The reactivity of serotonin, acetylcholine and kcl-induced contractions to relaxant agents in the rat gastric fundus

Inhibitory mechanisms of docosahexaenoic acid on carbachol-, angiotensin II-, and bradykinin-induced contractions in guinea pig gastric fundus smooth muscle

We studied the inhibitory actions of docosahexaenoic acid (DHA) on the contractions induced by carbachol (CCh), angiotensin II (Ang II), and bradykinin (BK) in guinea pig (GP) gastric fundus smooth muscle (GFSM), particularly focusing on the possible inhibition of store-operated Ca2+ channels (SOCCs). DHA significantly suppressed the contractions induced by CCh, Ang II, and BK; the inhibition of BK-induced contractions was the strongest. Although all contractions were greatly dependent on external Ca2+, more than 80% of BK-induced contractions remained even in the presence of verapamil, a voltage-dependent Ca2+ channel inhibitor. BK-induced contractions in the presence of verapamil were not suppressed by LOE-908 (a receptor-operated Ca2+ channel (ROCC) inhibitor) but were suppressed by SKF-96365 (an SOCC and ROCC inhibitor). BK-induced contractions in the presence of verapamil plus LOE-908 were strongly inhibited by DHA. Furthermore, DHA inhibited GFSM contractions induced by cyclopiazonic acid (CPA) in the presence of verapamil plus LOE-908 and inhibited the intracellular Ca2+ increase due to Ca2+ addition in CPA-treated 293T cells. These findings indicate that Ca2+ influx through SOCCs plays a crucial role in BK-induced contraction in GP GFSM and that this inhibition by DHA is a new mechanism by which this fatty acid inhibits GFSM contractions.

Electrophysiology, molecular modelling, and functional analysis of the effects of dietary quercetin and flavonoid analogues on Kir6.1 channels in rat stomach fundus smooth muscle

Flavonoids, ubiquitously distributed in the plant world, are regularly ingested with diets rich in fruit, vegetables, wine, and tea. During digestion, they are partially absorbed in the stomach. The present work aimed to assess the in vitro effects of quercetin and ten structurally related flavonoids on the rat gastric fundus smooth muscle, focussing on ATP-dependent K+ (Kir6.1) channels, which play a central role in the regulation of resting membrane potential, membrane excitability and, consequently, of gastric motility. Whole-cell currents through Kir6.1 channels (IKir6.1) were recorded with the patch-clamp technique and the mechanical activity of gastric fundus smooth muscle strips was studied under isometric conditions. Galangin ≈ tamarixetin > quercetin > kaempferol > isorhamnetin ≈ luteolin ≈ fisetin > (±)-taxifolin inhibited pinacidil-evoked, glibenclamide-sensitive IKir6.1 in a concentration-dependent manner. Morin, rutin, and myricetin were ineffective. The steric hindrance of the molecule and the number and position of hydroxyl groups on the B ring played an important role in the activity of the molecule. Molecular docking simulations revealed a possible binding site for flavonoids in the C-terminal domain of the Kir6.1 channel subunit SUR2B, in a flexible loop formed by residues 251 to 254 of chains C and D. Galangin and tamarixetin, but not rutin relaxed both high K+- and carbachol-induced contraction of fundus strips in a concentration-dependent manner. Furthermore, both flavonoids shifted to the right the concentration-relaxation curves to either pinacidil or L-cysteine constructed in strips pre-contracted by high K+, rutin being ineffective. In conclusion, IKir6.1 inhibition exerted by dietary flavonoids might counterbalance their myorelaxant activity, affect gastric accommodation or, at least, some stages of digestion.

Motor Dysfunction of Gastric Antral Smooth Muscle in Diabetic Rats: Contribution of ATP-Dependent Potassium Channels

Background

The goal of the current research was to further elucidate the role of adenosine triphosphate (ATP)-sensitive potassium (KATP) channels in the motility and contractility force of gastric smooth muscle of diabetic rats.

Materials and Methods

Male Wistar rats (190-230 g) were grouped into control and streptozotocin (STZ)-induced diabetes (55 mg/kg) rats. Thirty days later, gastric muscle contractility was measured using a myograph and a force transducer of antral segments immersed in a tissue bath. Gastric emptying response was measured through feeding of standard pellet. Furthermore, the expression of KATP channel subunits in antral smooth muscle was determined by western blot technique.

Results

The amplitude of KCl-evoked twitch contractions of diabetic antral strips was about 25% more than control (P < 0.05). Application of minoxidil, a KATP channel opener, dose dependently decreased the force of twitch contractions in both normal and diabetic antral strips. Application of 10 μM glibenclamide, a KATP channel blocker, did not antagonize the minoxidil-induced relaxation of antral strips. Diabetic gastric emptying was faster than normal, although not significant. Despite the relaxant effect of minoxidil on gastric emptying rate in normal rats (P < 0.05), this effect was not observed in diabetic rats. Also, glibenclamide increased gastric emptying and antagonized minoxidil-induced relaxation in normal rats (P < 0.05). Furthermore, the expression of KATP Kir6.1 and SUR2B subunits was substantially reduced in antral smooth muscle in diabetic condition (P < 0.01).

Conclusion

These results propose that KATP channels may contribute to the development of gastric motility disorders in diabetes.

Antispasmodic Effect of Asperidine B, a Pyrrolidine Derivative, through Inhibition of L-Type Ca2+ Channel in Rat Ileal Smooth Muscle

Antispasmodic agents are used for modulating gastrointestinal motility. Several compounds isolated from terrestrial plants have antispasmodic properties. This study aimed to explore the inhibitory effect of the pyrrolidine derivative, asperidine B, isolated from the soil-derived fungus Aspergillus sclerotiorum PSU-RSPG178, on spasmodic activity. Isolated rat ileum was set up in an organ bath. The contractile responses of asperidine B (0.3 to 30 µM) on potassium chloride and acetylcholine-induced contractions were recorded. To investigate its antispasmodic mechanism, CaCl2, acetylcholine, Nω-nitro-l-arginine methyl ester (l-NAME), nifedipine, methylene blue and tetraethylammonium chloride (TEA) were tested in the absence or in the presence of asperidine B. Cumulative concentrations of asperidine B reduced the ileal contraction by ~37%. The calcium chloride and acetylcholine-induced ileal contraction was suppressed by asperidine B. The effects of asperidine B combined with nifedipine, atropine or TEA were similar to those treated with nifedipine, atropine or TEA, respectively. In contrast, in the presence of l-NAME and methylene blue, the antispasmodic effect of asperidine B was unaltered. These results suggest that the antispasmodic property of asperidine B is probably due to the blockage of the L-type Ca2+ channel and is associated with K+ channels and muscarinic receptor, possibly by affecting non-selective cation channels and/or releasing intracellular calcium.

Potential Role of Tocotrienols on Non-Communicable Diseases: A Review of Current Evidence

Tocotrienol (T3) is a subfamily of vitamin E known for its wide array of medicinal properties. This review aimed to summarize the health benefits of T3, particularly in prevention or treatment of non-communicable diseases (NCDs), including cardiovascular, musculoskeletal, metabolic, gastric, and skin disorders, as well as cancers. Studies showed that T3 could prevent various NCDs, by suppressing 3-hydroxy-3-methylglutaryl-coenzyme A reductase (HMGCR) in the mevalonate pathway, inflammatory response, oxidative stress, and alternating hormones. The efficacy of T3 in preventing/treating these NCDs is similar or greater compared to tocopherol (TF). TF may lower the efficacy of T3 because the efficacy of the combination of TF and T3 was lower than T3 alone in some studies. Data investigating the effects of T3 on osteoporosis, arthritis, and peptic ulcers in human are limited. The positive outcomes of T3 treatment obtained from the preclinical studies warrant further validation from clinical trials.

Origanum majorana L. extract exhibit positive cooperative effects on the main mechanisms involved in acute infectious diarrhea

ETHNOPHARMACOLOGICAL RELEVANCE

Origanum majorana L. (Lamiaceae) is commonly used in Moroccan folk medicine to treat infantile colic, abdominal discomfort and diarrhea. Liquid stools and abdominal discomfort observed in acute infectious diarrhea are the consequences of imbalance between intestinal water secretion and absorption in the lumen, and relaxation of smooth muscle surrounding the intestinal mucosa.

AIM OF THE STUDY

The objective of our study was to see if aqueous extract of Origanum majorana L. (AEOM) may exhibit an effect on those deleterious mechanisms.

MATERIALS AND METHODS

The effect of AEOM on electrogenic Cl^- secretion and Na⁺ absorption, the two main mechanisms underlying water movement in the intestine, was assessed on intestinal pieces of mice intestine mounted, in vitro, in Ussing chambers. AEOM effect on muscle relaxation was measured on rat intestinal smooth muscle mounted in an isotonic transducer.

RESULTS

1) AEOM placed on the serosal (i.e. blood) side of the piece of jejunum entirely inhibited in a concentration-dependent manner the Forskolin-induced electrogenic chloride secretion, with an IC₅₀ = 654 ± 8 µg/mL. 2) AEOM placed on the mucosal (i.e. luminal) side stimulated in a concentration-dependent manner an electrogenic Na⁺ absorption, with an IC₅₀ = 476.9 ± 1 µg/mL. 3) AEOM (1 mg/mL) inhibition of Forskolin-induced electrogenic secretion was almost entirely prevented by prior exposure to Ca⁺⁺ channels or neurotransmitters inhibitors. 4) AEOM (1 mg/mL) proabsorptive effect was greater in the ileum and progressively declined in the jejunum, distal colon and proximal colon (minimal). 5) AEOM inhibited in a concentration-dependent manner smooth muscle Carbachol or KCl induced contraction, with an IC₅₀ = 1.64 ± 0.2 mg/mL or 1.92 ± 0.8 mg/mL, respectively.

CONCLUSION

the present results indicate that aqueous extract of Origanum majorana L. exhibit positive cooperative effects on the main mechanisms that are involved in acute infectious diarrhea.

Relaxant effect of atorvastatin on isolated rat gastric fundus strips: implications for Ca2+-signalling mechanisms

Statins are determined to have various pleiotropic effects apart from their lipid-lowering properties. Herein, we investigated the direct effects of atorvastatin on gastric smooth muscle tone. Atorvastatin effectively relaxed isolated rat gastric fundus strips precontracted with acetylcholine, potassium chloride, and serotonin. Incubation of the strips with nitric oxide synthase inhibitor, l-NOARG (10−4 M, 20 min), l-type voltage-operated Ca2+ channel (VOCC) blocker, nifedipine (10−6 M, 30 min), KATP channel blocker, glibenclamide (10−5 M, 30 min), or precursor of cholesterol, mevalonate (10−2 M, 45 min) did not change the relaxations to atorvastatin. However, pretreatment of fundus strips with atorvastatin (3×10−5–3×10−4 M, 30 min) inhibited the contractions to calcium chloride (10−4–10−1 M), acetylcholine (10–4 M), and caffeine (20 mM) in the calcium-free medium. Moreover, atorvastatin reduced the contractions induced by sarco-endoplasmic reticulum Ca2+-ATPase (SERCA) inhibitor, cyclopiazonic acid (10−7–3×10−5 M). The current study demonstrated that atorvastatin produces an acute relaxant effect on gastric fundus strips, which appears to be mediated by several Ca2+-signalling mechanisms such as the blockade of l-type VOCC-independent Ca2+ entry, decrease in smooth muscle Ca2+ sensitivity, inhibition of IP3- and ryanodine-sensitive intracellular stores to mediate Ca2+ release, as well as the activation of SERCA. This acute relaxing effect seems unlikely to be related with nitric oxide, KATP channels, and the mevalonate pathway.

Antidiarrheal effect of extract from the bark of Combretum leprosum in mice

This study investigated the effects of the ethanolic extract from the bark of Combretum leprosum (ECL) on intestinal transit and castor-oil induced diarrhea in mice. The oral administration of ECL (750 and 1000 mg/kg) slowed intestinal transit (ID50 of 455 mg/kg). The ECL (250-1000 mg/kg) reduced castor-oil induced diarrhea, in a time- and dose-dependent manner (p < 0.05). To determine if antidiarrheal effect of ECL involves α2-adrenergic or opioid receptor activation, the mice were pretreated with antagonists of these receptors, yohimbine or naloxone respectively. None of these drugs inhibited the antidiarrheal effect of ECL. To test if antidiarrheal effect of ECL is due to an antisecretory action, we realized the enteropooling assay on rats. The ECL increased bowel content and did not inhibit intestinal fluid secretion increase induced by misoprostol (100 µg/kg, s.c.). To determine if antimotility effect of ECL is due to a reduction on gastric motility, we realized the organ bath assay in the rat fundus stomach. Isotonic recordings show that the carbachol /KCl - induced contraction was not reversed by the addition of ECL. In conclusion, our results suggest that ECL contains antidiarrheal compounds and these compounds could induce a reduction of intestinal tract motility.

Extracellular acidosis selectively inhibits pharmacomechanical coupling induced by carbachol in strips of rat gastric fundus

NEW FINDINGS

What is the central question of this study? Acute acidosis that results from short-term exercise is involved in delayed gastric emptying in rats and the lower responsiveness of gastric fundus strips to carbachol. Does extracellular acidosis decrease responsiveness to carbachol in tissues of sedentary rats? How? What is the main finding and its importance? Extracellular acidosis inhibits cholinergic signalling in the rat gastric fundus by selectively influencing the G_q/11 protein signalling pathway. Acute acidosis that results from short-term exercise delays gastric emptying in rats and decreases the responsiveness to carbachol in gastric fundus strips. The regulation of cytosolic Ca²⁺ concentrations appears to be a mechanism of action of acidosis. The present study investigated the way in which acidosis interferes with gastric smooth muscle contractions. Rat gastric fundus isolated strips at pH 6.0 presented a lower magnitude of carbachol-induced contractions compared with preparations at pH 7.4. This lower magnitude was absent in carbachol-stimulated duodenum and KCl-stimulated gastric fundus strips. In Ca²⁺ -free conditions, repeated contractions that were induced by carbachol progressively decreased, with no influence of extracellular pH. In fundus strips, CaCl₂ -induced contractions were lower at pH 6.0 than at pH 7.4 but only when stimulated in the combined presence of carbachol and verapamil. In contrast, verapamil-sensitive contractions that were induced by CaCl₂ in the presence of KCl did not change with pH acidification. In Ca²⁺ store-depleted preparations that were treated with thapsigargin, the contractions that were induced by extracellular Ca²⁺ restoration were smaller at pH 6.0 than at pH 7.4, but relaxation that was induced by SKF-96365 (an inhibitor of store-operated Ca²⁺ entry) was unaltered by extracellular acidification. At pH 6.0, the phospholipase C inhibitor U-73122 relaxed carbachol-induced contractions less than at pH 7.4, and this phenomenon was absent in tissue that was treated with the RhoA kinase blocker Y-27632. Thus, extracellular acidosis inhibited pharmacomechanical coupling in gastric fundus by selectively inhibiting the G_q/11 protein signalling pathway, whereas electromechanical coupling remained functionally preserved.

Acid-gastric antisecretory effect of the ethanolic extract from Arctium lappa L. root: role of H+, K+-ATPase, Ca2+ influx and the cholinergic pathway

BACKGROUND

Arctium lappa L., popularly known as burdock, is a medicinal plant used worldwide. The antiulcer and gastric-acid antisecretory effects of ethanolic extract from roots of Arctium lappa (EET) were already demonstrated. However, the mechanism by which the extract reduces the gastric acid secretion remains unclear. Therefore, this study was designed to evaluate the antisecretory mode of action of EET.

MATERIALS AND METHODS

The effects of EET on H⁺, K⁺-ATPase activity were verified in vitro, whereas the effects of the extract on cholinergic-, histaminergic- or gastrinergic-acid gastric stimulation were assessed in vivo on stimulated pylorus ligated rats. Moreover, ex vivo contractility studies on gastric muscle strips from rats were also employed.

RESULTS

The incubation with EET (1000 µg/ml) partially inhibited H⁺, K⁺-ATPase activity, and the intraduodenal administration of EET (10 mg/kg) decreased the volume and acidity of gastric secretion stimulated by bethanechol, histamine, and pentagastrin. EET (100-1000 µg/ml) did not alter the gastric relaxation induced by histamine but decreased acetylcholine-induced contraction in gastric fundus strips. Interestingly, EET also reduced the increase in the gastric muscle tone induced by 40 mM KCl depolarizing solution, as well as the maximum contractile responses evoked by CaCl₂ in Ca²⁺-free depolarizing solution, without impairing the effect of acetylcholine on fundus strips maintained in Ca²⁺ -free nutritive solution.

CONCLUSION

Our results reinforce the gastric antisecretory properties of preparations obtained from Arctium lappa, and indicate that the mechanisms involved in EET antisecretory effects include a moderate reduction of the H⁺, K⁺-ATPase activity associated with inhibitory effects on calcium influx and of cholinergic pathways in the stomach muscle.

Effects of flavone on the contractile activity of the circular smooth muscle of the rabbit middle colon in vitro

The circular smooth muscles of the middle colon of the rabbit generate giant contractions of high amplitude and low frequency. Flavone, at various concentrations, reduces the giant contractions and the tonic contraction induced by 10 µM carbachol and 80 mM KCl. The contractions induced by dequalinium and tetraethylammonium are reduced by flavone (30 µM). At 100 µM, flavone decreases the contraction induced by 100 µM methylene blue and 1mM orthovanadate. These results suggest that flavone inhibit the giant contractions by (1) inhibition of voltage-dependent Ca(2+) channels, (2) activation of guanyl cyclase, (3) opening of K(+) channels and (4) inhibition of tyrosines kinases.

Melatonin therapy for REM sleep behavior disorder: a critical review of evidence

Rapid eye movement (REM) sleep behavior disorder (RBD) is a parasomnia associated with dream enactment often involving violent or potentially injurious behaviors during REM sleep that is strongly associated with synucleinopathy neurodegeneration. Clonazepam has long been suggested as the first-line treatment option for RBD. However, evidence supporting melatonin therapy is expanding. Melatonin appears to be beneficial for the management of RBD with reductions in clinical behavioral outcomes and decrease in muscle tonicity during REM sleep. Melatonin also has a favorable safety and tolerability profile over clonazepam with limited potential for drug-drug interactions, an important consideration especially in elderly individuals with RBD receiving polypharmacy. Prospective clinical trials are necessary to establish the evidence basis for melatonin and clonazepam as RBD therapies.

Pharmacological basis for the medicinal use of ginger in gastrointestinal disorders

Ginger (rhizome of Zingiber officinale) has been widely used for centuries in gastrointestinal disorders, particularly dyspepsia, but its precise mode of action has yet to be elucidated. This study was undertaken to study the prokinetic action of ginger and its possible mechanism of action. Prokinetic activity of ginger extract (Zo.Cr) was confirmed in an in vivo test when it enhanced the intestinal travel of charcoal meal in mice. This propulsive effect of the extract, similar to that of carbachol, was blocked in atropine-pretreated mice, a standard cholinergic antagonist. Likewise, Zo.Cr showed an atropine-sensitive dose-dependent spasmogenic effect in vitro as well as in isolated rat and mouse stomach fundus tissues. In atropinized tissue, it showed spasmolytic activity as shown by the inhibition of 5-HT- and K+-induced contractions. A spasmolytic effect was also observed in other gut preparations either as noncompetitive inhibition of agonist dose-response curves, inhibition of high K+(80 mM)-induced contractions, or displacement of Ca2+ dose-response curves to the right, indicating a calcium antagonist effect. Phytochemical analysis revealed the presence of saponins, flavonoids, and alkaloids in the crude extract. These data indicate that Zo.Cr contains a cholinergic, spasmogenic component evident in stomach fundus preparations which provides a sound mechanistic insight for the prokinetic action of ginger. In addition, the presence of a spasmolytic constituent(s) of the calcium antagonist type may explain its use in hyperactive states of gut like colic and diarrhea.