Progesterone in blood. IV. Progesterone in the blood of mares.

The research investigates the levels of progesterone hormone in the blood of pregnant and non-pregnant mares, concluding that the detectable progesterone levels are closely linked to the state of the mare’s ovaries and that placental progesterone likely has a localized effect.

Investigation Into Progesterone Levels

• The study involved measuring levels of progesterone, a key hormone in the reproductive system of mares, in both pregnant and non-pregnant mares.
• The measurements were taken from peripheral blood, which is blood that flows throughout the body, not just concentrated in the heart, meaning it could give an overall look at the hormone levels in the body.
• Besides mares, umbilical cord blood was also obtained during foaling to measure progesterone level.

Findings on Progesterone Levels

• Progesterone was found to be detectable in the blood of both pregnant and non-pregnant mares, the condition being the presence of a fully developed corpus luteum in the ovaries. Corpus luteum is a mass of cells that forms in an ovary and is responsible for the release of progesterone during early pregnancy.
• However, progesterone was not detectable in peripheral blood during the second half of gestation when the ovaries have become fibrotic, meaning they have hardened due to the penetration of fibrous tissue, despite high concentrations of progesterone in umbilical cord blood.

Discussion on the Disappearance of Progesterone

• The researchers discuss potential reasons behind the disappearance of detectable progesterone in blood circulation during the second half of pregnancy.
• They conclude that during this phase, placental progesterone likely exerts a local effect on the uterus, meaning it affects the uterus directly without needing to move into the maternal blood circulation system.
• Such action is possible due to the specific nature of the mare’s placenta which is diffuse and epithelio-chorial, characterised by the direct contact of maternal and fetal tissues.