Ultrastructural modifications provoked by tamoxifen either alone or combined with oestradiol in the uteri of fetal or newborn guinea-pigs.

The ultrastructural changes in the uterine epithelial cells of fetal and newborn guinea-pigs were examined by transmission electron microscopy after the administration of tamoxifen, oestradiol or a combination of tamoxifen and oestradiol. Tamoxifen provoked a substantial alteration of the mitochondria and the rough endoplasmic reticulum with the formation of numerous vacuoles and secretory granules, indicating an enhancement of synthetic and secretory activities. The mixture of oestradiol and tamoxifen increased the effect and most organelles became irreversibly altered, particularly in the uteri of newborn animals after a long treatment. It is concluded that, in addition to the agonistic oestrogen effects of tamoxifen on uterine growth, DNA and protein contents, tamoxifen also acts as an agonist on the ultrastructural changes of the uterine epithelial cells during the perinatal period of the guinea-pig.