Some Effects of Steroid Hormones on Carcinogenesis in Rats: Effects of Oestrogens on the Induction of Tumours in the Cervico-Vaginal Tract and in the Salivary Glands

Abstract

In rodents, estrogens promote keratinization in the epithelium of the cervico-vaginal tract and suppress the differentiation of the mucine-secreting columnar epithelium that is present in castrates, in dioestrus, and in pregnant animals. The estrogens promote growth of the normal cervical stroma and epithelium. They have, thus, a desirable effect in respect of keratinization and an undesirable one as regards growth stimulation of normal target tissues. This chapter describes the effect of estrogens on the induction of cervico-vaginal tumors in rats. Estrogens are known to provide one of the factors necessary for the induction of breast tumors in mice and castration reduces their incidence in rats. Castration reduces very significantly the incidence of cervico-vaginal sarcomas in rats; however, continuousoestrogenic treatment of castrates fail to increase the rate of induction of sarcomas, although it stimulates the growth of the cervico-vaginal stroma, induces the multiplication of epithelial cells, and promotes keratinization. The effect of estrogens on carcinogenesis, thus, differs from that on the normal target tissue of the cervico-vaginal tract. In intact animals too, continuous estrogenic treatment by the addition of stilboestrol to the drinking water inhibits the appearance of sarcomas and, as in spayed animals, fails to promote the induction of epithelial tumors in the female genital tract.