The comparison of the binding of Ru486 to progesterone receptor of pituitary and endometrium in ovariectomized rat

Following intramuscular injections of increasing doses of Ru486(0.1 mg/kg—2 mg/kg),free progesterone binding sites remaining in pituitary and endometri-um in estrogen-primed OVX rats decreased.Thirty minutes after administrationof Ru486(2 mg/kg)the binding sites of progesterone receptor in both tissues showeda significant initial decrease,and then gradually reached the lowest level in 2 h.Afterwards the levels of progesterone receptor began to increase.The resultssuggested that Ru486 could interact with progesterone receptor in both tissues.However,the binding ability of Ru486 for different tissue was not exactly thesame,and Ru486 binding to the progesterone receptor in endometrium mightbe easier.