Receptors for oestradiol in human placenta.

The binding of oestradiol in human placental tissue obtained from spontaneous and caesarean deliveries was investigated. Villous tissue was homogenized and the 800 g 'cytosol' supernatant treated with ammonium sulphate. The precipitate was redissolved and the preparation then equilibrated with [3H]oestradiol. After separation of bound and free steroid with dextran coated charcoal, receptor binding site concentrations and dissociation constants were determined. The presence of high-affinity, saturable binding was clearly demonstrated. Mean values (+/- s.d.) for receptor binding site concentrations were 64.6 +/- 22.9 (n = 6) and 33.8 +/- 32.9 (n = 8) fmol/mg protein for spontaneous and caesarean deliveries, respectively; respective dissociation constants were 16.0 +/- 7.6 and 7.0 +/- 6.0 pM. Heat denaturation studies, equilibration time studies and certain of the Scatchard plots suggested that forms of the oestradiol receptor of differing stability may be present in human placental tissue.