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Estrogen and phyto-estrogen binding in ewe pituitary, hypothalamus, and other structures Mathieson, Ronna Arlene


Phyto-estrogens are known to bind to estrogen receptors of the uterus and they caninitiate the early events of estrogen stimulation including water imbibition and synthesis of induced protein as well as late events such as uterine growth. There is indirect evidence that these compounds affect the functioning of the hypothalamus and pituitary with respect to the release of gonadotropins. The purpose of this study was to determine if the phytoestrogen compounds, genistein and coumestrol, could interact with the estrogen receptor molecules in the cytoplasm of pituitary and hypothalamus tissue from ewes. Estrogen binding characteristics were also examined. Cytosol preparations from the various experimental, tissues were incubated fifteen minutes at thirty degrees C. with ³H-estradiol; separation of bound from free label was carried out on Sephadex LH-20 columns. Estrogen binding parameters were determined by double reciprocal plots. Competitions with ³H-estradiol in the presence of either coumestrol or genistein were carried out in a similar manner. Apparent inhibition constants (K[sub I]) were determined from Dixon plots. The.apparent dissociation constants (K[sub D]) for estradiol in ewe pituitary cytosol was determined to be 0.26±0.12 nM. The apparent for K[sub I] coumestrol in the ewe pituitary cytosol was determined to be 59-61 nM and the apparent K[sub I] for genistein was determined to be 130-210 nM. These compounds were shown to displace estradiol from receptors in ewe hypothalamus and amygdala cytosols. Results of preliminary binding experiments with ewe pineal and uterus cytosols are also presented. These results suggest that phyto-estrogens can interfere with normal estrogen feedback mechanisms with respect to gonadotropin release in the ewe.

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