In the present study, we evaluated the relationship between the antihypertensive effect of sesamin, a lignan from sesame oil, and its antioxidative activity in deoxycorticosterone acetate (DOCA)-salt hypertensive rats. After a 5-week treatment period, systolic blood pressure was significantly elevated in normal diet-fed DOCA-salt animals compared with cases in sham-operated animals. Sesamin feeding, tempol (a superoxide dismutase mimetic) treatment or antihypertensive drugs combination (triple therapy; reserpine, hydralazine, hydrochlorothiazide) significantly suppressed the development of DOCA-salt-induced hypertension. Compared with sham-operated rats, the normal diet-fed DOCA-salt rats revealed marked increases in aortic superoxide (O(2)(-)) production. These increases in O(2)(-) production were significantly suppressed by sesamin feeding or tempol treatment, but not by triple therapy. Acetylcholine (Ach)-induced endothelium-dependent relaxation was markedly decreased in normal diet-fed DOCA-salt rats, compared with cases in sham-operated rats. Sesamin feeding and triple therapy significantly improved the DOCA-salt-induced impairment of endothelium-dependent relaxation. However, tempol treatment had no effect on the impaired vasodilator responses induced by DOCA-salt treatment. In DOCA-salt rats with or without sesamin feeding, systolic blood pressure significantly correlated with both aortic O(2)(-) production and endothelium-dependent vascular relaxation. These findings suggest that sesamin feeding inhibits the enhancement of aortic O(2)(-) production in DOCA-salt hypertensive rats, and this effect may contribute to the antihypertensive effect of sesamin. Sesamin feeding-induced improvement of endothelial dysfunction seems to result from the above antioxidative and antihypertensive effects.