Abstract
It has been suggested that some contraceptive derivatives of 19-nor-testosterone possess estrogenic activity that may facilitate the development of breast cancer. The aim of this work was to investigate the estrogenic properties of norethisterone (NET) and its A-ring–reduced derivatives by determining progesterone receptor (PR) and c-fos mRNA content of two estrogen-regulated genes in the uterus of ovariectomized rats. mRNA content was evaluated by Northern blot 1–6 h after 17β-estradiol administration. The highest PR and c-fos mRNA content was observed 3 h and 2 h after 17β-estradiol administration, respectively. NET did not modify either PR or c-fos mRNA content. In contrast, 5α- and 3β,5α-NET significantly increased mRNA content of both genes. The increase in c-fos mRNA content induced by these reduced compounds was lower than that found with estradiol treatment. The overall results indicate that NET administration can indirectly induce estrogenic effects through the action of its 5α-dihydro and 3β,5α-tetrahydro derivatives.
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