Progesterone and oestradiol levels and cytoplasmic receptor concentrations in the human myometrium at term, before labour and during labour.

Progesterone (P) and oestradiol (E2) cytoplasmic receptor levels in the myometrium of 12 women, who underwent cesarean section at term were determined by means of an exchange assay. Six of the women had an elective cesarean section, and the other six were in active labour when the operation was performed. Both the P and the E2 receptor concentrations were significantly higher in the myometrium of those women who were in labour. The plasma P and E2 levels did not change before labour and during labour. The myometrial E2 concentrations were also similar in both groups. The myometrial P concentration was lower in the labour group, but the difference was not statistically significant. This study is the first which compares the steroid receptor levels at term before labour and during labour in human myometrium, although only the unbound and the cytosol receptor levels were determined. The change of levels in receptor concentrations could be a sign of the decrease of the P dominance in the myometrium during labour.