17 beta-estradiol prevents oxidative stress and decreases blood pressure in ovariectomized rats

In this study, we tested whether estrogen deficiency is associated with oxi dative stress and decreased nitric oxide (NO) production, which could be re sponsible for an increased blood pressure in ovariectomized rats. Hemodynam ic studies were performed on conscious, chronically instrumented rats. Chro nic estrogen replacement on ovariectomized rats lowered blood pressure simi lar to 13 mmHg, from 119 +/- 3 mmHg in ovariectomized rats to 106 +/- 3 mmH g in ovariectomized-treated rats; it was also accompanied by an increase in cardiac index and vascular conductance, achieving hemodynamic values simil ar to those shown by sham-operated rats. N-G-nitro-L-arginine methyl ester administration lowered significantly less the vascular conductance (0.14 +/ - 0.01 vs. 0.22 +/- 0.03 and 0.26 +/- 0.01 ml.min(-1).mmHg(-1)/100 g; P < 0 .05) in ovariectomized rats than in the sham-operated and estrogen-treated ovariectomized rats, respectively. Estrogen replacement prevented the lower plasma levels of nitrites/nitrates observed in ovariectomized rats. The lo wer plasma total antioxidant status and reduced thiol groups and the increa se in plasma lipoperoxides presented in ovariectomized animals were reestab lished with the estrogen treatment. These results show that estrogen admini stration decreases blood pressure and increases vascular conductance in ova riectomized rats. This effect may be related to an increase in NO synthesis and/or preventing oxidative stress, then improving endothelial function.