Contractile effects of 5-hydroxytryptamine (5-HT) in the equine jejunum circular muscle: functional and immunohistochemical identification of a 5-HT1A-like receptor

REASONS FOR PERFORMING STUDY: Prokinetic drugs used to treat gastrointestinal ileus in man have equivocal results in horses. In man, prokinetic drugs have 5-hydroxytryptamine4(5-HT4) receptors as their target, but little is known about the 5-HT-receptor subtypes in the equine small intestine. OBJECTIVE: Functional and immunohistochemical identification of the serotonin receptor subtype(s) responsible for the 5-HT induced contractile response in the equine circular jejunum. METHODS: Isometric organ-bath recordings were carried out to assess spontaneous and drug-evoked contractile activity of equine circular jejunum. Histological investigations by immunofluorescence analyses were performed to check for presence and localisation of this functionally identified 5-HT receptor subtype. RESULTS: Tonic contractions were induced by 5-HT in horse jejunal circular muscle. Tetrodotoxin, atropine and NG-nitro L-arginine did not modify this response. A set of 5-HT receptor subtype selective antagonists excluded interaction with 5-HT1B, 1D, 2A, 3, 4 and 7 receptors. The selective 5-HT1A receptor antagonists WAY 100635 and NAN 190 caused a clear rightward shift of the concentration-response curve to 5-HT. The contractile effect of 5-CT, that can interact with 5-HT1A, 1B, 1D, 5 and 7 receptors was also antagonised by WAY 100635, identifying the targeted 5-HT receptor as a 5-HT1A-like receptor. Immunohistology performed with rabbit polyclonal anti-5-HT1A receptor antibodies confirmed the presence of muscular 5-HT1A receptors in the muscularis mucosae, and both longitudinal and circular smooth muscle layers of the equine jejunum. CONCLUSIONS: Contractile responses in equine jejunal circular smooth muscle induced by 5-HT involves 5-HT1A-like receptors.     

Extrapyramidal side effects following subcutaneous metoclopramide injection for the treatment of post operative ileus

Metoclopramide is used for the management of post operative ileus in horses for its gastrointestinal prokinetic effects. Adverse extrapyramidal signs have been reported following its use in horses as well as in man. This report describes the clinical signs exhibited during an adverse reaction suspected to be associated with subcutaneous administration of 0.25 mg/kg bwt metoclopramide at 6 h intervals.     

Equine gastrointestinal motility research: where we are and where we need to go

Equine gastrointestinal motility is a central issue in cases of equine colic, post operative convalescence and alimentary conditions encountered in practice. There are significant syndromes of intestinal dysmotility in the horse such as obstructive disorders and post operative ileus that are still poorly understood. This review describes the various areas of research that aim to elucidate the pathogenesis of intestinal hypo- or hypermotility by research methods, which include studies at the cellular level, and those that employ in vitro or in vivo techniques of evaluating the physiology and mechanical means of ingesta transit through the alimentary tract. The review discusses future directions for studies which will hopefully lead to better understanding and appropriate measures for diagnosis, therapy and prevention of ileus and other motility disorders.     

The equine gastrosplenic ligament: Anatomy and clinical considerations

A gelding was referred for colic and inguinal wound evaluation. Abdominal ultrasound showed distended, oedematous and immotile small intestine abaxial to the spleen. An exploratory laparotomy revealed jejunal incarceration through a rent in the gastrosplenic ligament (GSL). The rent in the GSL was opened and surgical correction (resection and anastomosis of nonviable jejunum) performed. The GSL was left open. The horse recovered uneventfully and one year after surgery no further episodes of colic have been observed.     

Prevention of post operative complications following surgical treatment of equine colic: Current evidence

Changes in management of the surgical colic patient over the last 30 years have resulted in considerable improvement in post operative survival rates. However, post operative complications remain common and these impact negatively on horse welfare, probability of survival, return to previous use and the costs of treatment. Multiple studies have investigated risk factors for post operative complications following surgical management of colic and interventions that might be effective in reducing the likelihood of these occurring. The findings from these studies are frequently contradictory and the evidence for many interventions is lacking or inconclusive. This review discusses the current available evidence and identifies areas where further studies are necessary and factors that should be taken into consideration in study design.     

Equine post operative ileus: A review of current thinking on pathophysiology and management

Equine post operative ileus (POI) is a serious post surgical complication in the horse, with a significant fatality rate. Despite the ongoing debate with regard to both the clinical definition of equine POI and the optimal management of this condition, there is increasing awareness and acceptance, supported by scientific research, that inflammation plays a key role in its pathophysiology. This review aims to outline the current thinking on the pathophysiology and management of this condition, with reference to the published literature on equine, rodent and human POI. Although studies conducted in other species are likely to provide an abundant source of information with potentially useful translational applications for the equine condition, such an approach needs to be cognisant of potential interspecies differences both in the pathogenesis of the condition and in basic gastrointestinal physiology.     

Role of prokinetic drugs for treatment of postoperative ileus in the horse

All horses undergoing coeliotomy for an acute abdominal crisis are at risk of developing ileus and should receive therapy aimed at promoting gastrointestinal function by restoring fluid and electrolyte balance. Adequate analgesia and prevention against peritonitis, bacteraemia and endotoxaemia should be provided. Horses that at the time of surgery have a strangulating or non-strangulating small intestinal obstruction should be considered to be at greater risk of developing a persistent ileus that is refractory to treatment than those horses with lesions involving the large intestine. In horses considered to be at greater risk of developing a persistent ileus, the use of prokinetic agents should be considered. Agents that may be used to improve gastrointestinal motility include adrenergic receptor antagonists, cholinergic agonists, benzamides, dopamine antagonists, macrolide antimicrobials, opiate receptor agonists and antagonists, somatostatin analogues and local anaesthetics. There are limited studies into the use of these agents in the horse. Until further research provides more information on motility disorders following intestinal surgery and the efficacy of prokinetic agents in this species, only selective use of some of these drugs can be recommended.     

Serum concentrations of lidocaine and its metabolites after prolonged infusion in healthy horses

REASONS FOR PERFORMING STUDY: Continuous-rate infusions (CRI) of lidocaine are often used for prolonged duration but, to date, only limited time/concentration relationships administered as a short term (24 h) CRI have been reported. OBJECTIVE: To determine the time/concentration profile of lidocaine and its active metabolites glycinexylidide (GX) and monoethylglycinexylidide (MEGX) during a 96 h lidocaine infusion. METHODS: Lidocaine was administered to 8 mature healthy horses as a continuous rate infusion (0.05 mg/kg bwt/min) for 96 h. Blood concentrations of lidocaine, GX and MEGX were determined using high performance liquid chromatography during and after discontinuation of the infusion. RESULTS: Serum lidocaine concentrations reached steady state by 3 h and did not accumulate thereafter. Concentrations were above the target therapeutic concentration (980 ng/ml) only at 6 and 48 h, and did not reach the range described as potentially causing toxicity (>1850 ng/ml) at any time. MEGX did not accumulate over time, while the GX accumulated significantly up to 48 h and then remained constant. The serum concentrations of lidocaine, MEGX and GX were below the limit of detection within 24 h of discontinuation of the infusion. None of the horses developed any signs of lidocaine toxicity during the study. CONCLUSIONS: The metabolism of lidocaine was not significantly impaired by prolonged infusion and no adverse effects were observed. Prolonged infusions appear to be safe in normal horses but the accumulation of GX, a potentially toxic active metabolite, is cause for concern.     

Effects of mosapride on motility of the small intestine and caecum in normal horses after jejunocaecostomy

The purpose of the present study was to evaluate the prokinetic effects of mosapride with non-invasive assessment of myoelectrical activity in the small intestine and caecum of healthy horses after jejunocaecostomy. Six horses underwent celiotomy and jejunocaecostomy, and were treated with mosapride (treated group) at 1.5 mg/kg per osos once daily for 5 days after surgery. The other six horses did not receive treatment and were used as controls (non-treated group). The electrointestinography (EIG) maximum amplitude was used to measure intestinal motility. Motility significantly decreased following surgery. In the treated group, the EIG maximum amplitude of the small intestine was significantly higher than in the controls from day 6~31 after treatment. These findings clearly indicate that mosapride could overcome the decline of intestinal motility after jejunocaecostomy in normal horses.     

Gastric and small intestinal ileus as a cause of acute colic in the post parturient mare

REASONS FOR PERFORMING STUDY: Ileus (functional obstruction of aboral gastrointestinal transit) is an uncommon cause of gastrointestinal dysfunction and colic in the horse. A number of specific conditions have been previously reported in association with ileus. This report describes the recognition of primary gastric and small intestinal ileus of undetermined cause in a series of post parturient mares. OBJECTIVES: To describe the clinical features, treatment and outcome of a series of episodes of primary gastric and small intestinal ileus. METHODS: A retrospective study was performed of colic episodes seen in an equine practice in Newmarket, UK over a 6 year period (2002-2007). RESULTS: Seventeen episodes of gastric and small intestinal ileus were identified, which occurred in 15 horses. All episodes occurred in post parturient mares. No previously reported cause of ileus was identified in any of the episodes. Fifteen of the 17 episodes received medical treatment (medical support and nasogastric decompression) and, in addition, surgical decompression was performed in 9 episodes. Two mares were subjected to euthanasia before treatment due to the presence of gastric rupture and the remaining 13 mares survived with a follow-up period of at least 10 months. Two mares suffered a further episode of gastric and small intestinal ileus, one 4 days and the other 2 years after the initial episode. CONCLUSIONS: Gastric and small intestinal ileus of, as yet, unknown aetiology appears to be a potential cause of acute colic in the post parturient mare. The outcome following treatment by decompression is good.     

Treatment of equine gastric impaction by gastrotomy

A 6‐year‐old Warmblood gelding was referred for treatment of a traumatic shoulder wound and while hospitalised developed a large gastric impaction which was unresponsive to medical management. Gastrotomy as a treatment for gastric impactions is rarely attempted in adult horses due to the limited surgical access to the stomach. This report describes the successful surgical treatment of the impaction by gastrotomy and management of the post operative complications encountered.     

Case report of atypical infiltrative lipomatosis of the equine mesojejunum

A 25‐year‐old mare was examined for persistent colic. Over the previous month, the mare had experienced several episodes of mild recurrent colic. The episode of colic persisted for 18 h and the pain became unresponsive to analgesic therapy. Euthanasia was undertaken. Post mortem examination revealed an atypical infiltrative lipoma of the mesojejunum, confirmed histopathologically. To the authors' knowledge, this is the first case report of a diffuse infiltrative lipoma of the equine mesojejunum.     

Outbreak of Lawsonia intracellularis on a Standardbred breeding farm in North Carolina

Lawsonia intracellularis is a cause of protein‐losing enteropathy in weanling foals commonly causing signs including diarrhoea, oedema and unthrifty appearance. It has previously been reported as sporadic cases throughout the USA, Canada and Europe. Only recently have outbreaks on a single farm location been reported. The cases reported here are an example of multiple foals on a single farm testing serologically positive for L. intracellularis. These foals ranged in severity from asymptomatic to severely hypoproteinaemic and septic; however, none of the foals ever displayed diarrhoea, which is the most common presenting sign of this disease process.     

Small intestinal volvulus in 115 horses: 1988-2000

OBJECTIVE: To evaluate the historical data, signalment, clinical signs, results of laboratory analyses, treatment, and outcome of horses with small intestinal (SI) volvulus. STUDY DESIGN: Retrospective study. SAMPLE POPULATION: One hundred and fifteen client-owned horses, aged 1 month to 21 years. METHODS: Clinical signs, laboratory data, surgical or necropsy findings, and outcome for horses with SI volvulus were obtained from medical records, identified by computer search and manual review. RESULTS: There was no statistical difference in signalment between cases and the hospital population. Seventy-four percent of horses were >/=3 years. There were considerable variations in clinical signs on admission; high heart rate and signs of severe pain were not consistent features. Examination per rectum identified distended small intestine in only 69% of horses. One hundred horses had surgery, and small intestine resection was performed in 25. Eighty-four horses were recovered from surgery, and 67 horses survived to hospital discharge (80% of horses recovered from surgery, 58% of 115 horses). Forty-eight percent that were ultimately discharged had a post-operative complication and these horses had a longer average stay than horses with no complication (11 days versus 8.9 days). CONCLUSIONS: We identified 115 horses with primary SI volvulus over a 12-year period. We found that the population of horses with this lesion was older than has previously been reported and that the prognosis for post-operative survival to hospital discharge is good (80%). Post-operative complications were common, and affected approximately half the horses that were ultimately discharged from the hospital. CLINICAL RELEVANCE: This information may aid diagnosis and prognosis and guide decision making for horses with this condition.