Plasma progestins in pregnant, postpartum and cycling mares.

This study evaluates the levels of progestin hormones in the blood of mares during pregnancy, postpartum, and the estrous cycle, revealing fluctuations that reflect the physiological changes in different phases.

Analysis of Progestins in Mares

The research involves:

• Extracting jugular vein plasma from 13 mares. This plasma was analysed using chromatography and a competitive binding radioassay.
• Quantifying two hormones: progesterone, which is crucial for maintaining pregnancy, and 17α-hydroxyprogesterone (170HP), a steroid hormone produced in the adrenal glands and gonads.

Progesterone Levels Throughout Pregnancy and Postpartum

The findings related to progesterone include:

• An increase in progesterone from 1.1 ng/ml to 7.5 ng/ml eight days into pregnancy. There’s a transient decrease to 4.8 ng/ml on day 28.
• From days 28 to 44, progesterone levels rise again, reaching a maximum concentration of 15.2 ng/ml by day 64.
• From days 180 to 300, progesterone gradually dropped and remained between 1 and 2 ng/ml.
• During the last 30 days of gestation, progesterone increased to 4.4 ng/ml 5 days prepartum but then decreased to less than 0.5 ng/ml 1 to 3 days postpartum.

Levels of 17α-Hydroxyprogesterone and Other Compounds

The research also:

• Demonstrated low levels of 17α-hydroxyprogesterone during gestation. Higher levels were found at two periods: between days 40 and 120, and during the last 30 days of gestation.
• Identified two unidentified compounds that appeared in the plasma between days 30 and 60 of gestation. These compounds gradually increased to day 300, significantly increasing 5 days before birth, but were not detected postpartum or during the estrous cycle.

Progesterone During the Estrous Cycle

The research on mares’ estrous cycles shows:

• Progesterone levels were less than 1 ng/ml during estrus, increasing from day 2 to day 12 of diestrus.
• Significant elevation of progesterone was observed by day 4 of diestrus, but there were no significant changes in the levels from day 4 through day 12.

In conclusion, this study provides a detailed chronological profile of fluctuations in progesterone and 17α-hydroxyprogesterone in mares during pregnancy, postpartum, and the estrous cycle. In addition, it pinpointed the presence of unidentified compounds that merit further investigation.