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

Evaluation of cardiac indices using M-mode echocardiography after administration of metoclopramide and ondansetron in donkeys (Equus asinus): an experimental study

The aim of the present study was to evaluate cardiac indices using M-mode echocardiography after the administration of metoclopramide and ondansetron in donkeys. For this purpose, 10 apparently healthy Egyptian Baladi donkeys (Equus asinus) were used in a crossover prospective study. Two trials were conducted with the administration of metoclopramide hydrochloride anhydrous at a dose of 0.25 mg Kg-1 and ondansetron hydrochloride sodium at a dose of 0.15 mg Kg-1. The control group (placebo) received a total volume of 50 mL of isotonic saline at 0.9%. An echocardiographic examination was performed using a Digital Color Doppler Ultrasound System equipped with a 2-3.9 MHz phased array sector scanner transducer. In general, the fractional shortening (FS%) was significantly affected by the time for metoclopramide (p = 0.031) and ondansetron (p = 0.047) compared with those of placebo, with treatment with metoclopramide provoking significantly higher percentages of FS% at T60 (p = 0.009) and T90 (p = 0.028) compared with those for ondansetron and placebo. The interaction of time x treatment also showed a statistically significant alteration of FS% (p < 0.05), while the values returned to the basal line at T240. Metoclopramide induced a significant decrease in E-point to septal separation (EPSS) at T90 (p = 0.005), and T240 (p = 0.007) compared with ondansetron and placebo. The time x treatment interaction also showed a significant (p < 0.05) variation in EPSS, with values returning to the basal line at T300. Mitral valve opening velocity (DE SLP) values were significantly affected by time (p = 0.004) in the metoclopramide group compared with those of ondansetron and placebo. Administration of metoclopramide and ondansetron provoked significant alterations of DE SLP at T60 (p = 0.039), T120 (p = 0.036), and T300 (p = 0.005) compared with placebo. In conclusion, caution should be exercised when administering both treatments, especially to animals with suspected cardiac problems.

Ultrasonographic evaluation of the effects of the administration of neostigmine and metoclopramide on duodenal, cecal, and colonic contractility in Arabian horses: A comparative study

Background and Aim

As means for enhancing gastrointestinal (GI) motility, prokinetics have previously been evaluated in different breeds of horses with varying success. No previous studies were conducted to evaluate the effect of prokinetics on the intestinal tract of Arabian horses breed. Using B-mode ultrasound in the quantification of intestinal contractility, this study aimed to compare the impact of neostigmine and metoclopramide on the intestinal motility of healthy Arabian horses.

Materials and Methods

Twenty-one clinically healthy Arabian horses were equally distributed into three groups. The control group was administered with 5 mL normal saline intramuscularly (IM). The second group was administered with neostigmine (0.044 mg/kg body weight [BW], IM), and the third group was administered with metoclopramide (0.25 mg/kg BW, IM). Duodenal, cecal, and colonic contractions were counted through ultrasonography for 3 min (pre-administration and 15, 30, 60, 120, and 180 min post-administration).

Results

In the neostigmine group, a significant (p<0.05) increase in duodenal, cecal, and colonic contractions was observed 15 min post-administration compared with that in the control group (15±1.0, 11.33±1.53, and 12.33±2.31 vs. 11.0±2.0, 6.33±0.58, and 5.33±0.58 contractions per 3 min, respectively), continuing to 60 min post-administration for the duodenum and cecum and 120 min for colon and then returning to the normal; however, the metoclopramide group showed a significant (p<0.05) increase only in cecal and colonic contractions 60 min post-administration compared with the control group (11.0±1.0 and 12.33±0.58 vs. 6±1.0 and 5.67±0.58 contractions per 3 min, respectively), continuing until the end of the experiment. Excessive sweating, excitation, and straining were recorded following the administration of neostigmine, whereas no side effects were observed in the metoclopramide group.

Conclusion

Neostigmine improves duodenal, cecal, and colonic contractions in healthy adult Arabian horses, whereas metoclopramide only improves cecal and colonic contractions. Metoclopramide appears to be safer and longer acting than neostigmine in the Arabian horse breed. Ultrasonography is a valuable noninvasive tool for the quantification of intestinal contractility. Future studies should consider the use of various dosages of metoclopramide and administration routes and investigate its impact on horses with GI transit disorders and inclusion in colic post-operative care.

Clinical features and management of equine post operative ileus: Survey of diplomates of the European Colleges of Equine Internal Medicine (ECEIM) and Veterinary Surgeons (ECVS)

REASONS FOR PERFORMING STUDY

There is a need for an improved understanding of equine post operative ileus (POI), in terms of both clinical definition and optimal management. Although the pharmacological strategies that are used to treat POI continue to evolve, little is known about the supplementary strategies used to prevent and manage this condition.

OBJECTIVES

To report the current strategies used to diagnose, prevent and manage POI following emergency abdominal surgeries.

STUDY DESIGN

Cross-sectional survey.

METHODS

An electronic survey invitation was sent by email to 306 European college diplomates (European Colleges of Equine Internal Medicine, ECEIM n = 120, and Veterinary Surgeons, ECVS n = 186).

RESULTS

The response rate was 33% (100 of 306). The median reported estimated incidence of POI was 10-20%. The presence of reflux on nasogastric intubation was the main criterion used to define POI. Lesions involving the small intestine were thought to be the leading risk factors for developing POI. Anti-inflammatory drugs, antimicrobial drugs and i.v. fluids were the primary preventative strategies when managing cases at high risk for POI. Flunixin meglumine and lidocaine were the drugs most commonly used to treat horses with POI. Supplementary preventative and treatment strategies for POI included control of endotoxaemia, fluid therapy, early ambulation and judicious timing of post operative feeding.

CONCLUSIONS

Appreciation of the potential risk factors associated with the development of POI appeared to have an impact on the choice of management strategies that are implemented. The majority of ECEIM and ECVS Diplomates in the survey used flunixin meglumine and lidocaine, often in combination, to treat horses with POI, which is likely to reflect the contributory role of inflammation in its pathophysiology. Various supplementary strategies were used to prevent and manage POI risk factors intraoperatively and post operatively.

Effects of acetylcholinesterase inhibition on quality of recovery from isoflurane-induced anesthesia in horses

OBJECTIVE

To compare effects of 2 acetylcholinesterase inhibitors on recovery quality of horses anesthetized with isoflurane.

ANIMALS

6 horses in phase 1, 7 horses in phase 2A, and 14 horses in phase 2B.

PROCEDURES

The study comprised 3 phases (2 randomized, blinded crossover phases in horses undergoing orthopedic procedures and 1 prospective dose-determining phase). In phase 1, horses were anesthetized with isoflurane and received neostigmine or saline (0.9% NaCl) solution prior to anesthetic recovery. Phase 2A was a physostigmine dose-determining phase. In phase 2B, horses were anesthetized with isoflurane and received neostigmine or physostigmine prior to recovery. Objective recovery events were recorded and subjective visual analogue scale scores of recovery quality were assigned from video recordings.

RESULTS

Recovery measures in phase 1 were not different between horses receiving neostigmine or saline solution. In phase 2A, 0.04 mg of physostigmine/kg was the highest cumulative dose that did not cause clinically relevant adverse behavioral or gastrointestinal effects. Horses receiving physostigmine had higher mean ± SD visual analogue scale recovery scores (70.8 ± 13.3 mm) than did horses receiving neostigmine (62.4 ± 12.8 mm) in phase 2B, with fewer attempts until sternal and standing recovery. Incidence of colic behavior did not differ among groups.

CONCLUSIONS AND CLINICAL RELEVANCE

Inhibition with physostigmine improved anesthetic recovery quality in horses anesthetized with isoflurane, compared with recovery quality for horses receiving neostigmine. Inhibition of central muscarinic receptors by inhalation anesthetics may underlie emergence delirium in horses recovering from anesthesia.

In vivo and in vitro effects of neostigmine on gastrointestinal tract motility of horses

OBJECTIVE

To determine the response to neostigmine of the contractile activity of the jejunum and pelvic flexure and the effects of a continuous rate infusion (CRI) of neostigmine in horses.

ANIMALS

7 adult horses and tissue from 12 adult horses.

PROCEDURES

A CRI of neostigmine (0.008 mg/kg/h) or placebo was administered to 6 horses in a crossover study design. Gastric emptying was evaluated by the acetaminophen test. The frequency of defecation and urination and the consistency and weight of feces were recorded throughout the experiment. The effect of neostigmine on smooth muscle contractile activity was evaluated in tissues from the jejunum and pelvic flexure. The effect of neostigmine and acetylcholine after incubation with muscarinic receptor antagonists (atropine and DAU 5884) and an acetylcholinesterase inhibitor (edrophonium) was also investigated in vitro.

RESULTS

No difference was observed between neostigmine and placebo for time to reach peak plasma acetaminophen concentration and absorption rate constant. A CRI of neostigmine increased fecal production and frequency of urination. Neostigmine induced a dose-dependent increase of contractile amplitude in jejunum and pelvic flexure muscle strips. Incubation of muscle strips with atropine and DAU 5884 inhibited the response to acetylcholine and neostigmine. Incubation of smooth muscle strips from the jejunum with edrophonium increased the response to acetylcholine and had no effect on the response to neostigmine in vitro.

CONCLUSIONS AND CLINICAL RELEVANCE

A CRI of neostigmine increased fecal production and urination frequency in horses. A CRI of neostigmine did not decrease gastric emptying. Neostigmine stimulated contractile activity of jejunum and pelvic flexure smooth muscle strips in vitro.

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 approximately 31 after treatment. These findings clearly indicate that mosapride could overcome the decline of intestinal motility after jejunocaecostomy in normal horses.

Effect of intraluminal distension or ischemic strangulation obstruction of the equine jejunum on jejunal motilin receptors and binding of erythromycin lactobionate

OBJECTIVE

To determine whether inflammation of the jejunum of horses decreases the number of motilin receptors and amounts of motilin receptor mRNA and alters erythromycin lactobionate binding affinity to the motilin receptor in jejunal tissues.

SAMPLE POPULATION

Jejunal segments in 6 adult horses.

PROCEDURE

Each horse was anesthetized, and a ventral median celiotomy was performed; 2 segments of jejunum underwent a sham operation, 2 segments underwent ischemic strangulation obstruction (ISO), and 2 segments underwent intraluminal distension (ILD). Treatments were maintained for 120 minutes. From each segment, full-thickness biopsy samples were collected and smooth-muscle homogenates were prepared. Affinity and distribution of motilin binding to these preparations were determined by use of iodine 125 (125I)-labeled synthetic porcine motilin. Via displacement experiments, competition between 125I-labeled motilin and erythromycin lactobionate for binding to motilin receptors in the different segments was investigated. A quantitative real-time PCR technique was used to assess motilin receptor mRNA content in the muscle preparations.

RESULTS

Compared with the ISO or ILD segments, the number of motilin receptors was significantly higher in the sham-operated segments; ILD segments contained the lowest number of motilin receptors. The expression of motilin receptor mRNA was significantly decreased in ILD segments but not in ISO segments. Erythromycin lactobionate displacement of 125I-labeled motilin from motilin receptors did not differ significantly among the jejunal segments.

CONCLUSIONS AND CLINICAL RELEVANCE

Results suggest that downregulation and decreased production of motilin receptors in inflamed jejunal tissue contribute to the altered prokinetic response to erythromycin in horses with gastrointestinal disease.

In vitro effects of bethanechol on equine gastrointestinal contractility and functional characterization of involved muscarinic receptor subtypes

The goal of this study was to investigate the effect of bethanechol (BeCh) on contractility patterns of smooth muscle preparations of equine duodenum descendens, jejunum, caecum and pelvic flexure in vitro. Concentration-response relationships were developed for BeCh using in vitro assays with and without preincubation of muscarinic (M) receptor antagonists for M2 and M3 receptors. BeCh induced a significant, concentration-dependent increase in contractile response in equine intestine in specimens with circular orientation. The maximal effect was largest for jejunal specimens with no difference in EC50 within the different locations investigated. The M2 antagonist, AF-DX 116, caused a rightward shift of the concentration-response curve and the M3 antagonist, 4-DAMP (1,1-dimethyl-4-diphenylacetoxypiperidinium iodide), almost completely inhibited the effect of BeCh over the entire concentration-response curve. These data provide evidence that, although the effect of BeCh is predominantly mediated by M3 receptors, M2 muscarinic receptors also play a role in BeCh-induced contraction in specimens of equine intestine. The involvement of other muscarinic receptor subtypes cannot be excluded. Further studies are necessary to understand the effect of BeCh in vivo including diseased animals.

Recent advances in equine abdominal surgery

Laparoscopy is a minimally invasive procedure that has applications as a diagnostic, therapeutic and prognostic technique. Specialized equipment is necessary to perform equine laparoscopy, and there is a large range of instruments, both disposable and non-disposable available. Laparoscopic procedures described include ovariectomy, cryptorchidectomy, adhesiolysis and herniorrhaphy. Laparoscopy can be performed in a standing or dorsally recumbent position, depending on surgeon preference, patient status and the procedure to be performed. Stapling equipment is frequently used in gastrointestinal surgery in horses. Advantages include decreased surgical time and a decrease in the risk of contamination. Stapling equipment is often used in creating anastomoses, both in the large and small intestines, as well as in vessel ligation. New surgical techniques intended to decrease adhesion formation include the use of carboxymethylcellulose and bioresorbable patches. Indwelling abdominal drains can be used for peritoneal lavage following surgery and also appear to decrease the risk of adhesion formation. Improvements in post-operative care, including the treatment of post-operative ileus and endotoxaemia can significantly improve the outcome of horses that have undergone surgery for abdominal disorders. Recommendations for the use of prokinetic agents in horses with ileus vary widely. Prokinetic agents include local anaesthetics, macrolide antimicrobials, cholinergic agonists and dopamine antagonists. Endotoxaemia is common in horses following surgery for gastrointestinal disorders. The antibiotic polymyxin B binds to the circulating endotoxin molecule, decreasing its half-life in the intra-vascular space and reducing associated inflammation. This drug appears to be an effective and affordable treatment option for horses with endotoxaemia. The use of specific cyclooxygenase inhibitors in veterinary medicine have been studied recently. Selective cyclooxygenase-2 inhibitors may provide comparable anti-inflammatory and analgesic properties to the non-selective non-steroidal anti-inflammatory drugs. These drugs appear to have similar clinical effectiveness and will hopefully minimize deleterious side effects. The optimal healing of ventral midline incisions in horses is related to many factors including appropriate suture patterns and bite size, in addition to appropriate post-operative exercise recommendations. Recent advances in surgical techniques and post-operative care should decrease the morbidity and mortality associated with abdominal surgery. This article provides an overview of some of these advances.

Evaluation of risk factors associated with development of postoperative ileus in horses

OBJECTIVE

To determine factors associated with development of postoperative ileus (POI) in horses undergoing surgery for colic.

DESIGN

Prospective case-control study.

ANIMALS

251 horses undergoing colic surgery, of which 47 developed POI.

PROCEDURE

Signalment, history, clinicopathologic data, pre- and postoperative treatments, lesions, complications, costs, and outcome were recorded for all horses during hospitalization.

RESULTS

Variables associated with increased odds of POI included small intestinal lesion, high PCV, and increased duration of anesthesia. There was modest evidence that pelvic flexure enterotomy and intraoperative administration of lidocaine may have reduced the odds of developing POI.

CONCLUSIONS AND CLINICAL RELEVANCE

Findings during the preoperative and intraoperative periods can be used to identify horses at increased risk of POI. Reducing surgical and anesthetic duration should decrease the incidence of POI.

Clinical application of prokinetics

Intestinal stasis or ileus is a significant cause of mortality and morbidity in horses and has been attributed to a variety of causes, including loss of intrinsic or extrinsic electrical activity, incoordination of contractile activity from regional stimuli, and dissociation between electrical and mechanical activity. Proposed mechanisms include systemic shock, electrolyte disturbances, persistent luminal distention, ischemia, inflammation, peritonitis, endotoxemia, and anesthesia. Because the cause of ileus is likely multifactorial, a variety of pharmaceutics have been used to target specific causes. Prokinetics are defined as agents that facilitate or enhance the net movement of feed material down the length of the intestinal tract and do not simply produce an uncoordinated increase in local contractile activity. The primary objective of pharmaceutic intervention is to augment the pathways that stimulate motility or attenuate the inhibitory neurons that predominantly suppress activity. The objective of this article is to summarize the actions of prokinetic agents available and suggest clinical applications.

Expression of the ether-a-go-go (ERG) potassium channel in smooth muscle of the equine gastrointestinal tract and influence on activity of jejunal smooth muscle

OBJECTIVE

To determine whether ether-a-go-go (ERG) potassium channels are expressed in equine gastrointestinal smooth muscle, whether ERG channel antagonists affect jejunal muscle contraction in vitro, and whether plasma cisapride concentrations in horses administered treatment for postoperative ileus (POI) are consistent with ERG channels as drug targets.

SAMPLE POPULATION

Samples of intestinal smooth muscle obtained from 8 horses free of gastrointestinal tract disease and plasma samples obtained from 3 horses administered cisapride for treatment of POI.

PROCEDURE

Membranes were prepared from the seromuscular layer of the duodenum, jejunum, ileum, cecum, large colon, and small colon. Immunoblotting was used to identify the ERG channel protein. Isolated jejunal muscle strips were used for isometric stress response to ERG channel blockers that included E-4031, MK-499, clofilium, and cisapride. Plasma concentrations of cisapride were determined in 3 horses administered cisapride for treatment of POI after small intestinal surgery.

RESULTS

Immunoblotting identified ERG protein in all analyzed segments of the intestinal tract in all horses. The selective ERG antagonist E-4031 caused a concentration-dependent increase in jejunal contraction. Clofilium, MK-499, and cisapride also increased jejunal contraction at concentrations consistent with ERG channel block; effects of E-4031 and cisapride were not additive. Peak plasma cisapride concentrations in treated horses were consistent with ERG block as a mechanism of drug action.

CONCLUSIONS AND CLINICAL RELEVANCE

The ERG potassium channels modulate motility of intestinal muscles in horses and may be a target for drugs. This finding may influence development of new prokinetic agents and impact treatment of horses with POI.

Binding of radiolabeled porcine motilin and erythromycin lactobionate to smooth muscle membranes in various segments of the equine gastrointestinal tract

OBJECTIVE

To identify and characterize motilin receptors in equine duodenum, jejunum, cecum, and large colon and to determine whether erythromycin lactobionate competes with porcine motilin for binding to these receptors.

SAMPLE POPULATION

Specimens of various segments of the intestinal tracts of 4 adult horses euthanatized for reasons unrelated to gastrointestinal tract disease.

PROCEDURE

Cellular membranes were prepared from smooth muscle tissues of the duodenum, jejunum, pelvic flexure, and cecum. Affinity and distribution of motilin binding on membrane preparations were determined by use of 125I-labeled synthetic porcine motilin. Displacement studies were used to investigate competition between 125I-labeled synthetic porcine motilin and erythromycin lactobionate for binding to motilin receptors in various segments of bowel.

RESULTS

Affinity of 125I-labeled synthetic porcine motilin for the equine motilin receptor was estimated to be 6.1nM. A significantly higher number of motilin receptors was found in the duodenum than in the pelvic flexure and cecum. The jejunum had a significantly higher number of motilin receptors than the cecum. Erythromycin lactobionate displacement of 125I-labeled porcine motilin from the equine motilin receptor did not differ significantly among various segments of bowel.

CONCLUSIONS AND CLINICAL RELEVANCE

Motilin receptors were found in the duodenum, jejunum, pelvic flexure, and cecum of horses. The highest number of motilin receptors was in the duodenum, and it decreased in more distal segments of bowel. Erythromycin lactobionate competed with motilin binding in the equine gastrointestinal tract. This suggests that 1 of the prokinetic actions of erythromycin in horses is likely to be secondary to binding on motilin receptors.

5-Hydroxytryptamine mediated contractions in isolated preparations of equine ileum and pelvic flexure: pharmacological characterization of a new 5-HT(4) agonist

The effects of 5-hydroxytryptamine (5-HT), HTF 919, a new 5-HT(4) agonist, and the antagonists SB 203-186 (5-HT(4)) and tropisetron (5-HT(3)) on intestinal motility were tested in vitro on isolated preparations of horse ileum and pelvic flexure. Concentration-response curves were created by cumulative application of the agonists with or without preincubation of the antagonists. The 5-HT preparation induced a concentration-dependent contraction in equine ileum and pelvic flexure. The results indicate that 5-HT receptors are present in all parts of equine intestine investigated in this study. Tropisetron was found to act as a noncompetitive antagonist in all locations of the equine intestine. SB 203-106 was confirmed as an antagonist to 5-HT in the equine ileum circular muscle, in pelvic flexure circular and longitudinal muscle. Nevertheless, a discernible increase of smooth muscle contractions caused by HTF 919 could only be observed in pelvic flexure. In accordance with an earlier study in the guinea pig, in the equine gut HTF 919 acted as a partial agonist for the 5-HT(4) receptor with an affinity constant in the nanomolar range. It is concluded that 5-HT receptors, and especially their subtypes, may represent a promising target for the treatment and prevention of gastrointestinal (GI) motility disorders in horses.

In vitro effects of erythromycin, lidocaine, and metoclopramide on smooth muscle from the pyloric antrum, proximal portion of the duodenum, and middle portion of the jejunum of horses

OBJECTIVE

To evaluate effects of erythromycin, lidocaine, and metoclopramide on smooth muscle of the pyloric antrum (PA), proximal portion of the duodenum (PD), and middle portion of the jejunum (MJ) of horses. Sample Population-Strips of smooth muscle from 7 horses.

PROCEDURE

Isolated muscle strips were suspended in a bath and attached to isometric force transducers. Once stable spontaneous contractions were observed, agents were added. Isometric stress responses were compared with the amplitude of spontaneous contractions.

RESULTS

A single dose of erythromycin to the PA increased contractile amplitude (CA) for the longitudinal smooth muscle (mean +/- SEM, 76+/-16 g/cm2) but decreased CA for circular smooth muscle (-79+/-23 g/cm2). The inhibitory effect was decreased by tetrodotoxin, N(G)-nitro-L-arginine methyl ester, and a vasoactive intestinal peptide antagonist. Erythromycin increased CA for the MJ, which was maximal at 10(-4)M (171+/-36 g/cm2). Lidocaine increased CA for the PD, which was maximal at 10(-4) M (60+/-5 g/cm2). Metoclopramide increased the CA, which was maximal at 10(-4) M for the PA (75+/-26 g/cm2), PD (279+/-33 g/cm2), and MJ (456+/-59 g/cm2).

CONCLUSIONS

Regional differences in responses to erythromycin, lidocaine, and metoclopramide were evident in the gastrointestinal tract of horses. Metoclopramide increased CA in all tissues used, whereas erythromycin inhibited CA in circular smooth muscle but stimulated CA in longitudinal smooth muscle from the PA. Inhibition is caused by stimulation of inhibitory nerves and is mediated, in part, by nitric oxide and vasoactive intestinal peptide.