Effect of domperidone and dopamine on colonic motor activity in patients with the irritable bowel syndrome

Drugs in Focus: Domperidone

Domperidone is a peripheral dopamine-2 receptor antagonist with prokinetic and antiemetic properties. Its prokinetic effects are mainly manifest in the upper gastrointestinal (GI) tract. Currently its use is restricted to relief of nausea and vomiting in children older than 12 years for a short period of time. However, among (pediatric) gastroenterologists, domperidone is also used outside its authorized indication ("off label") for treatment of symptoms associated with gastro-esophageal reflux disease, dyspepsia, and gastroparesis. Little is known about its efficacy in the treatment of GI motility disorders in children and controversial data have emerged in the pediatric literature. As its use is off label, appropriate knowledge of its efficacy is helpful to support an "off label/on evidence" prescription. Based on this, the purpose of this review is to summarize all evidence on the efficacy of domperidone for the treatment of GI disorders in infants and children and to report an overview of its pharmacological properties and safety profile.

Opposite effects of dopamine on the mechanical activity of circular and longitudinal muscle of human colon

BACKGROUND

Because dopamine (DA) has gained increasing evidence as modulator of gut motility, we aimed to characterize dopaminergic response in human colon, evaluating function and distribution of dopamine receptors in circular vs longitudinal muscle strips.

METHODS

Mechanical responses to DA and dopaminergic agonists on slow phasic contractions and on basal tone were examined in vitro as changes in isometric tension. RT-PCR was used to reveal the distribution of dopaminergic receptors.

KEY RESULTS

In spontaneous active circular muscle, DA induced an increase in the amplitude of slow phasic contractions and of the basal tone, via activation of D1-like receptors. DA contractile responses were insensitive to neural blockers or to atropine and inhibited by phospholipase C (PLC) pathway inhibitors. In precontracted circular muscle strips, DA, at the higher concentrations tested, caused a relaxant response via activation of D2-like receptors. In the longitudinal muscle, DA caused only muscular relaxation due to activation of D2-like receptors. DA relaxant responses were insensitive to neural blockers or to nitric oxide synthase inhibitor and reduced by a wide-spectrum K⁺ channel blockers. Transcripts encoding for all the dopaminergic receptor subtypes was observed in both circular and longitudinal preparations.

CONCLUSIONS AND INFERENCES

Dopamine is able to modulate contractile activity of the human colon. In the circular muscle layer, DA induces mainly muscular contraction activating non-neural D1-like receptors, coupled to PLC/IP3 pathway. In the longitudinal muscle layer, DA induces muscular relaxation acting on non-neural D2-like receptors leading to the increase in K⁺ conductance.

Levodopa ameliorated anorectal constipation in de novo Parkinson's disease: The QL-GAT study

BACKGROUND

Gastrointestinal tract (GIT) dysfunction is common in Parkinson's disease (PD) patients. However, it remains unclear whether levodopa affects GIT function in PD.

OBJECTIVE

To perform an open study of levodopa's effects on anorectal constipation in de novo PD patients by the quantitative lower-gastrointestinal autonomic test (QL-GAT).

METHODS

Nineteen unselected de novo PD patients (10 men, 9 women; mean age, 66 years; mean duration of the disease, 2.2 years) were recruited for the study. Eighteen of the patients reported constipation. These patients were treated with 200/20 mg b.i.d. of levodopa/carbidopa for 3 months. Pre- and post-treatment, objective parameters in the QL-GAT that comprised the colonic transit time (CTT) and rectoanal videomanometry were obtained.

RESULTS

Levodopa was well tolerated by all patients. There was a trend toward subjective improvements in bowel frequency and difficulty defecating. Levodopa did not significantly change CTT of the total colon or any segment of the colon. During rectal filling, levodopa significantly lessened the first sensation (p < 0.05). It also tended to augment the amplitude of spontaneous phasic rectal contraction (not statistically significant). During defecation, levodopa significantly lessened the amplitude in paradoxical sphincter contraction upon defecation (PSD) (p < 0.01). It also tended to augment the amplitude of rectal contraction and lessen the amplitude of abdominal strain (not statistically significant). Overall, levodopa significantly lessened post-defecation residuals (p < 0.05).

CONCLUSIONS

The QL-GAT in the present study showed for the first time that levodopa augmented rectal contraction, lessened PSD, and thereby ameliorated anorectal constipation in de novo PD patients.

Bladder, bowel, and sexual dysfunction in Parkinson's disease

Bladder dysfunction (urinary urgency/frequency), bowel dysfunction (constipation), and sexual dysfunction (erectile dysfunction) (also called “pelvic organ” dysfunctions) are common nonmotor disorders in Parkinson's disease (PD). In contrast to motor disorders, pelvic organ autonomic dysfunctions are often nonresponsive to levodopa treatment. The brain pathology causing the bladder dysfunction (appearance of overactivity) involves an altered dopamine-basal ganglia circuit, which normally suppresses the micturition reflex. By contrast, peripheral myenteric pathology causing slowed colonic transit (loss of rectal contractions) and central pathology causing weak strain and paradoxical anal sphincter contraction on defecation (PSD, also called as anismus) are responsible for the bowel dysfunction. In addition, hypothalamic dysfunction is mostly responsible for the sexual dysfunction (decrease in libido and erection) in PD, via altered dopamine-oxytocin pathways, which normally promote libido and erection. The pathophysiology of the pelvic organ dysfunction in PD differs from that in multiple system atrophy; therefore, it might aid in differential diagnosis. Anticholinergic agents are used to treat bladder dysfunction in PD, although these drugs should be used with caution particularly in elderly patients who have cognitive decline. Dietary fibers, laxatives, and “prokinetic” drugs such as serotonergic agonists are used to treat bowel dysfunction in PD. Phosphodiesterase inhibitors are used to treat sexual dysfunction in PD. These treatments might be beneficial in maximizing the patients' quality of life.

Comparison of the effects of central and peripheral dopamine receptor activation on evoked firing in the trigeminocervical complex

Dopaminergic mechanisms have been suggested to play a role in migraine. Here, electrophysiological techniques were used to study the effects of intravenously administered centrally or peripherally active dopamine receptor agonists and antagonists on evoked firing in the trigeminocervical complex (TCC). After establishing baseline firing evoked by electrical stimulation of the dural middle meningeal artery (MMA) and mechanical noxious and innocuous stimulation of the ophthalmic dermatome, D(1)- or D(2)-like receptor agonists or antagonists were administered intravenously and the effect on firing was determined. In addition, with use of intravital microscopy, we monitored changes in dural vessel diameter in response to varying doses of D(1)- or D(2)-like receptor agonists to determine whether their effects were related to blood vessel caliber. The central D(2)-like receptor agonist quinpirole hydrochloride inhibited firing in the TCC evoked by stimulation of the MMA. Conversely, the central D(2)-like receptor antagonists, eticlopride hydrochloride and remoxipride hydrochloride, facilitated MMA-evoked firing and also firing evoked by noxious and innocuous stimulation of the ophthalmic dermatome. Both the peripheral D(1)-like receptor agonist fenoldopam and the central D(1)-like receptor agonists cis-(+/-)-1-(aminomethyl)-3,4-dihydro-3-phenyl-1H-2-benzopyran-5,6-diol hydrochloride (A68930 hydrochloride) and dihydrexidine facilitated innocuous brush-evoked firing, with A68930 hydrochloride having the greatest effect. The data suggest that dopamine binding to peripheral D(1)-like receptors may play a role in peripheral sensitization, and that the inhibitory or excitatory effects seen with administration of dopamine receptor agonists are independent of blood vessel changes. In addition, these studies maintain that central D(2)-like receptors inhibit trigeminocervical neurons, and may provide insight into the conflicting literature on the role of dopamine and its receptors in migraine.

Bladder and bowel dysfunction in Parkinson's disease

Bladder dysfunction (urinary urgency/frequency) and bowel dysfunction (constipation) are common non-motor disorders in Parkinson's disease (PD). In contrast to motor disorder, the pelvic autonomic dysfunction is often non-responsive to levodopa treatment. Brain pathology mostly accounts for the bladder dysfunction (appearance of overactivity) via altered dopamine-basal ganglia circuit, which normally suppresses the micturition reflex. In contrast, peripheral enteric pathology mostly accounts for the bowel dysfunction (slow transit and decreased phasic contraction) via altered dopamine-enteric nervous system circuit, which normally promotes the peristaltic reflex. In addition, weak strain and paradoxical anal contraction might be the results of brain pathology. Pathophysiology of the pelvic organ dysfunction in PD differs from that in multiple system atrophy; therefore it might aid the differential diagnosis. Drugs to treat bladder dysfunction in PD include anticholinergic agents. Drugs to treat bowel dysfunction in PD include dietary fibers, peripheral dopaminergic antagonists, and selective serotonergic agonists. These treatments might be beneficial not only in maximizing patients' quality of life, but also in promoting intestinal absorption of levodopa and avoiding gastrointestinal emergency.

New developments in the treatment of functional dyspepsia

Functional dyspepsia is a clinical syndrome defined by chronic or recurrent pain or discomfort in the upper abdomen of unknown origin. Although generally accepted, investigators differently interpret this definition and clinical trials are often biased by inhomogeneous inclusion criteria. The poorly defined multifactorial pathogenesis of dyspeptic symptoms has hampered efforts to develop effective treatments. A general agreement exists on the irrelevant role played by Helicobacter pylori in the pathophysiology of functional dyspepsia. Gastric acid secretion is within normal limits in patients with functional dyspepsia but acid related symptoms may arise in a subgroup of them. Proton pump inhibitors appear to be effective in this subset of patients with dyspepsia. Non-painful dyspeptic symptoms are suggestive of underlying gastrointestinal motor disorders and such abnormalities can be demonstrated in a substantial proportion of patients. Postprandial fullness and vomiting have been associated with delayed gastric emptying of solids, and early satiety and weight loss to postcibal impaired accommodation of the gastric fundus. Prokinetics have been shown to exert beneficial effects, at least in some patients with dyspepsia. In contrast, drugs enhancing gastric fundus relaxation have been reported to improve symptoms, although conflicting results have also been published. An overdistended antrum may also generate symptoms, but its potential pathogenetic role and the effects of drugs on this abnormality have never been investigated formally. Visceral hypersensitivity plays a role in some dyspeptic patients and this abnormality is also a potential target for treatment. Both chemo- and mechanoreceptors can trigger hyperalgesic responses. Psychosocial abnormalities have been consistently found in functional digestive syndromes, including dyspepsia. Although useful in patients with irritable bowel syndromes (IBS), antidepressants have been only marginally explored in functional dyspepsia. Among the new potentially useful agents for the treatment of functional dyspepsia, serotonin 5-HT(4) receptor agonists have been shown to exert a prokinetic effect. Unlike motilides, 5-HT(4) receptor agonists do not appear to increase the gastric fundus tone and this may contribute to improve symptoms. 5-HT(3) receptor antagonists have been investigated mainly in the IBS and the few studies performed in functional dyspepsia have provided conflicting results. Also, kappa-opioid receptor agonists might be useful for functional digestive syndromes because of their antinociceptive effects, but available results in functional dyspepsia are scanty and inconclusive. Other receptors that represent potential clinical targets for antagonists include purinoceptors (i. e., P2X2/3 receptors), NMDA receptors (NR2B subtype), protease-activated receptor-2, the vanilloid receptor-1, tachykinin receptors (NK(1)/NK(2)) and cholecystokinin (CCK)(1) receptors.

Functional gut disorders: from motility to sensitivity disorders. A review of current and investigational drugs for their management

Functional gut disorders include several clinical entities defined on the basis of symptom patterns (e.g., functional dyspepsia, irritable bowel syndrome, functional abdominal pain, functional abdominal bloating), for which there is no established pathophysiological mechanism. Because there is no well-defined pathophysiological target, treatment should be aimed at symptom improvement. Prokinetics and antispasmodics have been widely used in the treatment of functional gut disorders on the assumption that disordered motility is the underlying cause of symptoms, and symptom improvement is indeed achievable with these compounds in some, but not all, patients with features of hypo- or hypermotility, respectively. In the first part of this review, we cover the basic pharmacology and discuss the rationale for the clinical use of prokinetics and antispasmodics. On the other hand, in the past few years, the explosive growth in the research focusing on visceral sensitivity and visceral reflexes has suggested that at least some patients with functional gut disorders have altered visceral perception. Thus, the second part of the review covers these developments and focuses on studies addressing the issue of drugs modulating visceral sensitivity.

Adrenergic mechanisms in the control of gastrointestinal motility: from basic science to clinical applications

Over the years, a vast literature has accumulated on the adrenergic mechanisms controlling gut motility, blood flow, and mucosal transport. The present review is intended as a survey of key information on the relevance of adrenergic mechanisms modulating gut motility and will provide an outline of our knowledge on the distribution and functional role of adrenoceptor subtypes mediating motor responses. alpha1-Adrenoceptors are located postsynaptically on smooth muscle cells and, to a lesser extent, on intrinsic neurons; alpha2-adrenoceptors may be present both pre- and postsynaptically, with presynaptic auto- and hetero-receptors playing an important role in the modulation of neurotransmitter release; beta-adrenoceptors are found mainly on smooth muscle cells. From a clinical standpoint, adrenoceptor agonists/antagonists have been investigated as potential motility inhibiting (antidiarrheal/antispasmodic) or prokinetic agents, although at present their field of application is limited to select patient groups.

Prokinetic agents for lower gastrointestinal motility disorders

Prokinetic agents are currently being investigated as potential therapies for motility disorders of the lower gastrointestinal tract. Cholinergic agonists such as bethanechol are known to improve postoperative ileus but are limited because of side effects. Dopamine antagonists such as domperidone appear to have maximal prokinetic effect in the proximal gastrointestinal tract and are effective for such conditions as gastroparesis and gastroesophageal reflux, but they appear to have little physiologic effect in the colon or in colonic motility disorders. Naloxone, an opioid antagonist, appears to hold promise in patients with irritable bowel syndrome, small intestinal pseudo-obstruction, and constipation. Erythromycin exerts its prokinetic effect by acting as a motilin agonist; it has been used in the treatment of diabetic gastroparesis and appears to improve symptoms of colonic pseudo-obstruction and postoperative ileus. Metoclopramide, a combined cholinergic agonist and dopamine antagonist, is currently used exclusively for proximal motility dysfunction. Cisapride appears to hold the most promise for patients with colonic motility disorders. In patients with postoperative ileus, cisapride is associated with an increased return of bowel function compared with placebo. In patients with chronic constipation, cisapride increases stool frequency and decreases laxative abuse in both adults and children. Hopefully, as an understanding of gastrointestinal motility increases, effective prokinetic agents will be developed that will improve symptoms of patients with large bowel motility disorders and may also help to predict those patients who benefit from surgical management for constipation.