Simple and Noninvasive Breath Test Using 13C-Acetic Acid to Evaluate Gastric Emptying in Conscious Rats and Its Validation by Metoclopramide

Effect of Chronic Ethanol Consumption on Exogenous Glucose Metabolism in Rats Using [1-13C], [2-13C], and [3-13C]glucose Breath Tests

The C3 carbon of glucose molecules becomes the C1 carbon of pyruvate molecules during glycolysis, and the C1 and C2 carbons of glucose molecules are metabolized in the tricarboxylic acid (TCA) cycle. Utilizing this position-dependent metabolism of C atoms in glucose molecules, [1-13C], [2-13C], and [3-13C]glucose breath tests are used to evaluate glucose metabolism. However, the effects of chronic ethanol consumption remain incompletely understood. Therefore, we evaluated glucose metabolism in ethanol-fed rats using [1-13C], [2-13C], and [3-13C]glucose breath tests. Ethanol-fed (ERs) and control rats (CRs) (n = 8 each) were used in this study, and ERs were prepared by replacing drinking water with a 16% ethanol solution. We administered 100 mg/kg of [1-13C], [2-13C], or [3-13C]glucose to rats and collected expired air (at 10-min intervals for 180 min). We compared the 13CO2 levels (Δ13CO2, ‰) of breath measured by IR isotope ratio spectrometry and area under the curve (AUC) values of the 13CO2 levels-time curve between ERs and CRs. 13CO2 levels and AUCs after administration of [1-13C]glucose and [2-13C]glucose were lower in ERs than in CRs. Conversely, the AUC for the [3-13C]glucose breath test showed no significant differences between ERs and CRs, although 13CO2 levels during the 110-120 min interval were significantly high in ERs. These findings indicate that chronic ethanol consumption diminishes glucose oxidation without concomitantly reducing glycolysis. Our study demonstrates the utility of 13C-labeled glucose breath tests as noninvasive and repeatable methods for evaluating glucose metabolism in various subjects, including those with alcoholism or diabetes.

Preparation of [1'-13 C]citric acid as a probe in a breath test to evaluate tricarboxylic acid cycle flux

[1'-13 C]Citric acid (1) was efficiently prepared from dimethyl 1,3-acetonedicarboxylate in two steps as a probe for a breath test. The synthetic method was selected because of the yield and reproducibility. Compound 1 was orally administrated to rats, and the time course of the increase of 13 CO2 /12 CO2 ratios (Δ13 CO2 ) in their breath was successfully followed, indicating the metabolism of 1. Thus, the 13 C-breath test using 1 is a promising method to evaluate tricarboxylic acid (TCA) cycle flux.

Effects of ethanol and sex on propionate metabolism evaluated via a faster 13C-propionate breath test in rats

BACKGROUND

Alcoholism is regarded as a risk factor for vitamin B₁₂ (VB₁₂) deficiency. Because VB₁₂ serves as a coenzyme of methylmalonyl-CoA mutase, a key enzyme in propionate metabolism, the ¹³C-propionate breath test (PBT) has been studied as a non-invasive diagnostic modality for VB₁₂ deficiency. However, the conventional PBT requires 2 h, which is inconvenient in clinical practice. We hypothesized that a faster PBT can be used to evaluate propionate metabolism and is more easily adaptable for clinical practice.

AIM

To evaluate a faster PBT for assessing the effects of long-term ethanol consumption on propionate metabolism in ethanol-fed rats (ERs).

METHODS

ERs were obtained by replacing standard drinking water (for control rats, CRs) with 16% ethanol solution in descendants of F344/DuCrj rats. Faster PBT was performed by administering ¹³C-propionate aqueous solution to male and female ERs and CRs by inserting a metal tubule from the mouth to the stomach; exhaled gas was collected in a bag to measure its ¹³CO₂/¹²CO₂ isotope ratio via infrared isotope spectrometry. Serum VB₁₂ and alanine transaminase (ALT) levels were measured via chemiluminescence immunoassay and the lactate dehydrogenase-ultraviolet method, respectively. We evaluated statistical differences in mean body weight, change in ¹³CO₂ (Δ¹³CO₂‰), peak Δ¹³CO₂‰, and serum VB₁₂ and ALT, between males and females and between ERs and CRs using the t-test and Mann-Whitney U test for normally and non-normally distributed variables, respectively.

RESULTS

Males weighed significantly more than females (P < 0.001); CRs weighed significantly more than ERs (P < 0.008). Δ¹³CO₂ reached a peak (C_max) at 20 min and 30 min in females and males, respectively, decreasing after 20-30 min without rebound in all groups. Males had significantly higher C_max and Δ¹³CO₂ at 15-45 min than females (P < 0.05; for all pairs). Propionate metabolism was enhanced in male ERs relative to male CRs, whereas metabolism did not differ markedly between ERs and CRs for females. Males had higher serum VB₁₂ levels than females, without prominent differences between the ER and CR groups. Male CRs had notably higher ALT levels than male ERs. Thus, chronic ethanol consumption may trigger fatty acid production via intestinal bacteria and changes in gut microbiome composition.

CONCLUSION

Faster PBT shows that 16% ethanol consumption promotes propionate metabolism without inducing liver injury. This PBT may be used clinically to evaluate gut flora status.

Effect of Acid Suppressants on Non–Helicobacter pylori Helicobacters Within Parietal Cells

We investigated the effect of increased pH induced by acid suppressants on the viability of non–Helicobacter pylori helicobacters (NHPHs) within parietal cell intracellular canaliculi and fundic glandular lumina by immunohistochemistry, electron microscopy, quantitative PCR, urea breath tests, and using a bilayer culture system. Three months before the experiment, mice were infected with the NHPH H. suis and then treated with famotidine (2 mg/kg body weight [BW], once daily), lansoprazole (30 mg/kg BW, once daily), or vonoprazan (20 mg/kg BW, once daily) for 3 days. Immunohistochemical studies using the TUNEL method, quantitative PCR analysis, and urea breath tests were performed. PCR analysis showed a decrease in the NHPH quantity after vonoprazan treatment. Urea breath tests revealed a significant decrease in the NHPH urease activity after vonoprazan, lansoprazole, and famotidine treatments for 3 days; however, 4 days after the treatment, urease activity reversed to the pretreatment level for each treatment group. Electron microscopy revealed an increase in the damaged NHPH after vonoprazan treatment. The TUNEL method revealed apoptotic NHPH within parietal cells after vonoprazan treatment. The bilayer culture results demonstrated that NHPH moved more quickly at a pH of 4.0 than at a pH of 3.0, 5.0, and 6.5, and electron microscopy revealed a change from the spiral form to the coccoid form under near-neutral pH conditions. We thus proposed that acid suppressants, especially vonoprazan, induce NHPH damage by altering pH.

Hangekobokuto, a traditional Japanese herbal medicine, ameliorates postoperative ileus through its anti-inflammatory action

Background/Aims: Gastroprokinetic agents are used for patients with postoperative ileus (POI), and the Japanese traditional herbal medicine daikenchuto (DKT) is one such agent used in the clinical setting. POI is caused by inflammation. DKT and rikkunshito have anti-inflammatory abilities in addition to their gastroprokinetic effects. The efficacy of Kampo formulations, including hangekobokuto (HKT), in patients with POI has been reported recently. Several authors have described the efficacy of honokiol, the primary component of Magnoliae Cortex, in HKT in mouse models of POI. We therefore analyzed the effect of HKT on POI model mice to determine the similarities in the mechanism of action between HKT and DKT.

Methods: HKT was administered orally to each mouse before and after intestinal manipulation was performed on the distal ileum. The gastrointestinal transit in vivo, leukocyte infiltration, and levels of inflammatory mediators, such as cytokines and chemokines, were analyzed.

Results: HKT significantly inhibited the infiltration of neutrophils and macrophages and led to the recovery of delayed intestinal transit. In addition, it significantly decreased inducible nitric oxide synthase (iNOS) as well as honokiol levels, suggesting anti-inflammatory activity. However, it did not inhibit the increase in levels of interleukin (IL)-1beta and IL-6, which are related to iNOS induction. In contrast, HKT increased levels of nerve growth factor (NGF) and suppressed those of nuclear factor-κB (NFκB), which are related to iNOS induction, suggesting the possibility of a neuronal anti-inflammatory mechanism.

Conclusions: HKT exerted a POI-relieving effect similar to DKT in a murine POI model, and findings suggest that it may exert its anti-inflammatory activity through NGF.

The rodent model of impaired gastric motility induced by allyl isothiocyanate, a pungent ingredient of wasabi, to evaluate therapeutic agents for functional dyspepsia

Functional dyspepsia (FD) is thought to be mainly based on gastric motility dysfunction and chronic hypersensitivity, yet FD animal models has been reported a few. We studied to establish the mouse model of impaired gastric motility induced by a pungent ingredient of wasabi allyl isothiocyanate (AITC), which is reliable to evaluate prokinetic agents. Male ddY mice were used. Gastric motility was measured by 13C-acetic acid breath test in conscious mice. AITC (80 mM) was given 60 min before the measurement of motility. Prokinetic agents including itopride (30, 100 mg/kg), mosapride (0.1-1 mg/kg), neostigmine (30 μg/kg), acotiamide (10-100 mg/kg), and daikenchuto (100-1000 mg/kg) were given 40 min before the measurement. AITC impaired gastric motility without mucosal damages, which reverted 24 h after AITC treatment. The decreased motility induced by AITC was restored by prokinetic agents such as itopride, mosapride, neostigmine, and acotiamide. In separate experiment, daikenchuto recovered the decreased motility induced by AITC, although daikenchuto had no effect on motility in normal condition. In conclusion, it is considered that the AITC-induced impaired gastric motility mouse model is useful to develop new prokinetic agents for treatment of FD, and to re-evaluate traditional Japanese herbal medicines.

pH-dependent ileocolonic drug delivery, part II: preclinical evaluation of novel drugs and novel excipients

Novel drugs and novel excipients in pH-dependent ileocolonic drug delivery systems have to be tested in animals. Which animal species are suitable and what in vivo methods are used to verify ileocolonic drug delivery?

Evaluation of Protein Requirements Using the Indicator Amino Acid Oxidation Method

The indicator amino acid oxidation (IAAO) method is a novel method for determining protein requirements. Recently, the protein requirement of healthy young men was reevaluated using this method, and the currently recommended protein requirement based on nitrogen balance study was found to be deficient. Similarly, with respect to experimental animals, the protein concentration used widely in the experimental diets was assumed to be deficient. However, only a few studies have tested the IAAO method in experimental animals. In particular, there are no studies on the protein requirement of adult rats measured using this method. Therefore, we applied the IAAO method to adult rats, to determine their casein protein requirement. Male Wistar/ST rats (15-18 wk old, housed in lighting (lights on from 23:00 to 11:00) conditions) were provided with the test diet including graded casein (5, 7, 9, 13, 17, 21 and 25%) every 2 h from 11:00 to 17:00. Tracer administration of ¹³C-phenylalanine was performed hourly from 14:00 to 17:00. Breath ¹³CO₂ was measured every 30 min after the first tracer administration. There were significant differences between the ¹³CO₂ concentration of the 5% and 17% casein groups at 17:00 and 18:00 (p<0.05). The mean casein protein requirement and recommended dietary allowance (RDA) were estimated to be 5.2 g/kg BW/d and 7.0 g/kg BW/d using the mixed-effect change point regression model, respectively. Our results indicated that the recommended casein value may be slightly deficient to satisfy the protein metabolic demand of some adult rats.

Coexistence of Alterations of Gastrointestinal Function and Mechanical Allodynia in the Reserpine-Induced Animal Model of Fibromyalgia

BACKGROUND

Fibromyalgia (FM) is a disorder characterized by widespread chronic pain as core symptom and a broad range of comorbidities. Despite the prevalence of gastrointestinal (GI) comorbidities in patients with FM, GI functions have rarely been investigated in animal models of FM.

AIMS

The purpose of the present study is to investigate the coexistence of alterations of GI function in the reserpine-induced myalgia (RIM) rat, a validated FM model associated with disruption of monoamine system.

METHODS

Paw withdrawal threshold (von Frey hair test) was assessed as pain-associated indicator. Gastric emptying (¹³C breath test), small intestinal transit (charcoal meal test), and fecal water content were investigated as GI functions.

RESULTS

The specific regimen of reserpine for the RIM rat, i.e., 1 mg/kg s.c., once daily for three consecutive days, caused a reduction of paw withdrawal threshold (i.e., mechanical allodynia) on days 3, 5, and 7 after the first injection. The ¹³CO₂ excreted from the RIM rat was significantly increased on day 7. The RIM rat exhibited an acceleration of small intestinal transit on day 5. Fecal water content collected from the RIM rat was significantly increased on days 3 and 5. The amount of noradrenaline was significantly decreased in GI tissues on days 3, 5, and 7 in the RIM rat. Conclusions This study revealed that accelerated gastric emptying, accelerated small intestinal transit, and increase in fecal water content coexist with mechanical allodynia in the RIM rat, simulating the coexistence of chronic pain and alterations of GI function in patients with FM.

13C-Acetic Acid Breath Test Monitoring of Gastric Emptying during Disease Progression in Diabetic Rats

Gastric motility disturbance is commonly found in long-standing hyperglycemia. Both delayed and rapid gastric emptying has been reported in diabetes. However, very few studies have followed the changes in gastric emptying during disease progression in diabetes because of technical limitations. ¹³C-Acetic acid breath test is a validated method which is non-invasive and can be used repeatedly or serially to evaluate gastric emptying changes in animal. We investigated the gastric emptying changes in different stages of diabetes using ¹³C-acetic acid breath test, as well as its related mechanisms involving interstitial cells of Cajal (ICCs), and stem cell factor (SCF) in streptozotocin-induced diabetic rats. The results showed that gastric emptying was accelerated at the early stage (12 weeks of diabetes) whereas intramuscular ICCs (ICC-IM) networks were not different from normal group. At long-term stage (28 weeks of diabetes), gastric emptying had returned to normal pattern with no delayed. ICC-IM networks were decreased in the diabetic group compared to 12th weeks, and were lower than in the normal group at the same time point. SCF levels were constantly high in the diabetic group than in the normal group. This result indicated that ¹³C-acetic acid breath test is useful to track the alteration in gastric emptying during disease progression. The change of gastric emptying was not found to be significantly associated with ICC-IM. Elevated SCF may help to preserve ICC-IM, especially in the early phase of diabetes.

High temporal resolution gastric emptying breath tests in mice

BACKGROUND

Gastric emptying is a complex physiological process regulating the division of a meal into smaller partitions for the small intestine. Disrupted gastric emptying contributes to digestive disease, yet current measures may not reflect different mechanisms by which the process can be altered.

METHODS

We have developed high temporal resolution solid and liquid gastric emptying breath tests in mice using [13 C]-octanoic acid and off axis- integrated cavity output spectroscopy (OA-ICOS). Stretched gamma variate and 2-component stretched gamma variate models fit measured breath excretion data.

KEY RESULTS

These assays detect acceleration and delay using pharmacological (7.5 mg/kg atropine) or physiological (nutrients, cold exposure stress, diabetes) manipulations and remain stable over time. High temporal resolution resolved complex excretion curves with 2 components, which was more prevalent in mice with delayed gastric emptying following streptozotocin-induced diabetes. There were differences in the gastric emptying of Balb/c vs C57Bl6 mice, with slower gastric emptying and a greater occurrence of two-phase gastric emptying curves in the latter strain. Gastric emptying of C57Bl6 could be accelerated by halving the meal size, but with no effect on the occurrence of two-phase gastric emptying curves. A greater proportion of two-phase gastric emptying was induced in Balb/c mice with the administration of PYY (8-80 nmol) 60 min following meal ingestion.

CONCLUSIONS AND INFERENCES

Collectively, these results demonstrate the utility of high temporal resolution gastric emptying assays. Two-phase gastric emptying is more prevalent than previously reported, likely involves intestinal feedback, but contributes little to the overall rate of gastric emptying.

Enteric Glial Dysfunction Evoked by Apolipoprotein E Deficiency Contributes to Delayed Gastric Emptying

BACKGROUND AND AIM

Diabetes is the main cause of gastroparesis accompanying decreased neuronal nitric oxide synthase (nNOS) in myenteric ganglia of the stomach. Decreased nNOS expression in the stomach also results from defects in apolipoprotein E (ApoE), which is secreted by astrocytes and has neuroprotective effects on the central nervous system. However, the roles of ApoE and enteric glial cells on gastric motility are uncertain. In this study, ApoE and enteric glial cell alterations in gastroparesis were investigated.

METHODS

Type 2 diabetic (db/db) mice and ApoE-knockout mice were analyzed. Gastric emptying was measured using the ¹³C acetic acid breath test. Expression levels of the pan-neuronal marker, protein gene product 9.5 (PGP 9.5), and glial marker, glial fibrillary acidic protein (GFAP) were examined by immunohistochemistry. Neural stem cells (NSCs) were injected into the gastric antral wall of ApoE-knockout mice.

RESULTS

Delayed gastric emptying was observed in 27% of db/db mice with significant decreases in serum ApoE levels and GFAP expression in the gastric antrum. Gastric emptying was also delayed in ApoE-knockout mice, with a significant decrease in GFAP expression, but no change in PGP 9.5 expression. Transplantation of NSCs improved gastric emptying in ApoE-knockout mice through supplementation of GFAP-positive cells.

CONCLUSIONS

Our results suggest that decreased enteric glial cells in ApoE-knockout mice are crucial for development of delayed gastric emptying, and NSC transplantation is effective in restoring myenteric ganglia and gastric motility.

Correlation Between Gastric Emptying and Gastric Adaptive Relaxation Influenced by Amino Acids

Background/Aims

Amino acids have many physiological activities. We report the correlation between gastric emptying and gastric adaptive relaxation using tryptophan and amino acids with a straight alkyl chain, hydroxylated chain, and branched chain. Here we sought to further clarify the correlation between gastric emptying and gastric adaptive relaxation by using other amino acids.

Methods

In Sprague-Dawley rats, gastric emptying was evaluated by a breath test using [1-¹³C] acetic acid. The expired ¹³CO₂ pattern, T_max, C_max, and AUC_120min values were used as evaluation items. Gastric adaptive relaxation was evaluated in a barostat experiment. Individual amino acids (1 g/kg) were administered orally 30 minutes before each breath test or barostat test.

Results

L-phenylalanine and L-tyrosine did not influence gastric emptying. All other amino acids, ie, L-proline, L-histidine, L-cysteine, L-methionine, L-aspartic acid, L-glutamic acid, L-asparagine, L-arginine, L-glutamine, and L-lysine significantly delayed and inhibited gastric emptying. L-Cysteine and L-aspartic acid significantly enhanced and L-methionine and L-glutamine significantly inhibited gastric adaptive relaxation. L-Phenylalanine moved the balloon toward the antrum, suggesting strong contraction of the fundus. T_max showed a significant positive correlation (r = 0.709), and C_max and AUC_120min each showed negative correlations (r = 0.613 and 0.667, respectively) with gastric adaptive relaxation.

Conclusion

From the above findings, it was found that a close correlation exists between gastric emptying and adaptive relaxation, suggesting that enhanced gastric adaptive relaxation inhibits gastric emptying.

Body heat responsive gelation of methylcellulose formulation containing betaine

We examined a methylcellulose (MC) formulation that gels at body temperature for enteral alimentation. Betaine was found to have a lowering effect on the gelation temperature of the MC solution. The thermal gelation temperature of a body heat-responsive (BHR) gelling MC formulation, consisting of 2% MC, 15% glucose, 1.2% sodium citrate, and 3.5% betaine mixture, was approximately 32 °C, indicating that it could gel in response to body heat. Glucose release from the BHR gels was delayed at 37 °C in an in vitro study. In rats, oral administration of BHR gelling MC formulation delayed an increase in blood glucose and appearance of ¹³CO₂ in expired air in a ¹³C-acetate breath test in comparison with the control. These results suggested that the BHR gelling MC formulation was gelled in the stomach and delayed gastric emptying after oral administration and glucose in the gels was absorbed slowly.

Gastric emptying after artificial ulceration in rats: differences due to the site of the ulcer and the effects of prokinetic drugs

Background This study aimed to evaluate the effects of the position of an acetic acid-induced gastric ulcer and the effects of prokinetic drugs on gastric emptying. Materials and Methods Male Sprague-Dawley rats were used in this study. Acetic acid ulcers were induced either in the region between the fundus and pylorus on the anterior wall of the stomach or in the glandular region on the greater curvature of the stomach to determine whether there were regional differences in the effect of the ulcers. Gastric emptying was evaluated with a breath test using [1-¹³C] acetic acid. In addition, the effects of the prokinetic drugs, metoclopramide and mosapride, on gastric emptying were also evaluated. Results Acetic acid induced ulcers in the region between the fundus and pylorus on the anterior wall of the stomach significantly delayed gastric emptying as compared with control rats, but not the acetic acid induced ulcers in the glandular region on the greater curvature of the stomach. Metoclopramide and mosapride did not improve the delayed gastric emptying even at doses that enhanced gastric emptying in normal rats. Conclusion These findings show that gastric emptying is influenced by the position of the ulcer and the region between the fundus and pylorus on the anterior wall plays an important role in gastric emptying. Moreover, it was found that metoclopramide and mosapride do not improve the delayed gastric emptying caused by acetic acid ulcers induced on the anterior wall in the region between the fundus and pylorus.

Effects of straight alkyl chain, extra hydroxylated alkyl chain and branched chain amino acids on gastric emptying evaluated using a non-invasive breath test in conscious rats

Aim: Some amino acids been known to influence gastric emptying. Thus we have evaluated the effects of straight alkyl chain, extra hydroxylated alkyl chain and branched chain amino acids on gastric emptying. Materials and Methods: Gastric emptying was evaluated in rats after feeding with Racol (nutrient formulae) containing [1-¹³C] acetic acid. Using a breath test, the content of ¹³CO₂ in their expired air was measured by infrared analyzers. Rats were orally administered with test amino acids, while control rats were administered orally with distilled water. Results: The expired ¹³CO₂ content in the expired air increased with time, peaked after about 30 min and decreased thereafter. Among the amino acids having an alkyl chain, l-serine, l-alanine and l-glycine, significantly decreased the ¹³CO₂ content and Cmax, and delayed Tmax, suggesting inhibition and delay of gastric emptying. AUC_120 min values of l-alanine and l-glycine also decreased significantly. l-Threonine significantly decreased ¹³CO₂ content and delayed Tmax, but had no influence on Cmax and AUC_120 min values, suggesting a delay of gastric emptying. l-Isoleucine and l-leucine and l-valine significantly decreased ¹³CO₂ content, suggesting inhibition of the gastric emptying, but Cmax, Tmax and AUC_120 min values were not significantly affected. Conclusion: The results show that the amino acids used in the present study had different effects on gastric emptying. Moreover, it was found that inhibition and delay of gastric emptying were clearly classifiable by analyzing the change in ¹³CO₂ content of the expired air and the Cmax, Tmax and AUC_120 min values.

Investigation of Metabolism of Exogenous Glucose at the Early Stage and Onset of Diabetes Mellitus in Otsuka Long-Evans Tokushima Fatty Rats Using [1, 2, 3-13C]Glucose Breath Tests

This study aimed to evaluate changes in glucose metabolism at the early stage and onset of diabetes in Otsuka Long-Evans Tokushima Fatty (OLETF) rats. Specifically, after the oral administration of [1, 2, 3-¹³C]glucose, the levels of exhaled ¹³CO₂, which most likely originated from pyruvate decarboxylation and tricarboxylic acid, were measured. Eight OLETF rats and eight control rats (Long-Evans Tokushima Otsuka [LETO]) were administered ¹³C-glucose. Three types of ¹³C-glucose breath tests were performed thrice in each period at 2-week intervals. [3-¹³C]glucose results in a ¹³C isotope at position 1 in the pyruvate molecule, which provides ¹³CO₂. The ¹³C at carbons 1 and 2 of glucose is converted to ¹³C at carbons 2 and 1 of acetate, respectively, which produce ¹³CO₂. Based on metabolic differences of the labeled sites, glucose metabolism was evaluated using the results of three breath tests. The increase in ¹³CO₂ excretion in OLETF rats was delayed in all three breath tests compared to that in control rats, suggesting that OLETF rats had a lower glucose metabolism than control rats. In addition, overall glucose metabolism increased with age in both groups. The utilization of [2-¹³C]glucose was suppressed in OLETF rats at 6–12 weeks of age, but they showed higher [3-¹³C]glucose oxidation than control rats at 22–25 weeks of age. In the [1-¹³C]glucose breath test, no significant differences in the area under the curve until 180 minutes (AUC₁₈₀) were observed between OLETF and LETO rats of any age. Glucose metabolism kinetics were different between the age groups and two groups of rats; however, these differences were not significant based on the overall AUC₁₈₀ of [1-¹³C]glucose. We conclude that breath ¹³CO₂ excretion is reduced in OLETF rats at the primary stage of prediabetes, indicating differences in glucose oxidation kinetics between OLETF and LETO rats.

Autonomic consequences of spinal cord injury

Spinal cord injury (SCI) results not only in motor and sensory deficits but also in autonomic dysfunctions. The disruption of connections between higher brain centers and the spinal cord, or the impaired autonomic nervous system itself, manifests a broad range of autonomic abnormalities. This includes compromised cardiovascular, respiratory, urinary, gastrointestinal, thermoregulatory, and sexual activities. These disabilities evoke potentially life-threatening symptoms that severely interfere with the daily living of those with SCI. In particular, high thoracic or cervical SCI often causes disordered hemodynamics due to deregulated sympathetic outflow. Episodic hypertension associated with autonomic dysreflexia develops as a result of massive sympathetic discharge often triggered by unpleasant visceral or sensory stimuli below the injury level. In the pelvic floor, bladder and urethral dysfunctions are classified according to upper motor neuron versus lower motor neuron injuries; this is dependent on the level of lesion. Most impairments of the lower urinary tract manifest in two interrelated complications: bladder storage and emptying. Inadequate or excessive detrusor and sphincter functions as well as detrusor-sphincter dyssynergia are examples of micturition abnormalities stemming from SCI. Gastrointestinal motility disorders in spinal cord injured-individuals are comprised of gastric dilation, delayed gastric emptying, and diminished propulsive transit along the entire gastrointestinal tract. As a critical consequence of SCI, neurogenic bowel dysfunction exhibits constipation and/or incontinence. Thus, it is essential to recognize neural mechanisms and pathophysiology underlying various complications of autonomic dysfunctions after SCI. This overview provides both vital information for better understanding these disorders and guides to pursue novel therapeutic approaches to alleviate secondary complications.

Effects of L-tryptophan on gastric emptying evaluated by breath test in relation to gastric accommodation evaluated by Barostat in rats

Gastric emptying has been known to correlate the pyloric sphincter contractile function and distention-induced gastric relaxation (gastric accommodation). In the present study, the effects of L-tryptophan on the gastric emptying and accommodation were evaluated by breath test using [1-(13)C]acetic acid and Barostat study, respectively, in rats. L-Tryptophan significantly decreased Cmax and AUC120min and delayed Tmax, indicating the inhibition of gastric emptying. L-Tryptophan significantly enhanced the gastric accommodation. These findings show that L-tryptophan may inhibit the gastric emptying through the enhanced gastric accommodation. Therefore, L-tryptophan may be useful for the therapy of postprandial dyspepsia, especially for early satiety.

Daikenchuto, a traditional Japanese herbal medicine, ameliorates postoperative ileus by anti-inflammatory action through nicotinic acetylcholine receptors

BACKGROUND

Daikenchuto (DKT), a gastrointestinal prokinetic Japanese herbal medicine, is prescribed for patients with postoperative ileus (POI) and adhesive bowel obstruction following abdominal surgery. Several mechanisms for the amelioration of POI by DKT have been suggested; however, it has remained unclear whether DKT shows anti-inflammatory effects in POI. In the present study, we investigated the effects of DKT in a mouse POI model and attempted to clarify the detailed mechanisms of action.

METHOD

Intestinal manipulation (IM) was applied to the distal ileum of mice. DKT was administered orally to the animals 4 times before and after IM. Gastrointestinal transit in vivo, leukocyte infiltration, cytokine mRNA expression and gastrointestinal motility were analyzed. We also investigated the effects of the α7nAChR antagonist methyllycaconitine citrate (MLA) on the DKT-mediated ameliorative action against POI, and we studied the effects of DKT on inflammatory activity in α7nAChR knockout mice.

RESULTS

DKT treatment led to recovery of the delayed intestinal transit induced by IM. DKT significantly inhibited the infiltration of neutrophils and CD68-positive macrophages, and inhibited mRNA expressions of TNF-α and MCP-1. MLA significantly reduced the anti-inflammatory action of DKT, and the amelioration of macrophage infiltration by DKT was partially suppressed in α7nAChR knockout mice.

CONCLUSIONS

In conclusion, in addition to the gastrointestinal prokinetic action, DKT serves as a novel therapeutic agent for POI characterized by its anti-inflammatory potency. The DKT-induced anti-inflammatory activity may be partly mediated by activation of α7nAChR.

Electrolyte-free milk protein solution influences sodium and fluid retention in rats

Milk is an effective post-exercise rehydration drink that maintains the net positive fluid balance. However, it is unclear which components are responsible for this effect. We assessed the effect of milk protein solution (MPS) obtained by dialysis on body fluid retention. Milk, MPS, milk electrolyte solution (MES), sports drink and water were administered to male Wistar rats at a dose of 6 ml/rat after treadmill exercise. Total body fluid retention was assessed by urine volume 4 h after administration of hydrating liquids. The rate of gastric emptying was evaluated by a tracer method using ¹³C-labelled acetate. Plasma osmolality, Na and K levels, and urinary Na and K were measured by HPLC and osmometry, respectively. The gastric emptying rate was not delayed by MPS. During 4 h of rehydration, cumulative urine volumes differed significantly between treatment groups (P < 0·05) with 4·9, 2·2 and 3·4 ml from water-, milk- and MPS-fed rats, respectively. Thus, MPS elicited 50 % of the total body fluid retention of milk. Plasma aldosterone levels were significantly higher in MPS- and milk-fed rats compared with water-fed rats. Plasma osmolality was maintained at higher levels in MPS-fed rats than in water- and MES-fed rats (P < 0·05). Cumulative urine Na excretion was also suppressed in the milk- and MPS-fed groups compared with the MES-fed group. Our results demonstrate that MPS obtained by dialysis clearly affects net body water balance without affecting gastric emptying after exercise. This effect was attributed to retention of Na and water, and maintenance of plasma osmolality.

Simultaneous measurement of gastric emptying and gastrocecal transit times in conscious rats using a breath test after ingestion of [1-13C] acetic acid and lactose-[13C] ureide

This study reports a method for the evaluation of both gastric emptying and gastrocecal transit times in rats simultaneously by using the same breath testing system measuring equipment. Male rats were used after fasting. Gastric emptying and gastrocecal transit time were evaluated by using [1-13C] acetic acid (8 mg/kg) and lactose-[13C] ureide (60 mg/kg), respectively. A mixture of both 13C-labelled compounds dissolved in Racol (liquid nutrient formula) was administered orally. The level of 13CO2 in the expired air was measured using an infrared spectrometer at appropriate intervals for a period of 420 min. The level of 13CO2 in the expired air from [1-13C] acetic acid increased with time and peaked at about 30 min before decreasing, while that from lactose-[13C] ureide increased after about 180 min. The time taken to reach the maximum value of gastric emptying (Tmax) was 27.5±0.9 min. Gastrocecal transit time was 180±11.5 min, which was calculated as the time before the 13CO2 value increased again. These results accorded with the results of gastric emptying and gastrocecal transit time evaluated by using each 13C-labelled compound separately. These results demonstrate that this method is useful for the simultaneous evaluation of gastric emptying and gastrocecal transit times in rats.

A new gastric-emptying mouse model based on in vivo non-invasive bioluminescence imaging

BACKGROUND

Different techniques were used to assess gastric emptying (GE) in small animals; most of them require sophisticated equipment, animal sacrifice and are expensive. In the present investigation a simple, non-invasive method based on bioluminescence imaging (BLI) is reported to study GE, using light-emitting Escherichia coli cells as a marker of the gastric content.

METHODS

A new thermostable red-emitting luciferase was chosen as reporter gene to transform E. coli cells. Bioluminescent (BL) bacteria were administered to fasting mice, after a solid meal, and in response to different doses of metoclopramide (MET) and hyoscine butylbromide (HY). Bioluminescence imaging allowed to evaluate the real time 2D spatial and temporal distribution of bacteria along the gastrointestinal tract in animals and to calculate GE rate in basal conditions and following pharmacological stimulation.

KEY RESULTS

  The administered BL bacteria were easily imaged and localized in the stomach and subsequently followed in the duodenum and upper intestine allowing to accurately calculate GE. Gastric emptying after the test meal was significantly slower (T(1/2) 16 ± 3 min) than that obtained in fasting conditions (T(1/2) 2 ± 1 min); administration of HY (1 mg kg(-1) b.w.) significantly (P < 0.05) increased T(1/2) that was delayed up to 25 ± 4 min; MET (1 mg kg(-1) b.w.) significantly (P < 0.05) accelerated T(1/2), that was achieved within 8 ± 2 min.

CONCLUSION & INFERENCES

The reported model is simple, inexpensive, reliable, sensitive and accurate; it can detect both acceleration and slowdown of GE. The model is useful in the investigation of new drug-induced alterations of gastric motility allowing to reduce the number of experimental animals.

Studies on absorption and metabolism of palatinose (isomaltulose) in rats

We evaluated the absorption and metabolism of palatinose in rats by the carbohydrate load test and the 13C- and H2-breath tests. We compared the results of these tests with those of sucrose, since sucrose is an isomer of palatinose and generally known to be degraded and absorbed from the small intestine. In the carbohydrate load test, blood glucose and plasma insulin levels after oral administration of palatinose rose more gradually and reached a maximum that was lower than that after sucrose administration. In the 13C-breath test, rats were orally administrated [1-13C]sucrose or [1-13C]palatinose and housed in a chamber. The expired air in the chamber was collected, and the level of 13CO2 in the expired air was measured at appropriate intervals for 360 min. The value of time taken to reach the maximum concentration for expired 13CO2 from [1-13Cglucose] ([1-13Cglc]) and [1-13Cfructose] ([1-13Cfru]) palatinose was significantly longer than that from [1-13Cglc] and [1-13Cfru]sucrose, respectively. The value of area under the curve (AUC) for [1-13Cglc]palatinose was larger than that for [1-13Cglc]sucrose, but AUC for [1-13Cfru] showed no difference between palatinose and sucrose. In the H2-breath test, the concentration of H2 in the expired air was measured for 420 min. H2 was hardly detected with both palatinose and sucrose and no significant difference was observed between the two groups. These results suggest that palatinose is utilised in vivo at a rate equal to that of sucrose.

Gastric emptying of enterally administered liquid meal in conscious rats and during sustained anaesthesia

BACKGROUND

Gastric motility studies are frequently conducted with anaesthetized animal models. Some studies on the same animal species have reported differences in vagal control of the stomach that could not be explained solely by slightly different experimental conditions. A possible limitation in the comparison between similar studies relates to the use of different anaesthetic agents. Furthermore, anaesthetic effects may also limit generalizations between mechanistic studies of gastric function and the gastric function of conscious animals. In the present study, we used the [(13)C]-breath test following a liquid mixed-nutrient test meal (Ensure), 1 ml) with the aim to investigate the rate of gastric emptying in animals that were either conscious or anaesthetized with either Inactin or urethane.

METHODS

One week after determining the maximum (13)CO(2) concentration, time to peak [(13)C] recovery and gastric half emptying time in control, conscious rats, we repeated the experiment in the same rats anaesthetized with Inactin or urethane.

KEY RESULTS

Our data show that Inactin anaesthesia prolonged the time to peak [(13)C] recovery but did not significantly reduce the maximum (13)CO(2) concentration nor delay gastric half emptying time. Conversely, urethane anaesthesia resulted in a significant slowing of all parameters of gastric emptying as measured by the maximum (13)CO(2) concentration, time to peak [(13)C] recovery and half emptying time.

CONCLUSIONS & INFERENCES

Our data indicate that Inactin(R) anaesthesia does not significantly affect gastric emptying while urethane anaesthesia profoundly impairs gastric emptying. We suggest that Inactin(R), not urethane, is the more suitable anaesthetic for gastrointestinal research.

Time-course of recovery of gastric emptying and motility in rats with experimental spinal cord injury

We have shown recently that spinal cord injury (SCI) decreases basal gastric contractions 3 days after injury. In the present study we used the [(13)C]-octanoic acid breath test and gastric strain gauges with the aim to investigate the time-course of recovery from postinjury gastric stasis in rats that underwent experimental SCI at the level of the third thoracic (T3) vertebra. Following verification of the [(13)C]-breath test sensitivity in uninjured rats, we conducted our experiments in rats that underwent T3-spinal contusion injury (T3-CI), T3-spinal transection (T3-TX) or laminectomy (control) surgery at 3 days, 1, 3 or 6 weeks postinjury. Our data show that compared to rats that underwent laminectomy, rats that received SCI showed a significant reduction in the cumulative per cent [(13)C] recovery. Although more marked in T3-TX rats, the delayed gastric emptying in T3-CI and T3-TX rats was comparable in the 3 days to 3 weeks period postinjury. At 6 weeks postinjury, the gastric emptying in T3-CI rats recovered to baseline values. Conversely animals in the T3-TX group still show a significantly reduced gastric emptying. Interestingly, the almost complete functional recovery observed in T3-CI rats using the [(13)C]-breath test was not reflected by analysis of spontaneous gastric contractions after SCI. These data indicate that T3-SCI produces a significant reduction in gastric emptying independent of injury severity (T3-CI vs T3-TX) that persists for at least 3 weeks after injury. However, 6 weeks postinjury T3-CI, but not T3-TX, rats begin to demonstrate functional recovery of gastric emptying.

Effect of atropine sulfate on gastric emptying and gastrocecal transit time evaluated by using the [1-(13)C]acetic acid and lactose-[(13)C]ureide breath test in conscious rats

Breath tests have been used to investigate many physiological functions. Recently, we have developed a breath test system by using a non-invasive technique in conscious rats. In this study, we investigated the effect of atropine sulfate on the gastric emptying and gastrocecal transit time using [1-(13)C]acetic acid and lactose-[(13)C]ureide, respectively. Gastric emptying was significantly delayed by atropine sulfate in a dose-dependent manner (0.03-0.3 mg kg(-1)), but the effects of 0.1 and 0.3 mg kg(-1) were almost equal. C(max) and T(max) values were also significantly and dose-dependently decreased and delayed, respectively. However, AUC(120 min) values were not significantly different for the three doses of atropine sulfate. This suggests that although atropine sulfate slows the emptying of the gastric content, it is excreted eventually to the same content as the control. The gastrocecal transit time was significantly delayed by atropine sulfate at a dose of 1 mg kg(-1), but not at a dose of 0.1 mg kg(-1). These findings demonstrate that the breath tests can evaluate the effect of atropine sulfate on the gastric emptying and gastrocecal transit time. The effective dose of atropine sulfate may be different for gastric emptying and gastrocecal transit time.

Non-invasive method for evaluation of gastrocecal transit time by using a breath test in conscious rats

The aim of this study was to establish a method for evaluating gastrocecal transit time using a simple and noninvasive 13C breath-test system in conscious rats. After fasting, rats were orally administered lactose-[13C]ureide. 13CO2 level in the expired air was measured at appropriate intervals. It was confirmed that priming dose of lactose-ureide was necessary for determining gastrocecal transit time. The level of 13CO2 in the expired air increased in a lactose-[13C]ureide dose-dependent manner. The gastrocecal transit time determined with 30 mg/kg of lactose-[13C]ureide was 160+/-24.5 min. This method is expected to contribute to the further understanding of intestinal pathophysiology.

The utility of noninvasive (13)C-acetate breath test using a new solid test meal to measure gastric emptying in mice

In clinical and experimental settings, the (13)C breath test is performed to measure gastric emptying and has advantages of noninvasiveness and repeatability. We intended to apply the (13)C breath test method to mice with an easy-to-handle solid test meal that is more physiological than liquid meals. Male ddY mice were trained to eat (13)C-acetate-containing pellets as the solid test meal. Thirty minutes after administration of metoclopramide (0.3-3 mg/kg, p.o.) or atropine sulfate (0.3-3 mg/kg, i.p.), mice received the test meal and were placed in chambers. The (13)CO(2) levels in the expired air were measured and the maximum concentration (C(max); per thousand) and the time to reach the maximum concentration (T(max); min) were determined. Metoclopramide significantly and dose-dependently increased C(max) and decreased T(max). On the other hand, atropine sulfate significantly and dose-dependently decreased C(max) and increased T(max). The (13)C-acetate breath test using a solid test meal is sensitive enough to detect both enhanced and delayed gastric emptying of the reference drugs.

Usefulness of breath test for evaluating pancreatic exocrine function using N-benzoyl-L-tyrosyl-1-13C-L-alanine sodium in non-invasive and conscious rats

N-Benzoyl-L-tyrosyl-1-13C-L-alanine sodium is a dipeptide used for evaluating pancreatic exocrine function. The method of evaluation, however, is not yet satisfactory, especially in experimental animals. The relation between diabetes and pancreatic exocrine function also is not clear. Therefore, this study sought to establish a method for evaluating pancreatic exocrine function and to validate the method by determining non-invasively the effect of alloxan-induced diabetes in conscious rats. After fasting, rats were orally administered Racol containing N-benzoyl-L-tyrosyl-1-13C-L-alanine sodium or 1-13C-L-alanine and housed in desiccators. The expired air in the desiccator was collected in a breath-sampling bag using a tube and aspiration pump, and the level of 13CO2 in this air was measured using an infrared spectrometer at appropriate intervals over a 120 min period. The rate of 13CO2 excretion increased, peaked and then decreased in a dose-dependent manner. The maximum concentration and area under the curve of 13CO2 excretion significantly and positively correlated with the doses of N-benzoyl-L-tyrosyl-1-13C-L-alanine sodium. In the rats made diabetes by the administration of alloxan, the level of expired 13CO2 air changed at significantly lower levels as compared with that of the control rats on day 3, although the level of expired 13CO2 air from 1-13C-L-alanine was also markedly lower than that of the control rats. These results showed that pancreatic exocrine function can be evaluated using this breath test system and that alloxan-induced diabetes affects this function.

13C-acetic acid is more sensitive than 13C-octanoic acid for evaluating gastric emptying of liquid enteral nutrient formula by breath test in conscious rats

Breath test using 13C-labeled compound has been used as a convenient method to evaluate gastric emptying. 13C-Labeled acetic acid or octanoic acid has been used in clinic. However, there is few report comparing two compounds. This study aimed to compare 13C-acetic acid and 13C-octanoic acid in newly-constituted breath test for monitoring gastric emptying in conscious rats. After fasting, rats were orally administered Racol (liquid enteral nutrient formula) containing 13C-labeled compound (same molar of 13C-acetic acid or 13C-octanoic acid) and housed in a chamber. The expired air in the chamber was collected in a breath-sampling bag using a tube and aspiration pump. The level of 13CO2 in the expired air was measured using an infrared spectrometer at appropriate intervals for 120 min. Expired 13CO2 air from 13C-acetic acid changed at significantly higher levels than that from 13C-octanoic acid. Cmax and AUC120 min values of expired 13CO2 from 13C-acetic acid were significantly higher than those from 13C-octanoic acid, but Tmax was not different between them. These results show that 13C-acetic acid is more sensitive for monitoring gastric emptying than 13C-octanoic acid in liquid test meal although both acids clearly monitored gastric emptying.