title: Skeletal muscle mitochondrial myopathy as a cause of exercise intolerance in a horse.
abstract: 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.
authors.affiliation: Department of Anatomy, School of Veterinary Medicine, University of California, Davis.
authors.forename: S J
authors.initials: SJ
authors.lastname: Valberg
authors.forename: G P
authors.initials: GP
authors.lastname: Carlson
authors.forename: G H
authors.initials: GH
authors.lastname: Cardinet
authors.forename: E K
authors.initials: EK
authors.lastname: Birks
authors.forename: J H
authors.initials: JH
authors.lastname: Jones
authors.forename: A
authors.initials: A
authors.lastname: Chomyn
authors.forename: S
authors.initials: S
authors.lastname: DiMauro
mesh_terms: D000140:Acidosis, Lactic / Q000378:metabolism / Q000662:veterinary; D000818:Animals; D005260:Female; D006734:Horse Diseases / Q000097:blood / Q000201:enzymology / Q000473:pathology / Q000503:physiopathology*; D006736:Horses; D007773:Lactates / Q000097:blood; D019344:Lactic Acid; D017240:Mitochondrial Myopathies / Q000097:blood / Q000201:enzymology / Q000473:pathology / Q000503:physiopathology / Q000662:veterinary*; D010101:Oxygen Consumption; D010805:Physical Conditioning, Animal
chemical_list: D007773:Lactates; D019344:Lactic Acid