Expression of endothelin in equine laminitis

Biosynthesis of endothelin-1 (ET-1), the most potent endogenous vasoconstri ctor yet identified, is increased following myocardial infarction (MI) in m an. Pathological events which occur in the connective tissues of the equine hoof during laminitis are similar in some respects, to changes occurring i n the myocardial connective tissues following MI in man. The objective of t his study was to determine whether ET-1 expression in connective tissues ob tained from the hoof of laminitic horses is increased compared with tissues obtained from healthy horses. Expression of ET-1 in connective tissues of the equine hoof was measured following tissue extraction from 3 groups of h orses: horses in which acute laminitis had been induced by the administrati on of starch; chronically foundered horses; nonlaminitic horses. The concen tration of ET-1 in laminar connective tissues obtained from all laminitic h orses (1573.0 +/- 392.8 pg/g of tissue; n = 10) was increased when compared with tissues obtained from nonlaminitic horses (392.5 +/- 117.4 pg/g of ti ssue; n = 5) (P < 0.05). The concentration of ET-1 in laminar connective ti ssues obtained from the experimentally induced, acute laminitic horses (104 3.6 +/- 254.4 pg/g of tissue; n = 7) and from the spontaneously affected, c hronic laminitic horses (2808.3 +/- 878.6 pg/g of tissue; n = 3) was increa sed compared with the control group (P < 0.05, P < 0.01, respectively). The concentration of ET-1 in laminar connective tissues obtained from the chro nic laminitic horses was greater than that of the experimentally induced, a cute laminitic group (P < 0.05). It is suggested that the data provide a st rong argument that increased ET-1 expression in the connective tissues of t he equine hoof represent a potentially important and hitherto unrecognised component of the pathophysiology of equine laminitis, Further studies are n eeded to determine whether inhibitors of ET-1 converting enzyme or antagoni sts of ET-1 receptors might be useful in the treatment and prevention of la minitis in horses.