OESTROGEN INHIBITION BY STEROIDS AND OTHER SUBSTANCES

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Abstract
SUMMARY: In intravaginal tests of cornification in the spayed mouse vagina, dimethylstilboestrol, ethylstilboestrol, n-propylstilboestrol, meso- and racemic-butoestrol inhibit oestradiol. None do so when given subcutaneously. MER 25 shows very weak inhibition, but acts subcutaneously. The steroids, 19-nortestosterone, 17-ethyl-19-nortestosterone and 17-ethinyl-19-nortestosterone, inhibit oestradiol when given both intravaginally and subcutaneously. In intravaginal tests of mitosis, increase in epithelial thickness or triphenyltetrazolium reduction (a measure of metabolic activity), the stilboestrols and butoestrols inhibit oestrone. Massive doses of MER 25 partially inhibited in such tests, but actually stimulated mitosis at low levels of oestrogen administration. None of the nor-steroids showed any inhibitory potency in dose ratios of up to 1000:1, while both 19-nortestosterone and 17-ethinyl-19-nortestosterone showed oestrogenic activity at levels of only 50:1. It is concluded that both the synthetic and steroid compounds inhibit directly, not by virtue of metabolites, but that only the synthetic compounds compete with oestrogens at an early stage. Failure to show parenteral activity in these compounds may be due to their weak pro-oestrogenic potencies. It is suggested that the very weak activity found with MER 25 may reflect a species difference between mouse and rat.

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