U-11555A is oestrogenic in vaginal smear tests in mice with a low slope and a subcutaneous med of not less than 5 mg. Its oestrogenic activity intravaginally was not fully investigated, but is not high. It is weakly anti-oestrogenic in similar tests, with an med against oestradiol of about 200 μg subcutaneously, perhaps a little lower intravaginally. No interactions were seen as they were with U-11100A† (Emmens & Martin, 1965).
U-11555A has an antifertility action in the mouse when injected on Days 1 to 3 or 4 to 6 of pregnancy, with meds of about 100 μg (Days 1 to 3) and 300μg (Days 4 to 6). In rats, U-11555A has a constant subcutaneous or oral med on Days 1 to 3 or 4 to 6 of about 400 μg. In simultaneous tests in rats, U-11100A had meds of about 20 μg (Days 1 to 3) and 60 μg (Days 4 to 6) and was significantly more potent orally than by injection.
From these results, the antifertility action of U-11555A can hardly be attributed to oestrogenic properties, as was that of U-11100A by Emmens & Martin (1965), and its action profile is not very similar to that of the latter. Its antifertility action in mice is in accord with its anti-oestrogenic potency in that species.
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