In the hypophysectomized albino rat which is protected from contact with steroids in the ration and environment the uterus and vagina are highly atrophic but are sensitive indicators of activity of substances which promote their growth. Both the pituitary growth hormone and certain steroids have the common property of inducing growth of these tissues.

The vaginal epithelium consists of 2 layers of cells which differ profoundly in their growth in response to steroids, depending on the molecular structure of these compounds. The differential response to modifications of chemical structures of steroids permits evaluation of the importance of the intramolecular components for the process of growth.

The number and site of functional groups, the geometry of the molecule and the state of oxidation are of high importance in determining physiologic activity of steroids in the androstane series; these features are less specific in the estrane series.

Side groups at positions C3 and C17 are of importance in the promotion of growth by steroids in the androstane series, but these active centers are not equivalent in their physiological influence. As a generalization, hydrogenation of the oxygen function at C17 (but not at C3) and dehydrogenation at critical areas of the ring structure increase the quantitative efficacy of steroids in promoting growth. The position of double bonds and the state of oxidation at both C3 and C17 determine the qualitative type of growth—cellular pattern, which a compound in the androstane series induces in the vaginal epithelium.

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