Skeletal muscle mitochondrial myopathy as a cause of exercise intolerance in a horse

Stephanie J. Valberg, Gary P. Carlson, George H. Cardinet, Eric K. Birks, James H. Jones, Anne Chomyn, Salvatore DiMauro

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Although exertional myopathies are commonly recognized in horses, specific etiologies have not been identified. This is the first report in the horse of a deficiency of Complex I respiratory chain enzyme associated with profound exercise intolerance. Physical examination, routine blood tests, endoscopy, and ultrasonograms of the heart and iliac arteries were unremarkable. With slow, incremental exercise (speeds 1.5–7 m/s), the Arabian mare showed a marked lactic acidosis, increased mixed venous PVO2, and little change in oxygen consumption. Muscle biopsies contained large accumulations of mitochondria with bizarre cristae formations. Biochemical analyses revealed a very low activity of the first enzyme complex in the mitochondrial respiratory chain (NADH CoQ reductase). The exercise intolerance and muscle stiffness in this horse were attributed to a profound lactic acidosis resulting from impaired oxidative energy metabolism during exercise. © 1994 John Wiley & Sons, Inc.

Original languageEnglish (US)
Pages (from-to)305-312
Number of pages8
JournalMuscle & Nerve
Issue number3
StatePublished - Mar 1994


  • Complex I
  • horse
  • mitochondria
  • muscle
  • myopathy


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