Pituitary hormone control of implantation in the mouse.

In hypophysectomized pregnant mice replacement therapy designed to mimic the normal physiological situation showed that FSH in combination with either prolactin or LH, or prolactin plus LH, could initiate implantation in the absence of the pituitary gland. No pituitary hormone was by itself capable of achieving this result. The combination of prolactin with FSH gave better results than a combination of LH with FSH. Prolactin from sheep, cattle or rats was equally effective in combination with rat FSH in initiating implantation. In mice exhibiting suckling-induced delay of implantation this delay was terminated by injection of FSH. GH by itself or in conjunction with other hormones had no significant effect on implantation or on any of the other parameters associated with implantation that were measured. On the basis of these experimental results it is suggested that prolactin and LH are involved with progesterone production and FSH with oestrogen production, both of which are required for implantation in the mouse.