Evaluation of the effects of the opioid agonist morphine on gastrointestinal tract function in horses

OBJECTIVE

To evaluate the effects of morphine administration for 6 days on gastrointestinal tract function in healthy adult horses.

ANIMALS

5 horses.

PROCEDURES

Horses were randomly allocated into 2 groups in a crossover study. Horses in the treatment group received morphine sulfate at a dosage of 0.5 mg/kg, IV, every 12 hours for 6 days. Horses in the control group received saline (0.9% NaCl) solution at a dosage of 10 mL, IV, every 12 hours for 6 days. Variables assessed included defecation frequency, weight of feces produced, intestinal transit time (evaluated by use of barium-filled spheres and radiographic detection in feces), fecal moisture content, borborygmus score, and signs of CNS excitement and colic.

RESULTS

Administration of morphine resulted in gastrointestinal tract dysfunction for 6 hours after each injection. During those 6 hours, mean +/- SD defecation frequency decreased from 3.1 +/- 1 bowel movements in control horses to 0.9 +/- 0.5 bowel movements in treated horses, weight of feces decreased from 4.1 +/- 0.7 kg to 1.1 +/- 0.7 kg, fecal moisture content decreased from 76 +/- 2.7% to 73.5 +/- 2.9%, and borborygmus score decreased from 13.2 +/- 2.9 to 6.3 +/- 3.9. Mean gastrointestinal transit time was also increased, compared with transit times in control horses.

CONCLUSIONS AND CLINICAL RELEVANCE

Morphine administered at 0.5 mg/kg twice daily decreased propulsive motility and moisture content in the gastrointestinal tract lumen. These effects may predispose treated horses to development of ileus and constipation.

Rattlesnake envenomation in 12 New World camelids

BACKGROUND

Rattlesnake envenomation of New World camelids is a seasonal problem with often dramatic clinical signs.

HYPOTHESIS

The purpose of this study was to identify the clinical signs, laboratory results, treatment methods, and outcome for rattlesnake envenomation in New World camelids.

ANIMALS

Medical records from 1988 to 2004 were searched for New World camelids presented for rattlesnake bite or clinical signs suspected to be related to recent envenomation. Twelve records were identified.

METHODS

From these records a retrospective study was performed.

RESULTS

Nine camelids presented for acute disease (2/9 arrived dead), whereas 3 presented for subacute onset of disease. Swelling of the lips, head and neck, tachypnea, dyspnea, tachycardia, and lethargy were the most common presenting signs. Snake bites were most commonly located to the muzzle (10/12). Common complete blood count (CBC) and serum biochemical abnormalities were neutrophilia, lymphopenia, increased muscle enzyme activity, hypoalbuminemia, hyperglycemia, hypokalemia, and thrombocytopenia. Treatment included combinations of intravenous fluid therapy, antimicrobials, anti-inflammatory drugs, tetanus prophylaxis, tracheostomy, supplemental oxygen, antivenom, total parenteral nutrition, and nursing care. Five of the 10 animals with acute onset of clinical signs survived, and all animals with subacute presentation died. The mortality rate for New World camelids with severe local tissue reaction and systemic signs of envenomation was 58%.

CLINICAL IMPORTANCE

New World camelids that sustain rattlesnake envenomation and severe facial swelling precluding prehension and mastication have a guarded prognosis for survival. Aggressive treatment is recommended to optimize the chances of survival. Animals with less severe local tissue reaction and absence of systemic signs have a better prognosis.

Pharmacokinetics of the opioid antagonist N-methylnaltrexone and evaluation of its effects on gastrointestinal tract function in horses treated or not treated with morphine

OBJECTIVE

To determine the pharmacokinetics and effects of the morphine antagonist N-methylnaltrexone (MNTX) on gastrointestinal tract function in horses when administered alone and in combination with morphine.

ANIMALS

5 healthy adult horses.

PROCEDURES

Horses were treated with MNTX (1 mg/kg, IV), and serial blood samples were collected for determination of drug pharmacokinetics. For evaluation of effects on the gastrointestinal tract when administered alone, MNTX was administered at a dosage of 0.75 mg/kg, IV, twice daily for 4 days. For evaluation of effects when administered concurrently with morphine, MNTX (0.75 mg/kg, IV, q 12 hours) and morphine (0.5 mg/kg, IV, q 12 hours) were administered for 6 days. Gastrointestinal variables evaluated were defecation frequency, weight of feces produced, fecal moisture content, intestinal transit time, and borborygmus scores.

RESULTS

The time-concentration data for MNTX disposition best fit a 2-compartment model with a steady-state volume of distribution of 244.6 +/- 21.8 mL/kg, t1/2 of 47.04 +/- 11.65 minutes, and clearance of 11.43 +/- 1.06 mL/min/kg. Adverse effects were not observed at doses <or= 1 mg/kg. Administration of MNTX increased daily fecal weight. When administered concurrently with morphine, MNTX partially prevented the effects of morphine on the gastrointestinal tract by increasing defecation frequency, fecal weight, fecal moisture content, and borborygmus score, and by preventing increases in intestinal transit time.

CONCLUSIONS AND CLINICAL RELEVANCE

Because MNTX does not cross the blood-brain barrier, administration of the drug should not alter the analgesic effects of opioids and may attenuate the adverse gastrointestinal effects associated with use of opioids in horses.

Laparoscopic Ovariectomy Using the Endo-GIA Stapling Device and Endo-Catch Pouches and Evaluation of Analgesic Efficacy of Epidural Morphine Sulfate in 10 Mares

OBJECTIVE

To evaluate use of ENDO-GIA staples and ENDO-Catch pouches for ovariectomy in mares and to evaluate the efficacy of epidural morphine analgesia.

STUDY DESIGN

Randomized clinical trial.

ANIMALS

Mares (n = 10) with normal ovaries.

METHODS

An Endo-GIA II stapler (United States Surgical Corp., Norwalk, CT) was used to amputate the ovaries bilaterally, in standing mares, and Endo-Catch II pouches (United States Surgical Corp.) were used for retrieval. Epidural morphine was used in 5 mares, and procedure duration, volume of lidocaine required to desensitize the ovarian pedicle, and sedation were compared with horses not administered epidural morphine.

RESULTS

Use of the Endo-GIA II stapling device was an easy and an efficient method of ovariectomy, which was facilitated by use of epidural morphine. For the epidural group, the mean (+/-SD) surgical time was 69.2 +/- 10.2 minutes compared with 124.4 +/- 21.2 minutes for mares not administered morphine. Less systemic sedation was required for mares administered epidural morphine.

CONCLUSIONS

Minimal ovarian manipulation was required to apply the stapler, hemorrhage was slight, and none of the mares had complications. Epidural morphine provided effective analgesia, improving patient comfort, and reduced the sedation needed to perform ovariectomy.

CLINICAL RELEVANCE

Endo-GIA II staples are an efficient method for ovariectomy in normal mares. Epidural morphine should be considered to facilitate ovariectomy because less sedation and local anesthetic administration is required.

Survey of Prokinetic Use in Horses with Gastrointestinal Injury

OBJECTIVE

To report prokinetic strategies used to manage horses after gastrointestinal surgery.

DESIGN

Electronic questionnaire.

SAMPLE POPULATION

Diplomates of the American College of Veterinary Surgeons (ACVS) who perform equine intestinal surgery.

PROCEDURE

A survey (21 questions) designed to determine use of prokinetic agents was sent electronically to 112 ACVS Diplomates known to perform equine intestinal surgery. Several clinical scenarios were also described to determine which, if any, prokinetic agent respondents would select.

RESULTS

Responses were obtained from 58 (52%) surgeons from 44 clinics. Selection of prokinetic agent for specific gastrointestinal conditions was relatively uniform whereas there was considerable variation in dose administered. For postoperative ileus (POI) associated with most intestinal lesions, 2% lidocaine was most commonly selected. Other prokinetics in decreasing frequency of use were erythromycin lactobionate, metoclopramide, and cisapride. Prokinetic agents were more commonly administered after small intestine strangulating obstructions and less commonly for large intestinal lesions. No novel agents were identified by respondents.

CONCLUSIONS

Prokinetic drugs are commonly used for the management and/or attenuation of POI in horses, but dosages and routes of administration are variable.

CLINICAL RELEVANCE

Although prokinetics are commonly used for management of POI in horses there is clearly a need for more controlled studies to define efficacious dosing and a need to develop new prokinetic drugs.

In vivo investigation of the efficacy of a customized solution to attenuate injury following low-flow ischemia and reperfusion injury in the jejunum of horses

OBJECTIVE

To evaluate the efficacy of a customized solution to attenuate intestinal injury following 20% low-flow ischemia and reperfusion in the jejunum of horses.

ANIMALS

10 healthy adult horses.

PROCEDURE

Two 30.5-cm-long segments of jejunum were exteriorized through a ventral midline incision and the mesenteric artery and vein supplying that portion of the intestine were instrumented with flow probes. Blood flow was decreased to 20% of baseline for 90 minutes followed by 90 minutes of reperfusion. In 5 horses, 60 mL of the customized solution was placed in the lumen of each segment (treatment-group horses), and 60 mL of lactated Ringer's solution was placed in the lumen of 5 additional horses (control-group horses). Biopsy specimens were obtained from 1 segment in both groups for histologic evaluation. Aliquots of luminal fluid were obtained from the other segment in both groups for determination of albumin concentrations as an index of mucosal permeability.

RESULTS

Compared with control-group horses, treatment-group horses had a significant decrease in luminal albumin concentration following reperfusion. Although differences in mucosal grades were not significantly different between control- and treatment-group horses, treatment-group horses had significantly greater jejunal villous length and area, compared with that of control-group horses.

CONCLUSIONS AND CLINICAL RELEVANCE

Intraluminal administration of the customized solution in the jejunum, compared with lactated Ringer's solution, results in an improvement in histologic findings and mucosal translocation of albumin in horses with mild intestinal injury.

In vitro investigation of the effects of nonsteroidal anti-inflammatory drugs, prostaglandin E2, and prostaglandin F2alpha on contractile activity of the third compartment of the stomach of llamas

OBJECTIVE

To determine the in vitro effect of prostaglandin (PG) E2, PGF2alpha, and the nonsteroidal anti-inflammatory drugs (NSAIDs) indomethacin, ketoprofen, and nabumetone on the contractile strength of the circular smooth muscle layer of the third compartment of the stomach of llamas.

SAMPLE POPULATION

Specimens of the third compartment obtained from 5 healthy adult llamas.

PROCEDURE

Full-thickness tissue samples were collected from the third compartment immediately after euthanasia. Specimens were cut into strips oriented along the circular muscle layer and mounted in a tissue bath system. Incremental amounts of ketoprofen, nabumetone, indomethacin, PGE2, and PGF2alpha were added, and contractile strength (amplitude of contractions) was recorded.

RESULTS

Generally, PGE2 reduced contractile strength of the circular smooth layer of the third compartment, whereas PGF2alpha, increased the strength of contractions. The activity of the NSAIDs was generally excitatory in a concentration-dependent manner, although significant changes were induced only by administration of indomethacin.

CONCLUSIONS AND CLINICAL RELEVANCE

On isolated smooth muscle strips of the third compartment of llamas, exogenous PGE2 and PGF2alpha had a variable effect on contractile strength. Administration of the NSAIDs did not inhibit contractility and would not be likely to induce stasis of the third compartment in the absence of an underlying disease process.

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.

Influence of topically applied cold treatment on core temperature and cell viability in equine superficial digital flexor tendons

OBJECTIVE

To determine rate and degree of cooling for the superficial digital flexor tendon (SDFT) during a standard cryotherapy application in horses and evaluate in vitro effects of cooling on survival of tendon cells.

SAMPLE POPULATION

6 limbs of 5 adult horses and cultured cells obtained from SDFT of 3 adult horses during necropsy.

PROCEDURE

In vivo data were acquired by use of a thermocouple temperature probe inserted into the SDFT of a forelimb of each standing sedated horse. After baseline temperatures were recorded, a commercial compression splint with circulating coolant was placed on each selected limb, which was then exposed to cold treatment for 60 minutes. Temperatures were recorded at 30-second intervals. Mean minimum core temperature was calculated and used to design a protocol for in vitro cold treatment of cells. Specimens were obtained from the SDFT of horses during necropsy; tendon cells were cultured in suspension and exposed to 1-hour of cold treatment that mimicked the in vivo procedure. Viability of cells after cold treatment was compared with viability of cells maintained at body temperature.

RESULTS

After 1 hour of cold treatment, SDFT core temperature was reduced by a mean of 21.8 degrees C, reaching a mean minimum temperature of 10 degrees C. Viability did not differ significantly between cold-treated and control cells.

CONCLUSION AND CLINICAL RELEVANCE

Results indicated that topical application of cryotherapy significantly reduced core SDFT temperature in standing sedated horses. Temperatures achieved in vivo during cold treatment were not detrimental to the in vitro viability of tendon cells.

Microvascular anatomy of the third compartment of the stomach of llamas

OBJECTIVE

To characterize the vascular anatomy of the third compartment of the stomach of llamas.

ANIMALS

7 adult llamas.

PROCEDURE

Immediately after each llama was euthanatized, vascular replicas of tissue from the third compartment were prepared by use of methylmethacrylate monomer and catalyst. Following chemical removal of tissue, the casts were further prepared for examination via scanning electron microscopy. By use of barium solution, microangiography was also performed on fixed tissue samples; the infused tissue was sectioned and imaged radiographically. Tissue samples were also collected for histologic evaluation after fixation and H&E staining.

RESULTS

The third compartment was supplied by 4 pairs of primary arteries and veins located around the circumference of the structure. From these vessels, smaller arteries and veins branched to supply the serosal surface and penetrated deeper through the tunica muscularis to supply the submucosal and mucosal layers. An extensive capillary network was arranged in a hexagonal array surrounding the gastric glands, such that the mucosal aspect of the replicas had a honeycomb-like appearance. Histologically, variably sized villous projections lined by a single layer of epithelial cells with an extensive glandular network were observed.

CONCLUSIONS AND CLINICAL RELEVANCE

The third compartment of the stomach of llamas is a highly vascular structure with an extensive anastomotic capillary network at the luminal surface. Branching vessels provide extensive collateral circulation, and it appears that surgical incisions should heal well. Incisions in the third compartment should be oriented parallel to the longitudinal plane.

In vitro investigation of the effects of cyclooxygenase-2 inhibitors on contractile activity of the equine dorsal and ventral colon

OBJECTIVE

To evaluate the effect of 2 cyclooxygenase (COX)-2 inhibitors on contractile activity of the circular smooth muscle layer of the equine dorsal and ventral colon.

SAMPLE POPULATION

Samples of the dorsal and ventral colon obtained from 10 healthy horses.

PROCEDURE

Full-thickness tissue samples were collected from the dorsal colon in the area of the diaphragmatic flexure and the ventral colon in the area of the sternal flexure. Samples were cut into strips oriented along the fibers of the circular muscle layer and mounted in a tissue bath system for determination of contractile strength. Incremental amounts of etodolac, nabumetone, and indomethacin were added, and contractile activity was recorded.

RESULTS

Response of the dorsal and ventral colon to nonsteroidal anti-inflammatory drugs (NSAIDs) was variable. Indomethacin induced the greatest reduction in contractile activity, followed by nabumetone. For etodolac, the difference from baseline values was only significantly reduced at the highest concentration used (1 X 10(5)M) for the ventral colon.

CONCLUSIONS AND CLINICAL RELEVANCE

The NSAIDs that are designed to target the COX-2 isoform appeared to have variable effects on the contractile activity of the equine dorsal and ventral colon. Etodolac appeared to have the least effect on contractile activity, compared with the effects attributable to nabumetone, and would potentially have the fewest adverse effects relative to motility of the dorsal and ventral colon.

In vitro evaluation of an intraluminal solution to attenuate effects of ischemia and reperfusion in the small intestine of horses

OBJECTIVE

To evaluate the efficacy of intraluminal administration of a customized solution during low-flow ischemia and reperfusion in the jejunum of horses.

SAMPLE POPULATION

Segments of jejunum obtained from 13 healthy adult horses.

PROCEDURE

In isolated segments of jejunum maintained in an extracorporeal circuit, arterial flow was reduced to 20% of baseline for 40 minutes (ischemia) followed by 60 minutes of reperfusion. In 2 groups, a customized solution (concentrations, 12.5 and 25%, respectively) was placed in the lumen prior to low-flow ischemia and maintained during reperfusion. The control group received intraluminal lactated Ringer's solution for the same duration. Various metabolic, hemodynamic, histologic, and permeability variables were recorded.

RESULTS

The 12.5% solution resulted in less histomorphologic injury and reduced mucosal permeability to albumin, compared with the 25% solution and the lactated Ringer's solution. Morphologic injury and permeability were reduced in tissues that received the 25% solution, compared with the control group, but this difference was not significant.

CONCLUSIONS AND CLINICAL RELEVANCE

Use of a 12.5% customized solution appeared to minimize injury in the isolated extracoporeal jejunal loop, which provides some indication that it might be useful in clinical situations.

Ultrasonographic and histologic evaluation of medial and middle patellar ligaments in exercised horses following injection with ethanolamine oleate and 2% iodine in almond oil

OBJECTIVE

To describe the ultrasonographic and quantitative histologic effect of injecting 2% iodine in almond oil (IAO) and ethanolamine oleate (EO) in the medial and middle patellar ligaments of horses and to determine whether a difference in response exists between IAO and EO treatment.

ANIMALS

10 healthy horses.

PROCEDURE

In 5 horses, the medial and middle patellar ligaments of 1 limb were injected with EO, whereas IAO was injected in the medial and middle patellar ligaments of another 5 horses. Ultrasonographic evaluation was performed on the experimental and control limb before injection of IAO and EO and prior to euthanasia to determine cross-sectional area and evaluate fiber pattern. The patellar ligaments were harvested 2 weeks after injection and examined histologically to evaluate the inflammatory response, fibroplasia, and chondroid metaplasia.

RESULTS

Injection of the patellar ligaments with IAO resulted in a greater increase in cross-sectional area on ultrasonography than EO. Both agents caused a decrease in echogenicity of the ligament. Histologically, significantly greater infiltration of inflammatory cells and fibroplasia developed after injection with IAO, compared with EO. Both agents resulted in significantly greater fibroplasia relative to control specimens.

CONCLUSIONS AND CLINICAL RELEVANCE

Injection of the medial and middle patellar ligaments with IAO induces more severe inflammation and fibroplasia than EO. Maturation of the inflammatory and fibrous response may contribute to resolution or attenuation of upward fixation of the patella by subsequent stiffening of the ligaments.

Comparison of intraosseous or intravenous infusion for delivery of amikacin sulfate to the tibiotarsal joint of horses

OBJECTIVE

To establish the route of infusion (IV or intraosseous) that results in the highest concentration of amikacin in the synovial fluid of the tibiotarsal joint and determine the duration of peak concentrations.

ANIMALS

21 horses.

PROCEDURE

Regional perfusion of a limb on 15 horses was performed. Amikacin sulfate was infused into the saphenous vein or via intraosseous infusion into the distal portion of the tibia (1 g in 56 ml of lactated Ringer's solution) or proximal portion of the metatarsus (1 g of amikacin in 26 ml of lactated Ringer's solution). Amikacin concentrations were measured in sequential samples from tibiotarsal joint synovial fluid and serum. Samples were obtained immediately prior to release of the tourniquet and 0.5, 1, 4, 8, 12, and 24 hours after the tourniquet was released. Radiographic contrast material was infused into the same locations as the antibiotic perfusate to evaluate distribution in 6 other horses.

RESULTS

Infusion into the saphenous vein produced the highest concentration of amikacin in the tibiotarsal joint, compared with the distal portion of the tibia (mean +/- SE, 701.8 +/- 366.8 vs 203.8 +/- 64.5 microg/ml, respectively). Use of a lower volume of diluent in the proximal portion of the metatarsus produced a peak value of 72.2 +/- 23.4 microg/ml.

CONCLUSIONS AND CLINICAL RELEVANCE

For regional perfusion of the tarsus, IV infusion is preferred to intraosseous infusion, because higher concentrations are achieved in the synovial fluid, and the procedure is easier to perform.

Use of an extracorporeal circuit to evaluate effects of intraluminal distention and decompression on the equine jejunum

OBJECTIVE

To use an extracorporeal circuit to evaluate effects of intraluminal distention on the jejunum of healthy horses.

SAMPLE POPULATION

2 jejunal segments from each of 5 horses.

PROCEDURE

Jejunal segments were harvested and maintained in an extracorporeal circuit. One segment was subjected to distention (intraluminal pressure, 25 cm H2O) followed by decompression, and 1 segment was maintained without distention. The influence of distention-decompression on vascular resistance was calculated. Mucosal permeability was evaluated by measuring the clearance of albumin from blood to lumen. After distention and decompression, tissue specimens were collected for histomorphologic evaluation. In addition, the contractile response of the circular smooth muscle layer was determined following incubation with 3 prokinetic agents.

RESULTS

Intestinal vascular resistance increased during intraluminal distention and returned to baseline values after decompression. Albumin clearance rate increased after distention, compared with baseline and control values. Histologic examination of the distended segments revealed grade-1 and -2 lesions of the mucosal villus. Edema and hemorrhage were evident in the submucosa and muscular layers. Mesothelial cell loss, edema, and hemorrhage were also evident in the serosa. Mucosal surface area and villus tip height decreased and submucosal volume increased in the distended tissue. Compared with responses in control specimens, distention decreased the contractile response induced by cisapride, erythromycin, and metoclopramide.

CONCLUSIONS AND CLINICAL RELEVANCE

Intraluminal distention of the jejunum followed by decompression increased mucosal permeability and injury and decreased responses to prokinetic agents. Horses with intraluminal intestinal distention may have a decreased response to prokinetic agents.