The equine placenta and equine chorionic gonadotrophin–an overview.

This research investigates the role of equine Chorionic Gonadotrophin (eCG) in the gestational process of horses. The hormone, produced by specialized cells in maternal uterine endometrium, is found in pregnant mares’ blood, peaking between days 60 and 80.

Chorionic Gonadotrophins in Equines and Primates

• The study states that Chorionic Gonadotrophins seem to be unique for primate and equid species. These hormones play essential roles in the process of equine pregnancy. In equines, the fetus does not implant in the maternal uterine endometrium until around day 37 of gestation.

Formation of Endometrial Cups

• When the fetus implants, specialized cells in the trophoblast, organized as the embryonic girdle, invade the endometrium, forming the so-called endometrial cups. As these cells migrate, their form changes and a gonadotrophic hormone appears in the mare’s blood. Researchers have confirmed that this hormone comes from the chorion, giving it the name equine Chorionic Gonadotrophin (eCG).

Elevated eCG Levels

• The levels of eCG peak between days 60 and 80 in pregnant mares, then gradually decrease until day 130. There is a significant variation in eCG levels between individuals. The study suggests there are no hormonal regulatory mechanisms controlling eCG synthesis and secretion, implying that the size and morphology of the endometrial cups limit it.

Structure of eCG

• The eCG hormone is a glycoprotein comprised of two parts, noncovalently bound alpha- and beta-subunits. The alpha-subunit consists of 96 amino acids and is identical for eCG and the pituitary hormones eLH, eFSH, and eTSH. The beta-subunit is similar to beta-hCG, both having a C-terminal extension, and consists of 149 amino acids whose structure is identical to that of beta-eLH.