Progesterone receptors in human oestrogen target tissues

The levels of specific oestrogen and progesterone receptors have been measured in myometrial, endometrial and vaginal tissues obtained from 18 women between the ages of 28-73 yr. High speed cytosols of the three tissues were incubated at four different concentrations of specific ligands: E2 for the oestrogen receptor (ERc) and Org-2058 for the progesterone receptor (PgRc). Separation of bound and free hormones was done by dextran-coated charcoal; data were analysed according to Scatchard. In the myometrium and endometrium both PgRc and ERc were found. In the vaginal tissues obtained from the same patients only ERc was present. There was no evidence of specific progesterone receptors in the vagina. Both clinical and histological findings indicate that the vagina is an oestrogen-sensitive organ. Therefore, it is surprising that progesterone receptors, which are considered to be a specific response of oestrogen target tissue, are absent in the human vagina. This finding suggests that the induction of the progesterone receptors is not a specific response to oestrogen stimulation in the human vagina.