Vascular action of high dose estrogen in rats

Effects of estradiol hemisuccinate and diethylstilbestrol diphosphate on the cardiovascular system in male rats were examined in vivo and in vitro. In conscious rats, intravenously administered estradiol or diethylstilbestrol inhibited vascular responses to norepinephrine in a dose-dependent manner. Diethylstilbestrol in high doses significantly lowered the blood pressure of conscious rats. In the isolated mesenteric arteries perfused with Krebs bicarbonate solution, estradiol or diethylstilbestrol in the perfusate similarly inhibited vascular reactivity to norepinephrine in a dose-dependent manner. As in the in vivo experiments, a decrease in the basal pressure of the mesenteric vascular bed was observed when diethylstilbestrol was added to the perfusate at high concentrations. The results of these in vivo and in vitro studies strongly suggest that estradiol and diethylstilbestrol act directly on the vascular beds and attenuate vascular response to norepinephrine. It is also suggested that diethylstilbestrol by itself causes vasodilatation and a reduction in blood pressure when present at high concentrations.