Oestrogen and progestin receptors in deciduoma of the rat

The ability of cytoplasmic and nuclear fractions from decidual tissue to bind [ 3H]-oestradiol-17β and the progesterone analogue [ 3H]-R-5020 was examined during the growth phase, maintenance and regression of trauma-induced unilateral deciduoma of pseudopregnant rats and compared to that of the control uterine horn. High affinity ( K d = 10 −10 to 10 −11 M) 8 S cytoplasmic oestrogen receptors, as well as nuclear oestrogen receptors, were detected at all stages of decidual life, but the concentration of both types of oestrogen receptors per unit DNA gradually decreased from the 6th to the 12th day of pseudopregnancy. Cytoplasmic progestin receptors ( K d = 10 −9 to 2 × 10 −9 M) sedimenting at 4–5 S and nuclear progestin receptors were present at all stages of decidual development. The concentration of these receptors declined sharply towards the 12th day of pseudopregnancy in the deciduoma, without comparable changes in the non-decidualized horn. It is possible that the terminal decline in the concentration of steroid receptors in the deciduoma accounts for the inability of exogeneous steroids to prolong the life-span of the deciduoma or to prevent its regression.