“…1957;Edgren et a i, 1966], On the other hand, an estrogen-like activity of some representatives of this group such as norethynodrel. norethisterone [Saunders and D rill, 1958] and lynestrenol [Desaulles and Krahenbuhl, 1964] has been demon strated by the vaginal-smear technique in rats treated both orally and parenterally, or by their influence on the weight of the uterus of mice treated s.c. [Pincus et al, 1956], Moreover, in contrast to an only slight 'phenolic conversion' of orally-administered norethynodrel [Arai et a i, 1962] and of parenterally-given norethisterone and d.l-norgestrel [Kamyab et al, 1967] in rabbits, in rats a direct metabolization of norethynodrel into I7u-ethynyloestradiol could be demonstrated [Martin et al, 1970],…”