Changes of plasma concentrations of steroid hormones, prostaglandin F2 alpha-metabolite and pregnant mare serum gonadotropin during pregnancy in thoroughbred mares.

The research traces the changes in plasma concentrations of various hormones, a prostaglandin derivative, and the pregnant mare serum gonadotropin in thoroughbred female horses (mares) over the course of their 11-month pregnancy period. The study reveals the fluctuations and correlations between these substances, suggesting their importance at different stages of pregnancy and in the functioning of the placenta, especially after Month 6.

Detailed Analysis of Hormones and Substances

• The researchers tracked the plasma concentrations of a series of substances – namely estrogens, gestagens, cortisol (F), pregnant mare serum gonadotropin (PMSG), and a prostaglandin derivative named 13,14-dihydro, 15-keto PGF2 alpha (PGFM).
• Initial investigations showed that levels of two types of estrogens (estrone (E1) and estradiol-17-beta (E2)) gradually increased throughout the pregnancy, peaking in the 8th month before decreasing towards the end of term.

Significance of Progesterone Derivatives

• Changes in progesterone (P) levels and its derivatives were also observed with two types of progesterone (17 alpha-OH-progesterone (17 alpha-OHP) and 20 alpha-OH-progesterone (20 alpha-OHP)) displaying distinct patterns. The former peaked early in pregnancy (3rd month) and the latter rose sharply after the 6th month of the mare’s pregnancy.

Other Concentrated Substances

• The concentrations of substances like PGFM, PMSG, and cortisol also showed noticeable fluctuations – PGFM levels spiked in the 2nd and 11th months while both F and PMSG were at their peak in the 2nd and 3rd months respectively.

Correlation between Hormones and Developmental Factors

• A factor analysis run by the researchers indicated a close correlation between certain hormones and the stage and development factors of pregnancy. For instance, E1, E2, and 20 alpha-OHP were associated with Factor 1 and increased as the pregnancy progressed.
• Similarly, PMSG, 17 alpha-OHP and progesterone were associated with Factor 2, which related to the development of the secondary corpus luteum.
• Further, cortisol and PGFM were grouped as Factor 3 and were found to influence the PGFM change in the 2nd month of pregnancy.

Findings of the Study

• Progesterone also appeared to have a complex relationship with Factors 1 and 3 and showed an inverse relation against PGFM.
• Ultimately, the researchers concluded that E1, E2, and 20 alpha-OHP (grouped under Factor 1) emerged as especially relevant parameters of placental function after the 6th month of pregnancy.