The equine endometrial cup reaction: a review.

This study investigates the role of eCG (equine chorionic gonadotropin) during equine pregnancy. The analysis suggests that eCG might not be responsible for secondary ovulations due to its limited FSH activity, but it could be crucial for the resurgence of primary corpus luteum. Furthermore, eCG shows a remarkable heterogeneity in different stages of gestation within the same mare. This review also discusses the function of cytotoxic antibodies during equine pregnancy, especially their relationships with the paternal MHC molecules.

Role of eCG in Equine Pregnancy

• The study emphasizes that the role of equine chorionic gonadotropin (eCG) in horse pregnancy is ambiguous, particularly because eCG demonstrates insignificant follicle-stimulating hormone (FSH) activity, suggesting that it may not induce secondary ovulations.
• eCG does display luteotropic activity, indicating that it could potentially trigger the revival of the primary corpus luteum, an important structure in regulating hormone production during pregnancy.

Heterogeneity of eCG

• Supporting evidence suggests that the receptor population on equine gonads varies considerably, enabling them to differentiate between eCG and equine luteinizing hormone (eLH), leading to diverse post-receptor impacts.
• eCG itself portrays a diversity not only between different individual animals but also within one animal at various gestation stages. This heterogeneity encompasses glycogenesis and the primary structure of eCG.
• Such differences could merely signify the disparity between stored and secreted hormones. In contrast, they could also hint that different eCG forms’ release might be under endocrine control, enabling the mare to generate forms suited to specific biological requirements.
• This suggests that certain eCG forms may influence the immunological events happening at the foeto-maternal interface.

The Function of Cytotoxic Antibodies in Equine Pregnancy

• The role of cytotoxic antibodies during equine pregnancy is still largely a mystery. Although they target the paternal MHC molecules, these antibodies are not harmful to the pregnancy since their target molecules disappear from the endometrial cup tissue when the antibodies begin to circulate.
• Such a unique regulatory mechanism of MHC expression remains poorly understood, calling for more detailed investigations in the future.