THE USE OF THE HUMAN VAGINAL SMEAR IN THE ASSAY OF ESTROGENS*

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Abstract
LABORATORY assay methods have proven inadequate to determine the relative clinical potency of the various estrogens. By rat assay, the apparent potency of estrone varies with the number of injections and the vehicle in which the hormone is injected. Laqueur (1) found the rat unit of estrone equivalent to 10 to 16 international units, but Rowe and Simond (2) obtained a value of only 3 or 4 international units. Estradiol benzoate is approximately ten times as potent as estrone when assayed in the rat, but only four times as potent (Laqueur) or of equal activity (Rowe and Simond (3)) when tested in the mouse. The outstanding example of misleading laboratory assay is the discrepancy between rat assays and clinical trials of the methyl ether of bis-dehyrdo-doisynolic acid. In the rat, this compound when given subcutaneously is more active than estradiol, whereas, clinically it is practically inert (Segaloff (4, 5)).