Catecholamine-induced relaxation and contraction of the lower oesophageal and pyloric sphincters of guinea-pig stomach: modification by domperidone

The ultra-performance liquid chromatography determination of domperidone and its process-related impurities

A rapid ultra-performance liquid chromatography (UPLC) method for the determination of domperidone in the presence of its process impurities and droperidol was developed and validated. The rapid chromatographic separation was achieved using a sub 2 µm Hypersil Zorbax eXtra Densely Bonded C18 column (30 × 4.6 mm, i.d., 1.8 µm). A gradient mobile phase consisting of Solvent A: 0.06 M ammonium acetate and Solvent B: methanol, with a flow rate of 1 mL/min was employed. The column temperature was set at 40°C, and the diode-array detector was set at 280 nm. An injection volume of 3 µL was used. The currently utilized European Pharmacopeia (Eur. Pharm.) method employed by Janssen Pharmaceuticals Ltd was run on a Hypersil Base-Deactivated Silica C18 column (100 × 4.6 mm, i.d., 3 µm) with a run time of 12.5 min. The developed UPLC method, with a run time of 7.5 min was determined to be accurate, precise, specific, robust and highly sensitive according to the International Conference on Harmonization guidelines. The method herein demonstrated a reduction in analysis time of 40%, allowing for a much higher sample throughput. A solvent consumption decrease of over 58% was also observed, which results in a dramatic reduction in running costs for Janssen Pharmaceuticals Ltd.

Responses of human clasp and sling fibers to neuromimetics

BACKGROUND AND AIMS

It has previously been demonstrated that clasp and sling fibers at the human gastroesophageal junction respond differently to acetylcholine (Ach). The present study was undertaken to investigate the differences between the physiological and pharmacological properties of the two types of muscle fiber.

METHODS

Recordings were made of the isometric tension of human sling and clasp fibers in response to Ach, dopamine (DA), phenylephrine (Phe), and isoprenaline (Iso). These specimens were obtained from 18 patients who were operated on for esophageal cancer.

RESULTS

Both Ach and Phe increased the tension of the two types of muscle; the values in the Ach group being 3-4-fold greater than those in the Phe group, while Iso decreased the tension of both types of muscle strip. The tension of the sling fibers was reduced by DA at lower concentration, and then increased gradually as the concentration was increased. In contrast, the tension of the clasp fibers did not obviously change when the concentration of DA was lower, but a slow elevation of tension was seen with the increase in DA concentration.

CONCLUSIONS

The sensitivities and maximum responses to each agent differed between the clasp fibers and sling fibers. This suggests that the two kinds of fiber have different roles in establishing tension in the lower esophageal sphincter, with implications for the medical and surgical treatment of disorders in this region.

Vagal and sympathetic influences on the ferret lower oesophageal sphincter

This study has investigated the relative involvement of cholinergic, adrenergic, nitric oxide and tachykininergic transmission in extrinsic neural influences on the lower oesophageal sphincter (LOS) in urethane anaesthetized ferrets. A micromanometric assembly (OD 1.75 mm) incorporating a sleeve sensor was used for high-fidelity oesophageal, LOS and gastric pressure measurement at low perfusion rates (< 0.1 ml/min). The LOS response to vagal and splanchnic nerve stimulation (0.5 ms pulse width, 10 s duration) was frequency- and voltage-dependent. LOS responses to stimulation at 20 V, 10 Hz were investigated in separate groups of animals with either L-NAME (100 mg/kg), hexamethonium (15 mg/kg), guanethidine (5 mg/kg), CP96,345 (NK-1 antagonist, 4 mg/kg), atropine (0.4 mg/kg) or propranolol (1 mg/kg). Propranolol treatment was followed by yohimbine (1 mg/kg) and prazosin (0.25 mg/kg). Vagal stimulation caused an immediate decrease in LOS pressure, followed by increase on cessation of stimulation, followed by a prolonged decrease (77 +/- 2%) for up to 5 min. L-NAME did not affect inhibition, but increased excitation 4-fold (p < 0.001). Guanethidine and CP96,345 had no major effect. Hexamethonium decreased the inhibitory (p < 0.05) and excitatory (p < 0.01) responses. Atropine reduced the excitatory response (p < 0.05). Some inhibition still remained if all treatments were combined. Splanchnic stimulation reduced LOS pressure by 70 +/- 6% for 101 +/- 17 s. L-NAME, guanethidine, hexamethonium and CP96,345 all independently significantly reduced inhibition. The combination of guanethidine and CP96,345 usually abolished splanchnic-induced inhibition. Atropine was without effect. Propranolol (1 mg/kg) changed the splanchnic-induced response from mainly inhibition to excitation (100 +/- 44% increase). LOS responses to noradrenaline (1-10 micrograms close IA) showed similar features to responses to splanchnic stimulation. We conclude that vagal stimulation evokes LOS relaxation via activation of established cholinergic and NANC mechanisms and other, unidentified mechanisms. Splanchnic stimulation activates adrenergic neurones probably via nicotinic and non-nicotinic ganglionic mechanisms, which in turn elicit beta adrenergic inhibitory effects on the LOS. Splanchnic stimulation also antidromically activates spinal afferent fibres. These may release substance P from peripheral myenteric plexus and prevertebral ganglionic endings causing activation of myenteric NANC inhibitory neurones and sympathetic neurones, respectively.

Transmitter mechanisms in vagal afferent-induced reduction of lower oesophageal sphincter (LOS) pressure in the rat

The extrinsic neural pathways and transmitter mechanisms involved in neural influences controlling lower oesophageal sphincter (LOS) pressure have been evaluated in three groups of experiments in urethane anaesthetized rats. A miniature perfused sleeve/sidehole catheter measured gastric, LOS and oesophageal pressures. Group 1: Vago-vagal and vago-spinal reflex pathways were activated simultaneously via the central nervous system by stimulation of the central cut end of the left vagus. This caused a prolonged drop in LOS pressure with a rapid onset and a slow return to baseline. Subsequent right (bilateral) vagotomy in these animals increased basal LOSP (P < 0.001). Central vagal stimulation-induced reduction of LOSP was not significantly changed in amplitude but was shorter in duration (P < 0.01) than before bilateral vagotomy. IV administration of the 5-HT3 receptor antagonist granisetron (50 micrograms/kg), after bilateral vagotomy had no effect on the response to central vagal stimulation. The nitric oxide (NO) synthase inhibitor L-nitroarginine methyl ester (L-NAME) (100 mg/kg) reduced the depth of relaxation (P < 0.01) and temporarily increased basal LOSP. Propranolol (1.5 mg/kg, i.v.) subsequently increased basal LOSP (P < 0.01), but had no further effect on the vagal stimulation-induced reduction in LOSP. Alpha adrenergic blockade with phentolamine (1 mg/kg, i.v.) decreased basal LOSP (P < 0.01), and nearly abolished the response to vagal stimulation (P < 0.01). Group 2: Both alpha 1- and alpha 2-adrenoceptors were shown to be involved by the combined use of the more selective antagonists yohimbine (1 mg/kg, i.v.) and prazosin (200 micrograms/kg) in place of phentolamine. Group 3: To observe neurotransmitter mechanisms in the vago-vagal pathway, central left vagal stimulation was performed after left vagotomy, and subsequently after blockade of sympathetic motor pathways with guanethidine (5 mg/kg), leaving intact efferent pathways in the right vagus. Guanethidine increased basal LOSP (P < 0.01), and reduced the duration of vagal-induced LOS relaxation (P < 0.05). Depth of relaxation was unchanged. Subsequently, granisetron and L-NAME had no significant effects. Finally, additional right vagotomy abolished the remaining response. Our data indicate the existence of vago-spinal and vago-vagal inhibitory reflex pathways to the rat LOS. The inhibitory vago-spinal pathway is mainly alpha-adrenergic, and has a minor NO-mediated component, but no 5-HT3 receptor-mediated mechanism. In the vago-vagal pathway, no significant involvement of NO-mediated or 5-HT3 receptor-mediated effects was observed. Other non-adrenergic inhibitory mechanisms were, however, apparent.(ABSTRACT TRUNCATED AT 400 WORDS)

Effect of domperidone on the release of insulin after intravenous glucose load in man

To determine whether the blockade of the dopaminergic system is capable of modifying glucose-induced insulin release in man, the responses of insulin to an iv glucose load were measured at various domperidone infusion rates. The infusion of 5 micrograms/kg/min of domperidone increased significantly plasma insulin levels during the acute phase of glucose-induced insulin release and lowered plasma glucose values at 50 and 60 min; the k of glucose disappearance improved significantly. At lower domperidone infusion rates the acute increment of insulin after glucose load was indistinguishable from the response observed at 5 micrograms/kg/min until 0.5 microgram/kg/min, while similar responses in control and experimental tests were observed at 0.25 microgram/kg/min. A group of subjects was submitted to an arginine load in order to establish whether the effect observed with domperidone was specific for the glucose-induced insulin release; but, this time, we did not observe any significant effect during the domperidone-induced dopaminergic blockade. Furthermore, we also measured the plasma prolactin levels, to see whether the specific and well known effect of domperidone on prolactin release matches with the effect on beta-cell function. As far as prolactin is concerned, we observed a dose response effect of domperidone infusion, with a detectable elevation of prolactin at infusion rate of 0.25 microgram/kg/min. Since domperidone is a specific antagonist of dopamine D2-receptors, we propose that dopamine might exert a specific inhibiting effect on glucose-induced insulin release through this class of dopamine receptors.

DA1 receptor mediates dopamine-induced relaxation of opossum lower esophageal sphincter in vitro

The objective of the present experiments was to determine the specific receptor subtype through which dopamine (DA) receptor agonists relax the lower esophageal sphincter in vitro. Opossum lower esophageal sphincter smooth muscle strips were placed in oxygenated Krebs' solution containing propranolol and cocaine. The tissues were placed at a tension that gave maximum relaxation to electrical field stimulation and were then pretreated with phenoxybenzamine. The effects of DA, and the DA receptor agonists epinine and apomorphine were determined. In addition, agonist responses were studied in the presence of the selective DA2 receptor antagonist domperidone, a mixed DA1/DA2 receptor antagonist metoclopramide, and the selective DA1 receptor antagonists bulbocapnine and SK&F 83566. The DA agonists relaxed the smooth muscle strips in the following order of potency: DA greater than epinine greater than apomorphine. Domperidone did not antagonize DA- or apomorphine-induced relaxation. Metoclopramide failed to alter DA-induced relaxation. Bulbocapnine and SK&F 83566 significantly inhibited the relaxation induced by DA. These data indicate that DA-induced lower esophageal sphincter relaxation in vitro is mediated by DA1 receptors.

The mechanism of action of dopamine to inhibit field stimulation-induced contractions of guinea pig stomach strips

Field stimulation (0.125-10 Hz) of longitudinal smooth muscle strips taken from the fundus of guinea pig stomach caused frequency related contraction responses (atropine-sensitive) associated with relaxation at the higher frequencies (both responses tetrodotoxin-sensitive). Dopamine, noradrenaline, adrenaline and apomorphine antagonised the contraction responses at all frequencies; the concentration-response curves were steep and the use of higher concentrations was precluded by changes in base line tension per se. That noradrenaline was approximately 10 fold more potent than dopamine, that the dopamine response was not antagonised by the dopamine antagonists haloperidol, domperidone or (-)sulpiride, but was mimicked by the alpha 2-agonist guanfacine and partially antagonised by the alpha 2-adrenoceptor antagonist yohimbine (which could also antagonise the inhibitory actions of guanfacine) would indicate that a component of dopamine's action to reduce cholinergic activity is effected via alpha 2-adrenoceptor mechanisms. A failure of phenylephrine to mimic, or prazosin to attenuate the agonist inhibitory responses would not indicate an additional alpha 1-adrenoceptor involvement. The persistence of the dopamine response following disruption of noradrenergic function by reserpine or inhibition of catecholamine reuptake processes (desmethylimipramine plus corticosterone, GBR 13098) would indicate a direct action of dopamine. It is concluded that the ability of dopamine to reduce cholinergic induced contractions in longitudinal smooth muscle of the stomach does not reflect a dopamine receptor or alpha 1-adrenoceptor stimulation but may involve an action on alpha 2-adrenoceptors.

Domperidone. A review of its pharmacological activity, pharmacokinetics and therapeutic efficacy in the symptomatic treatment of chronic dyspepsia and as an antiemetic

Domperidone is a dopamine antagonist that does not readily enter the central nervous system. Given parenterally or orally it increases gastric emptying of liquids and increases lower oesophageal sphincter pressure in healthy subjects. The antiemetic and pharmacodynamic profile of domperidone is similar to that of metoclopramide, although domperidone has a lower propensity to cause extrapyramidal side effects. Domperidone effectively alleviates symptoms of chronic postprandial dyspepsia and nausea and vomiting due to a wide variety of underlying causes and in some studies has been superior to metoclopramide. Vomiting associated with the administration of moderately emetic cytotoxic drugs is controlled in the majority of patients. Alleviation of the dose-limiting peripheral side effects (nausea and vomiting) of the anti-Parkinsonian drugs bromocriptine and levodopa, enables a higher optimum dose, with consequent improvement in Parkinsonian symptoms. Domperidone does not aggravate the extrapyramidal side effects of neuroleptic drugs. Control of cytotoxic-induced, and postprandial nausea and vomiting in children has been achieved with domperidone without evidence of extrapyramidal side effects. Indeed, side effects have seldom occurred with therapeutic doses of domperidone.

Domperidone. A review of its pharmacological activity, pharmacokinetics and therapeutic efficacy in the symptomatic treatment of chronic dyspepsia and as an antiemetic

Domperidone is a dopamine antagonist that does not readily enter the central nervous system. Given parenterally or orally it increases gastric emptying of liquids and increases lower oesophageal sphincter pressure in healthy subjects. The antiemetic and pharmacodynamic profile of domperidone is similar to that of metoclopramide, although domperidone has a lower propensity to cause extrapyramidal side effects. Domperidone effectively alleviates symptoms of chronic postprandial dyspepsia and nausea and vomiting due to a wide variety of underlying causes and in some studies has been superior to metoclopramide. Vomiting associated with the administration of moderately emetic cytotoxic drugs is controlled in the majority of patients. Alleviation of the dose-limiting peripheral side effects (nausea and vomiting) of the anti-Parkinsonian drugs bromocriptine and levodopa, enables a higher optimum dose, with consequent improvement in Parkinsonian symptoms. Domperidone does not aggravate the extrapyramidal side effects of neuroleptic drugs. Control of cytotoxic-induced, and postprandial nausea and vomiting in children has been achieved with domperidone without evidence of extrapyramidal side effects. Indeed, side effects have seldom occurred with therapeutic doses of domperidone.

Benzamide action at alpha 2-adrenoceptors modifies catecholamine-induced contraction and relaxation of circular smooth muscle from guinea-pig stomach

Dopamine was shown to act on the circular smooth muscle of the stomach body to cause contraction at a yohimbine-sensitive site (alpha 2) and a relaxation at a prazosin-sensitive site (alpha 1). Metoclopramide and tiapride failed to modify either response, failed to antagonise a relaxation to phenylephrine at alpha 1 sites in the same tissue, and failed to modify the contractions caused by dopamine and phenylephrine at an alpha 1-adrenoceptor site in the pyloric sphincter. However, (+)- and (-)-sultopride and (+)-sulpiride antagonised the dopamine-induced contractions of the stomach body indicating an alpha 2-antagonist action. An ability to attenuate the relaxation of this tissue may reflect a displacement of the contraction curve to the right rather than an alpha 1-antagonist action since the response to phenylephrine was not antagonised either in this tissue or in the pyloric sphincter. Within the central nervous system the (-)-enantiomers of sultopride and sulpiride have a highly selective dopamine receptor blocking action. This contrasts with the present findings in the stomach musculature of a non-stereospecific antagonism at alpha 2-type adrenoceptors.