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  • Author or Editor: Cyril R. Clarke x
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Abstract

Objective—To use force plate analysis to evaluate the analgesic efficacies of flunixin meglumine and phenylbutazone administered IV at typical clinical doses in horses with navicular syndrome.

Animals—12 horses with navicular syndrome that were otherwise clinically normal.

Procedure—Horses received flunixin (1.1 mg/kg), phenylbutazone (4.4 mg/kg), or physiologic saline (0.9% NaCl; 1 mL/45 kg) solution administered IV once daily for 4 days with a 14-day washout period between treatments (3 treatments/horse). Before beginning treatment (baseline) and 6, 12, 24, and 30 hours after the fourth dose of each treatment, horses were evaluated by use of the American Association of Equine Practitioners lameness scoring system (half scores permitted) and peak vertical force of the forelimbs was measured via a force plate.

Results—At 6, 12, and 24 hours after the fourth treatment, subjective lameness evaluations and force plate data indicated significant improvement in lameness from baseline values in horses treated with flunixin or phenylbutazone, compared with control horses; at those time points, the assessed variables in flunixin- or phenylbutazone-treated horses were not significantly different.

Conclusions and Clinical Relevance—In horses with navicular syndrome treated once daily for 4 days, typical clinical doses of flunixin and phenylbutazone resulted in similar significant improvement in lameness at 6, 12, and 24 hours after the final dose, compared with findings in horses treated with saline solution. The effect of flunixin or phenylbutazone was maintained for at least 24 hours. Flunixin meglumine and phenylbutazone appear to have similar analgesic effects in horses with navicular syndrome. (Am J Vet Res 2005;66:284–288)

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in American Journal of Veterinary Research

Abstract

Objective—To determine the pharmacokinetics of acetazolamide administered IV and orally to horses.

Animals—6 clinically normal adult horses.

Procedure—Horses received 2 doses of acetazolamide (4 mg/kg of body weight, IV; 8 mg/kg, PO), and blood samples were collected at regular intervals before and after administration. Samples were assayed for acetazolamide concentration by high-performance liquid chromatography, and concentrationtime data were analyzed.

Results—After IV administration of acetazolamide, data analysis revealed a median mean residence time of 1.71 ± 0.90 hours and median total body clearance of 263 ± 38 ml/kg/h. Median steady-state volume of distribution was 433 ± 218 ml/kg. After oral administration, mean peak plasma concentration was 1.90 ± 1.09 µg/ml. Mean time to peak plasma concentration was 1.61 ± 1.24 hours. Median oral bioavailability was 25 ± 6%.

Conclusions and Clinical Relevance—Oral pharmacokinetic disposition of acetazolamide in horses was characterized by rapid absorption, low bioavailability, and slower elimination than observed initially after IV administration. Pharmacokinetic data generated by this study should facilitate estimation of appropriate dosages for acetazolamide use in horses with hyperkalemic periodic paralysis. (Am J Vet Res 2000;61:965–968)

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in American Journal of Veterinary Research

Abstract

Objective—To develop and validate an ex vivo model for study of adherence of Mannheimia haemolytica (formerly Pasteurella haemolytica) to respiratory tract mucosa of cattle and to use this model to confirm adherence of M haemolytica serovar 1 (Mh1) to several relevant respiratory mucosal surfaces.

Sample Population—Excised nasal, nasopharyngeal, turbinate, and tonsillar mucosal tissue from the bovine upper respiratory tract.

Procedure—Mh1 was radiolabeled by use of tritiated leucine. Various concentrations of labeled bacteria were incubated with bovine upper respiratory tract tissues for various times. Tissue was washed to remove nonadherent bacteria, and percentage of bacteria adhered (percentage of adherence) was estimated using radioactivity. Using an optimal inoculum concentration and incubation time, percentage of Mh1 adherence was compared on nasal, nasopharyngeal, turbinate, and tonsillar mucosal tissue, and adherence to nasopharyngeal tissue was confirmed by scanning and transmission electron microscopy.

Results—The optimal Mh1 inoculum concentration was 1 × 107 colony forming units/ml and incubation time was 3 hours. Percentage of adherence of Mh1 to nasopharyngeal tissue was greater than adherence to other tissue types.

Conclusions and Clinical Relevance—The ex vivo model maintained the functional and structural integrity of bovine upper respiratory tract mucosa, as confirmed by light and electron microscopy. Electron microscopy revealed participation of epithelial cell cilia and surface mucus in adherence of Mh1 to nasopharyngeal tissue. Adherence of Mh1 was confirmed in repeated assays, indicating that this organism adheres to upper respiratory tract mucosa of cattle. (Am J Vet Res 2001;62:805–811)

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in American Journal of Veterinary Research

Abstract

Objective—To investigate the concentration-dependent effects of Mannheimia haemolytica (formerly Pasteurella haemolytica) leukotoxin (LKT) on apoptosis and oncosis in bovine neutrophils and to examine the role of calcium ions (Ca2+) in LKT-induced apoptosis.

Sample Population—Neutrophils isolated from blood samples obtained from healthy calves.

Procedure—Neutrophil suspensions were exposed to lytic or sublytic dilutions of LKT and then examined by use of transmission electron microscopy (TEM) or gel electrophoresis. Contribution of extracellular Ca2+ to LKT-induced apoptosis was investigated by incubating neutrophils with LKT or control solutions in buffer containing 1 mM CaCl2 or in Ca2+-free buffer containing 1 mM ethylene glycol-bis (b-aminoethyl ether)- N,N-tetraacetic acid (EGTA) prior to diphenyl amine analysis.

Results—Examination by TEM revealed that bovine neutrophils exposed to lytic dilutions of LKT had changes consistent with oncosis, whereas neutrophils exposed to sublytic dilutions of LKT and staurosporin, an inducer of apoptosis, had changes consistent with apoptosis. Effects of sublytic dilutions of LKT on apoptosis were confirmed by gel electrophoresis. Replacement of extracellular Ca2+ with EGTA, a Ca2+ chelator, reduced apoptosis attributable to the calcium ionophore A23187, but it did not have significant effects on apoptosis induced by LKT or staurosporin.

Conclusions and Clinical Relevance—The ability of LKT to cause apoptosis instead of oncosis is concentration- dependent, suggesting that both processes of cell death contribute to an ineffective host-defense response, depending on the LKT concentration in pneumonic lesions. Furthermore, although Ca2+ promotes A23187-induced apoptosis, it is apparently not an essential second messenger for LKT-induced apoptosis. ( Am J Vet Res 2001;62:136–141)

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in American Journal of Veterinary Research

Abstract

Objective—To characterize ultrastructural changes of bovine lymphocytes exposed to Pasteurella haemolytica leukotoxin (LKT).

Sample Population—Partially purified LKT from a wild type P haemolytica A1 strain and inactive pro-LKT from an isogeneic mutant P haemolytica strain. Isolated bovine lymphocytes were obtained from 2 healthy calves.

Procedure—Isolated bovine lymphocytes were incubated with various concentrations of LKT and pro-LKT for 3 hours at 37 C and examined by use of transmission electron microscopy. A cytochemical Klenow DNA fragmentation assay was used to examine lymphocytes for DNA fragmentation.

Results—Lymphocytes incubated with LKT at a high concentration (1.0 toxic U/ml) had ultrastructural evidence of cytoplasmic and nuclear membrane rupture and swelling or lysis of mitochondria. Low concentrations of leukotoxin (0.1 toxic U/ml) induced DNA fragmentation in 80% of lymphocytes. Ultrastructurally, these cells had nuclear membrane blebbing, cytoplasmic vaculation, chromatin condensation, nuclear fragmentation, and membrane-bound apoptotic bodies. Incubation of lymphocytes with LKT at extremely low concentrations (0.001 toxic U/ml) or with pro-LKT did not alter their ultrastructure. Inclusion of 0.5 mM ZnCl2 in the medium blocked leukotoxin-induced ultrastructural changes in bovine lymphocytes.

Conclusions and Clinical Relevance—Low concentrations of LKT induce apoptosis and high concentrations induce oncotic cell lysis in bovine lymphocytes. The ability of low LKT concentrations to induce apoptosis in host leukocytes may allow bacteria to escape host immune surveillance and colonize the host. (Am J Vet Res 2000;61:51–56)

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in American Journal of Veterinary Research