Effects of ovariectomy and estradiol injection on nuclear structures of endometrial epithelial cells

The changes of the rate of RNA synthesis produced by castration and estradiol injection on the surface endometrial cells of the rat are profited to study the variations in the number and size of nuclear ribonucleoprotein structures and in the disposition of chromatin. Two-dimensional measurements on sections contrasted with preferential procedures were employed to estimate the fraction of nuclear volume occupied by each element. Young adult rats in estrus are used as controls. 3 weeks after ovariectomy, the area fraction occupied by the nucleolus is reduced almost to a third of the control value, while the number of perichromatin granules per unit area of nucleus has significantly increased. A single injection of 20 microgram of estradiol produces a rapid decrease of the number of perichromatin granules to a fourth of the value of castrate animals, in 15-30 min, followed by a slow increase. Nucleolar area fraction begins to increase 2 h after estrogen administration and at 24 h it is higher than in controls. It is concluded that the changes of the nucleolar volume are due to the effects of estradiol on the synthesis of nucleolar RNA, while the variations of perichromatin granules are produced by the combination of the effect on extranucleolar RNA synthesis and on its processing and/or transporting to the cytoplasm. Both effects are independent and undergo different temporal courses.