Progesterone receptors in human vaginal tissue

Specific progesterone receptors were measured in both cytoplasmic and nuclear fractions of vaginal tissues obtained from 17 women between 33 and 53 years in age. Whereas nuclear receptors could be measured in 11 of 17 tissues examined, cytoplasmic receptors were detected in only four. The distribution of receptor-positive tissues was similar in the follicular and luteal phases and no significant difference was observed in the nuclear receptor concentration in the two phases. The receptor concentration from all tissues examined ranged from 31 to 105 pmol/mg of protein and the apparent dissociation constant was 1 to 2 nmol/L. The presence of progesterone receptors in the nuclear fraction and their absence in the cytoplasm raise questions about the authenticity of the classical two-step model for steroid hormone action.