Characterization of the receptors involved in the 5-HT-induced excitation of canine antral longitudinal muscle

Effects of cyproheptadine on body weight gain in children with nonorganic failure to thrive in Taiwan: A hospital-based retrospective study

Failure to thrive (FTT) impairs the expected normal physical growth of children. This study aimed to evaluate the effects of cyproheptadine hydrochloride on growth parameters in prepubertal children with FTT. The medical records of prepubertal children who were newly diagnosed with FTT at China Medical University Hospital between 2007 and 2016 were retrospectively examined. The patients were divided into two groups depending on whether they had (T-group) or had not (NT-group) received cyproheptadine hydrochloride (0.3 mg/kg daily) for at least 14 days. The mean length of the treatment period was 97.22 days (range: 14–532 days). Weight, height, and body mass index were adjusted for age using the median values in the growth charts for Taiwanese boys and girls as the reference. A total of 788 patients aged 3–11 years were enrolled, 50 in the T-group and 738 in the NT-group. No statistically significant difference in the median age-adjusted weight value was noted between the T-group and NT-group during the follow up period. In the T-group, age-adjusted weight and body mass index were inversely associated with age (P <0.001, P <0.001) and positively associated with medication duration (P = 0.026, P = 0.04). Our findings underscore the positive association between cyproheptadine hydrochloride treatment and weight gain among prepubertal children. Further prospective clinical studies with a. longer and consistent treatment course is warranted.

Cyproheptadine: A Potentially Effective Treatment for Functional Gastrointestinal Disorders in Children

Functional gastrointestinal disorders (FGIDs) negatively affect children's quality of life and health care costs. It has been proposed that alteration of gut serotonin leads to gastrointestinal dysmotility, visceral hypersensitivity, altered gastrointestinal secretions, and brain-gut dysfunction. Cyproheptadine, a serotonin antagonist, has been shown to be a potentially effective and safe treatment option in children who meet the clinical criteria for FGIDs. Well-designed multicenter trials with long-term follow-up are needed to further investigate its efficacy. [Pediatr Ann. 2017;46(3):e120-e125.].

A retrospective review of cyproheptadine for feeding intolerance in children less than three years of age: effects and side effects

AIM

Premature infants and those with brain injury often suffer from feeding intolerance and vomiting in the first several years of life. Cyproheptadine is a medication with antihistaminergic, antiserotonergic and anticholinergic effects, thought to increase gastric accommodation. We aimed to retrospectively review our experience using cyproheptadine for feeding intolerance and/or vomiting in children under the age of three.

METHODS

This is a retrospective chart review of 39 patients less than three years of age who were prescribed cyproheptadine for feeding intolerance or vomiting and had follow-up information available.

RESULTS

Starting dose ranged widely (from 0.069 to 0.825 mg/kg/day). Side effects such as sleepiness and constipation were rare. The medication had a significant positive effect, defined as resolution of vomiting, improved feeding tolerance or improved comfort with feeds, in 67% of children. An additional 28% showed possible improvement, defined as some improvement in vomiting or improvement in vomiting or feeding tolerance in conjunction with other changes in addition to cyproheptadine.

CONCLUSION

In our experience, cyproheptadine appears to be safe and effective in decreasing vomiting and feeding intolerance in children less than three years of age. A trial of cyproheptadine could be considered before invasive testing in infants with feeding issues.

Prucalopride: For functional constipation only?

Prucalopride is a new prokinetic agent, recently available in Europe for the treatment of functional constipation in adults in whom treatment with laxatives failed to provide adequate relief. However, due to its intrinsic properties (highly selective agonist activity and high affinity for 5-HT4 receptors, neuroprotection), this drug has shown the potential to be used in other pathologic conditions, in and outside of the gastrointestinal tract. We performed a systematic review of the evidence supporting these possible alternative uses of prucalopride. Further studies in this area are, however, mandatory.

Safety and efficacy of cyproheptadine for treating dyspeptic symptoms in children

OBJECTIVE

To present our experience using cyproheptadine, a potent serotonin antagonist used to stimulate appetite, to treat dyspeptic symptoms in children.

STUDY DESIGN

This was a retrospective open-label study conducted to evaluate the safety and efficacy of cyproheptadine in children with refractory upper gastrointestinal symptoms (eg, nausea, early satiety, vomiting, retching after fundoplication, abdominal pain). Response was graded as resolution if symptoms resolved and medication was discontinued, as significant improvement if symptoms resolved with no further interventions, and as failure with any other outcome.

RESULTS

A total of 80 children (65% females) aged <12 years (mean age, 10 years) were included. Response to therapy was reported in 55% of patients. Multivariate analysis revealed better response in children and females (P = .04 and .03, respectively). No associations were found between response to therapy response and gastric emptying, antroduodenal manometry, functional dyspepsia, vomiting, and use of cyproheptadine as first therapy. Early vomiting (occurring within 1 hour after starting a meal) responded better than late vomiting (P = .03), and patients with retching after undergoing Nissen fundoplication had an 86% response rate. Twenty-four patients (30%) complained of side effects, all mild, including somnolence (16%), irritability and behavioral changes (6%), increased appetite and weight gain (5%), and abdominal pain (2.5%), but only 2 of these patients discontinued therapy. Multivariate analysis demonstrated an association between side effects and lack of response to therapy (P = .04), but no associations with age and sex.

CONCLUSION

Cyproheptadine is safe and effective for treating dyspeptic symptoms in children, particularly in young children and those with early vomiting and retching after fundoplication.

The facilitating effect of prucalopride on cholinergic neurotransmission in pig gastric circular muscle is regulated by phosphodiesterase 4

The influence of the selective 5-HT(4) receptor agonist prucalopride on acetylcholine release from cholinergic nerve endings innervating pig gastric circular muscle and the possible regulation of this effect by phosphodiesterases (PDEs) was investigated, as PDEs have been shown to control the response to 5-HT(4) receptor activation in pig left atrium. Circular muscle strips were prepared from pig proximal stomach and either submaximal cholinergic contractions or tritium outflow after incubation with [(3)H]-choline, induced by electrical field stimulation, were studied. Prucalopride concentration-dependently increased the amplitude of submaximal cholinergic contractions and of acetylcholine release induced by electrical field stimulation. The effect of the highest concentration tested (0.3 μM) on cholinergic contractions was antagonized by the selective 5-HT(4) receptor antagonist GR113808 but not by granisetron or methysergide; the antagonism of prucalopride by GR113808 was confirmed in the release assay. The non-selective PDE-inhibitor 3-isobutyl-methyl-xanthine (IBMX) concentration-dependently reduced the amplitude of the cholinergic contractions; 3 μM IBMX reduced the cholinergic contractions maximally by 16% but it enhanced the facilitating effect of prucalopride from 51 to 83%. IBMX (10 μM) induced and enhanced the facilitating effect of prucalopride on electrically induced acetylcholine release. The selective inhibitors vinpocetine (PDE1), EHNA (PDE2) and cilostamide (PDE3) did not influence the effect of prucalopride on acetylcholine release but the PDE4-inhibitor rolipram (1 μM) enhanced the facilitating effect of prucalopride to the same extent as IBMX. These results demonstrate that 5-HT(4) receptors are present on the cholinergic nerves towards the pig gastric circular muscle, facilitating acetylcholine release; the intracellular transduction pathway of this facilitation is regulated by PDE4. Combination of a 5-HT(4) receptor agonist with selective inhibition of the PDE involved in this regulation of transmitter release might enhance the prokinetic effect of the 5-HT(4) receptor agonist.

Effect of mianserin on gastric sensorimotor function and gastric emptying: a randomized, placebo-controlled, double-blind, crossover study in healthy volunteers

BACKGROUND

Antidepressants such as mianserin can improve symptoms in some functional dyspeptic patients but their mechanism of action remains unclear. We aimed to assess the effects of mianserin on gastric sensorimotor function in man.

METHODS

In this randomized, placebo-controlled, double-blind, crossover study 12 healthy subjects (six men) underwent a gastric barostat study and a gastric emptying breath test after 7 days pretreatment with placebo or mianserin (20 mg; p.o.). Graded isobaric and isovolumetric distentions were performed to determine gastric compliance and sensitivity. Subsequently, intrabag pressure was held constant and the volume increase after administration of a liquid meal (200 mL; 300 kcal) was studied. Breath was sampled before and after ingestion of a test meal and half-emptying times for solids and liquids were determined from the breath samples. Mianserin was compared to placebo using t-tests and mixed model analysis (mean ± SD).

KEY RESULTS

Mianserin did not affect pressures or volumes needed to induce first perception or discomfort. During isovolumetric distensions compliance was decreased after mianserin treatment (1.8 ± 0.4 vs 2.0 ± 0.3 mmHg 100 mL(-1); P < 0.05). Premeal volumes were comparable in both treatment arms (221 ± 99 vs 220 ± 88 mL), but meal-induced relaxation during the first 30 min was significantly inhibited after mianserin treatment (F(6,40) = 2.58, P < 0.05). Mianserin did not affect either solid or liquid gastric emptying.

CONCLUSIONS & INFERENCES

Mianserin does not alter gastric emptying rate or sensitivity to gastric distension, but inhibits gastric accommodation to a meal in its early phase. These observations provide no explanation for the effects of mianserin in functional dyspeptic patients.

Serotonin modulates glutamatergic transmission in the rat olfactory tubercle

The olfactory tubercle (OT) is found in the brains of mammals that are highly dependent on their sense of smell. Its human analogue is the poorly understood anterior perforated substance. Previous work on rat brain slices identified two types of field potential responses from the OT. The association fibre (AF) pathway was sensitive to muscarinic modulation, whereas the lateral olfactory tract (LOT) fibre pathway was not. Here, we establish that serotonin (5-hydroxytryptamine; 5-HT) also inhibits field potential excitatory postsynaptic potentials (EPSPs) in the AF, but not in the LOT fibre, pathway. Parallel experiments with adenosine (ADO) excluded ADO mediation of the 5-HT effect. Exogenous 5-HT at 30 microm caused a long-lasting approximately 40% reduction in the amplitude of AF postsynaptic responses, without affecting the time-course of EPSP decline, indicating a fairly restricted disposition of the 5-HT receptors responsible. The 5-HT(1)-preferring, 5-HT(5)-preferring and 5-HT(7)-preferring agonist 5-carboxamidotryptamine caused similar inhibition at approximately 100 nm. The 5-HT(1A)-preferring ligand 8-hydroxy-di-n-propylamino-tetralin at 10 microm, and the 5-HT uptake inhibitor citalopram at 3 microm, caused inhibition of AF-stimulated field potential responses in the 5-10% range. Order-of-potency information suggested a receptor of the 5-HT(1B) or 5-HT(1D) subtype. The 5-HT(1D) agonist L-694,247 (1 microm) suppressed the AF response by approximately 10% when used on its own. After washing out of L-694,427, inhibition by 30 microm 5-HT was reduced to negligible levels. Allowing for a partial agonist action of L-694,427 and complex interactions of 5-HT receptors within the OT, these results support the presence of active 5-HT(1D)-type receptors in the principal cell layer of the OT.

Expression and function of 5-HT7 receptors in smooth muscle preparations from equine duodenum, ileum, and pelvic flexure

In horses, gastrointestinal (GI) disorders occur frequently and cause a considerable demand for efficient medication. 5-Hydroxytryptamine receptors (5-HT) have been reported to be involved in GI tract motility and thus, are potential targets for treating functional bowel disorders. Our studies extend current knowledge on the 5-HT(7) receptor in equine duodenum, ileum and pelvic flexure by studying its expression throughout the intestine and its role in modulating contractility in vitro by immunofluorescence and organ bath experiments, respectively. 5-HT(7) immunoreactivity was demonstrated in both smooth muscle layers, particularly in the circular one, and within the myenteric plexus. Interstitial cells of Cajal (ICC), identified by c-Kit labeling, show a staining pattern similar to that of 5-HT(7) immunoreactivity. The selective 5-HT(7) receptor antagonist SB-269970 increased the amplitude of contractions in spontaneous contracting specimens of the ileum and in electrical field-stimulated specimens of the pelvic flexure concentration-dependently. Our in vitro experiments suggest an involvement of the 5-HT(7) receptor subtype in contractility of equine intestine. While the 5-HT(7) receptor has been established to be constitutively active and inhibits smooth muscle contractility, our experiments demonstrate an increase in contractility by the 5-HT(7) receptor ligand SB-269970, suggesting it exerting inverse agonist properties.

In vitro and in vivo pharmacological characterization of PF-01354082, a novel partial agonist selective for the 5-HT(4) receptor

The pharmacological profile of PF-01354082, a selective 5-HT(4) receptor partial agonist, was investigated. PF-01354082 displayed high affinity for human 5-HT(4d) and dog 5-HT(4h) receptors in binding studies, having Ki values of 2.0 nM and 4.2 nM, respectively. By contrast, PF-01354082 did not show significant affinity for several other 5-HT receptors (5-HT(1A), 5-HT(1B), 5-HT(1D), 5-HT(2A), 5-HT(2B), 5-HT(2C), 5-HT(3A), and 5-HT(7)) or the dopamine D(2long) receptor. Functional assays using either cells expressing human recombinant 5-HT(4d) receptors or rat tunica muscularis mucosae demonstrated that PF-01354082 exhibited partial agonist activity at the 5-HT(4) receptor. The effects of PF-01354082 on in vitro receptor binding, ion channel activity, and sites of uptake were further investigated. PF-01354082 did not show biologically relevant binding activity at concentrations up to 10 microM except for binding to the 5-HT(4e) receptor. Furthermore, PF-01354082 decreased I(HERG) current by only 11% at a concentration of 300 microM, indicating that the compound had greater than 150,000-fold selectivity for the human 5-HT(4d) receptor over hERG channels. An in vivo study using a gastric motility model in conscious dogs demonstrated that oral administration of PF-01354082 resulted in marked and sustained stimulation of gastric motility in a dose-dependent manner. These results indicate that PF-01354082 is an orally active, highly selective, partial agonist of the human 5-HT(4) receptor that is expected to exert a favorable effect on gastrointestinal motor disorders with reduced adverse effects mediated by other related receptors.

Modulatory effects of serotonin on GABAergic synaptic transmission and membrane properties in the deep cerebellar nuclei

Cerebellar outputs from the deep cerebellar nuclei (DCN) are critical for generating and controlling movement. DCN neuronal activity is primarily controlled by GABAergic inhibitory transmission by Purkinje cells in the cerebellar cortex and is also modulated by nerve inputs originating from other brain regions within and outside the cerebellum. In this study, we examined the modulatory effects of 5-HT on GABAergic synapses in the DCN. 5-HT decreased the amplitude of stimulation-evoked inhibitory postsynaptic currents (eIPSCs) in DCN neurons, and this effect was abolished by a 5-HT(1B) antagonist, SB 224289. The decrease in IPSC amplitude was associated with an increased paired-pulse ratio of the IPSC. 5-HT also decreased the frequency of miniature IPSCs without altering the amplitude. These data suggest that 5-HT presynaptically inhibited GABA release. Furthermore, 5-HT elicited a slow inward current in DCN neurons. Pharmacological studies showed that 5-HT activated the 5-HT(5) receptor, which is positively coupled to G protein and elicited the slow inward current through enhancement of hyperpolarization-activated cation channel activation. Finally, we examined the effects of 5-HT on the spike generation that accompanies repetitive stimulation of inhibitory synapses. 5-HT increased the spontaneous firing rate in DCN neurons caused by depolarization. Increase in the 5-HT-induced tonic firing relatively decreased the contrast difference from the rebound depolarization-induced firing. However, the inhibitory transmission-induced silencing of DCN firing remained during the conditioning stimulus. These results suggest that 5-HT plays a regulatory role in spike generation and contributes to the gain control of inhibitory GABAergic synapses in DCN neurons.

Changes in the control of gastric motor activity during metamorphosis in the amphibian Xenopus laevis, with special emphasis on purinergic mechanisms

The stomach of the amphibian Xenopus laevis is subject to extensive remodelling during metamorphosis. We investigated the changes in gastric activity control during this period using in vitro circular smooth muscle preparations mounted in organ baths. The nitric oxide synthase inhibitor L-NAME increased mean force in metamorphic and juvenile frogs but not in prometamorphic tadpoles. Serotonin (5-HT) relaxed stomach muscle prior to metamorphosis but elicited a biphasic response in juveniles consisting of contraction at low concentrations and relaxation at high concentrations. The effects of 5-HT were blocked by methysergide. In the prometamorphic tadpole, ATP elicited relaxation that was blocked by the ectonucleotidase inhibitor ARL67156 and the adenosine A(1) receptor antagonist 1,3-dipropyl-8-cyclopentylxanthine (DPCPX), suggesting adenosine as the mediator. Exogenous adenosine and the A(1) receptor agonist N(6)-cyclopentyladenosine (CPA) induced relaxation at all stages. After metamorphosis, the potency of ATP decreased and neither DPCPX nor ARL67156 could block ATP-induced relaxation. Uridine 5'-triphosphate (UTP) induced relaxation prior to metamorphosis, but caused contraction of muscle strips from metamorphosing tadpoles. Single doses of UTP blocked phasic contractions in juveniles in a tetrodotoxin (TTX)-sensitive manner while the simultaneous increase in muscle tension was TTX insensitive. The P2X(1)/P2X(3) receptor agonist alpha-beta-MeATP elicited pyridoxalphosphate-6-azophenyl-2',4'-disulphonic acid (PPADS)-sensitive contractions at all stages investigated. These results indicate the development of an inhibitory nitrergic tonus during metamorphosis and a 5-HT receptor involved in muscle contraction. Also, the development of UTP receptors mediating increased tension and neural UTP receptors decreasing contraction frequency in juveniles is indicated. An adenosine A(1)-like receptor mediating relaxation and a P2X-like receptor mediating contraction is demonstrated at all stages.

5-Amino-6-chloro-N-[(1-isobutylpiperidin-4-yl)methyl]-2-methylimidazo[1,2-alpha]pyridine-8-carboxamide (CJ-033,466), a novel and selective 5-hydroxytryptamine4 receptor partial agonist: pharmacological profile in vitro and gastroprokinetic effect in conscious dogs

5-Hydroxytryptamine (5-HT) receptors and dopamine(2) (D(2)) receptor modulate gastrointestinal motility. Gastroprokinetic agents that act on several 5-HT receptor subtypes and/or D(2) receptors are used clinically. Although the 5-HT(4) receptor is known to mediate the gastroprokinetic effects of these agents, the absence of highly selective 5-HT(4) receptor agonists has made it difficult to confirm the physiological consequences of selective 5-HT(4) receptor stimulation. In this study, we report the in vitro pharmacological profiles and the in vivo gastroprokinetic effects of 5-amino-6-chloro-N-[(1-isobutylpiperidin-4-yl)methyl]-2-methylimidazo[1,2-alpha]pyridine-8-carboxamide (CJ-033,466), a novel, potent, and selective 5-HT(4) partial agonist. Compared with preceding 5-HT(4) agonists such as cisapride, mosapride, and tegaserod, CJ-033,466 had a superior in vitro profile, with nanomolar agonistic activities for the 5-HT(4) receptor and 1000-fold greater selectivity for the 5-HT(4) receptor over other 5-HT and D(2) receptors. In vivo studies in conscious dogs showed that CJ-033,466 dose-dependently stimulated gastric antral motility in both the fasted and postprandial states at the same dose range and that it was 30 times more potent than cisapride. Furthermore, CJ-033,466 accelerated the gastric emptying rate in a gastroparesis dog model at the minimally effective dose established in the gastric motility study. In conclusion, CJ-033,466 is a potent and highly selective 5-HT(4) agonist that stimulates physiologically coordinated gastric motility, and it has no activity on other 5-HT receptor subtypes and D(2) receptors. Therefore, CJ-033,466 could be used to treat gastroparesis, providing better gastroprokinetics and reduced side effects mediated by the other receptors.

Pharmacological characterization of 5-hydroxytryptamine-induced contraction in the chicken gastrointestinal tract

5-Hydroxytryptamine (5-HT) receptor subtypes involved in 5-HT-induced contraction of the chicken gastrointestinal tract were characterized pharmacologically using subtype-selective agonists and antagonists. The proventriculus (area of stomach adjacent to the oesophagus) and ileum are examined. 5-HT applied cumulatively caused sustained contraction of the proventriculus that was not decreased by tetrodotoxin, atropine or l-nitro-arginine methylester (l-NAME). alpha-Methyl-5-HT showed the same potency as that of 5-HT, indicating the involvement of the 5-HT(2) receptor. (+/-)-1-(2,5-dimethoxy-4-iodophenyl)-2-amino-propane (DOI), 5-methoxytryptamine and 1-(3-chlorophenyl)piperazine hydrochloride (mCPP) were potent, and 2-methyl-5-HT, 5-carboxamidotryptamine, BW723C86 and 6-chloro-2-(1-piperazinyl)pyrazine hydrochloride (MK212) were moderate, but (+/-)-8-hydroxy-2-dipropylaminotetralin hydrobromide (8-OH-DPAT), [endo-N-8-methyl-8-azabicyclo-(3,2,1)oct-3-yl]-2,3-dihydro-(1-methyl)ethyl-2-oxo-1H-benzimidazol-1-carboxamide (BIMU-8) and cisapride were weak agonists. Correlation of pEC(50) values of these agonists with documented pEC(50) values for 5-HT(2C) receptor was higher than 5-HT(2A) and 5-HT(2B). Cinanserin, ketanserin, methiothepin, methysergide, mianserin, (8-[5-(2,4-dimethoxy-5-(4-trifluoromethylphenylsulphonamido)phenyl-5-oxopentyl)-1,3,8-triazaspiro[4,5]decane-2,4-dione hydrochloride (RS102221), N-(1-methyl-1H-indolyl-5-yl)-N'-(3-methyl-5-isothiazolyl)urea (SB204741), spiperone and N-desmethylclozapine concentration-dependently inhibited the contractile responses to 5-HT. Correlation of pK(b)/pA(2) of antagonists with documented pK(i) for 5-HT(2C) receptor was highest among 5-HT(2) receptor subtypes. In the methysergide- and ketanserin-treated proventriculus, 5-HT, 2-methyl-5-HT and cisapride did not enhance the electrical field stimulation (5 Hz)-induced cholinergic contractions. 5-HT applied non-cumulatively caused transient contraction of ileum, and the responses were partly decreased by atropine or tetrodotoxin. 5-Methoxytryptamine, alpha-methyl-5-HT, 5-carboxamidotryptamine, L692,247 and DOI were potent agonists. However, 2-methyl-5-HT, cisapride, BW723C86, 8-OH-DPAT and 5-nonyloxytryptamine, mCPP and MK212 were less effective. Ketanserin and methysergide decreased the 5-HT-induced ileal contraction, but neither GR113808 nor SB269970 inhibited the responses. In conclusion, 5-HT causes contraction of the proventriculus via 5-HT(2C)-like receptors present on smooth muscle. 5-HT also causes contraction of the ileum, but the underlying mechanisms are complex, involving neural and smooth muscle components, and both 5-HT(1)- and 5-HT(2)-like receptors. Neural 5-HT receptors similar to 5-HT(3)/5-HT(4) receptors were not found in the chicken proventriculus and ileum.

Molecular and pharmacological characterization of serotonin 5-HT2A and 5-HT2B receptor subtypes in dog

We report the cloning, molecular characterization, and pharmacological characterization of the canine 5-HT2A and 5-HT2B receptors. The canine and human 5-HT2A receptors share 93% amino acid homology. The canine and human 5-HT2B receptors are also highly conserved (87% homology) with the exception of the carboxyl termini where the canine protein is 62 amino acids shorter. Both the canine 5-HT2A and 5-HT2B receptors have high affinity for [3H]5-HT (KD=4.50+/-0.89 nM and 3.10+/-0.82 nM, respectively) and, in general, the pharmacology of these two receptors matches closely the pharmacology of their human homologs for the 19 serotonergic ligands tested. However, the functional response (Ca2+ mobilization) of the canine 5-HT2B receptor to several agonists was weaker compared to the human 5-HT2B receptor. Using quantitative reverse transcriptase polymerase chain reaction, a high expression level of canine 5-HT2A receptor mRNA was detected in the brain and lower levels in peripheral tissues, whereas the highest levels of canine 5-HT2B receptor mRNA were observed in lungs and smooth muscles. A significant level of canine 5-HT2B receptor mRNA was detected in brain tissue. The availability of the full sequence and pharmacology of the canine 5-HT2A and canine 5-HT2B receptors provides useful information for the interpretation of previous and future pharmacological studies of 5-HT2A/2B ligands in dog.

5-HT7 receptor efficacy distribution throughout the canine stomach

This study aimed to determine, quantify and explain regional differences in the relaxant response to the selective 5-HT(1) and 5-HT(7) receptor agonist 5-carboxamidotryptamine (5-CT) throughout the canine stomach. Longitudinal muscle strips from eight gastric corpus regions and six antrum regions were mounted for isotonic measurement. The 5-CT-induced relaxation was examined on a prostaglandin F(2alpha)-induced submaximal response, expressed as percentage of this response and fitted to the operational model of agonism (OMOA). 5-HT(7) receptor messenger RNA (mRNA) expression was compared by means of quantitative PCR. 5-CT inhibited PGF(2alpha)-induced tonic contraction (corpus) and increase of phasic contraction amplitude (antrum). The consistent antagonism produced by the selective 5-HT(7) receptor antagonist SB-269970 (10 nm, pA(2) estimates 8.2-8.9) confirmed that in every region, the inhibition by 5-CT was 5-HT(7) receptor mediated. However, variation in the maximum effect (61-108%) and pEC(50) (6.4-8.6) was observed throughout the different regions. The OMOA explained these differences as differences in the efficacy parameter tau (ratio of receptor density and coupling efficiency; log tau estimates ranging from 0.1 to 2.1). The log tau gradient decreases going from the lesser to the greater curvature. A proportional difference (68%) in the relative expression of 5-HT(7) receptor mRNA between the lesser and the greater curvature indicates that differences in receptor density contribute to the observed functional differences. This study illustrates that 5-HT(7) receptors are present throughout the ventral wall of the canine stomach, but the efficacy (expressed as log tau) is clearly greater close to the lesser curvature. Differences in 5-HT(7) receptor expression at least partially explain the functional differences.

The problem of gastric atony

Normal gastrointestinal motility is crucial for maintaining an appropriate balance of microorganisms within the gut. Disruption of this system results in bacterial overgrowth and associated complications such as bacterial translocation, aspiration pneumonia, and sepsis. Critically ill animals are at increased risk of developing gastroparesis caused by primary gastrointestinal disturbances or severe metabolic derangements that impact gastrointestinal function. In the intensive-care setting, delayed gastric emptying complicates enteral nutrition, and the catabolic effects of severe illness further deplete the patient's caloric reserves, resulting in impaired wound healing, decreased immune function, and increased morbidity and mortality. The use of promotility drugs in critically ill patients is a safe, effective means to circumvent the problem of gastric atony and improve patient recovery. Understanding the drugs available and their interaction with the receptors involved in neuromuscular transmission within the gastrointestinal tract will aid the clinician in selecting the optimal prokinetic therapy.

Triptans and gastric accommodation: pharmacological and therapeutic aspects

In the past decade, several studies have reported a significant delay of gastric emptying induced by the anti-migraine agent sumatriptan (a 5-hydroxytryptamine (5-HT)1B/D receptor agonist) in healthy human beings. In patients with functional dyspepsia, sumatriptan improves gastric accommodation after food consumption and reduce perception of gastric distension, hence relieving epigastric symptoms. Recent studies have established that impaired accommodation after food consumption is a major patho-physiological mechanism in functional dyspepsia and restoration of accommodation is considered to be a potential therapeutic target. The precise site of action of sumatriptan in humans is at present unknown, although recent studies carried out using a canine model indicate that sumatriptan exerts its action on gastric accommodation through 5-HT1B receptors, since both GR127935 and SB216641 (respectively, non selective 5-HT1B/D and selective 5-HT1B receptor antagonists) fully antagonised the effects of sumatriptan. Gastric relaxation and enhanced accommodation to a distending stimulus seem to be a class effect of triptans, since it occurs not only with sumatriptan, but also with second-generation triptans (rizatriptan and naratriptan), at least in a canine model. In dyspeptic patients, administration of triptans would be able to restore gastric accommodation after a meal and to improve symptoms of early satiety, confirming the therapeutic potential of 5-HT1B/D receptor agonists in functional dyspepsia.

Effect of enterokinetic prucalopride on intestinal motility in fast rats

AIM: To evaluate the effects of prucalopride on intestinal prokinetic activity in fast rats and to provide experimental basis for clinical treatment of gastrointestinal motility diseases.

METHODS: Gastrointestinal propulsion rate was measured by the migration rate of activated charcoal, which reflexes gastrointestinal motility function. 120 Spraque-Dawley rats were randomly divided into four groups and received an intravenous injection of physiological saline (served as control), prucalopride 1 mg/kg, prucalopride 2 mg/kg and cisapride 1 mg/kg, respectively. The gastrointestinal propulsion rate was measured 1, 2 or 4 h after intravenous injection of the drugs.

RESULTS: Significant accelerations of gastrointestinal propulsion rate in prucalopride 1 mg/kg and 2 mg/kg groups were found compared with control group at 2 and 4 h (83.2% ± 5.5%, 81.7% ± 8.5% vs 70.5% ± 9.2%, P < 0.01; 91.2% ± 2.2%, 91.3% ± 3.9% vs 86.8% ± 2.6%, P < 0.01). The gastrointestinal propulsion rates at 1, 2 or 4 h were faster in prucalopride 1 mg/kg and 2 mg/kg groups than in cisapride group (84.0% ± 11.7%, 77.1% ± 11.9% vs 66.3% ± 13.6%, P < 0.01, P < 0.05; 83.2% ± 5.5%, 81.7% ± 8.5% vs 75.4% ± 5.9%, P < 0.01, P < 0.05; 91.2% ± 2.2%, 91.3% ± 3.9% vs 88.6% ± 3.5%, P < 0.05, P < 0.05). No difference of gastrointestinal propulsion rate was found between prucalopride 1 mg/kg group and prucalopride 2 mg/kg group (P > 0.05).

CONCLUSION: Prucalopride accelerates intestinal motility in fast rats, and has no dose dependent effect.

Smooth muscle 5-HT2A receptors mediating contraction of porcine isolated proximal stomach strips

1. The aim of this study was to characterize the 5-HT receptors involved in the 5-HT-induced contraction of longitudinal muscle (LM) strips of porcine proximal stomach. This was done in a classical organ bath set-up for isotonic measurement. 2. The concentration-contraction curve to 5-HT was not modified by 5-HT(3) and 5-HT(4) receptor antagonism. Methysergide, ketanserin and mesulergine antagonized the curve to 5-HT. Concomitantly, increasing concentrations of ketanserin and mesulergine progressively revealed a biphasic nature of the 5-HT curve. Ketanserin antagonized the low-affinity receptor while it did not modify the high-affinity receptor. 3. Tetrodotoxin did not influence the concentration-contraction curve to 5-HT neither in the absence nor presence of ketanserin, indicating that nerves are not involved. 4. Ketanserin competitively antagonized the monophasic concentration-response curve to alpha-Methyl-5-HT, yielding a Schild slope that was not significantly different from unity. After constraining the Schild slope to unity, a pK(B) estimate of 8.23+/-0.90 was obtained. This affinity estimate of ketanserin closely approximates previously reported affinities at 5-HT(2A) receptors. 5. In the presence of ketanserin (0.1 microM; exposing the high-affinity receptor), a wide range of 5-HT receptor antagonists covering all 5-HT receptors known, was tested. Only methysergide and ritanserin inhibited the response to 5-HT, thus expressing affinity for the high-affinity receptor. This did not reveal the identity of the receptor involved. 6 It can be concluded that 5-HT induces pig proximal stomach (LM) contraction via 5-HT(2A) receptors located on smooth muscle. A ketanserin-insensitive phase of contractions could not be characterized between the actually known classes of 5-HT receptors with the pharmacological tools that were used.

Pharmacological characterization of the 5-HT receptors mediating contraction and relaxation of canine isolated proximal stomach smooth muscle

1. We aimed to characterize 5-HT receptors mediating contraction and relaxation to 5-HT in dog proximal stomach longitudinal muscle (LM) strips. 2. Of the tryptamine analogues tested, 5-HT was the most potent contractile agent at basal length, while 5-CT was the most potent relaxant of PGF(2alpha)-induced contraction. Neither the contractions to 5-HT, nor the relaxations to 5-CT were influenced by tetrodotoxin, illustrating that action potential propagation is not involved. 3. The 5-HT-induced contraction was antagonized by mesulergine (0.03 to 0.3 microM) and ketanserin (2 - 20 nM), but the antagonism was not of a simple competitive nature, indicating multiple receptor involvement. Ketanserin (3 to 30 nM) and mesulergine (30 nM) competitively antagonized the alpha-Me-5-HT-induced contraction (pK(B): 8.83+/-0.09 and pA(2): 8.25+/-0.06 respectively). These affinity values are in line with literature affinities of ketanserin and mesulergine at 5-HT(2A) receptors in various bioassays. 4. The 5-CT-induced inhibition of PGF(2alpha)-induced contraction was competitively antagonized by mesulergine (pK(B) estimate: 8.52+/-0.12) and by the selective 5-HT(7) receptor antagonist SB-269970 (pK(B) estimate: 9.36+/-0.14). Both pK(B) estimates are in line with literature affinities of these compounds for 5-HT(7) receptors. Mesulergine (30 nM) and SB-269970 (10 nM) shifted the relaxant curve to 5-HT parallel to the right in the presence of ketanserin (0.3 microM) (pA(2) estimates of 8.08+/-0.10 and 8.75+/-0.14 respectively), indicative of 5-HT(7) receptor involvement. 5. It is concluded that 5-HT induces dog proximal stomach (LM) contraction via smooth muscle 5-HT(2A) receptors and relaxation via smooth muscle 5-HT(7) receptors.