The protective mechanism of estrogen on high blood pressure.

In 2 series of experiments on 144 SHRSP, the influence of treatment with different doses of 17-beta-estradiolbenzoate (EB) (0.031, 0.125, 0.5 mg/kg EB or placebo) on the development of hypertension from the 9th to 22nd week of life (increase of blood pressure (BP) of untreated male rats from 178 to 252 mm Hg and of untreated female rats from 151 to 192 mm Hg) and in well established hypertension from the 23th to 36th weeks of life (male untreated rats 238 mm Hg (prior to the observation] was investigated. In both series, observation periods consisted of a therapy phase of 14 weeks and a follow-up phase of the same duration. The untreated female rats had a longer life-span (88.5 weeks) than the untreated male rats (68.0 weeks). The estrogen treatment of female animals had an effect on BP only with the highest dose of EB and had no effect on the life-span of the animals. However, in male rats, the development of hypertension was inhibited by EB. Male rats treated at an earlier stage had a life-span equal to that of the female animals. When hypertension was already well-established treatment with EB had an antihypertensive effect in male rats (BP fall: 27-36 mm Hg), but no prolongation of the life-span was obtained.