Effects of phytoestrogens on acetylcholine- and isoprenaline-induced vasodilation in rat aorta

The influence of the phytoestrogen, isoflavones, on vasodilating responses of the thoracic aorta precontracted with norepinephrine, together with the stimulatory effect on uterine weight (uterotrophic effect), was investigate d in ovariectomized rats. In comparison with intact rats, acetylcholine (AC h)-induced vasodilation showed a tendency to be decreased by ovariectomy. O n the other hand, isoprenaline (ISO)induced vasodilation was significantly increased by ovariectomy. Estrogen replacement (17 beta -estradiol dipropio nate, 300 mug/kg per week, for 1 month) completely restored the impaired AC h- and ISO-induced vasodilation caused by ovariectomy. Dietary isoflavone a glycones (containing 52% genistein, 42% daidzein and 6% glycitein) of 157 m g/kg per day (not 67 mg/kg per day) for 1 month, in addition to the effects of estrogen replacement, completely restored the impaired vasodilation cau sed by ovariectomy. However, the uterotrophic effect of dietary isoflavones of 157 mg/kg per day was incomplete as compared with that by estrogen repl acement. These results indicate that phytoestrogen, isoflavones, certainly possess estrogenic actions on the vasodilating responses caused by ACh and ISO, as well as a weaker uterotrophic effect.