The present study investigated the effect of genistein. daidzein and estrad
iol on in vitro rat uterine responsiveness to oxytocin (OT) and PGF(2)alpha
or luprostiol (L). In a first experiment, animals were either sham-operate
d (SH; n = 5). or ovariectomized (OVX; n = 20) and orally treated for three
months with either genistein (G: n = 5; 10 mug/g BW/d) or daidzein (D; n =
5; 10 mug/g BW/d) or 17 alpha -ethinylestradiol (E; n = 5; 23 mug/kg BW/d)
or untreated (OVX; n = 5). At necropsy, the basal uterine tension was lowe
r in OVX, G and D than in SH, the highest value being measured in E. Oxytoc
in (10(-12); 10(-11) M) or PGF(2)alpha (10(-12); 10(-9) M) induced an incre
ase in SH, but not in OVX, E and G. In D, only the highest doses were effic
ient. In a second experiment, 20 intact animals were s.c. injected with eit
her genistein (G; n = 5; 10 mug/g BW) or daidzein (D; n = 5; 10 mug/g BW) o
r estradiol benzoate (E; n = 5; 23 mug/kg BW) or vehicle (C: controls; n =
5), and killed 24 h later. In C and E, OT (10(-15) to 10(-10) M) or L (10(-
12) to 10(-7) M) stimulated uterine contractile activity in a dose-dependen
t manner until a maximal level. On the opposite, in G and D, contractile ag
ents (except the highest luprostiol doses) did not stimulate myometrium con
tractions. Moreover, radioligand binding assays showed that genistein or da
idzein inhibited the specific binding of [H-3] estradiol to the calf uterus
estrogen receptor (ER). Therefore, it could be postulated that both genist
ein and daidzein might bind to the rat uterus ER, inducing either anti-estr
ogenic or very weak estrogenic effects (depending on the experimental condi
tions) on in vitro uterine responsiveness to OT and PGF(2)alpha or luprosti
ol. (C) 2001 Elsevier Science Ltd. All rights reserved.