Concentrations of circulating hormones during the interval between pulses of a PGF2α metabolite in mares and heifers.

This research focuses on the relationship between various hormones and a metabolite of prostaglandin F2α (PGFM) in both heifers (young female cows) and mares (adult female horses) during luteolysis. Different hormonal responses were observed in these two species between PGFM pulses, leading to plateaus, fluctuations, and correlations with other hormones like leutinizing hormone (LH) and prolactin (PRL).

Study subjects and setup

• The study involved seven mares and six heifers. The mares were chosen based on a 9-hour interval between 2 PGFM pulses. This interval represents the part of luteolysis where the corpus luteum (a hormone-secreting structure in female animals) is breaking down.
• In heifers, the interval between pulses varied, so researchers took the average 8-hour interval by using four hours after the peak of the first PGFM pulse and four hours before the peak of the second pulse. This interval was used to represent the average time between pulses in heifers.

Hormonal responses in mares

• In the mares, estradiol, a type of estrogen, increased significantly during each PGFM pulse and then plateaued for about 6 hours between pulses, leading to a stepwise increase.
• Progesterone, another hormone, decreased linearly throughout both the intra-pulse and inter-pulse intervals, indicating it’s reduced both within and between PGFM pulses.

Hormonal responses in heifers

• Heifers showed differing hormone patterns. Estradiol increased during the rising portion of each PGFM pulse, then decreased one hour before the peak of the first pulse and at the peak of the second pulse.
• This lowered estradiol in the second pulse was correlated with a simultaneous increase in prolactin (PRL).
• A noticeable decrease in estradiol also happened in individual heifers about 5 hours after the first peak of PGFM. This decrease coincided with a transient increase in luteinizing hormone (LH), suggesting a possible correlation there as well.

Summary of results

• In the period between PGFM pulses, estradiol plateaued in mares, while fluctuated in heifers.
• Heifers showed time-based relationships between estradiol and LH, and apparently between estradiol and PRL, which could be meaningful for future reproductive studies.