Skeletal muscle mitochondrial myopathy as a cause of exercise intolerance in a horse.
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.
Valberg
S J
SJ
Department of Anatomy, School of Veterinary Medicine, University of California, Davis.
Carlson
G P
GP
Cardinet
G H
GH
Birks
E K
EK
Jones
J H
JH
Chomyn
A
A
DiMauro
S
S
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
D007773:Lactates; D019344:Lactic Acid