Vascular dysfunction in horses with endocrinopathic laminitis

Endocrinopathic laminitis (EL) is a vascular condition of the equine hoof resulting in severelameness with both welfare and economic implications. EL occurs in association withequine metabolic syndrome and equine Cushing’s disease. Vascular dysfunction, mostcommonly due to endothelial dysfunction, is associated with cardiovascular risk in peoplewith metabolic syndrome and Cushing’s syndrome. We tested the hypothesis that horseswith EL have vascular, specifically endothelial, dysfunction. Healthy horses (n = 6) andhorses with EL (n = 6) destined for euthanasia were recruited. We studied vessels from thehooves (laminar artery, laminar vein) and the facial skin (facial skin arteries) by small vesselwire myography. The response to vasoconstrictors phenylephrine (10−9–10-5M) and 5-hydroxytryptamine (5HT; 10−9–10-5M) and the vasodilator acetylcholine (10−9–10-5M) wasdetermined. In comparison with healthy controls, acetylcholine-induced relaxation was dramatically reduced in all intact vessels from horses with EL (% relaxation of healthy laminararteries 323.5 ± 94.1% v EL 90.8 ± 4.4%, P = 0.01, laminar veins 129.4 ± 14.8% v EL 71.2 ±4.1%, P = 0.005 and facial skin arteries 182.0 ± 40.7% v EL 91.4 ± 4.5%, P = 0.01). In addition, contractile responses to phenylephrine and 5HT were increased in intact laminar veinsfrom horses with EL compared with healthy horses; these differences were endotheliumindependent. Sensitivity to phenylephrine was reduced in intact laminar arteries (P = 0.006)and veins (P = 0.009) from horses with EL. Horses with EL exhibit significant vascular dysfunction in laminar vessels and in facial skin arteries. The systemic nature of the abnormalities suggest this dysfunction is associated with the underlying endocrinopathy and not localchanges to the hoof