Steroids in the establishment and maintenance of pregnancy and at parturition in the mare.

The research article investigates how steroids contribute to establishing and maintaining pregnancy and the role they play during the birthing process in mares. The study uses innovative technology to measure levels of multiple steroid hormones in blood, foetal, and placental tissues, advancing current knowledge about pregnancy and birth strategies in horses.

Research Methodology

• The study made use of liquid chromatography mass spectrometry. This method allowed the researchers to measure numerous steroid hormones simultaneously in the blood and in the tissues of the foetus and placenta.
• This investigation was carried out throughout a normal gestation period as well as in mares with experimentally induced placentitis, which is inflammation of the placenta.

Key Findings

• The research revealed that the stimulation of luteal steroidogenesis by equine chorionic gonadotropin from the endometrial cups results in additional androgen and oestrogen secretion.
• As the endometrial cups and eCG disappear, progesterone reduces and is replaced by 5α-dihydroprogesterone, an effective agonist for the equine progesterone receptor, concurrent with the growth of the chorioallantoic placenta.
• From that point on, foetal pregnenolone and dehydroepiandrosterone secretion influences placental steroidogenesis, thereby providing a substrate for the synthesis of 5α-pregnane and oestrogen. This is an unusual instance of a ‘foeto-placental unit’.

Further Observations

• The research also sheds light on the unusual strategies seen during gestation and foaling.
• It was found that foetal gonadal dehydroepiandrosterone fuels placental oestrone sulphate secretion, which reaches far higher concentrations in mares than any other known species and then steadily decreases to term.
• The study also discovered how additional 5α-reduced (DHP) metabolites increase from mid-gestation to peak concentrations just before birth, going down prepartum, likely because of the selective loss of placental SRD5A1 expression and activity.
• Similar fluctuations were noticed in mares with induced placentitis, implying that progestin withdrawal in mares is both systemic (related to pregnanes) and local (dependent on receptors).
• The research also showed that some steroids detected by immuno-assay during equine pregnancy were not detected by mass spectrometry, highlighting the value of this analytical technique.