Inhibition of anaesthetic-induced emesis by a NK1 or 5-HT3 receptor antagonist in the house musk shrew, Suncus murinus

Involvement of leukotriene pathway in the development of sevoflurane-induced pica in rats

We previously reported that sevoflurane-induced pica, kaolin ingestion behavior, in rats has the potential to reflect postoperative nausea and vomiting (PONV) in humans. It is well-known that corticosteroids, which inhibit both prostaglandin and leukotriene syntheses due to phospholipase A₂ inhibition, are effective for reducing PONV; however, the precise mechanisms remain unclear. We investigated the involvement of the prostaglandin or leukotriene pathway in the development of sevoflurane-induced pica. We found that sevoflurane-induced pica was effectively inhibited by pretreatment with a leukotriene receptor antagonist (montelukast) or an inhibitor of 5-lipoxygenase (zileuton), rather than an inhibitor of cyclooxygenase (flurbiprofen). Furthermore, we observed that sevoflurane significantly increased urinary leukotriene excretion and 5-lipoxygenase mRNA expression in the spleen, but not hypothalamus. These results suggest that the production of leukotriene may lead to the development of sevoflurane-induced pica in rats, and that inhibition of the leukotriene pathway could be potentially useful for the treatment of PONV.

Improved Starch Digestion of Sucrase-deficient Shrews Treated With Oral Glucoamylase Enzyme Supplements

BACKGROUND AND OBJECTIVE

Although named because of its sucrose hydrolytic activity, this mucosal enzyme plays a leading role in starch digestion because of its maltase and glucoamylase activities. Sucrase-deficient mutant shrews, Suncus murinus, were used as a model to investigate starch digestion in patients with congenital sucrase-isomaltase deficiency.Starch digestion is much more complex than sucrose digestion. Six enzyme activities, 2 α-amylases (Amy), and 4 mucosal α-glucosidases (maltases), including maltase-glucoamylase (Mgam) and sucrase-isomaltase (Si) subunit activities, are needed to digest starch to absorbable free glucose. Amy breaks down insoluble starch to soluble dextrins; mucosal Mgam and Si can either directly digest starch to glucose or convert the post-α-amylolytic dextrins to glucose. Starch digestion is reduced because of sucrase deficiency and oral glucoamylase enzyme supplement can correct the starch maldigestion. The aim of the present study was to measure glucogenesis in suc/suc shrews after feeding of starch and improvement of glucogenesis by oral glucoamylase supplements.

METHODS

Sucrase mutant (suc/suc) and heterozygous (+/suc) shrews were fed with C-enriched starch diets. Glucogenesis derived from starch was measured as blood C-glucose enrichment and oral recombinant C-terminal Mgam glucoamylase (M20) was supplemented to improve starch digestion.

RESULTS

After feedings, suc/suc and +/suc shrews had different starch digestions as shown by blood glucose enrichment and the suc/suc had lower total glucose concentrations. Oral supplements of glucoamylase increased suc/suc total blood glucose and quantitative starch digestion to glucose.

CONCLUSIONS

Sucrase deficiency, in this model of congenital sucrase-isomaltase deficiency, reduces blood glucose response to starch feeding. Supplementing the diet with oral recombinant glucoamylase significantly improved starch digestion in the sucrase-deficient shrew.

Role of the abdominal vagus and hindbrain in inhalational anesthesia-induced vomiting

The incidence of postoperative nausea and vomiting (PONV) can be as high as 80% in patients with risk factors (e.g., females, history of motion sickness). PONV delays postoperative recovery and costs several hundred million dollars annually. Cell-based assays show that halogenated ethers (e.g., isoflurane) activate 5-HT₃ receptors, which are found on gastrointestinal vagal afferents and in the hindbrain - key pathways for producing nausea and vomiting. This project evaluated the role of the vagus and activation of the hindbrain in isoflurane-induced emesis in musk shrews, a small animal model with a vomiting reflex, which is lacking in rats and mice. Sham-operated and abdominal vagotomized shrews were exposed to 1 to 3% isoflurane to determine effects on emesis; vagotomy was confirmed by lack of vagal transport of the neuronal tracer Fluoro-Gold. In an additional study, shrews were exposed to isoflurane and hindbrain c-Fos was measured at 90min after exposure using immunohistochemistry. There were no statistically significant effects of vagotomy on isoflurane-induced emesis compared to sham-operated controls. Isoflurane exposure produced a significant increase in c-Fos-positive cells in the nucleus of the solitary tract and vestibular nuclei but not in the area postrema or dorsal motor nucleus. These results indicate that the abdominal vagus plays no role in isoflurane-induced emesis and suggest that isoflurane activates emesis by action on the hindbrain, as shown by c-Fos labeling. Ultimately, knowledge of the mechanisms of inhalational anesthesia-induced PONV could lead to more targeted therapies to control PONV.

Prophylactic use of intravenous ondansetron versus ketamine - midazolam combination for prevention of shivering during spinal anesthesia: A randomized double-blind placebo-controlled trial

BACKGROUND

The aim of this study was to compare the efficacy intravenous (IV) ondansetron with ketamine plus midazolam for the prevention of shivering during spinal anesthesia (SA).

MATERIALS AND METHODS

Ninety patients, aged 18-65 years, undergoing lower extremity orthopedic surgery were included in the present study. SA was performed in all patients with hyperbaric bupivacaine 15 mg. The patients were randomly allocated to receive normal saline (Group C), ondansetron 8 mg IV (Group O) or ketamine 0.25 mg/kg IV plus midazolam 37.5 μg/kg IV (Group KM) immediately after SA. During surgery, shivering scores were recorded at 5 min intervals. The operating room temperature was maintained at 24°C.

RESULTS

The incidences of shivering were 18 (60%) in Group C, 6 (20%) in Group KM and 8 (26.6%) in Group O. The difference between Groups O and Group KM with Group C was statistically significant (P < 0.05). No significant difference was noted between Groups KM with Group O in this regard (P > 0.05). Peripheral and core temperature changes throughout surgery were not significantly different among three groups (P > 0.05). Incidence (%) of hallucination was not significantly different between the three groups (0, 3.3, 0 in Group O, Group KM, Group C respectively, P > 0.05).

CONCLUSION

Prophylactic use of ondansetron 8 mg IV was comparable to ketamine 0.25 mg/kg IV plus midazolam 37.5 μg/kg IV in preventing shivering during SA.

Integration of vestibular and emetic gastrointestinal signals that produce nausea and vomiting: potential contributions to motion sickness

Vomiting and nausea can be elicited by a variety of stimuli, although there is considerable evidence that the same brainstem areas mediate these responses despite the triggering mechanism. A variety of experimental approaches showed that nucleus tractus solitarius, the dorsolateral reticular formation of the caudal medulla (lateral tegmental field), and the parabrachial nucleus play key roles in integrating signals that trigger nausea and vomiting. These brainstem areas presumably coordinate the contractions of the diaphragm and abdominal muscles that result in vomiting. However, it is unclear whether these regions also mediate the autonomic responses that precede and accompany vomiting, including alterations in gastrointestinal activity, sweating, and changes in blood flow to the skin. Recent studies showed that delivery of an emetic compound to the gastrointestinal system affects the processing of vestibular inputs in the lateral tegmental field and parabrachial nucleus, potentially altering susceptibility for vestibular-elicited vomiting. Findings from these studies suggested that multiple emetic inputs converge on the same brainstem neurons, such that delivery of one emetic stimulus affects the processing of another emetic signal. Despite the advances in understanding the neurobiology of nausea and vomiting, much is left to be learned. Additional neurophysiologic studies, particularly those conducted in conscious animals, will be crucial to discern the integrative processes in the brain stem that result in emesis.

Identification of neural networks that contribute to motion sickness through principal components analysis of fos labeling induced by galvanic vestibular stimulation

Motion sickness is a complex condition that includes both overt signs (e.g., vomiting) and more covert symptoms (e.g., anxiety and foreboding). The neural pathways that mediate these signs and symptoms are yet to identified. This study mapped the distribution of c-fos protein (Fos)-like immunoreactivity elicited during a galvanic vestibular stimulation paradigm that is known to induce motion sickness in felines. A principal components analysis was used to identify networks of neurons activated during this stimulus paradigm from functional correlations between Fos labeling in different nuclei. This analysis identified five principal components (neural networks) that accounted for greater than 95% of the variance in Fos labeling. Two of the components were correlated with the severity of motion sickness symptoms, and likely participated in generating the overt signs of the condition. One of these networks included neurons in locus coeruleus, medial, inferior and lateral vestibular nuclei, lateral nucleus tractus solitarius, medial parabrachial nucleus and periaqueductal gray. The second included neurons in the superior vestibular nucleus, precerebellar nuclei, periaqueductal gray, and parabrachial nuclei, with weaker associations of raphe nuclei. Three additional components (networks) were also identified that were not correlated with the severity of motion sickness symptoms. These networks likely mediated the covert aspects of motion sickness, such as affective components. The identification of five statistically independent component networks associated with the development of motion sickness provides an opportunity to consider, in network activation dimensions, the complex progression of signs and symptoms that are precipitated in provocative environments. Similar methodology can be used to parse the neural networks that mediate other complex responses to environmental stimuli.

Pathophysiological and neurochemical mechanisms of postoperative nausea and vomiting

Clinical research shows that postoperative nausea and vomiting (PONV) is caused primarily by the use of inhalational anesthesia and opioid analgesics. PONV is also increased by several risk predictors, including a young age, female sex, lack of smoking, and a history of motion sickness. Genetic studies are beginning to shed light on the variability in patient experiences of PONV by assessing polymorphisms of gene targets known to play roles in emesis (serotonin type 3, 5-HT3; opioid; muscarinic; and dopamine type 2, D2, receptors) and the metabolism of antiemetic drugs (e.g., ondansetron). Significant numbers of clinical trials have produced valuable information on pharmacological targets important for controlling PONV (e.g., 5-HT3 and D2), leading to the current multi-modal approach to inhibit multiple sites in this complex neural system. Despite these significant advances, there is still a lack of fundamental knowledge of the mechanisms that drive the hindbrain central pattern generator (emesis) and forebrain pathways (nausea) that produce PONV, particularly the responses to inhalational anesthesia. This gap in knowledge has limited the development of novel effective therapies of PONV. The current review presents the state of knowledge on the biological mechanisms responsible for PONV, summarizing both preclinical and clinical evidence. Finally, potential ways to advance the research of PONV and more recent developments on the study of postdischarge nausea and vomiting (PDNV) are discussed.

Post-anesthesia vomiting: impact of isoflurane and morphine on ferrets and musk shrews

Although partially controlled with antiemetic drugs, postoperative nausea and vomiting (PONV) continues to be a problem for many patients. Clinical research suggests that opioid analgesics and volatile anesthetics are the main triggers of PONV. The aim of this study was to develop an animal model for post-anesthesia vomiting for future studies to further determine mechanisms and preclinical drug efficacy. Ferrets (N=34) were initially used because they have served as a gold standard for emesis research. Ferrets were tested with several doses of morphine, inhaled isoflurane, and a positive control injection of cisplatin (a chemotherapy agent) to induce emesis. Musk shrews (a small animal model; N=36) were also tested for emesis with isoflurane exposure. A control injection of cisplatin produced emesis in ferrets (ip, 129.8±22.0 retches; 13.7±2.3 vomits; mean±SEM). Morphine also produced a dose-response on emesis in ferrets, with maximal responses at 0.9 mg/kg (sc, 29.6±12.6 retches; 1.8±0.9, vomits). Isoflurane exposure (2-4% for 10 min to 6h exposure) failed to induce vomiting, was not associated with an increased frequency in emesis when combined with a low dose of morphine (0.1 mg/kg, sc), and failed to produce consistent effects on food and water intake. In contrast to ferrets, musk shrews were very sensitive to isoflurane-induced emesis (0.5 to 3%, 10 min exposure; up to 11.8±2.4 emetic episodes). Overall, these results indicate that ferrets will not be useful for delineating mechanisms responsible for isoflurane-induced emesis; however, musk shrews may prove to be a model for vomiting after inhalation of volatile agents.

Utilization of the least shrew as a rapid and selective screening model for the antiemetic potential and brain penetration of substance P and NK1 receptor antagonists

Substance P (SP) is thought to play a cardinal role in emesis via the activation of central tachykinin NK1 receptors during the delayed phase of vomiting produced by chemotherapeutics. Although the existing supportive evidence is significant, due to lack of an appropriate animal model, the evidence is indirect. As yet, no study has confirmed that emesis produced by SP or a selective NK1 receptor agonist is sensitive to brain penetrating antagonists of either NK1, NK2, or NK3 receptors. The goals of this investigation were to demonstrate: 1) whether intraperitoneal (i.p.) administration of either SP, a brain penetrating (GR73632) or non-penetrating (e.g. SarMet-SP) NK1 receptor agonist, an NK2 receptor agonist (GR64349), or an NK3 receptor agonist (Pro7-NKB), would induce vomiting and/or scratching in the least shrew (Cryptotis parva) in a dose-dependent manner; and whether these effects are sensitive to the above selective receptor antagonists; 2) whether an exogenous emetic dose of SP (50 mg/kg, i.p.) can penetrate into the shrew brain stem and frontal cortex; 3) whether GR73632 (2.5 mg/kg, i.p.)-induced activation of NK1 receptors increases Fos-measured neuronal activity in the neurons of both brain stem emetic nuclei and the enteric nervous system of the gut; and 4) whether selective ablation of peripheral NK1 receptors can affect emesis produced by GR73632. The results clearly demonstrated that while SP produced vomiting only, GR73632 caused both emesis and scratching behavior dose-dependently in shrews, and these effects were sensitive to NK1-, but not NK2- or NK3-receptor antagonists. Neither the selective, non-penetrating NK1 receptor agonists, nor the selective NK2- or NK3-receptor agonists, caused a significant dose-dependent behavioral effect. An emetic dose of SP selectively and rapidly penetrated the brain stem but not the frontal cortex. Systemic GR73632 increased Fos expression in the enteric nerve plexi, the medial subnucleus of nucleus tractus solitarius, and the dorsal motor nucleus of the vagus, but not the area postrema. Ablation of peripheral NK1 receptors attenuated the ability of GR73632 to induce a maximal frequency of emesis and shifted its percent animals vomiting dose-response curve to the right. The NK1-ablated shrews exhibited scratching behavior after systemic GR73632-injection. These results, for the first time, affirm a cardinal role for central NK1 receptors in SP-induced vomiting, and a facilitatory role for gastrointestinal NK1 receptors. In addition, these data support the validation of the least shrew as a specific and rapid behavioral animal model to screen concomitantly both the CNS penetration and the antiemetic potential of tachykinin NK1 receptor antagonists.

Klinische Pharmakologie

The rule of three describes three steps which are needed for an optimal control of postoperative nausea and vomiting (PONV). Firstly, patients at high risk of PONV need to be identified. Knowledge about predictive factors may help to identify patients who may best profit from prophylaxis and those where prophylaxis is not worthwhile since the baseline risk is too low. Secondly, for high-risk patients a low emetogenic anaesthesia technique should be chosen, and thirdly, these patients should additionally receive a prophylactic antiemetic cocktail. At present, butyrophenones (e.g. droperidol), 5-HT(3) receptor antagonists ("setrons") and steroids (e.g. dexamethasone) are the most rational choices for the antiemetic cocktail. Although there is strong evidence that there is an additive effect when these antiemetics are combined, economic constraints may influence the number of antiemetics that are eventually chosen. Identification of high-risk patients remains the most difficult part of the rule of three. Risk scores have been proposed and have been widely implemented in clinical practice. The sensitivity and specificity of such scores, however, remain particularly unsatisfactory. Unless more reliable risk scores are developed, aggressive treatment of established PONV symptoms may be more useful and more cost-effective than prophylaxis for many patients.

[Prevention and treatment of postoperative nausea and vomiting in children. An evidence-based approach]

Significant improvement towards an efficacious control of postoperative nausea and vomiting (PONV) has taken place recently. These improvements may be summarised using the "rule of three". That rule describes a pragmatic and rational approach of PONV control. First, identify the patient at risk using predictive factors. Second, modify the anaesthesia technique to keep the baseline risk as low as possible. Third, administer antiemetics rationally, considering their degree of efficacy, their risk, and their potential additive effects. Despite considerable research efforts, identifying the patient at high risk of PONV remains a difficult task. However, today, we understand the degree of efficacy, dose-responsiveness, and adverse effects of most antiemetics. None of those molecules should be regarded as being universally efficacious, there is no gold standard, and, when used alone, their degree of efficacy is limited. Thus, they should be combined for improved efficacy. Among the most promising molecules are butyrophenones (droperidol, haloperidol), 5-HT(3) receptor antagonists (ondansetron, dolasetron, tropisetron, granisetron), and steroids (for instance, dexamethasone). The lack of relevant paediatric PONV data remains a major drawback and is highly unsatisfactory. Hopefully, future research will further improve the control of PONV not only in adults but also in children.

Synthesis and biological evaluation of a novel structural type of serotonin 5-HT3 receptor antagonists

A series of novel 3-substituted quinoxalin-2-carboxamides were designed as per the pharmacophoric requirement for 5-HT(3) receptor antagonists and prepared by microwave irradiation and also by conventional method. The compounds were characterized by spectral data (IR, (1)H NMR, and MS) and the purity was ascertained by microanalysis. The synthesized compounds were evaluated for 5-HT(3) antagonisms in longitudinal muscle-myenteric plexus preparation from guinea pig ileum against 5-HT(3) agonist, 2-methyl-5-HT. Among the test compounds, N-{3-[(4-methylpiperazin-1-yl)methyl]-4-hydroxyphenyl}-3-methoxyquinoxalin-2-carboxamide 4e showed most favorable 5-HT(3) receptor antagonism.

Cyclic urea derivatives as potent NK1 selective antagonists

A series of novel five- and six-membered ring urea derivatives have been described as potent and selective NK1 receptor antagonists. Several compounds in this series exhibited good oral activity and brain penetration. Syntheses of these compounds are also described herein.

Genital grooming and emesis induced by vanilloids in Suncus murinus, the house musk shrew

The potential of resiniferatoxin and capsaicin to modulate emesis and genital grooming was investigated in Suncus murinus. Resinifertoxin (3-30 nmol, i.c.v.), E-capsaicin (10-100 nmol, i.c.v.) and Z-capsaicin (100 nmol, i.c.v.) induced emesis (P<0.05) and subsequently antagonised the emetic response induced by intragastric copper sulphate (480.6 micromol/kg; P<0.05). However, resiniferatoxin failed to affect nicotine-induced (30.7 mol/kg, s.c.) emesis (P>0.05). Only resiniferatoxin induced genital grooming that was antagonised (P<0.05) by capsazepine (300-600 nmol, i.c.v.) and ruthenium red (3 nmol, i.c.v.). E-capsaicin-induced emesis was antagonised by capsazepine (300-600 nmol, i.c.v.; P<0.05) and ruthenium red (3 nmol, i.c.v.; P<0.05) but resiniferatoxin-induced emesis was resistant to capsazepine (30-600 nmol, i.c.v.; P>0.05). The emetic action of resiniferatoxin but not E-capsaicin was subject to tachyphylaxis. In cross-tachyphylaxis experiments, E-capsaicin reduced the genital grooming induced by resiniferatoxin (P<0.05). The data are discussed in relation to the classification of vanilloid receptors and mechanisms involved in emesis and genital grooming.

Tetrahydrocannabinol (THC) interferes with conditioned retching in Suncus murinus: an animal model of anticipatory nausea and vomiting (ANV)

Little is understood about effective countermeasures to the expression of anticipatory nausea and vomiting (ANV) in chemotherapy patients. We present a model of ANV based on the emetic reactions of the Suncus murinus (musk shrew). Following two pairings of a novel distinctive contextual cue with the emetic effects of an injection of lithium chloride, the context acquired the potential to elicit retching in the absence of the toxin. The expression of this conditioned retching reaction was completely suppressed by pretreatment with THC at a dose that did not suppress general activity. This provides the first experimental evidence in support of anecdotal reports that THC suppresses ANV.

Potential of substance P antagonists as antiemetics

The introduction of serotonin 5-HT3 receptor antagonists into clinical practice allowed for a dramatic improvement in the management of nausea and vomiting. Despite this, postoperative and chemotherapy-induced emesis remains a significant, unresolved issue in many patients even when a combination of antiemetic drugs is used. Numerous neurotransmitters have been implicated in triggering emesis; however, the tachykinin substance P, by virtue of its localisation within both the gastrointestinal vagal afferent nerve fibres and brainstem emetic circuitry, and its ability to induce vomiting when administered intravenously, is thought to play a key role in emetic responses. Because substance P is the most likely endogenous ligand for the neurokinin-1 (NK1) receptor, the development of nonpeptide NK1 receptor antagonists led scientists to evaluate these compounds as antiemetics. The five NK1 receptor inhibitors that have been studied initially in humans are: vofopitant (GR-205171), CP-122721, ezlopitant (CJ-11974), MK-869 (L-754030) and its prodrug L-758298. Except for monotherapy in acute cisplatin-induced emesis, this new class of drugs has proven to be highly effective in the control of both chemotherapy-induced nausea and vomiting, and postoperative nausea and vomiting. No major adverse event was reported in the preliminary trials. Further investigation is mandatory in order to assess the optimal treatment regimen and to make sure the wide spectrum activity of the NK1 receptor inhibitors does not cause significant adverse effects in the context of the treatment of nausea and vomiting.

Ondansetron given before induction of anesthesia reduces shivering after general anesthesia

The neurotransmitter pathways involved in the mechanism of postanesthetic shivering (PAS) are poorly understood. Meperidine, clonidine, and physostigmine are all effective treatments, indicating that opioid, alpha(2)-adrenergic, and anticholinergic systems are probably involved. We investigated the effect of ondansetron, a 5-HT(3) antagonist used to treat postoperative nausea and vomiting, on intraoperative core and peripheral temperatures and PAS. Eighty-two patients (age, 18-60 yr) undergoing orthopedic, general, or urological surgery were randomized into three groups in this double-blinded, placebo-controlled, study: Group O4 (n = 27) received ondansetron 4 mg IV, Group O8 (n = 27) received ondansetron 8 mg IV, and Group C (n = 28) received saline IV immediately before the anesthetic induction. Core (tympanic) and fingertip temperature (dorsum of middle finger) were recorded. Anesthesia was induced with IV fentanyl 1 microg/kg and propofol 2.0-2.5 mg/kg and maintained with 1 minimum alveolar anesthetic concentration isoflurane in 70% nitrous oxide/oxygen. The occurrence of shivering was documented clinically during recovery by nursing staff, who were unaware of the group assignment. PAS occurred in 16 of 28 (57%) patients in Group C, compared with 9 of 27 (33%) in Group O4 (P = 0.13) and 4 of 27 (15%) patients in Group O8 (P = 0.003). Within each group, core temperature decreased and peripheral temperature increased significantly, but there were no significant differences among the groups at any time interval. We conclude that ondansetron 8 mg IV given during the induction of anesthesia prevents PAS without affecting the core-to-peripheral redistribution of heat during general anesthesia. This suggests that serotonergic pathways have a role in the regulation of PAS.

IMPLICATIONS

In a randomized, double-blinded, placebo-controlled, clinical study, ondansetron 8 mg IV, given just before the induction, reduced the incidence of postanesthetic shivering compared with saline. The anticipated core-to-peripheral redistribution of body temperature during general anesthesia was not affected. This implies that ondansetron probably acts by a central inhibitory mechanism, and that 5-hydroxytryptaminergic pathways have a role in regulating postanesthetic shivering.