Abstract
Discussion and Summary
We have demonstrated the existence of an ovarian factor in the rat, which inhibits the uterine response to estrin, and which operates in a cyclic manner corresponding to the estrus cycle of the animal. Although the development of uterine inhibition during the cycle is paralleled by the development of corpora lutea in the ovary, we do not believe that the inhibition is due to progestin. This conclusion is based on evidence that progestin, in amounts sufficient to inhibit the effects of estrin on the uterus, always results in progestational phenomena in this organ. 2 , 3 , 4 But, at no time in the present or previous 1 work did we observe progestational changes in the uterus. Furthermore, the antagonism between progestin and estrin also includes the inhibition of vaginal cornification, 2 , 3 while in our work the vaginal mucosa never failed to become cornified after estrin administration.
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