Effect of diet on oestrogen bio-assay in mice

Abstract The uterotrophic effect of an oestrogen in the mouse uterine-weight bio-assay was increased by at least 50% when the oestrogen was fed in a semi-synthetic diet instead of in ground rat cubes; when it was administered sc, the change in diet had no effect. Whichever diet was fed, the same maximum uterine weight was achieved. These observations suggest that there was probably a more rapid or complete absorption of the oestrogen from the gut of animals on the semi-synthetic diet, and highlights the difficulty of estimating the oestrogenic activity of an unknown sample by feeding it to mice and comparing the uterotrophic effect with that of known amounts of a standard oestrogen, e.g. diethylstilboestrol, added to the regular diet.