Date of Award

1992

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Veterinary Physiology, Pharmacology, and Toxicology (Veterinary Medical Sciences)

First Advisor

Charles R. Short

Second Advisor

Steven A. Barker

Abstract

A profound decrease in perfusion of the laminar capillaries has been documented during acute equine laminitis, resulting in ischemia of the laminar tissue. Oxygen radicals are believed to mediate ischemia/reperfusion injury. The effects of (1) three hours of surgical ligation of the major blood supply of the equine digit followed by ligature release, (2) resection of the medial and lateral palmar digital arteries, and (3) digital intraarterial infusions of an oxygen radical generating system, were investigated. Laminitis was not induced by any of these manipulations. Clinical signs and alterations in hemograms observed following these procedures are reported. Preliminary identification of xanthine oxidase and superoxide dismutase activities in laminar tissue is described. Due to similarities in physiologic alterations and histopathologic lesions, laminitis has been described as the manifestation of a Shwartzman reaction. The effects of palmar digital intraarterial infusions of E. coli endotoxin followed in 24 hours by jugular vein infusion of the same endotoxin were investigated. Clinical signs and alterations in hemograms were consistent with the known effects of endotoxin in the horse. Laminitis did not develop. Exposure to black walnut (Juglans nigra) trees or shavings has been associated with the development of laminitis in the horse. Experimentally, laminitis may be consistently induced by the intragastric administration of an aqueous extract of black walnut heartwood. The laminogenic agent in black walnut has not been reported. In the present study the partial characterization of black walnut heartwood extracts was accomplished by gas chromatographic/mass spectrometric methods. Subsequently, identified components of the extracts were individually administered to horses, as were various crude fractions obtained from pH fractionations and precipitations of black walnut heartwood extracts. The clinical effects and laminogenic potentials of each is reported.

Pages

178

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