The effects of DDE, PCB and chlordane on the binding of progesterone to its cytoplasmic receptor in the eggshell gland mucosa of birds and the endometrium of mammalian uterus.

1. The specific binding of progesterone to its cytoplasmic receptor in the mucosa of the shell gland from egg-laying ducks, domestic fowls and from the endometrium of the rabbit uterus was compared. The effect of DDE, PCBs and chlordane added in vitro was also studied. 2. The KD value for progesterone with regard to its receptor was about four times lower in the domestic fowl and the rabbit than in the duck. 3. The chlorinated hydrocarbons decreased the binding of progesterone to its receptor. Their potency was higher in the duck than in the domestic fowl. In rabbit uterine mucosa their effects were similar to those observed in the duck. 4. DDE is an inhibitor of calmodulin: other calmodulin inhibitors as calmidazolium and trifluoperazin also reduced the binding of progesterone in similar concentrations. It is suggested that DDE reduced the progesterone binding by inhibiting calmodulin.