The effect of tumour necrosis factor-α and insulin on equine digital blood vessel function in vitro.

OBJECTIVE AND DESIGN: Insulin and inflammatory cytokines may be involved in equine laminitis, which might be associated with digital vascular dysfunction. This study determined the effects of TNF-α and insulin on the endothelial-dependent relaxant responses of equine digital blood vessels and on equine digital vein endothelial cell (EDVEC) cGMP production. MATERIAL: Isolated rings of equine digital arteries (EDAs) and veins (EDVs) were obtained and EDVECs were cultured from horses euthanized at an abattoir. METHODS: The effect of incubation with TNF-α (10 ng/ml) and/or insulin (1,000 µIU/ml) for 1.5 h or overnight under hyperoxic and hypoxic conditions on carbachol (endothelium-dependent) induced relaxation was assessed. The time course and concentration dependency of the effect of TNF-α and the effect of insulin (1,000 µIU/ml) on EDVEC cGMP production was determined. RESULTS: Incubation of EDAs overnight with TNF-α under hypoxic conditions resulted in endothelial-dependent vascular dysfunction. EDVs produced a more variable response. TNF-α increased EDVEC cGMP formation in a time- and concentration-dependent manner. Insulin had no significant effects. CONCLUSIONS: There is a mismatch between the results obtained from isolated vessel rings and cultured endothelial cells suggesting TNF-α may reduce the biological effect of NO by reducing its bioavailability rather than its formation, leading to endothelial cell dysregulation.