Mechanisms involved in the muscle relaxing effects of STW 5 in guinea pig stomach

INTRODUCTION

The herbal preparation STW 5 ameliorates functional dyspepsia partly by relaxing smooth muscle of the proximal stomach, thus improving gastric accommodation. We explored the unknown pathways responsible for this effect by testing targets known to modulate gastric smooth muscle relaxation.

METHODS

STW 5-induced relaxation of smooth muscle strips from guinea pig gastric corpus before and after pharmacological interventions were recorded with force transducers in an organ bath. ORAI1 mRNA expression was tested in the proximal stomach.

KEY RESULTS

Blockade of Ca2+ -activated K+ and Cl- channels, voltage-gated L- or T-type Ca2+ channels, TRPA1-, TRPV1-, adenosine or 5-HT4 receptors, antagonizing ryanodine receptors, inhibiting cyclooxygenase or sarcoplasmic reticulum calcium ATPase did not affect STW 5-evoked relaxation. Likewise, protein-kinase A or G were not involved. However, the relaxation evoked by STW 5 was significantly reduced by phorbol-12-myristat-13-acetat, an activator of protein-kinase C, by 2- aminoethyldiphenylborinate, an inhibitor of the IP3 receptor-mediated Ca2+ release from the sarcoplasmic reticulum or by SKF-96365, a nonselective store-operated calcium entry (SOCE) blocker. Furthermore, the mixed TRPC3/SOCE inhibitor Pyr3, but not the selective TRPC3 blocker Pyr10, reduced the effect of STW 5. Finally, BTP2, a potent blocker of ORAI-coupled SOCE, almost abolished STW 5-evoked relaxation. Expression of ORAI1 could be demonstrated in the corpus/fundus.

CONCLUSIONS & INFERENCES

STW 5 inhibited SOCE, most likely ORAI channels, which are modulated by IP3- and PKC-dependent mechanisms. Our findings impact on the design of drugs to induce muscle relaxation and help identify phytochemicals with similar modes of actions to treat gastrointestinal disturbances.

Effect of spraying l-menthol on peristalsis resumption during endoscopic submucosal dissection of gastric tumors

Background and Aim

l‐Menthol has smooth muscle‐relaxing and antiperistaltic effects. We examined its effectiveness against peristalsis resumption during endoscopic submucosal dissection (ESD) of gastric tumors.

Methods

We retrospectively examined clinical data of 485 patients (501 lesions) who underwent ESD for upper gastrointestinal tumors in 2017. We included 119 patients (127 lesions) in whom peristaltic movement resumed during ESD and l‐menthol was applied; 366 patients (374 lesions) without l‐menthol application were used as controls. Video recordings were reviewed to determine whether l‐menthol suppressed peristalsis resumption.

Results

In cases with l‐menthol application, 2 (2.9%), 36 (14.3%), and 89 (71.2%) lesions were found in the upper (U), middle (M), and lower (L) regions, respectively. In the control group, the corresponding values were 66 (17.6%), 215 (57.5%), and 93 (24.9%), respectively. l‐Menthol efficacy was observed in 116 of the 127 treated lesions (91.3%), over 90% of which were in the posterior wall of the U region, anterior wall and greater curvature of the M region, and anterior wall and lesser curvature of the L region. The most and least effective areas for l‐menthol application were the anterior wall of gastric antrum and posterior wall of the M region, respectively. The mean time from application to peristalsis inhibition was 8.7 s. No adverse effects were observed; perforation and secondary hemorrhage were not significantly different between the groups.

Conclusion

Direct l‐menthol application to the submucosal layer during mucosal resection affects smooth muscles and rapidly inhibits peristalsis resumption. Clinically, l‐Menthol can be used to suppress peristalsis recurrence during ESD, without adverse effects.

Rikkunshito induces gastric relaxation via the β-adrenergic pathway in Suncus murinus

BACKGROUND

Rikkunshito (RKT) is a gastroprotective herbal medicine. In this study, we investigated the role of RKT in the relaxation of the gastric body (fundus and corpus) and antrum.

METHODS

We used Suncus murinus, a unique small model animal with similar gastrointestinal motility to humans and dogs. RKT was added at 0.1, 1.0, and 5.0 mg/mL to induce relaxation in vitro; the outcome measure was the intensity of relaxation. The number of spontaneous antral contractions in the absence or the presence of RKT was also counted.

KEY RESULTS

Rikkunshito induced the relaxation of the gastric body and antrum and decreased the number of spontaneous antral contractions in a dose-dependent manner. The responses to RKT (1.0 mg/mL) were not affected by pretreatment with atropine, N-nitro-l-arginine methyl ester, ritanserin, or ondansetron. On the other hand, timolol almost completely reversed the relaxation induced by RKT (1.0 mg/mL) on the gastric body and antrum and the occurrence of the spontaneous antral contractions. Both butoxamine, a β(2) -adrenoreceptor antagonist, and L 748337, a β(3) -adrenoreceptor antagonist, but not CGP 20712, a β(1) -adrenoreceptor antagonist, significantly reversed the RKT-induced (1.0 mg/mL) gastric relaxation.

CONCLUSIONS & INFERENCES

These results indicate that RKT stimulates and modulates gastric relaxation through β(2) - and β(3) -adrenergic, but not β(1) -adrenergic, pathways in S. murinus.

Inhibition of gastric motility by hyperglycemia is mediated by nodose ganglia KATP channels

The inhibitory action of hyperglycemia is mediated by vagal afferent fibers innervating the stomach and duodenum. Our in vitro studies showed that a subset of nodose ganglia neurons is excited by rising ambient glucose, involving inactivation of ATP-sensitive K(+) (K(ATP)) channels and leading to membrane depolarization and neuronal firing. To investigate whether nodose ganglia K(ATP) channels mediate gastric relaxation induced by hyperglycemia, we performed in vivo gastric motility studies to examine the effects of K(ATP) channel activators and inactivators. Intravenous infusion of 20% dextrose induced gastric relaxation in a dose-dependent manner. This inhibitory effect of hyperglycemia was blocked by diazoxide, a K(ATP) channel activator. Conversely, tolbutamide, a K(ATP) channel inactivator, induced dose-dependent gastric relaxation, an effect similar to hyperglycemia. Vagotomy, perivagal capsaicin treatment, and hexamethonium each prevented the inhibitory action of tolbutamide. Similarly, N(G)-nitro-l-arginine methyl ester, an inhibitor of nitric oxide synthase, also blocked tolbutamide's inhibitory effect. To show that K(ATP) channel inactivation at the level of the nodose ganglia induces gastric relaxation, we performed electroporation of the nodose ganglia with small interfering RNA of Kir6.2 (a subunit of K(ATP)) and plasmid pEGFP-N1 carrying the green fluorescent protein gene. The gastric responses to hyperglycemia and tolbutamide were not observed in rats with Kir6.2 small interfering RNA-treated nodose ganglia. However, these rats responded to secretin, which acts via the vagal afferent pathway, independently of K(ATP) channels. These studies provide in vivo evidence that hyperglycemia induces gastric relaxation via the vagal afferent pathway. This action is mediated through inactivation of nodose ganglia K(ATP) channels.

Secretin-induced gastric relaxation is mediated by vasoactive intestinal polypeptide and prostaglandin pathways

Secretin has been shown to delay gastric emptying and inhibit gastric motility. We have demonstrated that secretin acts on the afferent vagal pathway to induce gastric relaxation in the rat. However, the efferent pathway that mediates the action of secretin on gastric motility remains unknown. We recorded the response of intragastric pressure to graded doses of secretin administered intravenously to anaesthetized rats using a balloon attached to a catheter and placed in the body of the stomach. Secretin evoked a dose-dependent decrease in intragastric pressure. The threshold dose of secretin was 1.4 pmol kg(-1) h(-1) and the effective dose, 50% was 5.6 pmol kg(-1) h(-1). Pretreatment with hexamethonium markedly reduced gastric relaxation induced by secretin (5.6 pmol kg(-1) h(-1)). Bilateral vagotomy also significantly reduced gastric motor responses to secretin. Administration of N(G)-nitro-L-arginine methyl ester (10 mg kg(-1)) did not affect gastric relaxation induced by secretin. In contrast, intravenous administration of a vasoactive intestinal polypeptide (VIP) antagonist (30 nmol kg(-1)) reduced the gastric relaxation response to secretin (5.6 pmol kg(-1) h(-1)) by 89 +/- 5%. Indomethacin (2 mg kg(-1)) reduced gastric relaxation induced by secretin (5.6 pmol kg(-1) h(-1)) by 87 +/- 5%. Administration of prostaglandin (48 mg kg(-1) h(-1)) prevented this inhibitory effect. Indomethacin also reduced gastric relaxation induced by VIP (300 pmol kg(-1)) by 90 +/- 7%. These observations indicate that secretin acts through stimulation of presynaptic cholinergic neurons in a vagally mediated pathway. Through nicotinic synapses, secretin stimulates VIP release from postganglionic neurons in the gastric myenteric plexus, which in turn induces gastric relaxation through a prostaglandin-dependent pathway.

In vivo characterization of 5-HT1A receptor-mediated gastric relaxation in conscious dogs

Accumulating data have been published emphasizing the important role of 5-hydroxytryptamine (5-HT) receptors in proximal stomach relaxation. However, a proper in vivo characterization of 5-HT receptors mediating gastric relaxation is still missing. In the current study, we focus on the in vivo characterization of 5-HT1A receptors mediating relaxation of the proximal stomach in conscious dogs. Beagle dogs were equipped with a gastric fistula. In the conscious state, volume changes within an intragastric bag were measured at constant pressure by means of a barostat. Results are presented as the maximum volume increase after treatment (mean+/-s.e.m.). All drugs were injected intravenously. The 5-HT1A receptor agonist flesinoxan (10, 50, 100 and 150 microg kg-1) induced a dose-dependent relaxation of the canine proximal stomach (50+/-10, 230+/-51, 290+/-38 and 275+/-33 ml, respectively; n=9-11). The selective 5-HT1A receptor antagonist WAY-100635 dose-dependently inhibited the flesinoxan-induced relaxation. NG-nitro-l-arginine methyl ester did not affect this relaxation, suggesting that nitrergic nerves are not involved. After supradiaphragmatic vagotomy, the baseline of the intragastric volume was larger compared to that before vagotomy (317+/-50 vs 142+/-28 ml, respectively; n=5). Compensation for this by either reduction of the intraballoon pressure or infusion of a contractile dose of bethanechol did not establish a condition in which flesinoxan was able to relax the stomach. In contrast, nitroprusside induced a significant gastric relaxation when tone was increased by bethanechol. It is concluded that flesinoxan induces proximal gastric relaxation in conscious dogs via 5-HT1A receptors. The response is mediated through a vagal pathway without involvement of nitrergic nerves.

NANC inhibitory neurotransmission in mouse isolated stomach: involvement of nitric oxide, ATP and vasoactive intestinal polypeptide

1. The neurotransmitters involved in NANC relaxation and their possible interactions were investigated in mouse isolated stomach, recording the motor responses as changes of endoluminal pressure from whole organ. 2. Field stimulation produced tetrodotoxin-sensitive, frequency-dependent, biphasic responses: rapid transient relaxation followed by a delayed inhibitory component. 3. The inhibitor of the synthesis of nitric oxide (NO), l-NAME, abolished the rapid relaxation and significantly reduced the slow relaxation. Apamin, blocker of Ca2+-dependent K+ channels, or ADPbetaS, which desensitises P2y purinoceptors, reduced the slow relaxation to 2-8 Hz, without affecting that to 16-32 Hz or the fast relaxation. alpha-Chymotrypsin or vasoactive intestinal polypeptide 6-28 (VIP6-28), antagonist of VIP receptors, failed to affect the fast component or the delayed relaxation to 2-4 Hz, but antagonised the slow component to 8-32 Hz. 4. Relaxation to sodium nitroprusside was not affected by l-NAME, apamin or ADPbetaS, but was reduced by alpha-chymotrypsin or VIP6-28. Relaxation to VIP was abolished by alpha-chymotrypsin, antagonised by VIP6-28, but was not affected by l-NAME, apamin or ADPbetaS. Relaxation to ATP was abolished by apamin, antagonised by ADPbetaS, but was not affected by l-NAME or alpha-chymotrypsin. 5. The present results suggest that NO is responsible for the rapid relaxation and partly for the slow relaxation. ATP is involved in the slow relaxation evoked by low frequencies of stimulation. VIP is responsible for the slow relaxation evoked by high frequencies of stimulation. The different neurotransmitters appear to work in parallel, although NO could serve also as a neuromodulator that facilitates release of VIP.