Fourth World Conference on Early Pregnancy CONTINUUM BETWEEN IMPLANTATION AND PERINATAL EVENTS

Tropic Effects Of LH And hCG On Early Pregnancy Events In Women's Reproductive Tract

Ch. V. Rao

Department of Ob/Gyn, University of Louisville Health Sciences Center, Louisville, KY 40292 USA

Presentation

Women's fallopian tubes and uterus are functional targets of LH and hCG actions. They contain receptor mRNA and receptor protein which can bind ¹²⁵ I-hCG in a hormone specific manner. These receptors, which mediate the actions of LH and hCG, increase from the proliferative to the secretory phase and are regulated by gonadotroins as well as by estradiol and progesterone. LH/hCG increases production of prostaglandins, synthesis of oviductal glycoprotein, releases sperm bound to tubal epithelial cells, and promotes early embryonic growth and development in co-cultures of tubal epithelial cells and early embryos. These actions promote gamete maturation, fertilization, early embryonic growth and development and its timely transport for implantation in the uterus. The uterine actions of LH/hCG (increase in prostaglandins production by endometrial glands and stromal cells, and increase the differentiation of stromal cells into decidual cells) promote the  implantation of blastocyst. Following implantation, trophoblast hCG may promote the invasion of intermediate trophoblasts into decidua. Other LH/hCG actions during early pregnancy include: a) an increase in uterine blood flow by enchancing the synthesis of vasodilatory and decreasing the synthesis of vasoconstrictive eicosanoids in uterine arteries; b) maintaining uterine quiescence by decreasing myometrial gap junctions and intracellular Ca²⁺ levels; and c) immunoprotecting the fetus by preventing T-cell activation at maternal-fetal interface through up-regulation of indoleamine 2,3 dioxygenase that breaks down tryptophan. Thus hCG, once thought to be involved only in maintaining corpus luteum function until the luteo-placental shift occurs, has now been found to promote a number of early pregnancy events. These events are probably initiated by elevated periovulatory LH levels and continued by raising hCG levels in a fertile cycle.

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