A new phenothiazine derivative trifluoperazine ('Stelazine') appears to be more effective than chlorpromazine in causing delayed nidation in the rat.
Treatment, started on day 3 of normal pregnancy and repeated every 24 hr., induced delayed nidation in over 80% of the animals treated. This delay was corrected, and implantation brought about, immediately after the exogenous supply of 0·1 μg. of oestradiol.
In a second series of experiments, a single injection of Stelazine was given to females, subsequently spayed and treated with progesterone, and was found to postpone the stage from which ovariectomy is compatible with ovum implantation.
The results obtained support the hypothesis that nidation is induced, under normal conditions, by a release of oestrogen on day 4 of pregnancy. It is suggested that tranquillizers influence ovum implantation by postponing, through the pituitary cycle, this discharge of oestrogen.