Lack of an appropriate animal model has delayed the better understanding of mechanisms related to higher cardiovascular risk in women after menopause. The aging female rat may share some menopausal changes observed in women. However, most studies have attempted to mimic menopause by ovariectomizing young (6-12 weeks old) animals without taking into accounts the influence of aging and of declining ovarian function. Therefore, the present study examined changes in vascular reactivity in the aging (15 months old) female rat after ovariectomy and the effects of chronic raloxifene therapy on vascular reactivity and eNOS protein expression. Aortic rings were prepared from the three experimental groups of rats: sham-operated control, ovariectomized and ovariectomized aging rats receiving daily oral administration of raloxifene for 3 months. Aortic rings were suspended in organ baths for the measurement of isometric tension. Rings with endothelium contracted significantly more to phenylephrine after inhibition of nitric oxide/cyclic GMP-signaling pathway by L-NAME or ODQ (as an index of basal nitric oxide release) in control and raloxifene-treated ovariectomized rats than in ovariectomized rats. This effect was abolished upon mechanical removal of the endothelium. Phenylephrine induced greater contractions only in rings with endothelium from ovariectomized rats as compared with control rats and raloxifene treatment normalized this response. In the presence of L-NAME or ODQ, phenylephrine-induced contraction was similar in rings from the three groups. Rings relaxed more to thapsigargin and acetylcholine in raloxifene-treated ovariectomized rats than in ovariectomized rats. There was no significant difference in aortic eNOS protein contents among the different groups. These results suggest that chronic oral administration of raloxifene to aging ovariectomized female rats augmented the bioavailability of endothelial nitric oxide in isolated aortic rings without altering eNOS protein levels.