Anti-Progestational Activity of Estrogens in Rabbit Endometrium

Abstract

The anti-progestational activity of 4 estrogens[long dash]estrone, estradiol, estriol, and stilbestrol[long dash]administered subcutaneously with progesterone into Clauberg rabbits has been demonstrated by estimation of endometrial carbonic anhydrase content and simultaneous measurement of uterine G/M ratio. All these estrogens inhibit the effect of progesterone on carbonic anhydrase content and G/M ratio of the endometrium. Intensity of inhibition depends upon dosage. The anti-progestational activities of these estrogens are approximately the same. When administered alone, these estrogens produce no significant change in either carbonic anhydrase titers or G/M ratios. The linear relationship with negative slope which is obtained between the log dose of the estrogens and the endometrial carbonic anhydrase content of the progesterone-treated Clauberg rabbit suggests the usefulness of this method as an assay procedure. Comparison of the log dose-response curves of progesterone with and without estradiol indicates that estrogen may depress reactivity of the endometrium to progesterone rather than neutralize or inactivate progesterone in the body.