Leptin and leptin receptor are expressed in the human endometrium and endometrial leptin secretion is regulated by the human blastocyst

Embryonic implantation is a crucial event for the human reproductive functi on. Cytokines and paracrine molecules have been proposed as putative local regulators of this process. The leptin or the OB protein has been linked to the reproductive function and inflammatory response. In the present study, we describe for the first time the expression of leptin and leptin recepto r (long form) in the secretory endometrium and that endometrial leptin secr etion is regulated in vitro by the human blastocyst. Leptin and leptin rece ptor messenger RNA and protein were identified in secretory endometrium and in cultured endometrial epithelial cells (EECs) by RT-PCR, Western blot, a nd immunohistochemistry. The concentrations of immunoreactive leptin secret ed by human embryos alone or cocultured with EECs were also assessed. We fo und that human blastocysts secrete significantly higher levels of leptin th an arrested embryos. In contrast, leptin concentrations secreted by arreste d embryos cocultured with EECs were significantly higher than blastocysts c ocultured with EECs. These findings suggest that the human endometrium is a site for local production and a target tissue for circulating leptin. Expr ession of leptin and its functional receptor in the endometrium and regulat ion of endometrial leptin secretion by the human embryo suggests that the l eptin system may be implicated in the human implantation process.