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- Author or Editor: Peter C. Rakestraw x
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Abstract
Objective—To identify indications for and short- and long-term outcome of permanent tracheostomy performed in standing horses.
Design—Retrospective case series.
Animals—82 horses undergoing permanent tracheostomy.
Procedures—Data obtained from medical records included signalment, diagnosis, surgical technique, complications, use of the horse before and after surgery, and owner satisfaction. Follow-up information was obtained through a telephone questionnaire administered to owners.
Results—Indications for permanent tracheostomy included nasopharyngeal cicatrix (n = 59), arytenoid chondropathy (55), and laryngeal hemiplegia (20); 54 horses had multiple indications for tracheostomy. Complications identified prior to discharge included partial dehiscence (n = 8), transient fever (10), and excessive swelling (13). Complications identified after discharge included partial dehiscence (n = 3), inversion of skin (2), and stenosis of the tracheostomy requiring repair (1). Long-term follow-up information was available for 64 horses. Fifty-seven of the 64 (89%) horses returned to their previous use, and owners of 63 (98%) horses reported being very satisfied with the results. The owner of 1 (2%) horse was unsatisfied with the results. The 1-year survival rate was 97% (95% confidence interval, 95% to 100%). Mean estimated truncated survival time (ie, failure-free period) was 9.7 years (95% confidence interval, 9.3 to 10.1 years).
Conclusions and Clinical Relevance—Results suggested that permanent tracheostomy can be safely performed in standing horses and was a viable treatment for horses with obstructive disease of the upper respiratory tract that was unresponsive to medical treatment or other surgical treatments.
Abstract
Objective—To evaluate electrical activity of jejunal circular muscle in horses and characterize electrical responses to stimulation by intrinsic inhibitory neurons.
Sample Population—Portions of jejunum obtained from horses euthanatized for reasons other than gastrointestinal tract disease.
Procedure—Isolated circular muscle preparations were perfused with oxygenated modified Krebs solution. Glass microelectrodes were used for intracellular recording of membrane potentials from single smooth muscle cells. Electrical activity and responses to electrical field stimulation (EFS) of intrinsic neurons in the presence of guanethidine and atropine were recorded. Mediators of responses to nerve stimulation were also evaluated, using N-nitro-L-arginine methyl ester (L-NAME) and apamin.
Results—Mean resting membrane potential (RMP) was 41.5 ± 1.8 mV. Small membrane potential oscillations were observed in muscle cells. Single or multiple action potentials were often superimposed on the peaks of these oscillations. Spontaneous oscillations and action potentials were blocked by nifedipine. Transient hyperpolarizations of smooth muscle cell membrane potentials (inhibitory junction potentials [IJP]) were observed in response to electrical field stimulation. The IJP evoked by stimulus trains consisted of an initial fast component followed by a slow component. The L-NAME did not have a significant effect on RMP and did not significantly affect the fast component of IJP at any stimulus frequency tested. In contrast, L-NAME abolished the slow component of IJP observed after trains of pulses. In the continued presence of L-NAME, apamin had no significant effect on RMP but effectively reduced the fast component of IJP.
Conclusions and Clinical Relevance—Findings suggest that inhibitory neurotransmitters supplying equine jejunum act through different ionic mechanisms. Understanding these mechanisms may suggest new therapeutic targets for treatment of motility disorders. (Am J Vet Res 2000;61:362–368)
Abstract
Objective—To determine short- and long-term outcomes, including recurrence rates, for horses with cecal impaction treated medically or surgically.
Design—Retrospective case series.
Animals—114 horses.
Procedures—Medical records were reviewed for information on signalment, history, clinical findings, treatment (medical vs surgical), and short-term outcome. Information on longterm outcome was obtained through a mail survey and telephone interview with owners.
Results—54 horses were treated medically, 49 horses were treated surgically, and 11 horses were euthanized after initial examination without further treatment. Horses treated surgically were significantly more likely to have signs of moderate or severe pain than were horses treated medically. Forty-four of the 54 (81%) horses treated medically were discharged from the hospital. Twelve of the 49 horses treated surgically were euthanized at surgery because of cecal rupture. Thirty-five of the 37 (95%) horses that were allowed to recover from surgery were discharged from the hospital. In 34 horses treated surgically, typhlotomy without a bypass procedure was performed. Long-term (≥ 1 year) follow-up information was available for 19 horses treated medically and 28 horses treated surgically. Eighteen (95%) and 25 (89%) of the horses, respectively, were alive at least 1 year after treatment.
Conclusions and Clinical Relevance—Results suggested that medical and surgical treatment were both associated with favorable outcomes in horses with cecal impactions. In this population, typhlotomy alone without cecal bypass was associated with a low recurrence rate. The long-term prognosis for horses that were discharged from the hospital was good.
Abstract
Objective—To determine the role of nitric oxide and an apamin-sensitive nonadrenergic noncholingeric inhibitory transmitter on contractility of the ventral colon of horses.
Sample population—Strips of the circular and longitudinal muscle layers and taenia of the ventral colon from 14 horses.
Procedure—Muscle strips were suspended in tissue baths and attached to force transducers. Contractile activity of circular, longitudinal, and taenia muscle strips in response to electrical field stimulation was measured after addition of apamin and a nitric oxide inhibitor, N-nitro-L-arginine methyl ester (L-NAME).
Results—Electrical field stimulation reduced contractile activity in the circular muscle layer and taenia but not the longitudinal muscle layer. Addition of L-NAME significantly reduced inhibitory contractile activity at all frequencies for the circular muscle layer, whereas a significant effect was evident for the taenia only at the highest frequency. The combination of L-NAME and apamin resulted in a significant reduction in inhibition of the taenia at all frequencies but for circular muscle only at lower frequencies.
Conclusions and Clinical Relevance—Nitric oxide and an apamin-sensitive neurotransmitter appear to mediate a component of inhibitory transmission in the circular muscle and taenia, but not the longitudinal muscle layer, of the equine ventral colon. Nitric oxide has a role in regulating contractile activity of the equine ventral colon, and nitric oxide synthase inhibitors may be useful in horses with ileus of the large colon. (Am J Vet Res 2000;61:64–68)
Abstract
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, NG-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 10–4M (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. (Am J Vet Res 2000;61:413–419)
Abstract
Objective—To identify risk factors for enterolithiasis in horses.
Design—Matched case-control study.
Animals—26 horses with enteroliths, 104 horses with other causes of colic that underwent surgery (52 horses, surgical control group) or were treated medically (52 horses, nonsurgical control group).
Procedure—Medical records were reviewed for horses with enteroliths and control horses. Information collected included signalment, anamnesis, and findings on physical examination and clinicopathologic testing at admission. Horses with enteroliths and control horses were compared by means of conditional logistic regression to identify factors associated with enterolithiasis.
Results—Horses that were fed alfalfa hay, spent ≤ 50% of time outdoors, or were Arabian or miniature breeds had an increased risk of developing enteroliths. Horses with enteroliths were more likely to have been hyperbilirubinemic and to have had clinical signs > 12 hours prior to admission.
Conclusions and Clinical Relevance—Breed and diet appear to influence the risk of enterolithiasis; other management factors also may influence development of enteroliths. Duration of clinical signs may be longer and signs may be less severe among horses with enteroliths, compared with horses with other causes of colic. (J Am Vet Med Assoc 2000;216:1787–1794)
Abstract
Objectives
To determine the in vitro effect of various prostaglandins (PG) and nonsteroidal anti-inflammatory drugs (NSAID) on contractile activity of the large-colon taenia of horses.
Animals
14 healthy horses.
Procedure
The taenia was collected from the ventral colon, cut into strips (2 × 10 mm), and mounted in a tissue bath system (20-ml capacity) that contained oxygenated Krebs buffer solution warmed to 37.5 ± 0.5 C. After equilibration, incremental doses of PGE2, PGF2α, PGI2, flunixin meglumine, carprofen, ketoprofen, and phenylbutazone were added to the baths, and contractile activity was recorded. Magnitude of the response was calculated by comparing contractile activity before and after administration of the PG or NSAID to the tissue baths.
Results
PGE2 and PGF2α caused a significant increase in contractile activity, whereas PGL2 induced an inhibitory response. Activity of NSAID on contraction was predominantly inhibitory. At low concentrations, ketoprofen induced an excitatory effect, which then became inhibitory at high concentrations. Compared with the other NSAID, carprofen significantly reduced contractile activity at lower concentrations.
Conclusions
PGE2 and PGF2α appear to enhance contractility of large-colon taenia of horses, whereas PGL2 was inhibitory in the in vitro model. Administration of NSAID also inhibited contractility, with carprofen having the most potent effect.
Clinical Relevance
Administration of NSAID in combination with liberation of endogenous PG may predispose horses to development of intestinal stasis and subsequent impaction. (Am J Vet Res 1999;60:1004-1009)
Abstract
Objective
To determine the role of nitric oxide and an apamin-sensitive nonadrenergic-noncholinergic inhibitory transmitter in in vitro contractile activity of the third compartment in llamas.
Sample Population
Isolated strips of third compartment of the stomach from 5 llamas.
Procedure
Strips were mounted in tissue baths containing oxygenated Kreb's buffer solution and connected to a polygraph chart recorder to measure contractile activity. Atropine, guanethidine, and indomethacin were added to tissue baths to inhibit muscarinic receptors, adrenoreceptors, and prostaglandin synthesis. Responses to electrical field stimulation following addition of the nitric oxide antagonist Νω-nitro-L-arginine methyl ester (L-NAME) and apamin were evaluated.
Results
Electrical field stimulation (EFS) resulted in a reduction in the amplitude and frequency of contractile activity, followed by rebound contraction when EFS was stopped. Addition of L-NAME resulted in a significant reduction in inhibition of contractile activity. Addition of apamin also resulted in a significant reduction in inhibitory contractile activity at most stimulation frequencies. The combination of L-NAME and apamin resulted in a significant reduction in inhibition at all frequencies.
Conclusion
Nitric oxide and a transmitter acting via an apamin-sensitive mechanism appear to be involved in inhibition of contractile activity of the third compartment in llamas.
Clinical Relevance
Results suggest that nitric oxide plays an important role in mediating contractile activity of the third compartment in llamas. Use of nitric oxide synthase inhibitors may have a role in the therapeutic management of llamas with lesions of the third compartment. (Am J Vet Res 1998;59:1166— 1169)
