Maternal recognition of pregnancy in the horse: a mystery still to be solved.

The research focuses on the complex process of maternal recognition of pregnancy in horses, a phenomenon that has yet to be fully understood. Some key elements considered are the conceptus’ role in reducing the secretion of specific prostaglandins, the potential use of cyclooxygenase-2 as a regulator, and the critical influence of conceptus mobility.

Conceptus and Maternal Recognition

• Maternal recognition of pregnancy in horses is achieved through a series of events that ensure the maintenance of pregnancy. In particular, this involves prolonging the lifespan of the corpus luteum, a hormone-secreting structure that develops in an ovary after an ovum has been discharged.
• An interesting aspect in horses is that the signal for pregnancy recognition, derived from the conceptus or embryo, is not yet identified. This makes pregnancy recognition in horses vastly different from many other domestic species.

Prostaglandin Secretion and Cyclooxygenase-2

• During the early stages of gestation in horses, the presence of the conceptus is noted to reduce the secretion of prostaglandin F(2α) by the endometrium. This reduction is partly linked to the reduced expression of cyclooxygenase-2, an enzyme responsible for the formation of prostanoids, including prostaglandin.
• Given its interaction with the embryo and its effect on prostaglandin release, cyclooxygenase-2 has been proposed as a potential regulator of endometrial prostaglandin F(2α) release. The presence of this enzyme may be modulated by a yet-unidentified factor secreted by the conceptus, which seems to act against the luteolytic, or luteum degrading factor.

Oxytocin Responsiveness and Conceptus Mobility

• Alterations in the responsiveness to oxytocin, a hormone that can trigger uterine contractions, has been implicated in adjusting the release of prostaglandins in pregnant mares.
• Conceptus mobility has been established as a crucial factor in securing pregnancy. The study, however, indicates that other substances produced by the conceptus, such as oestrogens and prostaglandin E(2), are not confirmed to act as the critical antiluteolytic factor.

Inducing Luteal Function and Transcriptome Comparisons

• The review discusses multiple methods to stimulate extended luteal function in non-pregnant mares that may be relevant to understanding the process of maternal recognition of pregnancy.
• The study also presents an analysis of recently published microarray experiments that compared the transcriptome of pregnant and non-pregnant endometria and different stages of conceptus development. Key findings from these studies include preventing conceptus adhesion, providing nutrients to the conceptus, and avoiding immunological rejection.