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To compare the extent of inflammation and catabolic collagen response in the middle carpal joints (MCJs) of healthy horses following intra-articular injection of 2% lidocaine, 2% mepivacaine, lactated Ringer solution (LRS), or 0.1% methyl parahydroxybenzoate.


17 adult horses.


In the first of 2 experiments, the left middle carpal joint (MCJ) of each of 12 horses was injected with 10 mL of 2% lidocaine (n = 3), 2% mepivacaine (3), or LRS (control; 6). After a 4-week washout period, the right MCJ of the horses that received lidocaine or mepivacaine was injected with 10 mL of LRS, and the right MCJ of horses that received LRS was injected with 10 mL of 2% lidocaine (n = 3) or 2% mepivacaine (3). In experiment 2, the left MCJ of each of 5 horses was injected with 10 mL of 0.1% methyl parahydroxybenzoate. After a 48-hour washout period, the right MCJ of each horse was injected with 10 mL of LRS. Synovial fluid (SF) samples were aseptically collected before and at predetermined times after each injection. Synovial fluid WBC count, neutrophil percentage, and total protein, neutrophil myeloperoxidase, neutrophil elastase, and Coll2-1 concentrations were compared among treatments.


Both lidocaine and mepivacaine induced SF changes indicative of inflammation and a catabolic collagen response, but the magnitude of those changes was more pronounced for lidocaine. Methyl parahydroxybenzoate did not cause any SF changes indicative of inflammation.


Results suggested that mepivacaine was safer than lidocaine for intra-articular injection in horses.

Full access
in American Journal of Veterinary Research


Objective—To compare measurements of myeloperoxidase (MPO) in plasma, laminar tissues, and skin obtained from control horses and horses given black walnut heartwood extract (BWHE).

Animals—22 healthy 5- to 15-year-old horses.

Procedures—Horses were randomly assigned to 4 groups as follows: a control group given water (n = 5) and 3 experimental groups given BWHE (17) via nasogastric intubation. Experimental groups consisted of 5, 6, and 6 horses that received BWHE and were euthanatized at 1.5, 3, and 12 hours after intubation, respectively. Control horses were euthanatized at 12 hours after intubation. Plasma samples were obtained hourly for all horses. Laminar tissue and skin from the middle region of the neck were harvested at the time of euthanasia. Plasma and tissue MPO concentrations were determined via an ELISA; tissue MPO activity was measured by use of specific immunologic extraction followed by enzymatic detection.

Results—Tissues and plasma of horses receiving BWHE contained significantly higher concentrations of MPO beginning at hour 3. Laminar tissue and skin from horses in experimental groups contained significantly higher MPO activity than tissues from control horses. Concentrations and activities of MPO in skin and laminar tissues were similar over time.

Conclusions and Clinical Relevance—In horses, BWHE administration causes increases in MPO concentration and activity in laminar tissue and skin and the time of increased MPO concentration correlates with emigration of WBCs from the vasculature. These findings support the hypothesis that activation of peripheral WBCs is an early step in the pathogenesis of acute laminitis.

Full access
in American Journal of Veterinary Research


Objective—To culture equine myoblasts from muscle microbiopsy specimens, examine myoblast production of reactive oxygen species (ROS) in conditions of anoxia followed by reoxygenation, and assess the effects of horseradish peroxidase (HRP) and myeloperoxidase (MPO) on ROS production.

Animals—5 healthy horses (5 to 15 years old).

Procedures—Equine skeletal myoblast cultures were derived from 1 or 2 microbiopsy specimens obtained from a triceps brachii muscle of each horse. Cultured myoblasts were exposed to conditions of anoxia followed by reoxygenation or to conditions of normoxia (control cells). Cell production of ROS in the presence or absence of HRP or MPO was assessed by use of a gas chromatography method, after which cells were treated with a 3,3′-diaminobenzidine chromogen solution to detect peroxidase binding.

Results—Equine skeletal myoblasts were successfully cultured from microbiopsy specimens. In response to anoxia and reoxygenation, ROS production of myoblasts increased by 71%, compared with that of control cells. When experiments were performed in the presence of HRP or MPO, ROS production in myoblasts exposed to anoxia and reoxygenation was increased by 228% and 183%, respectively, compared with findings for control cells. Chromogen reaction revealed a close adherence of peroxidases to cells, even after several washes.

Conclusions and Clinical Relevance—Results indicated that equine skeletal myoblast cultures can be generated from muscle microbiopsy specimens. Anoxia-reoxygenationtreated myoblasts produced ROS, and production was enhanced in the presence of peroxidases. This experimental model could be used to study the damaging effect of exercise on muscles in athletic horses.

Full access
in American Journal of Veterinary Research