[Progestins and the endometrium]

Natural progesterone and synthetic progestins lead in the endometrium to the inhibition of mitosis, reduction of estrogens and progesterone receptors and decidualisation of the endometrium. This latter process seems to be of main importance for the implantation. Furtheron, progesterone and progestins induce the formation of IGF-binding proteins (IGFBP's), which for instance lead to the binding of IGF-1 and thereby to a reduction of proliferative or mitogenic effects of the estrogens on the endometrium. In addition, progesterone or progestins induce or inhibit a number of other factors. Among others, protein PP 14 is induced in the endometrium by progesterone or progestins. This protein has immunological properties. While on the one hand the enzyme glutathionperoxydase is blocked, there is on the other hand an induction of transglutamase activity. Furthermore, progestins in high doses lead to a reduction of the microvasculature and a dilatation of the venoles. Therefore, progesterone and progestins are best suited for treatment and prevention of abnormal proliferation of the of the endometrim even up to carcinoma in situ or endometrial cancer. For this, the severity of endometrial changes and the age of the patients have to be taken into account. This also applies to the prevention of pathological endometrial changes.