A total of 60 women with 6-7 weeks' amenorrhoea were randomly allocate
d to three groups. The women in the first group (control) took a place
bo 24 h before undergoing vacuum aspiration. The subjects in the secon
d and third groups were given orally 200 mg of RU 486, 12 or 24 h befo
re surgical interruption of their pregnancy. Villi and decidua were co
llected and frozen in liquid nitrogen. There were no significant diffe
rences in villous cytosolic steroid concentrations between the control
and RU 486-treated groups. The RU 486 concentration was lower in vill
ous cytosol than in decidua and serum. The immunostaining of progester
one receptor in villous and extravillous trophoblast was weak and loca
lized in both cytoplasm and nucleus. RU 486 treatment had no effect on
the immunostaining of progesterone receptors in trophoblast populatio
ns except in the placental bed giant cells, where the weak and diffuse
progesterone receptor staining in the cytoplasm of controls seemed to
be concentrated in the nucleus after RU 486 treatment. In conclusion,
RU 486 might have no effect on the immunostaining of progesterone rec
eptor and on steroid concentrations in villi in vivo.