Excitation of neurons in the canine area postrema by prostaglandins

Emesis in dogs: a review

Emesis is a common presenting sign in small animal practice. It requires a rational approach to management that is based upon a sound understanding of pathophysiology combined with logical decision making. This review, which assesses the weight of available evidence, outlines the physiology of the vomiting reflex, causes of emesis, the consequences of emesis and the approach to clinical management of the vomiting dog. The applicability of diagnostic testing modalities and the merit of traditional approaches to management, such as dietary changes, are discussed. The role and usefulness of both traditional and novel anti-emetic drugs is examined, including in specific circumstances such as following cytotoxic drug treatment. The review also examines areas in which common clinical practice is not necessarily supported by objective evidence and, as such, highlights questions worthy of further clinical research.

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.

The COX inhibitors indomethacin and meloxicam exhibit anti-emetic activity against cisplatin-induced emesis in piglets

We analysed the effects of four cyclooxygenases (COX) inhibitors on cisplatin-induced emesis in piglets. Ninety-five animals receiving cisplatin (5.5 mg kg(-1), i.v.) were observed for 60 h. One hour prior to cisplatin, controls (n=29) were dosed with a saline solution while experimental animals received an i.v. or i.p. injection of one of the COX inhibitors. Additional injections of COX inhibitor were given at 15 and 39 h after cisplatin administration (or every 6h in one group receiving diclofenac). The latencies to the first emetic episode (EE) compared to controls (2.1+/-0.4 h) increased in groups receiving naproxen (4.66+/-0.94 h, n=9, 30 mg kg(-1)) and indomethacin (6.19+/-1.13 h, n=7, 10 mg kg(-1)) i.v. Indomethacin significantly decreased the incidence of both the acute (by 40%) and delayed (by 66%) phases of emesis. The total number of EE during the 60 h compared to controls (28.3+/-1.9 EE) was significantly reduced in piglets receiving indomethacin (14.9+/-3.2 EE, n=7) and meloxicam (17.6+/-3.6 EE, n=11, 0.3 mg kg(-1)). Four piglets receiving meloxicam (0.3 mg kg(-1), i.v.) did not vomit during the delayed phase. The anti-emetic activity of two COX inhibitors suggests that prostaglandins contribute to the activation of the emetic reflex in response to cisplatin.

Characterization of lipopolysaccharide-induced emesis in conscious piglets: effects of cervical vagotomy, cyclooxygenase inhibitors and a 5-HT(3) receptor antagonist

The emetic response to intraperitoneal (i.p., 0.5, 2, 8 mg kg(-1)) and intravenous (i.v., 200 microg kg(-1)) administration of bacterial lipopolysaccharides (LPS) was characterized in conscious piglets observed for 4 h. The latencies and the incidence of the emetic response to LPS (i.p.) decreased and increased, respectively, in a dose-dependent manner. In 14 additional piglets, a bilateral vagotomy performed 4 h prior to LPS administration abolished the vomiting induced by i.p. LPS (2 mg kg(-1)), and decreased its incidence by 77% in the i.v. injected animals. Sham-operated animals (n=6) exhibited a similar emetic pattern to the controls injected intraperitoneally with LPS (2 mg kg(-1)). In 7 piglets, the administration of granisetron, a 5-HT(3) receptor antagonist (i.v., 2 mg kg(-1)), 30 min prior to the i.p. LPS injection (2 mg kg(-1)) failed to reduce significantly the emetic activity; whereas, in 6 animals, a combination of meloxicam (0.3 mg kg(-1)) and indomethacin (5 mg kg(-1)), two cyclooxygenase (COX) inhibitors, administered per os 1.5 h prior to the i.p. LPS (2 mg kg(-1)) abolished the emetic response to endotoxins. The present results show that the activation of the medullary "vomiting centre" in response to i.p. administration of LPS is mediated via vagal afferents and is likely to involve prostaglandins.