Characterization and Properties of a High Affinity Oestradiol Receptor in Neonatal Rat Brain

The high affinity oestrogen « receptor )) (K d oestradiol ioIO M) from the neonatal rat brain shows the same hydrodynamic properties as other oestrogen « receptors » when analysed on sucrose density gradients before and after purification using ammonium sulphate precipitation. After this purification procedure, which also separates the small amount of « receptor » from the larger amount of lower affinity oestrogen binding protein (K d oestradiol IO -BM), the apparent affinities of the putative neonatal oestrogen « receptor » for oestrone and oestradiol are increased towards the affinities of the adult hypothalamic oestrogen « receptor for these steroids. When [!H]oestradiol was injected intracerebrally, diethylstilboestrol-suppressible radioactivity was measured in the purified nuclear fraction of the neonatal brain and was maximal half to one hour after injection. It was localised mainly in the hypothalamic region and a sex difference in nuclear uptake was found. When this radioactivity was extracted, it sedimented at 4.5S when analysed