NEW UNDERSTANDING IN THE BIOCHEMISTRY OF IMPLANTATION - POTENTIAL DIRECT ROLES OF LUTEINIZING-HORMONE AND HUMAN CHORIONIC-GONADOTROPIN

Luteinizing hormone/human chorionic gonadotropin (LH/hCG) receptors ar e present in human implantation sites that contain intermediate tropho blasts, decidual cells, and blood vessels. These receptors also are in human endometrial stromal cells, endometrial glands, myometrial smoot h muscle, and T lymphocytes. Highly purified exogenous hCG and LH can promote the differentiation of stromal cells into decidua, increase th e levels of cyclooxygenase-2 (COX-2) in glandular epithelial cells, de crease the resistance index, increase prostacyclin, decrease thromboxa ne B-2 synthesis in uterine arteries, and inhibit contractions of the uterus. These changes are required for the successful implantation of the blastocyst. Thus, it is likely that LH and hCG directly promote im plantation in humans and possibly in other species.