Estrogen or the AT1 Antagonist Olmesartan Reverses the Development of Profound Hypertension in the Congenic mRen2.Lewis Rat

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Abstract
The influence of estrogen on the regulation of cardiovascular function remains a controversial and complex area of investigation. We assessed the effects of estrogen depletion in the congenic mRen(2).Lewis rat, established from the back-cross of the original (mRen2)-27 transgenic onto the Lewis inbred strain. Ovariectomy of heterozygous mRen(2).Lewis at 4 to 5 weeks resulted in a progressive increase in blood pressure compared with the sham surgery congenics at weeks 6 to 11. At 11 weeks, the ovariectomized mRen(2).Lewis (OVX) systolic blood pressure averaged 195±3.7 mm Hg versus 141±4.0 mm Hg for sham. Plasma Angiotensin (Ang) II, serum ACE activity, plasma renin concentration, as well as urinary excretion of Ang II, 8-isoprostane F 2α , and endothelin-1 were elevated; however, renal mRNA levels of eNOS were suppressed after ovariectomy. Estrogen replacement reduced blood pressure below both the sham and OVX by 11 weeks (125±2.9 mm Hg, n=7, P 1 receptor antagonist olmesartan (CS866; week 12 to 16) essentially normalized blood pressure to 113±5.4 mm Hg (n=6, P <0.01 versus OVX and sham). The attenuation of the hypertension was still evident 7 weeks after complete withdrawal of treatment (124±4.1 mm Hg at week 23). In summary, the OVX mRen.2.Lewis exhibited a rapid and sustained increase in blood pressure. Estrogen or olmesartan lowered pressure by a similar extent. We conclude that the ovary exerts considerable influence on the regulation of the blood pressure in the mRen2.Lewis strain, possibly by limiting activation of the renin-angiotensin system.