A study of anti-progestational compound RU38486 action on the estrogen-induced enlargement of the rat pituitary gland.

Long term administration of estradiol to intact and ovariectomized female rats caused enlargement of the pituitary gland. This process was partially antagonized in intact animals when antiprogestational compound RU38486 was given concomitantly. In ovariectomized rats, however, this effect of RU38486 was not apparent. Since administration of the compound to ovariectomized animals did not alter estrogen-receptor translocation or estrogen induced hypervascularity in the pituitary gland, this inhibitory effect of RU38486 seems not to be exerted through estrogen-receptor binding antagonism but rather due to a progesterone receptor blockade at the hypothalamic-pituitary axis.