Sumatriptan is an agonist at 5-HT receptors on myenteric neurones in the guinea-pig gastric antrum

Gastric accommodation: Physiology, diagnostic modalities, clinical relevance, and therapies

BACKGROUND

Gastric accommodation is an essential gastric motor function which occurs following ingestion of a meal. Impaired gastric fundic accommodation (IFA) is associated with dyspeptic symptoms. Gastric accommodation is mediated by the vagal pathway with several important physiologic factors such as duodenal nutrient feedback playing a significant role. IFA has been described as a pathophysiologic factor in several gastrointestinal disorders including functional dyspepsia, diabetic gastropathy, post-Nissen fundoplication, postsurgical gastrectomy, and rumination syndrome. Modalities for gastric accommodation assessment include gastric barostat, intragastric meal distribution via scintigraphy, drinking tests (eg, water load), SPECT, MRI, 2D and 3D ultrasound, and intragastric high-resolution manometry. Several treatment options including sumatriptan, buspirone, tandospirone, ondansetron, and acotiamide may improve symptoms by increasing post-meal gastric volume.

PURPOSE

Our aim is to provide an overview of the physiology, diagnostic modalities, and therapies for IFA. A literature search was conducted on PubMed, Google Scholar, and other sources to identify relevant studies available until December 2020. Gastric accommodation is an important gastric motor function which if impaired, is associated with several upper gastrointestinal disorders. There are an increasing number of gastric accommodation testing modalities; however, each has facets which warrant consideration. Evidence regarding potentially effective therapies for IFA is growing.

The effects of 5-hydroxytryptamine1a receptor agonist, buspirone on the gastric fundus accommodation in an animal model using guinea pigs

BACKGROUND

To date, few animal experiments have been conducted to examine the effects and mechanisms of buspirone in inducing the relaxation of the gastric fundus. The aim of this study is to examine the effects and mechanisms of buspirone, 5-HT(1a) receptor agonist, in the accommodation of gastric fundus muscle in an animal experimental model using guinea pigs.

METHODS

In the current study, we performed an immunohistochemistry for 5-HT(1a) receptors in the tissue samples collected from the stomach of guinea pig, an ex vivo experiment to examine the electrical field stimulation (EFS)-induced relaxation of the circular muscle in the gastric fundus in guinea pigs and an in vivo experiment to measure the intragastric pressure through the insertion of the balloon catheter in the fundus.

KEY RESULTS

Immunohistochemical stains for 5-HT(1a) receptor could confirm the expression of 5-HT(1a) receptor in guinea pig stomach. There was a significant dose-dependent inhibition of the EFS-induced relaxation of fundic muscle strips following the treatment with WAY-100635 (5-HT(1a) antagonist), but this was significantly improved following the treatment with buspirone. An in vivo measurement of the gastric fundic tone showed that there was a significant decrease in the intragastric pressure at same volume by pretreatment with buspirone as compared with the vehicle control, but this could be prevented with the treatment with WAY-100635.

CONCLUSIONS & INFERENCES

Based on our results, it can be concluded that buspirone is effective in relaxing the gastric fundus via 5-HT(1a) receptor pathway in both in vitro and in vivo experimental models using guinea pigs.

Symptomatic management for gastroparesis: antiemetics, analgesics, and symptom modulators

Although prokinetic agents typically are used for gastroparesis, antiemetic, analgesic, and neuromodulatory medications may help manage nausea, vomiting, pain, or discomfort. Antiemetic benefits are supported by few case reports. An open series reported symptom reductions with transdermal granisetron in gastroparesis. Opiates are not advocated in gastroparesis because they worsen nausea and delay emptying. Neuromodulators have theoretical utility, but the tricyclic agent nortriptyline showed no benefits over placebo in an idiopathic gastroparesis study raising doubts about this strategy. Neurologic and cardiac toxicities of these medications are recognized. Additional controlled study is warranted to define antiemetic, analgesic, and neuromodulator usefulness in gastroparesis.

Efficacy of buspirone, a fundus-relaxing drug, in patients with functional dyspepsia

BACKGROUND & AIMS

Impaired accommodation and hypersensitivity to gastric distention are believed to be involved in the development of functional dyspepsia (FD). Buspirone, a 5-hydroxytryptamine 1A receptor agonist, relaxes the proximal stomach in healthy individuals. We studied the effects of buspirone on symptoms and mechanisms of FD.

METHODS

We performed a randomized, double-blind, placebo-controlled, crossover study of 17 patients (13 women; mean age, 38.5 ± 2.4 years). The study included 2 treatment periods of 4 weeks each, separated by a 2-week washout period. In the first period, 7 participants were given buspirone (10 mg, 3 times daily for 4 weeks) and 10 were given placebo 15 minutes before meals; patients switched groups for the second period. We assessed meal-related symptoms and severity, along with gastric sensitivity, accommodation, and emptying (by using barostat and breath tests) before and after 4 weeks of treatment.

RESULTS

Buspirone significantly reduced the overall severity of symptoms of dyspepsia (7.5 ± 1.3 vs 11.5 ± 1.2 for placebo; P < .005) and individual symptoms of postprandial fullness, early satiation, and upper abdominal bloating, whereas placebo had no significant effect (all P < .05). Buspirone did not alter the rate of gastric emptying of solids or sensitivity to gastric distention, but it significantly increased gastric accommodation, compared with placebo (229 ± 28 vs 141 ± 32 mL, respectively; P < .05), and delayed gastric emptying of liquids (half-life = 64 ± 5 vs 119 ± 24 minutes, respectively). Adverse events were similar when patients were given buspirone or placebo.

CONCLUSIONS

In patients with FD, 4 weeks of administration of buspirone significantly improved symptoms and gastric accommodation, compared with placebo, whereas gastric emptying of liquids was delayed.

The migrating motor complex: control mechanisms and its role in health and disease

The migrating motor complex (MMC) is a cyclic, recurring motility pattern that occurs in the stomach and small bowel during fasting; it is interrupted by feeding. The MMC is present in the gastrointestinal tract of many species, including humans. The complex can be subdivided into four phases, of which phase III is the most active, with a burst of contractions originating from the antrum or duodenum and migrating distally. Control of the MMC is complex. Phase III of the MMC with an antral origin can be induced in humans through intravenous administration of motilin, erythromycin or ghrelin, whereas administration of serotonin or somatostatin induces phase III activity with duodenal origin. The role of the vagus nerve in control of the MMC seems to be restricted to the stomach, as vagotomy abolishes the motor activity in the stomach, but leaves the periodic activity in the small bowel intact. The physiological role of the MMC is incompletely understood, but its absence has been associated with gastroparesis, intestinal pseudo-obstruction and small intestinal bacterial overgrowth. Measuring the motility of the gastrointestinal tract can be important for the diagnosis of gastrointestinal disorders. In this Review we summarize current knowledge of the MMC, especially its role in health and disease.

The influence of citalopram on interdigestive gastrointestinal motility in man

BACKGROUND

Administration of 5-hydroxytryptamine (5HT) and selective 5HT receptor ligands modifies interdigestive motility in animals and in man.

AIM

To study the effect of citalopram, a selective 5-HT reuptake inhibitor, on interdigestive motility in man.

METHODS

In 20 healthy subjects, antroduodenojejunal motor activity was studied manometrically. Basal interdigestive motor activity was recorded until the passage of two activity fronts. Ten minutes after the second activity front, placebo or 20 mg of citalopram was administered intravenously in a double-blind randomized fashion. Recording continued until the passage of two more activity fronts had occurred.

RESULTS

Administration of citalopram induced a premature small intestinal phase 3 after 35 +/- 6.4 min, compared to 120 +/- 17 min after placebo P < 0.01. Citalopram shortened MMC cycle length at the expense of phase 1 and phase 2 and significantly increased the motility index during phase 2 in the antrum and the small intestine.

CONCLUSIONS

In the interdigestive state in man, intravenous administration of the selective 5-HT reuptake inhibitor citalopram induces a premature intestinal phase 3 and suppresses gastric activity fronts. Phase 2 motility is stimulated both in the stomach and in the small bowel after citalopram. These data suggest that 5HT is involved in the control of interdigestive motility.

Serotonin and the GI tract

Serotonin (5-hydroxytryptamine, 5-HT) participates in several functions of the gastrointestinal tract. Receptors in seven families (5-HT(1)-5-HT(7)) were identified, many of which are present on enterocytes, intrinsic and extrinsic neurons, interstitial cells, and gut myocytes. Most 5-HT is released from enterochromaffin cells in response to physiologic and pathologic stimuli. Roles of 5-HT in health include control of normal gut motor activity, secretion, and sensation, and regulation of food intake and cell growth. Abnormalities of serotonergic function contribute to symptom genesis in functional bowel disorders, inflammatory and infectious diseases of the gut, emetic responses to varied stimuli, obesity, and dysregulation of cell growth. Therapies acting as agonists or antagonists of 5-HT receptors or that modulate 5-HT reuptake play prominent roles in managing these conditions, although use of many agents is hampered by cardiopulmonary complications. Novel agents are in testing, which may exhibit efficacy without significant toxicity.

Whither dyspepsia? A historical perspective of functional dyspepsia, and concepts of pathogenesis and therapy in 2009

Functional dyspepsia is a highly prevalent but heterogeneous disorder; multiple pathogenetic mechanisms are likely involved but the underlying causal pathways in functional dyspepsia remain obscure. The term functional dyspepsia was popularized by the famed Walter Alvarez at the Mayo Clinic early last century. Prominent Australian gastroenterologists who have contributed to our understanding of functional dyspepsia include Peter Baume, Barry Marshall, Douglas Piper, Nick Talley, John Kellow, and Gerald Holtmann. Specific dyspeptic symptoms have not generally correlated very well with any particular physiologic disturbance, although gastric disaccommodation and duodenal eosinophilia have been linked to early satiety in this condition. Genetic markers have been tentatively identified, and functional dyspepsia can follow bacterial gastroenteritis. No objective diagnostic tools for functional dyspepsia are currently agreed upon, although meal induction of symptoms appears reproducible and may have diagnostic utility. The symptomatic criteria for functional dyspepsia (Rome III criteria) are based on expert consensus and the exclusion of organic causes. Various therapeutic modalities for functional dyspepsia have been explored; however, empirical approaches are still employed for the treatment of functional dyspepsia. Better approaches for functional dyspepsia are likely to follow an improved understanding of the underlying pathophysiological abnormalities.

5-hydroxyindalpine, an agonist at the putative 5-HT receptor, has no activity on human recombinant monoamine receptors but accelerates distension-induced peristalsis in mouse isolated colon

Although the putative 5-HT(1P) receptor has been implicated to have a role in peristalsis, experiments which suggest this function are preliminary or have measured only components of the reflex. We have, therefore, further characterized a reported agonist at this receptor (5-hydroxyindalpine; 5-OHIP) and investigated the effects of 5-OHIP and 5-hydroxytrytophan-dipeptide (5-HTP-DP), a reported 5-HT(1P) receptor antagonist, on distension-induced peristalsis in mouse colon. The effects of 5-OHIP on intracellular calcium, cyclic adenosine monophosphate concentrations or GTPgammaS binding were measured in cell lines expressing human recombinant 5-HT(1A, 1B, 1D, 2A, 2B, 2C, 3, 4, 6, 7) and alpha(1A), alpha(1B), D(1), D(2), D(3), H(1), H(3) receptors. The effects of 5-OHIP and 5-HTP-DP on peristalsis were assessed by measuring changes in frequency and times to reach threshold of peristaltic contractions, as well as the threshold and maximum pressures of each peristaltic stroke. 5-hydroxyindalpine (1 nmol L(-1)-10 micromol L(-1)) had no significant activity at any of the receptors studied. However, 5-OHIP (0.1 nmol L(-1)-1 micromol L(-1)) concentration-dependently increased the frequency of peristalsis (EC(50) = 4.4 nmol L(-1)) and reduced the time taken to reach threshold and threshold pressure, without altering maximum pressures. The maximum effect of 5-OHIP was at 1 micromol L(-1) (68.0 +/- 14.5% increase in frequency); 10 micromol L(-1) decreased peristalsis. 5-hydroxytrytophan-dipeptide (1-300 nmol L(-1)) also increased the frequency of peristalsis and prevented the actions of 5-OHIP. The higher concentration (1 micromol L(-1)) transiently inhibited peristalsis and after recovery, prevented the actions of 5-OHIP but not the excitatory activity of the cholinesterase inhibitor neostigmine. In summary, the present data demonstrate an interaction of '5-HT(1P)-ligands' with the peristaltic reflex. However, the absence of an effect of 5-OHIP on a range of different monoamine receptors continues to highlight the need to investigate the identity of the putative 5-HT(1P) receptor.

Serotonin pharmacology in the gastrointestinal tract: a review

Serotonin (5-hydroxytryptamine or 5-HT) plays a critical physiological role in the regulation of gastrointestinal (GI) function. 5-HT dysfunction may also be involved in the pathophysiology of a number of functional GI disorders, such as chronic constipation, irritable bowel syndrome and functional dyspepsia. This article describes the role of 5-HT in the enteric nervous system (ENS) of the mammalian GI tract and the receptors with which it interacts. Existing serotonergic therapies that have proven effective in the treatment of GI functional disorders and the potential of drugs currently in development are also highlighted. Advances in our understanding of the physiological and pathophysiological roles of 5-HT in the ENS and the identification of selective receptor ligands bodes well for the future development of more efficacious therapies for patients with functional GI disorders.

5-HT4 receptor agonists: similar but not the same

5-Hydroxytryptamine(4) (5-HT(4)) receptors are an interesting target for the management of patients in need of gastrointestinal (GI) promotility treatment. They have proven therapeutic potential to treat patients with GI motility disorders. Lack of selectivity for the 5-HT(4) receptor has limited the clinical success of the agonists used until now. For instance, next to their affinity for 5-HT(4) receptors, both cisapride and tegaserod have appreciable affinity for other receptors, channels or transporters [e.g. cisapride: human ether-a-go-go-related gene (hERG) is K(+) channel and tegaserod: 5-HT(1) and 5-HT(2) receptors]. Adverse cardiovascular events observed with these compounds are not 5-HT(4) receptor-related. Recent efforts have led to the discovery of a series of selective 5-HT(4) receptor ligands, with prucalopride being the most advanced in clinical development. The selectivity of these new compounds clearly differentiates them from the older generation compounds by minimizing the potential of target-unrelated side effects. The availability of selective agonists enables the focus to shift to the exploration of 5-HT(4) receptor-related differences between agonists. Based on drug- and tissue-related properties (e.g. differences in receptor binding, receptor density, effectors, coupling efficiency), 5-HT(4) receptor agonists are able to express tissue selectivity, i.e. behave as a partial agonist in some and as a full agonist in other tissues. Furthermore, the concept of ligand-directed signalling offers great opportunities for future drug development by enlarging the scientific basis for the generation of agonist-specific effects in different cell types, tissues or organs. Selective 5-HT(4) receptor agonists might thus prove to be innovative drugs with an attractive safety profile for better treatment of patients suffering from hypomotility disorders.

Mechanisms of serotonergic agents for treatment of gastrointestinal motility and functional bowel disorders

Most of the body's serotonin is released in the gut where it plays an important role in the control of gastrointestinal (GI) motility, sensitivity and muscle tone by activating different receptor subtypes. This review focuses on the known effects of selective serotonin reuptake inhibitor and serotonin receptor agonists and antagonists on the sensorimotor function of the GI tract and describes the therapeutic potential of these actions for GI motility and functional bowel disorders.

The serotonin signaling system: from basic understanding to drug development for functional GI disorders

Serotonin is an important gastrointestinal signaling molecule. It is a paracrine messenger utilized by enterochromaffin (EC) cells, which function as sensory transducers. Serotonin activates intrinsic and extrinsic primary afferent neurons to, respectively, initiate peristaltic and secretory reflexes and to transmit information to the central nervous system. Serotonin is also a neurotransmitter utilized by a system of long descending myenteric interneurons. Serotonin is synthesized through the actions of 2 different tryptophan hydroxylases, TpH1 and TpH2, which are found, respectively, in EC cells and neurons. Serotonin is inactivated by the serotonin reuptake transporter (SERT)-mediated uptake into enterocytes or neurons. The presence of many serotonin receptor subtypes enables selective drugs to be designed to therapeutically modulate gastrointestinal motility, secretion, and sensation. Current examples include tegaserod, a 5-HT(4) partial agonist, which has been approved for treatment of irritable bowel syndrome (IBS) with constipation in women and for chronic constipation in men and women. The 5-HT(3) antagonists, granisetron and ondansetron, are useful in combating the nausea associated with cancer chemotherapy, and alosetron is employed in the treatment of IBS with diarrhea. Serotonergic signaling abnormalities have also been putatively implicated in the pathogenesis of functional bowel diseases. Other compounds, for which efficacy has not been rigorously established, but which may have value, include tricyclic antidepressants and serotonin selective reuptake inhibitors to combat IBS, and 5-HT(1) agonists, which enhance gastric accommodation, to treat functional dyspepsia. The initial success encountered with serotonergic agents holds promise for newer and more potent insights and therapies of brain-gut disorders.

Functional Dyspepsia: Impaired Fundic Accommodation

Functional dyspepsia is a heterogeneous disorder in which distinct pathophysiological abnormalities are present in subgroups of patients. Accommodation of the proximal stomach to a meal is impaired in 40% of patients with functional dyspepsia. This is associated with symptoms of early satiety and weight loss. The presence of early satiety as a relevant or severe symptom is a good predictor of impaired accommodation. Gastric barostat or proximal gastric ultrasound may confirm the presence of impaired accommodation after a meal. Sophisticated analysis of scintigraphic gastric emptying images or a simple caloric drinking test are under investigation in the diagnosis of impaired accommodation. It seems logical to have patients eat more frequent, smaller sized meals. Cisapride is the only well-evaluated form of pharmacological treatment for this condition, and has been withdrawn from the US market (see Important Note under Treatment, below). Small or preliminary studies suggest some benefit from buspirone or selective serotonin reuptake inhibitors (SSRIs).