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- Author or Editor: Rustin M. Moore x
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Abstract
Objective—To examine the secretory response (in the presence and absence of prostaglandin inhibition) in vitro and structural alterations of colonic mucosa in horses after intragastric administration of black walnut extract (BWE).
Animals—14 adult horses.
Procedure—Seven horses were administered BWE intragastrically and monitored for 11 hours. Tissue samples were obtained from the right ventral, left ventral, and right dorsal colons (RVC, LVC, and RDC, respectively) of the 7 BWE-treated and 7 control horses. Tissue samples were examined via light microscopy, and the extent of hemorrhage, edema, and granulocytic cellular infiltration (neutrophils and eosinophils) was graded. Colonic mucosal segments were incubated with or without flunixin meglumine (FLM) for 240 minutes; spontaneous electrical potential difference and short-circuit current (Isc) were recorded and used to calculate mucosal resistance.
Results—Colonic tissues from BWE-treated horses (with or without FLM exposure) had an overall greater Isc during the 240-minute incubation period, compared with tissues from control horses. The resistance pattern in RVC, LVC, and RDC samples (with or without FLM exposure) from BWE-treated horses was decreased overall, compared with control tissues (with or without FLM exposure). Histologically, colonic mucosal tissues from BWE-treated horses had more severe inflammation (involving primarily eosinophils), edema, and hemorrhage, compared with tissue from control horses.
Conclusions and Clinical Relevance—In horses, BWE administration appears to cause an inflammatory response in colonic mucosal epithelium that results in mucosal barrier compromise as indicated by decreased mucosal resistance with presumed concomitant electrogenic chloride secretory response, which is not associated with prostaglandin mediation. (Am J Vet Res 2005;66:443–449)
Abstract
Objective—To evaluate changes in digital vascular function in horses with carbohydrate overload (CHO)-induced laminitis and determine the effects of an endothelin (ET) receptor antagonist and nitroglycerin on laminitis-associated vascular dysfunction.
Animals—20 adult horses without abnormalities of the digit.
Procedures—Hemodynamic variables were recorded before (baseline) and hourly after all horses were administered a CHO ration via nasogastric tube. In 4 groups of 5 horses each, saline (0.9% NaCl) solution or ET receptor antagonist (10−5M in digital blood) was administered into the digital arterial circulation according to 1 of 2 schedules. During anesthesia, blood flow; arterial, venous, and capillary pressures; and total, precapillary, and postcapillary resistances were measured in an isolated perfused digit of each horse. In all groups, nitroglycerin was infused (10−5M in digital blood), and digital microvascular assessments were repeated.
Results—The CHO caused a significant decrease in right atrial pressure by 14 hours that was not affected by administration of saline solution or ET receptor antagonist. In isolated digits of anesthetized horses, CHO resulted in a significant decrease in digital blood flow associated with a significant increase in total and postcapillary resistances. Treatment with the ET receptor antagonist and nitroglycerin caused a significant decrease in total resistance. Postcapillary resistance was significantly decreased following treatment with the ET receptor antagonist but was not altered by treatment with nitroglycerin.
Conclusions and Clinical Relevance—Treatment with an ET receptor antagonist and nitroglycerin resulted in significant improvement in vascular resistance in isolated perfused digits of anesthetized horses with CHO-induced laminitis.
Abstract
Objective—To characterize the in vitro effects of oxytocin, acepromazine, xylazine, butorphanol, detomidine, dantrolene, isoproterenol, and terbutaline on skeletal and smooth muscle from the equine esophagus.
Animals—14 adult horses without digestive tract disease.
Procedure—Circular and longitudinal strips from the skeletal and smooth muscle of the esophagus were suspended in tissue baths, connected to force-displacement transducers interfaced with a physiograph, and electrical field stimulation was applied. Cumulative concentration-response curves were generated for oxytocin, acepromazine, xylazine, detomidine, butorphanol, isoproterenol, terbutaline, and dantrolene. Mean maximum twitch amplitude for 3 contractions/min was recorded and compared with predrug-vehicle values for the skeletal muscle segments, and area under the curve (AUC) for 3 contractions/min was compared with predrug-vehicle values for the smooth muscle segments.
Results—No drugs caused a significant change in skeletal muscle response. In smooth muscle, isoproterenol, terbutaline, and oxytocin significantly reduced AUC in a concentration-dependent manner. Maximum reduction in AUC was 69% at 10–4M for isoproterenol, 63% at 10–5M for terbutaline, and 64% at 10–4M for oxytocin.
Conclusions and Clinical Relevance—Isoproterenol, terbutaline, and oxytocin cause relaxation of the smooth muscle portion of the esophagus. The clinical relaxant effects on the proximal portion of the esophagus reported of drugs such as oxytocin, detomidine, and acepromazine may be the result of centrally mediated mechanisms. (Am J Vet Res 2002;63:1732–1737)
Abstract
Objective—To compare effects of oxytocin, acepromazine maleate, xylazine hydrochloride-butorphanol tartrate, guaifenesin, and detomidine hydrochloride on esophageal manometric pressure in horses.
Animals—8 healthy adult horses.
Procedure—A nasogastric tube, modified with 3 polyethylene tubes that exited at the postpharyngeal area, thoracic inlet, and distal portion of the esophagus, was fitted for each horse. Amplitude, duration, and rate of propagation of pressure waveforms induced by swallows were measured at 5, 10, 20, 30, and 40 minutes after administration of oxytocin, detomidine, acepromazine, xylazine-butorphanol, guaifenesin, or saline (0.9% NaCl) solution. Number of spontaneous swallows, spontaneous events (contractions that occurred in the absence of a swallow stimulus), and high-pressure events (sustained increases in baseline pressure of > 10 mm Hg) were compared before and after drug administration.
Results—At 5 minutes after administration, detomidine increased waveform amplitude and decreased waveform duration at the thoracic inlet. At 10 minutes after administration, detomidine increased waveform duration at the thoracic inlet. Acepromazine administration increased the number of spontaneous events at the thoracic inlet and distal portion of the esophagus. Acepromazine and detomidine administration increased the number of high-pressure events at the thoracic inlet. Guaifenesin administration increased the number of spontaneous events at the thoracic inlet. Xylazine-butorphanol, detomidine, acepromazine, and guaifenesin administration decreased the number of spontaneous swallows.
Conclusions and Clinical Relevance—Detomidine, acepromazine, and a combination of xylazine butorphanol had the greatest effect on esophageal motility when evaluated manometrically. Reduction in spontaneous swallowing and changes in normal, coordinated peristaltic activity are the most clinically relevant effects. (Am J Vet Res 2002;63:1738–1744)
Abstract
Objective—To compare plasma and synovial fluid endothelin-1 (ET-1) and nitric oxide (NO) concentrations in clinically normal horses and horses with joint disease.
Animals—36 horses with joint disease, and 15 horses without joint disease.
Procedure—Horses with joint disease were assigned to 1 of the 3 groups (ie, synovitis, degenerative joint disease [DJD], or joint sepsis groups) on the basis of findings on clinical and radiographic examination and synovial fluid analysis. Endothelin-1 and NO concentrations were measured in plasma from blood samples, collected from the jugular vein and ipsilateral cephalic or saphenous vein of the limb with an affected or unaffected joint, as well as in synovial fluid samples obtained via arthrocentesis from the involved joint.
Results—Plasma ET-1 concentrations between affected and unaffected groups were not significantly different. Median concentration and concentration range of ET-1 in synovial fluid obtained from the joint sepsis group (35.830 pg/mL, 7.926 to 86.614 pg/mL; n = 7) were significantly greater than values from the synovitis (17.531 pg/mL, 0.01 to 46.908 pg/mL; 18), DJD (22.858 pg/mL, 0.01 to 49.990 pg/mL; 10), and unaffected (10.547 pg/mL, 0.01 to 35.927 pg/mL; 10) groups. Plasma and synovial fluid NO concentrations between affected and unaffected groups were not significantly different.
Conclusions and Clinical Relevance—Endothelin-1 is locally synthesized in the joints of horses with various types of joint disease. Synovial fluid concentrations of ET-1 varied among horses with joint disease, with concentrations significantly higher in the synovial fluid of horses with joint sepsis. These results indicate that ET-1 may play a role in the pathophysiologic mechanism of joint disease in horses. (Am J Vet Res 2002;63:1648–1654)
