BINDING OF PHYTO-OESTROGEN AND OESTRADIOL-17β BY CYTOPLASMIC RECEPTORS IN THE PITUITARY GLAND AND HYPOTHALAMUS OF THE EWE

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Abstract
The binding of the phyto-oestrogens, genistein and coumestrol by oestrogen receptors in pituitary and hypothalamiccytosol of the ewe was studied in relation to the binding of [3H]-oestradiol-17β. It was determined that the interaction of these compounds was competitive. The apparent dissociation constant for oestradiol-17β in ewe pituitary cytosol was determined to be 0·26 ± 0·12 (s.e.m.) nmol/l. Apparent inhibition constants for coumestrol and genistein were determined to be 60 and 170 nmol/l respectively. These results suggested that phyto-oestrogens can interfere with the normal oestrogen feedback mechanisms with respect to release of gonadotrophin in the ewe.