The Role of Vascular Mechanisms in the Development of Acute Equine Laminitis

Abstract

ACUTE LAMINITIS has long been attributed to factors or events that precede the onset of laminitis. Between 1759 and 1907 the overconsumption of grain, inflammation of the feet, suppression of perspiration (anhydrosis), excessive rest, excessive bleeding, road concussion, poor shoeing, unilateral weight bearing, sudden environmental temperature changes, prolonged standing (in the cold and aboard ships), diarrhea, and postpartum complicat i o n~' -~ were all designated as causes. Today, commonly listed etiologic factors include ingestion of large amounts of grain, cold water, lush grass, or black walnut shavings, repeated concussion, endometritis or other severe infections, colic, exhaustion, stress, drug toxicities, and endocrine dysfunctions.8-'2 At Texas A&M University (Table 1) the factors recorded as the cause presume a causal relationship between some preceding event and the acute laminitis. Logically, any event that precedes laminitis might be a cause, but etiologic validity depends on the definition of "cause" and the role that coincidence might have in the appearance of the disease.The many "causes" of laminitis have led to the belief that laminitis is a complex disorder brought about by several interacting factors. The current understanding of the pathophysiology of laminitis does not explain how these diverse factors predispose the horse to laminitis. The diagnosis of acute laminitis is based on clinical signs. Because all horses develop similar clinical signs regardless of the cause of laminitis, a common pathophysiologic mechanism is believed to be responsible.Currently, metabolic abnormalities and endotoxemia are proposed as etiologies of acute laminitis. The meta- bolic hyp~thesis'~-'~ proposes that laminitis results from derangement of metabolic processes, resulting in structural failure of laminar epithelium. The restriction of histopathologic changes to the epidermal layers and the reduced incorporation of methionine into laminar epithelium of horses with acute laminitis is consistent with decreased keratin metab01isrn.I~ In this hypothesis inflammation, mechanical collapse of the digit and vascular pathologies occur as secondary events.

Identification of Equine Cecal Bacteria Producing Amines in an In Vitro Model of Carbohydrate Overload

“…Serotonin is a particularly potent vasoconstrictor of equine digital arteries and veins (4, 6). Although not universally accepted, digital lamellar ischemia followed by reperfusion injury is thought to be the sequence of events leading to acute equine laminitis (22,23).…”

“…Serotonin is a particularly potent vasoconstrictor of equine digital arteries and veins (4, 6). Although not universally accepted, digital lamellar ischemia followed by reperfusion injury is thought to be the sequence of events leading to acute equine laminitis (22,23).Virginiamycin, a streptogramin antibiotic, has been used to prevent starch overload-induced laminitis, by preventing the overgrowth of gram-positive bacteria which ferment carbohydrate and produce lactic acid (40). It is not known whether it is the inhibition of lactate production per se and/or inhibition…”

Effect of Dietary Nonstructural Carbohydrate Content on Activation of 5′‐Adenosine Monophosphate‐Activated Protein Kinase in Liver, Skeletal Muscle, and Digital Laminae of Lean and Obese Ponies

“…Vascular events also have been suggested to be involved in the pathogenesis of laminitis,27 with hypoperfusion and subsequent energy deprivation and hypoxia proposed as important contributors to dermo‐epidermal separation 28, 29. Although systemic hypertension has been reported in IR ponies at risk for pasture‐associated laminitis,30 the role that insulin and IR play in the vasculature of the equine digit and laminar perfusion is poorly described.…”

Avaliação anatômica e radiográfica da região distal dos membros torácicos de asininos (Equus asinus) utilizados como veículo de tração animal

“…Contudo, em pesquisas realizadas por Goetz (1989); Green et al (1991); Hood et al (1993) e Hunt, Kobluk e Steckel (1995, acrescenta-se ainda uma isquemia das laminas regionais, atribuindo-se a denominação de laminite a um complexo de doenças causadoras destas alterações.…”