Concentrations of circulating hormones normalized to pulses of a prostaglandin F2alpha metabolite during spontaneous luteolysis in mares.

This research investigates the hormonal changes in mares (female horses) during a natural biological process called luteolysis using a substance known as the prostaglandin F2alpha metabolite. The study reveals essential details about these hormonal shifts, including the decrease in progesterone concentration and increases in cortisol, prolactin, and estradiol concentrations before, during, and after the peak of the metabolic process.

Study Design and Method

• The researchers aimed to explore the temporal relationships between hormonal changes and the pulse of a specific metabolite called 13,14-dihydro-15-keto-PGF(2alpha) (PGFM).
• They conducted their experiment on 11 mares and collected samples on an hourly basis to examine the changes occurring during the luteolytic period.
• They defined the PGFM pulse as ranging from 4 hours before the peak to 4 hours after it, with all hormonal data normalized based on the PGFM peak (Hour 0).

Key Findings

• The concentration of progesterone was found to decrease between Hours -4 and -3 and continued to decline linearly throughout the PGFM pulse.
• Cortisol and prolactin concentration both increased (P < 0.004) in the period from Hours -4 to 0, but declined (P < 0.002) from Hours 0 to 4.
• Estradiol concentration rose (P < 0.02) during Hours -4 to 0 but did not significantly change after Hour 0.
• There was no significant change in the concentrations of follicle-stimulating hormone and luteinizing hormone during the PGFM pulse.
• The percentage of corpus luteum area, which is an important area in female reproductive organs, indicating blood flow using color-Doppler signals remained steady from Hours -4 to 0, but started reducing (P < 0.004) between Hours 0 and 2.

Conclusions

• The researchers conclude that progesterone concentration diminished linearly during a PGFM pulse, while cortisol, prolactin, and estradiol concentrations increased up to the peak of the pulse.
• The results contradicted previous observations, where progesterone and gonadotropin levels were reported to rise following a single bolus luteolytic treatment with prostaglandin F(2alpha), suggesting that the natural secretion of prostaglandin F(2alpha) does not trigger increases in these hormones.