Tissue specific effects of progesterone on progesterone and estrogen receptors in the female urogenital tract.

The effect of progesterone administration on progesterone and estrogen receptors in the uterus, vagina and urethra of rabbits was studied. After 24 h of progesterone treatment the concentration of cytosolic progesterone receptors decreased to about 25% of the control value in the uterus, whereas no significant change in receptor concentration was observed in the vagina or the urethra. The concentration of the nuclear progesterone receptor did not change in any of the three tissues studied. The apparent dissociation constant (Kd) of nuclear progesterone receptor increased after progesterone treatment in all three tissues. Although the Kd of the cytosolic progesterone receptor also increased in all tissues, the difference was significant for only the vagina and urethra. The concentration of cytosolic estrogen receptors in the uterus decreased significantly (P less than 0.001) after progesterone treatment whereas the Kd value increased slightly (P less than 0.05). In vagina or the urethra, there was no change in either estrogen receptor concentration or Kd values after progesterone treatment. These data clearly showed that the reduction by progesterone of progesterone and estrogen receptor concentrations occurs only in the uterus and not in the vagina or the urethra.