title: Contracture test and histologic and histochemical analyses of muscle biopsy specimens from horses with exertional rhabdomyolysis.
abstract: Biopsy specimens of the cutaneous omobrachialis muscle were obtained from 10 horses with a problem of myositis from mild exercise. One horse had been evaluated previously and malignant hyperthermia-like contractures developed in its muscle biopsy specimen during the contracture test. In this study, the halothane-caffeine contracture test and histologic and histochemical evaluations were performed on muscle biopsy specimens. In the contracture test, no muscle biopsy specimen developed contracture in the presence of 2 or 4% halothane alone. The mean (+/- SEM) caffeine-specific concentration in the presence of halothane was 5.23 +/- 0.5 mM for 2% halothane, and 4.46 +/- 0.6 mM for 4% halothane. The caffeine-specific concentration values were not significantly different. Contracture response for any muscle specimen did not resemble contracture associated with malignant hyperthermia. The cutaneous omobrachialis muscle was composed of type-II fibers, with type-I fibers seldom seen. For 9 of the 10 horses, overall fiber morphology was normal; 1 horse had necrotic fibers. Of the 10 muscle specimens, 9 had fibers that had positive reaction for alkaline phosphatase activity; 3 muscle specimens contained ringed myofibers. Three horses of this study were administered general anesthesia; 2 were research horses, anesthetized with halothane and succinylcholine, and 1 was a clinical case given halothane anesthesia plus a non-depolarizing muscle relaxant. One research horse developed a malignant hyperthermia-like reaction to anesthesia, with severe rhabdomyolysis evident after anesthesia, and an episode of muscle cramping in its stall 2 days after anesthesia. The other 2 horses had unremarkable postanesthetic periods.
authors.affiliation: Department of Veterinary Surgery, School of Veterinary Medicine, University of California, Davis 95616.
authors.forename: S V
authors.initials: SV
authors.lastname: Hildebrand
authors.forename: D
authors.initials: D
authors.lastname: Arpin
authors.forename: G
authors.initials: G
authors.lastname: Cardinet
mesh_terms: D000758:Anesthesia / Q000662:veterinary; D000818:Animals; D001707:Biopsy, Needle / Q000662:veterinary; D002110:Caffeine; D003286:Contracture / Q000209:etiology / Q000662:veterinary*; D005260:Female; D005334:Fever / Q000150:complications / Q000662:veterinary; D006221:Halothane; D006734:Horse Diseases / Q000209:etiology* / Q000473:pathology; D006736:Horses; D008297:Male; D005082:Physical Exertion; D012206:Rhabdomyolysis / Q000209:etiology / Q000473:pathology / Q000662:veterinary*
chemical_list: D002110:Caffeine; D006221:Halothane