The effect of cooling on the contractility of equine digital small lamellar arteries: modulating role of the endothelium.

The equine hoof displays thermoregulatory functions, and the blood vessels lying under the hoof wall are temperature sensitive. The aim of this study was to investigate the effect of cooling on the contractile responses to α-adrenoceptor and 5-HT receptor stimulation in equine small lamellar arteries using wire myography. The role of the endothelium in the response mediated by 5-HT was also evaluated.

Functional role of alpha2-adrenoceptor subtypes in the cooling-enhanced vasoconstriction of isolated cutaneous digital veins of the horse.

Cooling-enhanced contractile responses in cutaneous arteries have been reported to involve the activation of alpha(2C)-adrenoceptors, but their role in cutaneous veins is not clearly understood. The aim was to pharmacologically characterize the subtype of postsynaptic alpha(2)-adrenoceptors in the equine digital vein mediating contraction at two temperatures. The increase in isometric tension of endothelium-denuded equine digital vein in response to UK-14304 was studied in the absence and presence of relatively selective alpha(2)-adrenoceptor antagonists at temperatures of either 30 degrees C (the peripheral digit temperature of horses maintained in a thermoneutral environment) or 22 degrees C.

Evaluation of the induction of vasoactive mediators from equine digital vein endothelial cells by endotoxin.

Objective: To determine the effect of endotoxin (lipopolysaccharide [LPS]) on vasoactive mediator production by cultured equine digital vein endothelial cells (EDVECs).

Sample Population: EDVECs obtained from forelimb digital veins of 7 healthy adult horses.

Procedures: EDVECs were incubated with or without LPS (1 microg/mL) for 0, 2, 4, 6, 22, and 24 hours.

Effect of dietary fructans and dexamethasone administration on the insulin response of ponies predisposed to laminitis.

Objective: To determine whether pasture, and specifically the addition of fructan carbohydrate to the diet, induces exaggerated changes in serum insulin concentration in laminitispredisposed (LP) ponies, compared with ponies with no history of the condition, and also to determine insulin responses to the dexamethasone suppression test.

Design: Prospective study.

Animals: 10 LP and 11 control adult nonobese mixed-breed ponies.

Cooling augments vasoconstriction mediated by 5-HT1 and alpha2-adrenoceptors in the isolated equine digital vein: involvement of Rho kinase.

The vasculature of the equine digit fulfils an important role in thermoregulation. In other species, it has been found that cooling may enhance the response of cutaneous vessels to 5-hydroxytryptamine (5-HT) and alpha(2)-adrenoceptor agonists. Translocation of alpha(2)-adrenoceptors to the smooth muscle cell membrane, mediated by Rho kinase, is thought to be involved in the cooling-enhanced response in mouse tail arteries.

Seasonal changes in plasma concentrations of cecum-derived amines in clinically normal ponies and ponies predisposed to laminitis.

Objective: To measure concentrations of amines formed in the cecum of clinically normal ponies, determine amine concentrations in plasma samples collected in spring and winter, and compare concentrations of amines and serotonin in plasma samples obtained from clinically normal ponies and ponies predisposed to laminitis.

Sample Population: Cecal contents obtained from 10 ponies euthanatized at an abattoir and blood samples obtained from 42 adult ponies.

Procedure: Cecal contents were assayed for amines by high-performance liquid chromatography (HPLC).

Effects of monoamines formed in the cecum of horses on equine digital blood vessels and platelets.

Objective: To determine in vitro vasoactive potency of monoamines formed in the cecum and found in the systemic circulation of horses.

Sample Population: Segments of digital blood vessels obtained from 6 healthy mixed-breed horses and ponies euthanatized at an abattoir and platelets isolated from 4 healthy ponies.

Procedure: Paired rings of digital artery and vein from the same horse were examined, and isometric tension was recorded.