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
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. (Am J Vet Res 2002;63:1545–1550)
Objective—To describe management of anesthesia for transvenous electrical cardioversion (TVEC) in horses and report perianesthetic complications.
Design—Retrospective case series.
Animals—62 horses with atrial fibrillation and without underlying cardiac disease and 60 horses without atrial fibrillation.
Procedures—Medical records of horses with atrial fibrillation anesthetized for TVEC were reviewed, as were records of horses without atrial fibrillation anesthetized for magnetic resonance imaging (MRI). The TVEC group horses were compared with MRI group horses for incidence of intraoperative bradycardia and use of inotropic drugs. Data obtained included patient signalment, weight, duration of anesthesia, heart rate and arterial blood pressure during anesthesia, anesthetic drugs administered, mode of ventilation, perioperative complications, and quality of recovery.
Results—The TVEC group horses were > 1 year of age and were predominantly Standardbreds. The TVEC group horses underwent a total of 76 anesthetic episodes. For 40 (52.6%) anesthetic episodes, horses received xylazine only for premedication, and for 26 (34.2%) anesthetic episodes, horses received xylazine and butorphanol. Induction of anesthesia consisted of ketamine administration in various combinations with diazepam and guaifenesin for 74 (97.4%) anesthetic episodes and ketamine alone for 2 (2.6%). Bradycardia in horses was encountered during 15 of 76 (19.7%) anesthetic episodes. Minor signs of possible postanesthetic myopathy occurred following 6 (7.9%) anesthetic episodes. No significant difference was found between TVEC and MRI group horses regarding incidence of bradycardia and inotropic drug administration.
Conclusions and Clinical Relevance—Short-duration anesthesia for TVEC of atrial fibrillation in horses without underlying cardiac disease was a safe procedure.
Objective—To evaluate influence of electrode position on cardioversion energy (CE; energy delivered in the shock at which cardioversion was achieved) during transvenous electrical cardioversion (TVEC) in horses with atrial fibrillation.
Animals—37 horses with atrial fibrillation (41 cardioversion events).
Procedures—Records were reviewed to identify horses that underwent TVEC for treatment of atrial fibrillation. Signalment and CE were recorded. Electrode positions in the right atrium and pulmonary artery were identified on intraoperative radiographs. An orthogonal coordinate space was created, and electrode y- and z-axis coordinates and shadow lengths were determined. Trigonometric modeling was used to estimate x-axis electrode positions that resulted in observed shadows. Postmortem casts of catheterized horses were used to assess electrode paths and anatomic relationships. Model assumptions were tested by use of these and a theoretical data set. Relationships between signalment, electrode position, and CE were assessed via multivariate analysis.
Results—Sex and y-axis differences between electrode positions were significant predictors of CE. Population stratification based on examination of residuals improved model strength; populations differed in z-axis variables and in CE. Decreasing distance between electrodes and pulmonary artery electrode positions ventral to the right atrium were associated with increased CE. Agreement between estimated and actual x-axis coordinates was poor.
Conclusions and Clinical Relevance—Optimal electrode positioning can reduce the energy requirement for successful TVEC and may eventually support application of TVEC under short-term IV anesthesia and potentially increase chances of treatment response. Further investigation into these relationships is warranted.
Case Description—4 racehorses were examined because of markedly abnormal behavior following administration of fluphenazine decanoate.
Clinical Findings—Clinical signs included restlessness, agitation, profuse sweating, hypermetria, aimless circling, intense pawing and striking with the thoracic limbs, and rhythmic swinging of the head and neck alternating with episodes of severe stupor. Fluphenazine was detected in serum or plasma from all 4 horses. The dose of fluphenazine decanoate administered to 3 of the 4 horses was within the range (25 to 50 mg) routinely administered to adult humans.
Treatment and Outcome—In 2 horses, there was no response to IV administration of diphenhydramine hydrochloride, but the abnormal behavior in these 2 horses appeared to resolve following administration of benztropine mesylate, and both horses returned to racing. The other 2 horses responded to diphenhydramine administration. One returned to racing. The other was euthanized because of severe neurologic signs, respiratory failure, and acute renal failure.
Clinical Relevance—Findings indicate that adverse extrapyramidal effects may occur in horses given fluphenazine decanoate. These effects appear to be unpredictable and may be severe and life threatening. Use of fluphenazine decanoate as an anxiolytic in performance horses is not permitted in many racing and horse show jurisdictions, and analytic procedures are now available to detect the presence of fluphenazine in serum or plasma.