Effect of age on rabbit aortic responses to relaxant endothelium-dependent and endothelium-independent agents.

The aim of this study was to evaluate the effects of aging on endothelium-dependent and endothelium-independent relaxation of rabbit thoracic aorta from New Zealand white rabbits aged 4-6 and 7-12 months. The contractile response to noradrenaline (NA) decreased with increasing age, but NA [EC50] did not vary significantly. Acetylcholine (Ach)-induced relaxation of aortic rings precontracted with NA [EC50] did not change significantly with increasing age. The relaxation induced by ATP of aortic rings, precontracted with NA [EC50], was significantly greater in young than in adult rabbits. This difference between young and adult animals became more evident in aortic rings deprived of endothelium: in adult animals, the ATP-induced relaxation of aortic rings with endothelium was significantly greater than in the rings without endothelium. The endothelium-independent relaxation by sodium nitrite (NaNO2) at lower concentrations was significantly greater in young than in adult rabbit aortic rings precontracted with NA [EC50]. Concluding, the age-induced changes in vascular response in male New Zealand white rabbits are related to an impaired mechanism at smooth muscle level.