Jpn. J. Pharmacol. 87 (1), 67-73 (2001)

Effects of Phytoestrogens on Acetylcholine- and Isoprenaline-Induced Vasodilation in Rat Aorta

Kiyoshi Yamaguchi, Hideo Honda, Chiaki Wakisaka, Atsushi Tohei and Hiroshi Kogo*

Department of Pharmacology, Tokyo University of Pharmacy and Life Science, 1432-1, Horinouchi, Hachioji, Tokyo 192-0392, Japan

*Corresponding author. FAX: +81-426-76-4526, E-mail:

Abstract: 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 investigated in ovariectomized rats. In comparison with intact rats, acetylcholine (ACh)-induced vasodilation showed a tendency to be decreased by ovariectomy. On the other hand, isoprenaline (ISO)-induced vasodilation was significantly increased by ovariectomy. Estrogen replacement (17b-estradiol dipropionate, 300 mg/kg per week, for 1 month) completely restored the impaired ACh- and ISO-induced vasodilation caused by ovariectomy. Dietary isoflavone aglycones (containing 52% genistein, 42% daidzein and 6% glycitein) of 157 mg/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 caused by ovariectomy. However, the uterotrophic effect of dietary isoflavones of 157 mg/kg per day was incomplete as compared with that by estrogen replacement. 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.

Keywords: Isoflavones (genistein and daidzein), Estradiol, Acetylcholine, Isoprenaline, Rat aorta
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