[Inhibition of implantation in the rat due to bromocriptine (author's transl)]

The increase in the number of the ovarian LH/HCG-receptors and the rise in serum progesterone concentration during pregnancy in the rat depend on the presence of prolactin during the process of luteinization. Blocking of the hypophyseal prolactin secretion in rats by twice daily injections of 2 micrograms/g of body weight of bromocriptine from the first day of pregnancy onwards prevents the increase in ovarian HCG-binding, progesterone production, and the implantation of blastocysts. The lack of implantation is not due to a teratogenic effect of bromocriptine but is due to deficient decidual changes caused by a lack of progesterone production by luteal cells.