predicted the newborn stomach content volumes with a correlation coefficient (R) of 0.93 and 0.81 (P < 0.01) for measurements obtained on full stomach and after 4 hours of fasting, respectively. In wild-type mice, gastric emptying was age dependent and associated with a greater residual volume at 1 to 3 days (65% ± 7%), as compared with 5- to 8-day-old pups (33% ± 4%; P  < 0.01), after fasting. In contrast, an equal duration of fasting resulted in a significantly greater residual gastric content volume in 5- to 8-day-old hph-1 mice (68%  ± 7%; P < 0.01), as compared with same-age wild-type mice.

CONCLUSIONS

Ultrasonography offers a sensitive and accurate estimate of gastric content volume in newborn mice. In wild-type newborn mice, gastric emptying rate is age dependent and significantly reduced in the immediate postnatal period. The newborn hph-1 mice have a significantly higher gastric residual volume, as compared with wild-type same-age animals.

Novel antidiabetic nutrients identified by in vivo screening for gastric secretion and emptying regulation in rats

Diabetes mellitus is a disease characterized by elevated blood glucose levels and represents a worldwide health issue. Postprandial hyperglycemia is considered a major predictor of diabetic complications, and its reduction represents a specific treatment target in Type 1 and 2 diabetes. Since postprandial glucose excursions depend to a large extent on gastric secretion and emptying, amylin and glucagon-like peptide 1 analogs are prescribed to reduce them. Although gastric function is considered mainly sensitive to ingested calories, its chemospecificity is not well understood. To identify ingestible nutrients reducing postprandial hyperglycemia, we applied intragastrically more than 40 individual nutrients at an isomolar dose to rats and quantified their impact on gastric secretion and emptying using a novel in vivo computed tomography imaging method. We identified l-tryptophan, l-arginine, l-cysteine, and l-lysine as the most potent modulators with effective strength comparable to a supraphysiological dose of amylin. Importantly, all identified candidates reduced postprandial glucose excursion within an oral glucose tolerance test in healthy and diabetic rats. This clinical beneficial effect originated predominantly from their impact on gastric function, as none of the candidates altered plasma glucose concentrations induced by intraperitoneal or intraduodenal glucose tolerance tests. Overall, these data demonstrate a remarkable chemospecificity of stomach function, unveil a strong role of the stomach for glycemic control and identifies nutrients with antidiabetic potential.

L-lysine dose dependently delays gastric emptying and increases intestinal fluid volume in humans and rats

BACKGROUND

Novel sensory inputs for the control of food intake and gastrointestinal (GI) function are of increasing interest due to the rapid increase in nutrition-related diseases. The essential amino acid L-lysine was demonstrated to have a selective impact on food intake, gastric emptying, and intestinal transit in rats, thus indicating a potential novel direct sensory input to assess dietary protein content and quality. The aim of this study was to assess translational aspects of this finding and to investigate the dose-dependent effect of L-lysine on human and rat GI function.

METHODS

L-lysine doses from 0-800 mg in rats and 0.5-7.5 g in humans were analyzed for their effect on gastric emptying and GI secretion. Human GI function was assessed non-invasively using magnetic resonance imaging (MRI), rat data were acquired using standard lethal measurement methods. L-lysine dose dependently delayed gastric emptying and stimulated GI secretion in rats as reflected by residual phenol red content and increased gastric wet weight.

KEY RESULTS

The dose-dependent delay in gastric emptying observed in rats was confirmed in humans with an increase in halftime of gastric emptying of 4 min/g L-lysine, p < 0.01. Moreover, a dose-dependent increase in intestinal fluid accumulation was observed (0.4 mL/min/g L-lysine, p < 0.0001). No effect on alkaline tide, glucose concentration, hematocrit, or visceral sensations was detected.

CONCLUSIONS & INFERENCES

This translational study demonstrates comparable dose-dependent effects of intragastric L-lysine on GI function in humans and rats and suggests a broader role for individual amino acids in the control of GI motility and secretion in vivo.