There are three distinct substances in the human placenta that are capable of producing estrus precociously when administered to immature rats or mice; the first is ether soluble, the second ether insoluble but alcohol soluble, the third alcohol insoluble. From the ether-soluble fraction Browne,1 in our laboratory isolated an active principle in crystalline form; it proved to be identical with trihydroxy-estrin or theelol, whose most characteristic physiologic property is that, while highly active in immature intact rodents, it is relatively less active in adult or immature ovariectomized animals; possibly, as we have suggested, because in the presence of ovarian tissue it undergoes conversion into some more active modification such as ketohydroxyestrin (theelin). The active principle of the second fraction has been termed emmenin in a previous report;2 it displays the same characteristic property, and we believe it to be a compound of trihydroxy-estrin with some unknown substance that
COLLIP JB, SELYE H, ANDERSON EM, THOMSON DL. PRODUCTION OF ESTRUS: RELATIONSHIP BETWEEN ACTIVE PRINCIPLES OF THE PLACENTA AND PREGNANCY BLOOD AND URINE AND THOSE OF THE ANTERIOR PITUITARY. JAMA. 1933;101(20):1553–1556. doi:10.1001/jama.1933.02740450027007
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