Detection and comparison of nitric oxide in clinically normal horses and those with naturally acquired small intestinal strangulation obstruction.

The purpose of this study was to determine whether nitric oxide (NO) is present in clinically normal horses under basal conditions and if it increases secondary to naturally acquired small intestinal strangulation obstruction. Thirty-one horses were used; 20 horses with naturally acquired small intestinal strangulation obstruction and 11 clinically normal horses with no signs of gastrointestinal tract disease. Jugular venous blood, abdominal fluid, and urine were collected for NO quantification. Plasma, abdominal fluid, and urine were stored at -70 degrees C until analyzed for NO using a chemiluminescent method. Biopsy specimens collected from the affected jejunal segment, during anesthesia or after immediately after euthanasia, or from the midjejunum of control horses, were divided into subsections for fixation in zinc formalin and cryopreservation in OCT gel. Nicotinamide adenine dinucleotide phosphate (reduced) (NADPH) diaphorase histochemical stains were performed on cryopreserved tissues and inducible nitric oxide synthase (iNOS) and nitrotyrosine immunohistochemical stains were performed on formalin-fixed, paraffin-embedded tissues. There were significantly greater plasma and abdominal fluid NO concentrations in affected horses as compared with controls, but there were no significant differences between horses for urine NO concentrations. There was a significant decrease in NADPH diaphorase stain in mucosal epithelium, vasculature, and leukocytes, and in submucosal plexi in affected horses compared with control horses. There was a significant increase in iNOS staining in mucosal and submucosal leukocytes and in mucosal leukocyte nitrotyrosine staining of the affected compared with control horses. Endothelial NOS and neuronal NOS are present under basal conditions in the jejunum of horses and probably mediate physiologic or cytoprotective effects. Plasma and abdominal fluid, but not urine, NO concentrations increase subsequent to small intestinal strangulation obstruction; this may be associated with increased mucosal and submucosal iNOS staining in leukocytes, which was likely due to increased expression subsequent to stimuli associated with ischemia. The increased nitrotyrosine staining in mucosal leukocytes of affected horses likely reflects the presence of peroxynitrite subsequent to increased NO and superoxide production and may reflect a cytotoxic role of NO in small intestinal strangulation obstruction in horses.     

Survival of horses following strangulating large colon volvulus

Reasons for performing study: The pattern of long‐term survival and specific factors associated with long‐term survival have not previously been evaluated in horses with a strangulating large colon volvulus (LCV). Objectives: To provide data on the long‐term survival of horses with LCV and to identify pre‐, intra‐ and post operative variables associated with survival. Methods: Clinical data and long‐term follow‐up information were obtained from 116 horses with a strangulating LCV (≥360°) undergoing general anaesthesia. Two multivariable Cox proportional hazards models for post operative survival time were developed: Model 1 included all horses and evaluated preoperative variables and Model 2 included horses that survived anaesthesia and evaluated pre‐, intra‐ and post operative variables. Results: The study population comprised 116 horses. Eighty‐nine (76.7%) survived general anaesthesia. Of these, the percentage that survived until discharge, to one year and to 2 years was 70.7%, 48.3% and 33.7%, respectively. Median survival time for horses that survived general anaesthesia was 365 days. In Model 1 increased preoperative packed cell volume (PCV) was significantly associated with reduced post operative survival (hazard ratio [HR] 1.08, 95% confidence interval [CI] 1.05–1.11). However, this effect changed over time. In Model 2 abnormal serosal colour intraoperatively (HR 3.61, 95% CI 1.55–8.44), increased heart rate at 48 h post surgery (HR 1.04, 95% CI 1.02–1.06), and colic during post operative hospitalisation (HR 2.63, 95% CI 1.00–6.95), were all significantly associated with reduced post operative survival. Conclusions: Survival time in horses with a LCV was associated with preoperative PCV, serosal colour, heart rate at 48 h post operatively and colic during post operative hospitalisation. Potential relevance: This study provides evidence‐based information on the long‐term survival of horses with LCV and identifies parameters that may assist decision‐making by clinicians and owners.     

Resection and anastomosis for treatment of strangulating volvulus of the large colon of horses.

Strangulating volvulus of the large colon was treated by resection and anastomosis of the colon in 9 horses. Tissue specimens were obtained at the site of the resection for histologic evaluation. An attempt was made to correlate the appearance of the colon at the time of surgery to the histologic evaluation and the eventual outcome. Six of the 9 horses (66%) survived. This is in contrast to a reported survival of 34.7 to 36% after decompression and reduction of colonic volvulus. Survival after surgery could not be predicted on the basis of visual assessment or histologic examination.     

Use of colonic luminal pressure to predict outcome after surgical treatment of strangulating large colon volvulus in horses

OBJECTIVE: To evaluate the relationship of colonic luminal pressure (CLP) measurements to outcome in horses with large colon volvulus (LCV) after either manual correction or large colon resection and anastomosis (LCRA). STUDY DESIGN: Retrospective study. ANIMALS: Horses (n=57) that had LCV. METHODS: Records for horses with LCV (March 1997-December 2003) were reviewed. Inclusion criteria were strangulating LCV proximal to the cecocolic ligament (>270 degrees), recorded CLP, and successful recovery from anesthesia. CLP measurements and survival/mortality rates were compared between horses that had manual correction (M) or LCRA (R). RESULTS: Of 57 horses, 27 had M and 30 had LCRA. For group M, CLP measurements had a sensitivity of 0.60 and specificity of 0.77 for predicting survival, whereas for group R, sensitivity was 0.50 and specificity was 0.54. CONCLUSION: In our LCV population, elevated CLP measurements had poor accuracy for predicting outcome in horses after surgical correction, especially after LCRA. CLINICAL RELEVANCE: CLP measurements based on a single hospital population of horses with LCV should be used with caution for other hospital populations of LCV. CLP may be only one of many variables needed for predicting outcome of horses with strangulating LCV, especially after LCRA.     

Coagulation profiles in 27 horses with large colon volvulus

Objective: The objective of this study was to evaluate coagulation profiles in horses with surgical treatment of large colon volvulus (LCV), and determine if an association exists between hemostatic dysfunction and outcome. Design: Prospective clinical investigation from February to December 2000. Setting: Large animal intensive care unit in a veterinary teaching hospital. Interventions: Blood was collected from horses intra‐operatively, 24, and 48 hours following surgical treatment for LCV. Measurements: Coagulation profiles, thrombin–antithrombin (TAT) levels, and D‐dimer concentrations were determined for each time point. The number of tests abnormal in the standard coagulation profile, defined as the degree of hemostatic dysfunction, was determined for each horse for the duration of the study period. The association between each test and outcome, as well as the degree of hemostatic dysfunction for each horse and outcome, was determined using univariate analysis and logistic regression. TAT levels and D‐dimer concentrations were compared to the results of the standard coagulation profile and to patient outcome using univariate analysis and logistic regression. Main results: Seventy percent of horses evaluated with surgical treatment of LCV had evidence of hemostatic dysfunction (3/6 tests abnormal). Only 18% of those patients had clinical signs recognized by the attending clinician as a coagulopathy. There was an association between the development of a coagulopathy and outcome, with horses with 4/6 tests abnormal being more likely to be euthanized, and those with 3/6 tests abnormal having a prolonged hospital stay. Platelet count, prothrombin time, and TAT levels may be helpful in predicting outcome in horses with LCV. Conclusions: Hemostatic function should be evaluated in horses with surgical treatment of LCV to detect subclinical coagulopathies and direct subsequent intervention.     

Plasma concentrations of endothelin-like immunoreactivity in healthy horses and horses with naturally acquired gastrointestinal tract disorders

OBJECTIVE: To compare plasma endothelin (ET)- like immunoreactivity between healthy horses and those with naturally acquired gastrointestinal tract disorders. ANIMALS: 29 healthy horses and 142 horses with gastrointestinal tract disorders. PROCEDURE: Blood samples were collected from healthy horses and from horses with gastrointestinal tract disorders prior to treatment. Magnitude and duration of abnormal clinical signs were recorded, and clinical variables were assessed via thorough physical examinations. Plasma concentrations of ET-like immunoreactivity were measured by use of a radioimmunoassay for human endothelin-1, and CBC and plasma biochemical analyses were performed. RESULTS: Plasma ET-like immunoreactivity concentration was significantly increased in horses with gastrointestinal tract disorders, compared with healthy horses. Median plasma concentration of ET-like immunoreactivity was 1.80 pg/ml (range, 1.09 to 3.2 pg/ml) in healthy horses. Plasma ET-like immunoreactivity was greatest in horses with strangulating large-intestinal obstruction (median, 10.02 pg/ml; range, 3.8 to 22.62 pg/ml), peritonitis (9.19 pg/ml; 789 to 25.83 pg/ml), and enterocolitis (8.89 pg/mI; 6.30 to 18.36 pg/ml). Concentration of ET-like immunoreactivity was significantly associated with survival, PCV, and duration of signs of pain. However, correlations for associations with PCV and duration of pain were low. CONCLUSIONS AND CLINICAL RELEVANCE: Horses with gastrointestinal tract disorders have increased plasma concentrations of ET-like immunoreactivity, compared with healthy horses. The greatest values were detected in horses with large-intestinal strangulating obstructions, peritonitis, and enterocolitis. This suggests a potential involvement of ET in the pathogenesis of certain gastrointestinal tract disorders in horses.     

Strangulating volvulus of the ascending colon in horses

Of 57 horses with strangulating volvulus of the ascending colon, 42 were mares (including 21 postparturient mares), 8 were stallions, and 7 were geldings. Volvulus occurred most frequently in the summer (n = 24) and spring (n = 17). Pain was evaluated as severe in 41 horses, moderate in 9, and mild in 4. The abdominal fluid from 30 horses varied from clear yellow in 19 horses, to cloudy yellow in 3 horses, and serosanguineous in 8 horses. Protein content and nucleated cell count in the abdominal fluid were 2.5 +/- 1 g/dl and 1,000 +/- 900 microliters, respectively. Fifty horses had greater than or equal to 360 degrees volvulus and 7 had a 270 degrees volvulus, with 49 occurring in a counterclockwise direction. The site of volvulus in all horses was at the mesenteric attachment of the colon, except for a 360 degrees volvulus at the sternal and diaphragmatic flexures in 1 horse. Survival rates for horses with a greater than or equal to 360 degrees and a 270 degrees volvulus were 36% and 71%, respectively. The difference in survival rates reflected the severe vascular occlusion in the colon of horses with greater than or equal to 360 degrees volvulus. In nonsurvivors, hemorrhage in the submucosa and lamina propria (P less than 0.005) and edema in the submucosa (P less than 0.01) were greater than those in survivors. In nonsurvivors, greater than 97% of the superficial epithelium was lost. In horses that survived, only 60% of the cells were lost or degenerated.(ABSTRACT TRUNCATED AT 250 WORDS)     

Gastric impaction associated with displacement and volvulus of the large colon in seven mature horses

Gastric impaction associated with large colon volvulus (LCV) was identified in seven horses. Right dorsal displacement of the large colon and suspected nephrosplenic entrapment was identified in 2 of the 7 horses as well as LCV with concurrent gastric impaction. All horses underwent surgery for LCV and none survived. Five horses died or were subjected to euthanasia intraoperatively or in recovery. One horse was subjected to euthanasia post operatively due to persistent gastric reflux, following resolution of the gastric impaction. One horse was subjected to euthanasia post operatively due to a suspected gastric rupture, which was confirmed on post mortem examination. It is hypothesised that a large mass in the cranial abdomen, such as a gastric impaction may disrupt the normal anatomical large colon alignment or may cause colonic motility or microbiota alterations, and thus increase the risk of large colon displacement and volvulus.     

Prevention of large colon displacements and volvulus

Results of these studies have demonstrated that colopexy of the left large colon to the abdominal wall is a relatively simple and quick procedure that is permanent 1 year after surgery. The technique does not appear to be associated with long-term weight loss or abdominal pain after surgery. It has been used in pregnant mares, both experimentally and clinically, without apparent complications. In addition, horses used for pleasure-riding and show hunting have returned to performance and have not had complications. Large colon resection is a useful technique, especially for animals with strangulating large intestinal lesions. The surgeon must decide whether a technique to prevent recurrence should be performed at the first surgery or whether it should be performed only in horses with recurrence of these lesions. Until a large number of large colon resections or colopexies are performed on horses either at the initial surgery or after recurrence, it is impossible to predict the true efficacy of these techniques.     

Growth factor and receptor mRNA expression in the intestine of horses with large colon volvulus: a pilot study

REASONS FOR PERFORMING STUDY: Growth factors (GF) are important for maintenance and repair of intestinal mucosal structure and function, but there have been no studies investigating growth factor (GF) or growth factor receptor (GF-R) mRNA expression in the intestine of horses with large colon volvulus (LCV). OBJECTIVES: (1) To determine mRNA expression for epidermal growth factor (EGF), EGF receptor (EGF-R), insulin-like growth factor-I (IGF), IGF receptor (IGF-R), vascular endothelial growth factor (VEGF) and VEGF receptor (VEGF-R) in the intestine of horses with an LCV compared to normal intestine. (2) To measure the correlation between histological intestinal injury and mRNA expression. METHODS: In 5 horses, samples were collected from the mid-jejunum (small intestine, SI), pelvic flexure (PF) and right dorsal colon (RDC) prior to creation of the LCV (NORM), 1 h following creation of the LCV (ISCH) and 1 h following correction of the LCV (REPER). In 2 clinical cases of LCV, samples were collected from the PF and RDC. Samples were assessed histologically for the amount of intestinal injury. The mRNA expressions of growth factors and receptors were determined using qRT-PCR. RESULTS: VEGF and VEGF-R mRNA expression was greater in horses with an LCV compared to NORM. Expression of IGF-R mRNA increased in the SI during ISCH and REPER. CONCLUSION AND POTENTIAL RELEVANCE: The increase compared to NORM in VEGF and VEGF-R mRNA expression in horses with LCV may be important in early intestinal healing and may also explain, in part, the increase in vascular permeability in horses with a LCV. Expression of IGF and IGF-R in the SI warrants further investigation and may be important for understanding post operative complications in horses with SI lesions.     

Assessment of apoptosis in epidermal lamellar cells in clinically normal horses and those with laminitis

OBJECTIVE: To determine and compare the number, type, location, and distribution of apoptotic epidermal cells in the laminae of clinically normal horses and horses with laminitis. SAMPLE POPULATION: Formalin-fixed samples of digital lamellar tissue from 47 horses (including clinically normal horses [controls; n = 7], horses with acute [4] and chronic [7] naturally acquired laminitis, and horses with black walnut extract-induced [11] or carbohydrate overload-induced [18] laminitis). PROCEDURE: Blocks of paraffin-embedded lamellar tissues were stained for DNA fragmentation with the terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling (TUNEL) technique. Differential immunohistochemical staining for caspases 3 and 14 were used to confirm apoptosis. RESULTS: The number of TUNEL-positive epidermal cells per 0.1 mm of primary laminae was significantly greater in the acute laminitis group than in the other groups. In the acute laminitis group, there were 17 and 1,025 times as many TUNEL-positive basal layer cells and keratinocytes, respectively, compared with the control group. Apoptosis of TUNEL-positive basal layer cells was confirmed by results of caspase 3 immunohistochemical staining. The TUNEL-positive keratinocytes did not stain for caspases 3 or 14. CONCLUSIONS AND CLINICAL RELEVANCE: The large number of apoptotic basal layer cells detected in the lamellar tissue of horses with acute naturally acquired laminitis suggests that apoptosis may be important in the development of acute laminitis. The role of the large number of TUNEL-positive keratinocytes detected in the interface of primary and secondary epidermal laminae of horses with acute laminitis remains to be elucidated.     

Antithrombin III activity in horses with large colon torsion

A chromogenic peptide substrate assay was used to determine serially plasma antithrombin III (AT III) activity in 4 groups of horses. Group I consisted of healthy, mature horses in which AT III activity was determined twice daily for 7 consecutive days. Groups 2 and 3 contained healthy horses in which AT III activity was monitored for 7 days after controlled, but varying, conditions of general anesthesia and surgery (median celiotomy). Group 4 was made up of patients with a presurgical diagnosis of colonic torsion. In healthy awake horses (group I), there was no difference in AT III values over time. Postoperative AT III activity in the halothane-anesthetized horses (group 2) and in the sham-operated horses (group 3) was not significantly (P = 0.05) different from base-line values at any time. A significant decrease (P = 0.05) in AT III activity was observed on postoperative days 1 through 3 in the group of horses with large colon torsion, but returned to preoperative values by day 4 after surgery in the horses that survived. In those horses that did not survive, AT III activity remained below base-line values for the duration of observation. Seemingly, plasma AT III activity in horses was not significantly affected by halothane anesthesia or surgery. Serial evaluation of AT III activity may be useful for predicting survival in horses with large colon torsion.     

Small-intestinal volvulus as a complication of acquired inguinal hernia in two horses

Volvulus of the small intestine was diagnosed as a complication of acquired inguinal herniation in 2 horses. One of the horses continued to have signs of pain after reduction of the hernia. The volvulus was diagnosed at a second surgery, but the intestine was devitalized, and the horse was euthanatized. Ventral midline exploratory surgery was performed on the second horse, in conjunction with an inguinal approach. The small-intestinal volvulus was diagnosed and corrected at this time. It is suggested that ventral midline abdominal exploration be performed when acquired inguinal herniation causes acute small-intestinal obstruction in horses.     

Long term ECG recording with Holter monitoring in clinically healthy horses.

The electrocardiogram of 9 horses was continuously recorded for 24 h with Holter monitoring to examine the variations in heart rate and rhythm during daily routine procedures and at night. Three horses had transient sinus bradycardia, and 3 had periods of sinus tachycardia. Heart blocks were detected in 3 horses, and all horses had periods of sinus arrhythmia. These changes in the heart rate and rhythm were apparently caused by variations in autonomic nervous system tone and they are probably "normal" findings in resting, undisturbed horses. Ventricular premature depolarisations were not observed in any horse, but some single supraventricular premature contractions were detected. There was preliminary evidence that in order to register the real resting heart rate and rhythm of a horse the ECG should be recorded over a long period, and also at night and without the presence of the investigator.     

Colopexy of the large colon in four horses

Colopexy of the left ventral colon to the abdominal wall was performed in 4 horses with recurrence of large-colon displacement or volvulus. Horses were discharged between 5 and 27 days after surgery. At follow-up evaluation (mean, 10.5 months; range, 7 to 13 months) of the horses, none had recurrence of signs of abdominal pain, and all had normal body weight. Three horses were exercised regularly; signs of abdominal pain were not observed.