Clomiphene and tamoxifen action in the rat uterus.

The antioestrogens clomiphene and tamoxifen exhibit both agonistic and antagonistic properties in the rat uterus. The effect of these antioestrogens on RNA polymerase activities in the rat uterus was investigated. Both compounds stimulated an early increase in the activity of endogenous RNA polymerase B similar to that observed after oestradiol treatment. A secondary stimulation of activity of RNA polymerase B was observed after treatment with oestradiol and both antioestrogens. In addition, the activity of endogenous RNA polymerase A was increased initially at 1 h by all three compounds but this activity was maintained at 24 h only by oestradiol.