Evaluation of adaptive relaxation of the rat stomach using an orally inserted balloon instead of surgical intervention by demonstrating the effects of capsaicin and Nω-nitro-L-arginine methylester

TRPV1 Dysfunction Impairs Gastric Nitrergic Neuromuscular Relaxation in High-Fat Diet-Induced Diabetic Gastroparesis Mice

Diabetic gastroparesis (DGP) is characterized by delayed gastric emptying of solid food. Nitrergic neuron-mediated fundus relaxation and intragastric peristalsis are pivotal for gastric emptying and are impaired in DGP. Transient receptor potential vanilloid 1 (TRPV1) ion channels are expressed in gastrointestinal vagal afferent nerves and have a potential role in relevant gastrointestinal disorders. In this study, mice with high-fat diet (HFD)-induced type 2 diabetes mellitus (T2DM), associated with gastroparesis, were used to determine the role of TRPV1 in DGP. After feeding with HFD, mice exhibited obesity, hyperglycemia, insulin resistance, and delayed gastric emptying. Cholinergic- and nitrergic neuron-mediated neuromuscular contractions and relaxation were impaired. The antral tone of the DGP mice was attenuated. Interestingly, activating or suppressing TRPV1 facilitated or inhibited gastric fundus relaxation in normal mice. These effects were neutralized by using a nitric oxide synthase (NOS) inhibitor. Activation or suppression of TRPV1 also increased or reduced NO release. TRPV1 was specifically localized with neuronal NOS in the gastric fundus. These data suggest that TRPV1 activation facilitates gastric fundus relaxation by regulating neuronal NOS and promoting NO release. However, these effects and mechanisms disappeared in mice with DGP induced by HFD diet. TRPV1 expression was only marginally decreased in the fundus of DGP mice. TRPV1 dysfunction may be a potential mechanism underlying the dysfunction of DGP gastric nitrergic neuromuscular relaxation.

Modified Liu-Jun-Zi decoction alleviates visceral hypersensitivity in functional dyspepsia by regulating EC cell-5HT3r signaling in duodenum

ETHNOPHARMACOLOGICAL RELEVANCE

Modified Liu-Jun-Zi (MLJZ) is derived from one of the most famous traditional Chinese prescription Liu-Jun-Zi. It exhibits therapeutic effects in functional dyspepsia (FD), but the underlying mechanisms remain not well understood. Enterochromaffin (EC) cells contribute to the pathogeneses of visceral hypersensitivity in functional gastrointestinal disorders. But whether and how EC cells in duodenum participate in the mechanism of FD remain unsettled.

AIM OF THE STUDY

To detect the crucial factors related to EC cells, and to evaluate the therapeutic effect of MLJZ and to determine whether MLJZ relieves visceral hypersensitivity in FD by regulating EC cell-5-hydroxytryptamine 3 receptor (5HT3r) signaling.

MATERIALS AND METHODS

FD rats were established by iodoacetamide gavage combined with tail clamping method. The verification of FD model and the evaluation of the therapeutic effect of MLJZ was taken place by hematoxylin-eosin (HE) staining and visceral sensitivity measurement. The expression of EC cells and 5-hydroxytryptamine (5HT) in duodenum was detected by Immunohistochemistry (IHC) staining and enzyme-linked immunosorbent assay (ELISA). IHC staining and quantitative polymerase chain reaction (qPCR) were applied to measure the expression of tryptophan hydroxylase-1 (TPH1), paired box gene 4 (PAX4), transient receptor potential A1 (TRPA1), transient receptor potential C4 (TRPC4) and 5HT3r. Duodenum sections were stained by double immunofluorescence (IF) to study the synthesis of 5HT in EC cells.

RESULTS

The gastric sensitivity increased in FD rats while MLJZ decoction significantly attenuated visceral hypersensitivity. The duodenum of FD rats displayed increased expressions of EC cells, 5HT, TPH1, PAX4 and 5HT3r. And the overexpression was reduced in response to MLJZ decoction treatment.

CONCLUSIONS

EC cell-5HT3r signaling pathway is abnormally active in FD with visceral hypersensitivity. And MLJZ decoction can alleviates visceral hypersensitivity in FD by regulating EC cell-5HT3r signaling in duodenum.

Influence of amino acids on gastric adaptive relaxation (accommodation) in rats as evaluated with a barostat

Aim: The present study aimed to evaluate the effects of selected straight alkyl chain, hydroxylated chain and branched chain amino acids on gastric adaptive relaxation, as these have previously been shown to have differing effects on gastric emptying. Materials and Methods: Gastric adaptive relaxation was evaluated using a barostat in rats under urethane anesthesia. The pressure within the balloon, introduced from the mouth to the stomach, was changed stepwise from 1 to 8 mmHg. The increased volume just after the increase of balloon pressure was defined as distension-induced gastric adaptive relaxation (accommodation). Amino acids were administered orally or intravenously. Results: As compared with control rats administered with distilled water, those rats that were orally administered amino acids having straight alkyl chain and extra hydroxylated alkyl chain, such as glycine and l-serine, had significantly enhanced gastric adaptive relaxation, but administration of l-alanine and l-threonine did not. Branched chain amino acids, such as l-isoleucine, l-leucine and l-valine, also did not significantly influence gastric adaptive relaxation. Glycine and l-serine showed the same efficacy when administered intravenously. Conclusion: Among the amino acids evaluated in the present study, glycine and l-serine significantly enhanced gastric adaptive relaxation, suggesting that short alkyl chain amino acids may enhance gastric adaptive relaxation as compared with the other amino acids. These findings may suggest that glycine and l-serine would be useful in the therapy of functional dyspepsia, especially for early satiety, because the dysfunction of adaptive relaxation is one of the causes of early satiety.

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.

Change in the Interstitial Cells of Cajal and nNOS Positive Neuronal Cells with Aging in the Stomach of F344 Rats

The gastric accommodation reflex is an important mechanism in gastric physiology. However, the aging-associated structural and functional changes in gastric relaxation have not yet been established. Thus, we evaluated the molecular changes of interstitial cell of Cajal (ICC) and neuronal nitric oxide synthase (nNOS) and the function changes in the corpus of F344 rats at different ages (6-, 31-, 74-wk and 2-yr). The proportion of the c-Kit-positive area in the submucosal border (SMB) and myenteric plexus (MP) layer was significantly lower in the older rats, as indicated by immunohistochemistry. The density of the nNOS-positive immunoreactive area also decreased with age in the SMB, circular muscle (CM), and MP. Similarly, the percent of nNOS-positive neuronal cells per total neuronal cells and the proportion of nNOS immunoreactive area of MP also decreased in aged rats. In addition, the mRNA and protein expression of c-Kit and nNOS significantly decreased with age. Expression of stem cell factor (SCF) and the pan-neuronal marker PGP 9.5 mRNA was significantly lower in the older rats than in the younger rats. Barostat studies showed no difference depending on age. Instead, the change of volume was significantly decreased by L-NG63-nitroarginine methyl ester in the 2-yr-old rats compared with the 6-wk-old rats (P = 0.003). Taken together, the quantitative and molecular nNOS changes in the stomach might play a role in the decrease of gastric accommodation with age.

Anethole restores delayed gastric emptying and impaired gastric accommodation in rodents

Functional dyspepsia (FD), a functional gastrointestinal disorder, is characterized by persistent or recurrent postprandial upper abdominal discomfort and epigastric pain. The high prevalence of FD and associated healthcare costs suggests that treatment of this condition by methods other than prescribed medicines, such as natural products, could be beneficial. Delayed gastric emptying and impaired gastric accommodation play important roles in the development of FD. Anethole (1-methoxy-4-((E)-propenyl)-benzene), a major component of essential fennel oil, has been used as a flavoring, in alcoholic beverage production and in pharmaceutical formulations for many years. In this study, we examined the effects of anethole on delayed gastric emptying and impaired gastric accommodation in rodents. Oral administration of anethole improved clonidine-induced delayed gastric emptying but did not affect normal gastric emptying in mice. Fennel oil and Anchu-san (a Japanese herbal medicine containing anethole) also restored delayed gastric emptying. Furthermore, oral administration of anethole stimulated gastric accommodation in rats. These results suggest that anethole could be beneficial for the treatment of FD.

Effect of colonic distension on gastric adaptive relaxation in rats: barostatic evaluation using an orally introduced gastric balloon

While the gastrocolonic reflex has been known, the cologastric relationship has not been clarified especially with regard to gastric adaptive relaxation. Therefore, in this study we have examined the correlation between gastric adaptive relaxation and colonic distension. Male Sprague-Dawley rats were used after fasting for 18 h. Colonic distension was performed by injecting 2.2 ml of air into a colonic balloon inserted into the colon for 5 min in conscious state. After urethane anesthesia, gastric adaptive relaxation was investigated by using a slightly modified gastric balloon introduced into the stomach through the mouth. Gastric balloon volumes increased gradually just after an increment in the gastric balloon pressure (1 to 8 mmHg), and reached a plateau within 1 min. This increased volume was defined as gastric adaptive relaxation. In control rats, gastric adaptive relaxation increased with pressure increments in a pressure dependent manner. In the colon-distended rats, gastric adaptive relaxation increased also in a pressure dependent manner, but was significantly inhibited as compared with control at 8 mmHg (P<0.05). These findings show that colonic distension inhibits the gastric adaptive relaxation and suggests the existence of a cologastric relationship in rats.

Aldioxa improves delayed gastric emptying and impaired gastric compliance, pathophysiologic mechanisms of functional dyspepsia

Delayed gastric emptying and impaired gastric accommodation (decreased gastric compliance) play important roles in functional dyspepsia (FD). Here we screen for a clinically used drug with an ability to improve delayed gastric emptying in rats. Oral administration of aldioxa (dihydroxyaluminum allantoinate) partially improved clonidine- or restraint stress-induced delayed gastric emptying. Administration of allantoin, but not aluminium hydroxide, restored the gastric emptying. Both aldioxa and allantoin inhibited clonidine binding to the α-2 adrenergic receptor, suggesting that antagonistic activity of the allantoin moiety of aldioxa on this receptor is involved in the restoration of gastric emptying activity. Aldioxa or aluminium hydroxide but not allantoin restored gastric compliance with restraint stress, suggesting that aluminium hydroxide moiety is involved in this restoration. We propose that aldioxa is a candidate drug for FD, because its safety in humans has already been confirmed and its ameliorating effect on both of delayed gastric emptying and impaired gastric compliance are confirmed here.

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.