The effect of dopamine on rat gastric motility

Enhancement of ghrelin-signaling system by Rikkunshi-To attenuates teriparatide-induced pica in rats

Teriparatide is clinically used for the treatment of osteoporosis; however, nausea is often observed in patients. Its insufficient control affects the ability to continue teriparatide therapy. Rikkunshi-To (RKT), a traditional Japanese herbal medicine, improves the gastrointestinal function via activation of the ghrelin-signaling system. We investigated the therapeutic effects of RKT on teriparatide-induced nausea in rats and the involvement of ghrelin in these effects. We previously reported that ovariectomized rats showed pica (kaolin ingestion), a behavior that can be used to assess nausea in rats, after the subcutaneous administration of teriparatide; thus, the behavior was used as an index of nausea. Ovariectomized rats were fed diets with or without RKT (1%) for 2 weeks, and then they received the subcutaneous injection of teriparatide (400 μg/kg). Teriparatide significantly increased the incidence of pica, while suppressing intestinal motility and plasma ghrelin levels in rats fed normal diets; however, rats fed diets with RKT showed improvements in all of the teriparatide-induced adverse reactions. These therapeutic effects were antagonized by a ghrelin receptor antagonist ([D-Lys³]-GHRP-6; 200 nmol/rat). These findings suggest that the enhancement of ghrelin-signaling is involved in RKT's therapeutic effect, and that RKT is a potentially useful treatment for teriparatide-induced nausea.

Effects of Rhizoma Parisdis total saponins and its main compounds on gastric emptying via regulating muscarinic receptors in vitro and in vivo

The aim of this study was to explore the inhibitory effect of Rhizoma Parisdis total Saponins (RPS) and the main monomer compounds (polyphyllin I, II, VI and H) on gastric emptying and gastrointestinal motilityin vitroandin vivo.

DA-9701: A New Multi-Acting Drug for the Treatment of Functional Dyspepsia

Motilitone^® (DA-9701) is a new herbal drug that was launched for the treatment of functional dyspepsia in December 2011 in Korea. The heterogeneous symptom pattern and multiple causes of functional dyspepsia have resulted in multiple drug target strategies for its treatment. DA-9701, a compound consisting of a combination of Corydalis Tuber and Pharbitidis Semen, has being developed for treatment of functional dyspepsia. It has multiple mechanisms of action such as fundus relaxation, visceral analgesia, and prokinetic effects. Furthermore, it was found to significantly enhance meal-induced gastric accommodation and increase gastric compliance in dogs. DA-9701 also showed an analgesic effect in rats with colorectal distension induced visceral hypersensitivity and an antinociceptive effect in beagle dogs with gastric distension-induced nociception. The pharmacological effects of DA-9701 also include conventional effects, such as enhanced gastric emptying and gastrointestinal transit. The safety profi le of DA-9701 is also preferable to that of other treatments.

The possible involvement of dopamine D3 receptors in the regulation of gastric emptying in rats

AIM

The inhibitory effect of dopamine on gastric motility is thought to be mediated via a decrease in acetylcholine release resulting from stimulation of enteric neuronal dopamine D(2) receptors. The aim of this study was to investigate the possible involvement of the dopamine D(3) receptor in the regulation of gastric motility in rats using selective dopamine D(3) receptor agonists or a dopamine D(3) receptor antagonist.

MAIN METHODS

Gastric emptying was assessed using the phenol red method after rats were treated with varying doses of dopamine D(3) receptor agonists or a dopamine D(3) receptor antagonist.

KEY FINDINGS

S(+)-PD 128,907 (0.01-1 mg/kg, s.c.), a selective dopamine D(3) receptor agonist, dose-dependently delayed gastric emptying in rats. Other dopamine D(3) receptor agonists (i.e., R(+)-7-OH-DPAT [0.03-1 mg/kg, s.c.] and quinpirole [0.01-1 mg/kg, s.c.]) also delayed gastric emptying in rats. Both the selective dopamine D(1) and D(5) receptor agonist SKF-38393 and the selective dopamine D(4) receptor agonist PD 168,077 failed to delay gastric emptying in rats. The selective dopamine D(3) receptor antagonist (+)-S 14297 (10mg/kg, s.c.) partially inhibited the S(+)-PD 128,907-induced delay in gastric emptying. Although an administration of S(+)-PD 128,907 (1-100 μg/kg) into the 4th cerebral ventricle partially and dose-dependently delayed gastric emptying in rats, its administration into the lateral cerebral ventricle did not affect gastric emptying.

SIGNIFICANCE

The results presented here suggest that peripheral dopamine D(2) receptors and, at least in part, dopamine D(3) and central dopamine D(2)/D(3) receptors play an important role in the regulation of gastric motility in rats.

Review article: clinical implications of enteric and central D2 receptor blockade by antidopaminergic gastrointestinal prokinetics

Antidopaminergic gastrointestinal prokinetics (bromopride, clebopride, domperidone, levosulpiride and metoclopramide) have been exploited clinically for the management of motor disorders of the upper gastrointestinal tract, including functional dyspepsia, gastric stasis of various origins and emesis. The prokinetic effect of these drugs is mediated through the blockade of enteric (neuronal and muscular) inhibitory D2 receptors. The pharmacological profiles of the marketed compounds differ in terms of their molecular structure, affinity at D2 receptors, ability to interact with other receptor systems [5-hydroxytryptamine-3 (5-HT3) and 5-HT4 receptors for metoclopramide; 5-HT4 receptors for levosulpiride) and ability to permeate the blood-brain barrier (compared with the other compounds, domperidone does not easily cross the barrier). It has been suggested that the serotonergic (5-HT4) component of some antidopaminergic prokinetics may enhance their therapeutic efficacy in gastrointestinal disorders, such as functional dyspepsia and diabetic gastroparesis. The antagonism of central D2 receptors may lead to both therapeutic (e.g. anti-emetic effect due to D2 receptor blockade in the area postrema) and adverse (including hyperprolactinaemia and extrapyramidal dystonic reactions) effects. As the pituitary (as well as the area postrema) is outside the blood-brain barrier, hyperprolactinaemia is a side-effect occurring with all antidopaminergic prokinetics, although to different extents. Extrapyramidal reactions are most commonly observed with compounds crossing the blood-brain barrier, although with some differences amongst the various agents. Prokinetics with a high dissociation constant compared with that of dopamine at the D2 receptor (i.e. compounds that bind loosely to D2 receptors in the nigrostriatal pathway) elicit fewer extrapyramidal signs and symptoms. A knowledge of central and peripheral D2 receptor pharmacology can help the clinician to choose between the antidopaminergic prokinetics to obtain a more favourable risk/benefit ratio.

Distribution of urocortin in the rat's gastrointestinal tract and its colocalization with tyrosine hydroxylase

Urocortin (Ucn), a newly identified member of the corticotropin-releasing factor (CRF) family, is not only expressed in the brain, but also abundantly present in the peripheral tissues, especially in the gastrointestinal tract (GI) as determined by radioimmuoassay. In order to determine the precise localization of urocorin in the GI, we mapped the distribution of urocortin-like immunoreactivity (ir) in the GI of the rat using an immunofluorescence histochemical technique. Ucn, both in the brain and the peripheral tissues, is involved in the regulatory control of host-defense mechanism during stress. In order to study the possible involvement of the sympathetic system in the expression of GI urocortin in response to stress, we examined the effect of chemical sympathectomy on urocortin-ir and its colocalization with tyrosine hydroxylase (TH). UCn was expressed in all parietal cells of the stomach, myenteric and submucosal plexuses as well as in cells in Lieberkühn crypts of the small and large intestine. Most of the acid secreting parietal cells contained both Ucn and TH. Chemical sympathectomy did not affect Ucn immunoreactivity of parietal cells.

KDR-5169, a new gastrointestinal prokinetic agent, enhances gastric contractile and emptying activities in dogs and rats

KDR-5169, 4-amino-5-chloro-N-[1-(3-fluoro-4-methoxybenzyl)piperidin-4-yl]-2-(2-hydroxyethoxy)benzamide hydrochloride dihydrate, is a new prokinetic with a dual action, i.e., stimulation of the 5-HT4 receptor and antagonism of the dopamine D2 receptor. In this study, we determined in vitro activities of KDR-5169 towards both receptors and demonstrated the effect of the compound on gastrointestinal motor activity in conscious dogs and rats. In dogs, intravenous KDR-5169 stimulated upper gastrointestinal motility in the fasting state and also eliminated the depressive effect of 3,4-dihydroxyphenylalanine (L-DOPA) on this motility in the postprandial state. The effect of KDR-5169 on gastric emptying was further characterized by the use of three rat gastroparesis models (dopamine D2 receptor agonist (quinpirol)-, abdominal surgery-, or combined-situation-induced). Domperidone (a dopamine D2 receptor antagonist) was effective in the quinpirol-delay and combination-delay models, and cisapride and mosapride (5-HT4 receptor agonists) were effective in the surgery-delay model. Only KDR-5169 eliminated the delay of gastric emptying in all three models. In addition, KDR-5169 accelerated emptying to above the normal level in the combination-delay model. These results suggest that KDR-5169 would be effective in various types of gastric ileus caused by different mechanisms.

Demonstration of dopamine immunoreactivity in open and closed type endocrine cells of gerbil (Meriones unguiculatus) stomach

Dopamine-immunoreactive cells were identified in the stomach of gerbils using a selective antibody against glutaraldehyde-conjugated dopamine. In the pyloric area dopamine-containing cells were exclusively localized in the basal part of the mucous membrane, whereas in the fundic area dopaminergic cells were seen throughout the basodistal extent of the mucous membrane. Dopamine-containing cells belong to the class of closed and open type endocrine cells and were found in the fundic area and in the pyloric area respectively. These findings are discussed along with the likely modulatory function of dopamine in peripheral tissues.

Inhibitory effect of dopamine on gastric motility in rats

BACKGROUND

There is disagreement with regard to the involvement of dopamine (DA) receptors in gastric motility. The mechanisms of the inhibitory effect of DA on rat gastric motility was investigated in association with acetylcholine (Ach) release in the present study.

METHODS

In vivo vagotomized, splanchnicectomized rats and control rats were used, and gastric movement was determined as the gastric motility index after DA administration. In vitro study of Ach release from the circular muscle strips of the gastric corpus was investigated after administration of domperidone, SCH23390, phentolamine, or propranolol.

RESULTS

In the in vivo study DA inhibited gastric motility in a dose-dependent manner. Vagotomy and splanchnicectomy had no effect on the inhibitory effect of DA. In vitro study DA inhibited [3H]-Ach release in a dose-dependent manner. The inhibitory effect of DA was antagonized by domperidone but not by phentolamine, propranolol, or SCH23390.

CONCLUSIONS

Inhibition of gastric motility by dopamine is independent of extrinsic innervation and seems to be mediated by DA2 receptors in the gastric wall.

Gastric and duodenal anti-ulcer activity of SKF 38393, a dopamine D1-receptor agonist in rats

The effect of SKF 38393 (1-phenyl-7,8-diol-2,3,4,5-tetrahydro-1H-3-benzazepine), a specific dopamine D1-receptor agonist, was studied on pylorus-ligation and water immersion plus restraint stress-induced gastric ulcers, and cysteamine-induced duodenal ulcers in rats. Repeated administration of SKF 38393 (5 and 10 mg kg-1, p.o.) for six days was found to be effective in the prevention of gastric ulceration induced by water immersion plus restraint stress in rats. In 19-h pylorus-ligated rats, repeated treatment with SKF 38393 showed a significant reduction in the number and severity of ulcers. SKF 38393 did not alter the total gastric-mucosal carbohydrates:protein ratio; however, the gastric content volume and the free and total acidity were significantly reduced. In cysteamine-induced duodenal ulcers, the treatment with SKF 38393 for 6 days prevented the duodenal lesions. Our data suggests the involvement of dopamine D1 receptors in the anti-ulcer activity of SKF 38393, which could be largely attributed to its anti-secretory effect. Its anti-ulcer activity against water immersion plus restraint, also points towards a central mode of action, but its failure to alter the carbohydrate:protein ratio rules out any protective effect through the strengthening of the gastric mucosal barrier.