Comparison of Intravaginal and Subcutaneous Tests for Estrone and Estradiol Monobenzoate

Abstract

It was known from previous experiments 1 , 2 that by administering estradiol monobenzoate intravaginally, cornification of ovariectomized rats'vaginæ could be induced with about 1/200th of the amount needed subcutaneously. It was also known that by the subcutaneous rat test, estradiol monobenzoate in oil is 5 to 10 times as potent as estrone in oil. It seemed of interest, therefore, to determine the relative potencies of these two substances as judged by the intravaginal method. For, it might be argued, that if estradiol monobenzoate appears more potent merely because of slower absorption and excretion following subcutaneous injection, the local test might find it no more potent than estrone. If, however, it is more potent because a greater growth-stimulating property is determined by its chemical structure the ratio (estradiol monobenzoate: estrone) might be expected to remain the same, or be even greater because fewer variables are involved in the local test.

Sixty adult rats of the Long-Evans strain were ovariectomized, and 2 or more weeks later were “primed” with 1γ of estradiol monobenzoate. One week later, after the vaginal reaction had subsided the higher levels of estrone and estradiol monobenzoate were tested, and then the successively lower levels, at weekly intervals. The International Standards∗ were dissolved in and diluted with sesame oil, and a single subcutaneous injection of 0.1 cc made. Vaginal smears were examined 48 and 72 hours later. For intravaginal tests, 0.01 cc of the various dilutions was administered on 2 successive days by means of a micropipette, 1 , 2 and vaginal smears examined 24 and 48 hours after the second administration.

In both intravaginal and subcutaneous tests, a rat was considered a positive reactor if cornification was induced even though epithelial cells and some leucocytes were still present (border-line reaction).