Luteolysis and associated interrelationships among circulating PGF2α, progesterone, LH, and estradiol in mares.

The research is about how the process of luteolysis – decay of the corpus luteum – in mares affects certain hormonal levels. Specifically, it examines the interrelationships between PGF2α, progesterone, LH, and estradiol before, during, and after luteolysis.

Study Methodology

The researchers involved in this study analysed the hormonal changes in 10 mares during the stages of luteolysis. The results are drawn from the data collected through hourly blood tests for four days, starting from the 12th day following ovulation.

Luteolysis’ Duration and Phase Identification

• The luteolytic period is defined as the time when progesterone levels decrease at a common transitional hour (Hour 0) at the end of preluteolysis and start of luteolysis until progesterone levels reach 1 ng/mL.
• The study found that the length of luteolysis was approximately 22.9 hours. This is contrasted with two days as depicted in previously published progesterone profiles from sampling every 6 to 24 hours.

Changes in PGF2α Levels

• In mares with complete data, the concentrations of PGF2α metabolite remained below the sensitivity level of the assay or consisted of two or three small pulses before luteolysis.
• During luteolysis, the PGF2α pulses became more visible or prominent.
• Rhythmicity or regular periodicity of PGF2α pulses wasn’t detected during preluteolysis, but seven of the nine mares showed rhythmicity during luteolysis and postluteolysis combined.

Changes in LH Pulses

• The nadir-to-nadir interval for LH pulses and the peak-to-peak interval between adjacent pulses were longer during preluteolysis than during luteolysis. The exact numbers mentioned for illustration purposes were 5.2 hours vs. 3.6 hours and 9.4 hours vs. 4.7 hours, respectively.

Interplay of Hormones

• During luteolysis, progesterone concentrations decreased linearly within the hours of each PGF2α pulse. This finding is different from previous studies in cattle in which an LH pulse had a positive effect on progesterone and estradiol concentration.
• The balancing effect noticed in heifers, where an LH pulse increased the progesterone concentration countering the negative effect of PGF2α was not observed in mares.

In conclusion, this research article provides an in-depth study of the hormonal interplays during the process of luteolysis in mares, which showed a different pattern from that observed in other animals like cattle/heifers.