Oestrogen receptor in mammary gland cytosol of virgin, pregnant and lactating mice.

A macromolecular component binding 3H-labelled 17 beta-oestradiol in a specific manner and sedimenting in the 8-10-S region on sucrose gradient has been detected in the mammary gland cytosol of ovariectomized adult virgin mice. The dissociation constant of the macromolecule-oestradiol complex is 4.2 times 10(-10)M at 4 degrees C. The binding sites for 17beta-oestradiol of cytosol are 3.7 times 10(-14) mole/mg of protein. Incubation of cytosol with different enzymes suggests that the oestrogen-binding cytosol component is proteinaceous. The binding activity is destroyed by incubation at high temperatures and by some but not all SH-reagents tested. Competition studies show a specificity for oestrogens relative to other steroid hormones. The conclusion is that mammary gland cytosol of virgin mice contains oestradiol receptor. The receptor content does not increase in a specific manner during pregnancy and lactation but rather proportionally to total mammary gland protein.