INITIATION OF BLASTOCYST IMPLANTATION BY LUTEINIZING HORMONE

Implantation of blastocysts in the rat is initiated by estrogen. Delay of blastocyst implantation is obtained if the pituitary is removed the day after vaginal sperm are observed and progesterone is provided exogenously or endogenous progesterone secretion is maintained by prolactin injection or by prolactin secreted from a pituitary autograf t. This study shows that luteinizing hormone (LH) will induce blastocyst implantation when administered at any time up to 12 days after breeding. Follicle-stimulating hormone and prolactin were without effect. This supports the hypothesis that LH stimulates secretion of physiological quantities of estrogen from luteinized ovaries with or without the capability to secrete progesterone. (Endocrinology 80: 172, 1967)