Binding of phyto-oestrogen and oestradiol-17 beta by cytoplasmic receptors in the pituitary gland and hypothalamus of the ewe.

The binding of the phyto-oestrogens, genistein and coumestrol by oestrogen receptors in pituitary and hypothalamic cytosol of the ewe was studied in relation to the binding of [3H]-oestradiol-17 beta. It was determined that the interaction of these compounds was competitive. The apparent dissociation constant for oestradiol-17 beta in ewe pituitary cytosol was determined to be 0 x 26 +/- 0 x 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 gonadotrophine in the ewe.