[Action of synthetic progestin]

Chemical compound that can bind the progesterone receptor in the nucleus and cause proliferative change of the endometrium is designated as progestin (gestagen, progestogen). Progesterone (natural progestin) is secreted from corpus luteum of the ovary. Synthetic progestin can be divided into two groups: (1) progesterone derivatives, such as medroxyprogesterone acetate and (2) testosterone derivatives, such as norethisterone. The former has progestane structure and a marked progestational activities but little estrogenic and androgenic activities. While, most of the testosterone derivatives keep androgenic activities and show even estrogenic activities due to its estrane structure or production of estrogen as the metabolite. Thus, understanding the characteristics of mode of action in each synthetic progestin, we should select the appropriate one for clinical treatment.