Emetic action of the prostanoid TP receptor agonist, U46619, in Suncus murinus (house musk shrew)

Mechanisms of Nausea and Vomiting: Current Knowledge and Recent Advances in Intracellular Emetic Signaling Systems

Nausea and vomiting are common gastrointestinal complaints that can be triggered by diverse emetic stimuli through central and/or peripheral nervous systems. Both nausea and vomiting are considered as defense mechanisms when threatening toxins/drugs/bacteria/viruses/fungi enter the body either via the enteral (e.g., the gastrointestinal tract) or parenteral routes, including the blood, skin, and respiratory systems. While vomiting is the act of forceful removal of gastrointestinal contents, nausea is believed to be a subjective sensation that is more difficult to study in nonhuman species. In this review, the authors discuss the anatomical structures, neurotransmitters/mediators, and corresponding receptors, as well as intracellular emetic signaling pathways involved in the processes of nausea and vomiting in diverse animal models as well as humans. While blockade of emetic receptors in the prevention of vomiting is fairly well understood, the potential of new classes of antiemetics altering postreceptor signal transduction mechanisms is currently evolving, which is also reviewed. Finally, future directions within the field will be discussed in terms of important questions that remain to be resolved and advances in technology that may help provide potential answers.

Interference with acute nausea and anticipatory nausea in rats by fatty acid amide hydrolase (FAAH) inhibition through a PPARα and CB1 receptor mechanism, respectively: a double dissociation

RATIONALE

Fatty acid amide hydrolase (FAAH) inhibition elevates anandamide (AEA), which acts on cannabinoid (CB1 and CB2) receptors, as well as N-palmitoylethanolamide (PEA) and N-oleoylethanolamine (OEA), which act on peroxisome proliferator-activated receptor alpha (PPARα). Here, we determine the mechanism of action of FAAH inhibition on acute and anticipatory nausea (AN).

OBJECTIVE

We compared the effectiveness and mechanism of action of two FAAH inhibitors, URB597 and PF-3845, to reduce acute nausea and AN in rodent models of conditioned gaping.

MATERIALS AND METHODS

For assessment of acute nausea, rats were pretreated with vehicle (VEH), URB597 (0.3 and 10 mg/kg, experiment 1a) or PF-3845 (10 mg/kg, experiment 1b) 120 min prior to a saccharin-lithium chloride (LiCl) pairing. To assess the CB1 receptor or PPARα mediation of the effect of PF-3845 on acute nausea, rats were also pretreated with rimonabant or MK886, respectively. For assessment of AN, following four pairings of a novel context with LiCl, rats received a pretreatment of VEH, URB597 (0.3 mg/kg, experiment 2a), or PF-3845 (10, 20 mg/kg, experiment 2b) 120 min prior to placement in the AN context. To assess the CB1 receptor or PPARα mediation of the effect, rats were also pretreated with rimonabant or MK886, respectively.

RESULTS

PF-3845 (10 mg/kg, but not URB597 0.3 or 10 mg/kg) suppressed acute nausea via PPARα, but not CB1 receptors. URB597 (0.3 and 10 mg/kg) or PF-3845 (10 and 20 mg/kg) reduced AN via CB1 receptors, but not PPARα.

CONCLUSIONS

FAAH inhibition reduces acute nausea and AN through PPARα and CB1 receptor mediated effects, respectively.

Looking beyond 5-HT(3) receptors: a review of the wider role of serotonin in the pharmacology of nausea and vomiting

The concept that 5-hydroxytryptamine (5-HT; serotonin) is involved in the emetic reflex was revealed using drugs that interfere with its synthesis, storage, release and metabolism ahead of the discovery of selective tools to modulate specific subtypes of receptors. This review comprehensively examines the fundamental role of serotonin in emesis control and highlights data indicating association of 5-HT1-4 receptors in the emetic reflex, whilst leaving open the possibility that 5-HT5-7 receptors may also be involved. The fact that each receptor subtype may mediate both emetic and anti-emetic effects is discussed in detail for the first time. These discussions are made in light of known species differences in emesis control, which has sometimes affected the perception of the translational value of data in regard to the development of novel anti-emetic for use in man.

Mechanism of the prostanoid TP receptor agonist U46619 for inducing emesis in the ferret

U46619 is a potent thromboxane A(2) mimetic with emesis-inducing actions that are mediated via prostanoid TP receptors. We investigated its emetic mechanism of action in more detail using the ferret as model animal. The emesis induced by U46619 (30 microg/kg, intraperitoneal) was antagonized significantly by (+)-(2S,3S)-3-(2-methoxybenzylamino)-2-phenylpiperidine hydrochloride (CP-99,994; 1 and 10 mg/kg; P < 0.05) and metoclopramide (0.3 and 3 mg/kg), but not by domperidone (3 mg/kg), sulpiride (0.1 mg/kg), ondansetron (0.1 and 1 mg/kg) alone or combined with droperidol (3 mg/kg), GR125487 (1 mg/kg), promethazine (3 mg/kg), or scopolamine (3 mg/kg); GR 125487 (1 mg/kg) prevented the anti-emetic action of metoclopramide (3 mg/kg). U46619 0.3 microg administered into the fourth ventricle rapidly induced emesis. However, bilateral abdominal vagotomy was ineffective in reducing the emetic response (P > 0.05). Our data suggests that U46619 induces emesis via an extra-abdominal mechanism, probably within the brain. Metoclopramide probably has a mechanism of action to prevent U46619-induced emesis via 5-HT(4) receptor activation and NK(1) tachykinin receptor antagonists could be useful to prevent emesis induced by TP receptor activation in man.

Metabolism and excretion of CP-122,721, a non-peptide antagonist of the neurokinin NK1 receptor, in dogs: identification of the novel cleaved product 5-trifluoromethoxy salicylic acid in plasma

The metabolism and excretion of a potent and selective substance P receptor antagonist, CP-122,721, have been studied in beagle dogs following oral administration of a single 5 mg kg(-1) dose of [(14)C]CP-122,721. Total recovery of the administered dose was on average 89% for male dogs and 95% for female dogs. Approximately 94% of the radioactivity recovered in urine and feces was excreted in the first 72 h. Male bile duct-cannulated dogs excreted a mean of approximately 56% of the dose in bile, approximately 11% in feces, and approximately 25% in urine. The sum of radioactivity in bile and urine indicates >80% of the [(14)C]CP-122,721-derived radioactivity was absorbed by the gastrointestinal tract. CP-122,721 was extensively metabolized in dogs, and only a small amount of parent CP-122,721 was excreted as unchanged drug. There were no significant gender-related quantitative/qualitative differences in the excretion of metabolites in urine or feces. The major metabolic pathways of CP-122,721 were O-demethylation, aromatic hydroxylation, and indirect glucuronidation. The minor metabolic pathways included: Aliphatic oxidation at the piperidine moiety, O-dealkylation of the trifluoromethoxy group, and N-dealkylation with subsequent sulfation and/or oxidative deamination. In addition, the novel cleaved product 5-trifluoromethoxy salicylic acid (TFMSA) was identified in plasma. These results suggest that dog is the most relevant animal species in which the metabolism of CP-122,721 can be studied for extrapolating the results to humans.

Differential action of anti-emetic drugs on defecation and emesis induced by prostaglandin E2 in the ferret

In the present studies we investigated the mechanism of action of prostaglandin E2 (1 mg/kg, i.p.) to induce emesis and defecation and/or tenesmus in the ferret. The emesis was antagonized significantly (P<0.05) by ondansetron (0.3 and 1 mg/kg, i.p.) and (+)-(2S,3S)-3-(2-methoxybenzylamino)-2-phenlypiperidine hydrochloride (CP-99,994; 10 mg/kg, i.p.), but neither compound reduced defecations and/or tenesmus, with ondansetron (0.3 mg/kg) actually producing a slight increase (P<0.05). Droperidol (1 and 3 mg/kg), metoclopramide (0.3 and 3 mg/kg), domperidone (0.3 and 3 mg/kg), promethazine (0.3 and 3 mg/kg) and scopolamine (0.3 and 3 mg/kg) failed to reduce prostaglandin E2 induced emesis. However, droperidol (1 and 3 mg/kg) and scopolamine (0.3 and 3 mg/kg) reduced significantly the defecatory and/or tenesmus response (P<0.05). Bilateral abdominal vagotomy was ineffective to reduce emesis and defecations and/or tenesmus. The data suggests that 5-HT3 receptor and NK1 tachykinin receptor antagonists could be useful in the clinic to prevent emesis but not defecations induced by prostaglandin E2.