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Objective--To investigate the effects of acute exercise and long-term training on Na+,K+-ATPase content, mRNA isoforms, and protein concentration in equine muscle. Animals--6 Standardbreds. Procedures--Horses performed a bout of exercise on a treadmill before and after 18 weeks of combined interval and endurance training. Muscle biopsy specimens were obtained from vastus lateralis muscle (VLM) and pectoralis descendens muscle (PDM) before and after exercise. The NaNa+,K+-ATPase content, mRNA isoforms, and protein concentrations were determined by use of [³H]ouabain binding, real-time PCR assay, and western blotting, respectively. Results--6 NaNa+,K+-ATPase mRNA isoforms were present in equine muscle, but only α2 and β1 proteins were detected. Exercise before training resulted in increases of mRNA isoforms α1, α2, β3, and β2 inVLM and α1 and β3 in PDM. Training increased resting values for mRNA isoforms α3 and β1 inVLM and β3 in PDM.The NaNa+,K+-ATPase, [³H]ouabain binding, and proteins of mRNA α2 and β1 increased in VLM, whereas in PDM, only α2 protein increased as a result of training. After training, effects of strenuous exercise on mRNA expression were no longer detectable. Conclusions and Clinical Relevance--Equine muscle contained all NaNa+,K+--ATPase mRNA isoforms, but only α2 and β1 proteins could be detected. Expression of these isoforms changed as a result of strenuous exercise and long-term training, representing an adaptive response. Determination of NaNa+,K+---ATPase gene expression may be relevant for understanding alterations in excitability during neuromuscular diseases. [ABSTRACT FROM AUTHOR]

Objective--To determine the effects of short-term IV administration of hydrocortisone or equine growth hormone (eGH) or long-term IM administration of eGH to horses on tissue sensitivity to exogenous insulin. Animals--5 Standardbreds and 4 Dutch Warmblood horses. Procedure--The euglycemic-hyperinsulinemic clamp technique was used to examine sensitivity of peripheral tissues to exogenous insulin 24 hours after administration of a single dose of hydrocortisone (0.06 mg/kg), eGH (20 µg/kg), or saline (0.9% NaCl) solution and after long-term administration (11 to 15 days) of eGH to horses. The amounts of metabolized glucose (M) and plasma insulin concentration (I) were determined. Results--Values for M and the M-to-I ratio were significantly higher 24 hours after administration of a single dose of hydrocortisone than after single-dose administration of eGH or saline solution. After long-term administration of eGH, basal I concentration was increased and the mean M-to-I ratio was 22% lower, compared with values for horses treated with saline solution. Conclusions and Clinical Relevance--Increases in M and the M-to-I ratio after a single dose of hydrocortisone imply that short-term hydrocortisone treatment increases glucose use by, and insulin sensitivity of, peripheral tissues. Assuming a single dose of hydrocortisone improves sensitivity of peripheral tissues to insulin, it may be an interesting candidate for use in reducing insulin resistance in peripheral tissues of horses with several disease states. In contrast, long-term administration of eGH decreased tissue sensitivity to exogenous insulin associated with hyperinsulinemia. Therefore, increased concentrations of growth hormone may contribute to insulin resistance in horses with various disease states. [ABSTRACT FROM AUTHOR]

Gross morphology of healthy and degenerated intervertebral discs (IVDs) is largely similar in horses as in dogs and humans. For further comparison, the biochemical composition and the histological and biochemical changes with age and degeneration were analyzed in 41 warmblood horses. From 33 horses, 139 discs and 2 fetal vertebral columns were evaluated and scored histologically. From 13 horses, 73 IVDs were assessed for hydration, DNA, glycosaminoglycans, total collagen, hydroxyl-lysyl-pyridinoline, hydroxylysine, and advanced glycation end-product (AGE) content. From 7 horses, 20 discs were assessed for aggrecan, fibronectin, and collagen type 1 and 2 content. Histologically, tearing of the nucleus pulposus (NP) and cervical annulus fibrosus (AF), and total histological score (tearing and vascular proliferation of the AF, and chondroid metaplasia, chondrocyte-like cell proliferation, presence of notochordal cells, matrix staining, and tearing of the NP) correlated with gross degeneration. Notochordal cells were not seen in IVDs of horses. Age and gross degeneration were positively correlated with AGEs and a fibrotic phenotype, explaining gross degenerative changes. In contrast to dogs and humans, there was no consistent difference in glycosaminoglycan content and hydration between AF and NP, nor decrease of these variables with age or degeneration. Hydroxylysine decrease and collagen 1 and AGEs increase were most prominent in the NP, suggesting degeneration started in the AP. In caudal cervical NPs, AGE deposition was significantly increased in grossly normal IVDs and total collagen significantly increased with age, suggesting increased biomechanical stress and likelihood for spinal disease in this part of the vertebral column.

A 6-year-old Friesian stallion was examined because of signs of exercise intolerance, stiff gait and symmetrical hind weakness, and increased serum liver enzymes. On presentation, the horse showed muscle atrophy of the hindquarters. Neurological investigation showed no abnormalities. Laboratory findings revealed a prolonged prothrombin time and increased levels of alkaline phosphatase (AF), aspartate aminotransferase (ASAT), gamma-glutamyl-transferase (GGT), lactate dehydrogenase (LDH), and bile acids. Histological evaluation of the liver revealed severe cirrhosis and intracytoplasmic greyish brown granules in almost all hepatocytes, sinusoidal Kuppfer cells, and macrophages. These granules stained strongly for copper. Treatment to slow hepatic fibrosis was advised and included oral prednisolone administration for at least 1 month. A diet to support liver function was formulated by a nutritional specialist, and vitamin E was advised as dietary supplement to support neuromuscular function. Soon after diagnosis, the animal showed signs of intravascular haemolysis, with the presence of Heinz bodies in peripheral blood smears, and haemoglobinuria. On the basis of this haemolytic crisis and the poor prognosis of the chronic hepatic disease, the horse was euthanized at the owners' request. Although we could not establish the cause of the hepatic copper accumulation, this case report highlights that excessive copper in the liver should be considered in the differential diagnosis of hepatic cirrhosis and Heinz body anaemia in the horse.

Objective: To evaluate the application of analysis of motor unit action potentials (MUAP) in horses and to obtain values of MUAP for the subclavian muscle of horses., Animals: 10 healthy adult Dutch Warmblood horses., Procedure: Electromyographic examination of the subclavian muscle in conscious nonsedated horses was performed to evaluate insertional activity, spontaneous activity, MUAP variables, and recruitment patterns. Muscle and body temperatures were measured at the beginning and end of the procedure. Amplitude, duration, number of phases, and number of changes in direction (ie, turns) for all representative MUAP were analyzed to determine values for this muscle in this group of horses., Results: Mean +/- SD duration of insertional activity was 471.7 +/- 33.45 milliseconds. Mean MUAP amplitude in the examined horses was 379 RV (95% confidence interval [CI], 349 to 410 microV). Mean MUAP duration of the subclavian muscle was 727 milliseconds (95% CI, 6.84 to 7.71 milliseconds). Mean number of phases was 2.9, and mean number of turns was 3.0. Prevalence of polyphasic MUAP defined as MUAP with > 4 phases, was 77%. Number of MUAP that had > 5 turns was 2.4%. Satellite potentials were found in 1.0% of the MUAP CONCLUSIONS AND CLINICAL RELEVANCE: This study revealed that electromyography including MUAP analysis can be performed in horses, and values for the subclavian muscle in healthy adult horses can be obtained. Analysis of MUAP could be a valuable diagnostic tool for use in discriminating between myogenic and neurogenic problems in horses.