Exogenous motilin affects postprandial proximal gastric motor function and visceral sensation

Why is motilin active in some studies with mice, rats, and guinea pigs, but not in others? Implications for functional variability among rodents

The gastrointestinal (GI) hormone motilin helps control human stomach movements during hunger and promotes hunger. Although widely present among mammals, it is generally accepted that in rodents the genes for motilin and/or its receptor have undergone pseudonymization, so exogenous motilin cannot function. However, several publications describe functions of low concentrations of motilin, usually within the GI tract and CNS of mice, rats, and guinea pigs. These animals were from institute-held stocks, simply described with stock names (e.g., "Sprague-Dawley") or were inbred strains. It is speculated that variation in source/type of animal introduces genetic variations to promote motilin-sensitive pathways. Perhaps, in some populations, motilin receptors exist, or a different functionally-active receptor has a good affinity for motilin (indicating evolutionary pressures to retain motilin functions). The ghrelin receptor has the closest sequence homology, yet in non-rodents the receptors have a poor affinity for each other's cognate ligand. In rodents, ghrelin may substitute for certain GI functions of motilin, but no good evidence suggests rodent ghrelin receptors are highly responsive to motilin. It remains unknown if motilin has functional relationships with additional bioactive molecules formed from the ghrelin and motilin genes, or if a 5-TM motilin receptor has influence in rodents (e.g., to dimerize with GPCRs and create different pharmacological profiles). Is the absence/presence of responses to motilin in rodents' characteristic for systems undergoing gene pseudonymization? What are the consequences of rodent supplier-dependent variations in motilin sensitivity (or other ligands for receptors undergoing pseudonymization) on gross physiological functions? These are important questions for understanding animal variation.

Research on mechanism of charred hawthorn on digestive through modulating "brain-gut" axis and gut flora

ETHNOPHARMACOLOGICAL RELEVANCE

Hawthorn is a traditional Chinese medicine for high-calorie-diet-induced dyspepsia (HC-DID) for thousands of years old. Based on traditional Chinese medicine (TCM) theory and clinical and non-clinical trials, its stir-frying processed product, charred hawthorn, possesses better effect. At present, most research mainly focuses on chemical constituents of hawthorn before and after stir-frying process, but there is no relevant action-mechanism study about fragrant odor promoting HC-DID during the stir-frying process of the hawthorn.

AIM OF THE STUDY

The purpose of the present study is to research on mechanism of hawthorn decoction coupled with odor of charred hawthorn on digestive in rats with HC-DID.

MATERIALS AND METHODS

The SPF Kunming (KM) mice and Sprague Dawley (SD) rats were randomly divided into 7 groups: control group, model group, cisapride group, hawthorn group (HT), charred hawthorn group (CHT), odor of charred hawthorn (OCHT), CHT + OCHT group. The rats were modeled as HC-DID, whose treatment by intragastric administration and odor administration. Obvious symptoms of HC-DID were observed. Gastrointestinal motility were detected. Histopathology was performed in hypothalamus and gastrointestinal tract. Related brain-gut peptides were assayed in serum, hypothalamus and gastrointestinal tract. Illumina Miseq platform was used for 16S rDNA high-throughput sequencing to detect the intestinal flora structure of the caecum of rats.

RESULTS

Traditional Chinese medicine decoction of hawthorn (HT and CHT) regulated the body weight, food intake, gastrointestinal motility and abnormal secretion of brain-gut peptides in rats with HC-DID, and the odor of charred hawthorn also had good curative effect for it. Moreover, the intestinal dysbiosis was induced by high-calorie diet in rats with dyspepsia, and hawthorn decoction could ease this trend.

CONCLUSION

The above study showed that hawthorn decoction coupled with the odor of charred hawthorn effectively alleviate HC-DID in rats by regulating the "Brain-Gut" axis and gut flora. Odor treatment of hawthorn could be a potential therapeutic approach for HC-DID.

Treatment with Xiaochaihu decoction increases serum levels of motilin and gastrin in rats with dyspepsia

AIM: To observe the influence of treatment with Xiaochaihu decoction on serum levels of motilin (MTL) and gastrin (GAS) in a rat model of dyspepsia (syndrome of liver-qi stagnation and spleen-qi deficiency) and to analyze the mechanisms behind therapeutic effects of Xiaochaihu decoction on dyspepsia.

METHODS: Forty-eight rats were randomly divided into four groups (n = 12 for each): blank group (BG), model group (MG), Xiaochaihu decoction group (XG), and domperidone group (DG). Except the BG group, dyspepsia was induced in rats of the other three groups by applying chronic restraint stress + excessive fatigue + irregular food for 21 consecutive days. XG and DG rats were then intragastrically administered with Xiaochaihu decoction and domperidone daily for 14 d, and BG and MG rats were given equal volume of physiological saline. On day 35, the treatment was discontinued and all rats were fasted for 24 h with free access to water. Blood samples were collected on day 36 for testing.

RESULTS: Compared to the BG group, serum MTL content in the MG group significantly decreased (P < 0.01). Compared to the MG group, serum MTL content in the XG and DG groups significantly increased (both P ≤ 0.01). Compared to the BG group, serum GAS content in the MG group significantly decreased (P < 0.01). Compared to the MG group, serum GAS content in the XG and DG groups significantly increased (both P ≤ 0.01).

CONCLUSION: Treatment with Xiaochaihu decoction increased serum levels of MTL and GAS in rats with dyspepsia.

The roles of motilin and ghrelin in gastrointestinal motility

In structure, ghrelin resembles motilin. The two peptides are considered to be members of the motilin-ghrelin peptide family. Motilin is considered to be an endocrine regulator of the interdigestive migrating contractions, the fasted motor pattern in the gastrointestinal (GI) tract. It has been reported that ghrelin stimulates GI motility. The gastrokinetic capacity of ghrelin has been well documented in the rodent. However, there have been few positive reports of the gastrokinetic capacity of ghrelin in dogs. Some reports with human subjects have shown that an i.v. ghrelin injection accelerated gastric emptying of a meal and improved meal-related symptoms. These results suggest that ghrelin has potential as a prokinetic. However, it seems unlikely that plasma ghrelin would play a physiological role in these digestive physiological events and stimulate gastric emptying, as these outcomes would appear to be in contradiction with the suppression of the endogenous release of ghrelin after eating. The physiological roles of ghrelin need to be clarified.

Motilides: a long and winding road: lessons from mitemcinal (GM-611) on diabetic gastroparesis

Mitemcinal (GM-611) is a macrolide motilin receptor agonist with acid-resistance and without antibiotic activity. Since ABT-229 (a first generation of motilin receptor agonist) had failed to demonstrate symptomatic relief in functional dyspepsia and diabetic gastroparesis, there is a controversy for which of prokinetics or relaxants is clinically beneficial. Currently, oral mitemcinal has been focused on diabetic gastroparesis under clinical development. It showed to accelerate gastric-emptying in diabetic animals and in patients with gastroparesis. The latest double-blind, placebo-controlled study demonstrated to be effective at improving diabetes-related gastroparesis symptoms. A sub-group analysis, which included patients with BMI < 35 kg/m2 and hemoglobin A1c < 10%, there were significantly more symptomatic relieves in the 10 mg mitemcinal group than in the placebo group. The frequency of adverse events did not differ between groups. Mitemcinal shows promise in the subset of patients who should be confirmed in future studies.

Influence of motilin on gastric fundus tone and on meal-induced satiety in man: role of cholinergic pathways

BACKGROUND

Motilin agonists are strong gastroprokinetics, but their impact on symptoms in delayed gastric emptying has been disappointing. It has been speculated that it is due to the contractile effect of motilin agonists on the proximal stomach, but the pathway involved and the symptomatic consequences have been incompletely elucidated.

AIMS

To study whether motilin enhances proximal stomach tone and enhances meal-induced satiety and to evaluate whether this effect involves a cholinergic pathway.

METHODS

A gastric barostat was used to study, in healthy subjects, the effect of motilin (300 ng/kg/30 min i.v.) or saline on fasting gastric fundus tone and on post-prandial relaxation. To evaluate the involvement of a cholinergic pathway, atropine (12 microg/kg/h) was administered intravenously simultaneously with or before and during motilin infusion in the fasting state. Finally, a satiety drinking test was performed in 21 subjects twice after pretreatment with placebo or motilin and with placebo or atropine.

RESULTS

Administration of motilin caused a significant increase of fasting fundus tone expressed as decrease of the mean balloon volume (324 +/- 60 mL vs 213 +/- 62 mL, p < 0.05). Simultaneous administration of atropine and motilin did not generate a significant volume change (192 +/- 60 mL vs 181 +/- 83 mL, NS), but pretreatment with atropine alone induced a relaxation, and when motilin was added this revealed an ongoing contraction (192 +/- 24 mL vs 136 +/- 21 mL, p < or = 0.05). Motilin infusion also inhibited gastric accommodation (p < or = 0.05 vs placebo) and increased satiety during a satiety drinking test (p < or = 0.05 vs placebo).

CONCLUSIONS

Administration of motilin causes a contraction of the proximal stomach in humans and increases meal-induced satiety. The effect of motilin is atropine-resistant and involves a direct muscular pathway or a non-cholinergic neural pathway.

Effects of a nonpeptide motilin receptor antagonist on proximal gastric motor function

AIM

To assess the effects of the motilin receptor antagonist RWJ-68023 on basal and motilin-stimulated proximal gastric volume.

METHODS

Eighteen healthy male volunteers received RWJ-68023 in two different doses or placebo for 135 min. After 45 min, subjects received a motilin infusion for 90 min. Proximal gastric volume was measured with a barostat at constant pressure and during isobaric distensions. Abdominal symptoms were scored using visual analogue scales. Motilin and RWJ-68023 concentrations were assessed by radioimmunoassay and liquid chromatography-mass spectrometry, respectively.

RESULTS

Both dosages of RWJ-68023 were safe and well tolerated. The most common adverse events were of gastrointestinal origin. RWJ-68023 did not affect basal proximal gastric volume, but the high-dose RWJ-68023 reduced the contractile effect of motilin on the stomach. This antagonizing effect of RWJ-68023 was only significant (P = 0.014) during the distension procedure.

CONCLUSIONS

The RWJ-68023 doses used in this study were selected to accomplish plasma concentrations that would block the motilin effect entirely. However, the antagonizing effect of RWJ-68023 was partial and only present when the tonic condition of the stomach was modulated by motilin.

Gallbladder volume as a biomarker for the motilin effect in healthy volunteers and patients with functional dyspepsia

AIM

To investigate a motilin effect on gallbladder volume in healthy volunteers and patients with functional dyspepsia.

METHODS

Forty-three healthy volunteers and 10 patients with functional dyspepsia received motilin (4 pmol.min/kg) or placebo in four separate double-blind, randomized, placebo-controlled, cross-over studies. The gallbladder volume was measured by ultrasonography. Analysis of variance of the combined data of these studies was performed to investigate a motilin effect on gallbladder volume and potential differences between patients and healthy volunteers.

RESULTS

The baseline gallbladder volume was similar for placebo and motilin treatment, as well as for patients and healthy volunteers. Motilin, compared with placebo, significantly decreased the gallbladder volume in healthy volunteers (P = 0.003) and patients (P < 0.0001). A linear concentration-response relationship was observed. The decrease in gallbladder volume by motilin was greater in patients (P = 0.03). The motilin effect was consistent between studies.

CONCLUSION

The interdigestive gallbladder volume is a non-invasive end-point for motilin activity, displaying a consistent response across studies, a clear response to motilin and a clear concentration-response relationship. However, it is less suitable as a biomarker for future pharmacological studies on motilin agonists or antagonists as the effect is probably indirect, and a relatively large study population of 27 subjects is required to demonstrate a 15% decrease in gallbladder volume. Further investigation is required to confirm altered gallbladder motility as a feature of functional dyspepsia.

Motilin effects on the proximal stomach in patients with functional dyspepsia and healthy volunteers

This study investigates motilin effects on the proximal stomach in patients with functional dyspepsia (FD) and healthy volunteers. Eight healthy volunteers and 12 patients with FD were infused with synthetic motilin or placebo. Proximal gastric volume was measured with a barostat at constant pressure and during isobaric distensions. Abdominal symptoms were scored by visual analog scales. Plasma motilin concentrations were measured by radioimmunoassay. Motilin concentrations and baseline gastric volumes were similar for patients and healthy volunteers. Motilin, compared with placebo, reduced gastric volume by 112 ml [F(29,195); confidence interval (CI) 95%] in patients and by 96 ml [F(-7,200); CI 95%] in healthy volunteers. In patients, motilin decreased compliance by 76 ml/mmHg [F(9,143); CI 95%] compared with placebo, which was similar in volunteers [66 ml/mmHg; F(11,120); CI 95%]. Patients were more nauseous during motilin compared with placebo (P = 0.04), whereas healthy volunteers did not experience nausea. We conclude that in a fasted condition, FD patients have a similar proximal gastric motor response to motilin as healthy volunteers, but experience an exaggerated sensation of nausea.