Wise Burroughs

ESTROGENIC ACTIVITY OF SOME NATURALLY OCCURRING ISOFLAVONES

The biological significance of the naturally occurring isoflavones was not recognized until recently, although several of them had been isolated, chemically characterized, and synthesized. Perhaps the first evidence indicative of the biological activity of isoflavones was the fact that a serious breeding problem in sheep occurred when these animals were grazed on subterranean clover (Bennetts et al., 1946), due to the presence of an estrogen or estrogens. Subsequently, the isoflavone, genistein, was isolated from the subterranean clover (Bradbury and White, 1951) and was considered to be the principal estrogen in that plant (Biggers and Curnow, 1954). Our interest in the estrogenic isoflavones was initiated three years ago when it was observed that the growth stimulating effect of stilbestrol implantation noted by others with lambs was not obtained (Culbertson, 1952) when the lambs received liberal amounts of alfalfa and clover hays. Attempts were then made to determine whether the hays used in this experiment contained any estrogenic activity. This work eventually led to a general survey of estrogenic substances in feeds, including soybean oil meal, which was known to contain considerable amounts of an isoflavone glucoside, genistin (Walz, 1931 ; Walter, 1941). Apparently isoflavones are responsible for a t least a part, if not all, of the estrogenic activity that has been found in many plant products. Subsequently, some of the common naturally occurring isoflavones were synthesized in our laboratory and their estrogenic activity was determined. This report will treat some of these experiments in detail.