DESIGN OF A BIOLOGICAL ASSAY METHOD FOR THE DETECTION AND ESTIMATION OF ESTROGENICRESIDUES IN THE EDIBLE TISSUES OF DOMESTIC ANIMALS TREATED WITH ESTROGENS

Experimental designs are described for the biological assay of the edible tissues of stilbestrol-treated animals for residual estrogenic activity. When residual estrogenic activity is found, an estimate of the amount in terms of stilbestrol equivalents can be made by serial dilution of the unknown or treated tissue with the control or nontreated tissue and by comparing the response of these diets with a standard dosage-response line simultaneously established by adding known amounts of stilbestrol to the control tissue diet. When residual estrogenic activity cannot be detected, the design of the assay provides a method for calculating the maximum amount which could be present and remain undetected. The immature rat compares favorably with the immature mouse for the determination of stilbestrol in tissues. Stilbestrol was found to be from 10 to 20 times as active as the natural estrogens, estradiol-17βand estrone, in the mouse uterine weight method of assay when administered orally in the diet.