Controlling interrelationships of progesterone/LH and estradiol/LH in mares.

This research looks into the relationship between progesterone, estradiol, and luteinising hormone (LH) during the ovulation cycle of mares. The findings suggest that progesterone and LH concentrations decrease similarly from day 6 until the onset of luteolysis on day 14, with LH affecting the progesterone levels. Moreover, the rate of increase in the LH concentration during the ovulatory surge differs, depending on the ovulation stage.

Understanding Hormonal Interactions During Ovulation

The study examines the interplay between estradiol, progesterone, and the luteinising hormone during a mare’s ovulation cycle.

• The analysis begins with the first ovulation, labeled as Day 0, and spans the full interovulatory interval.
• Progesterone concentration increases starting from Day 0, with the maximum level reached on Day 6 and luteolysis beginning on Day 14. Luteolysis is the process where the corpus luteum, a hormone-secreting structure that develops in the ovary after ovulation, gradually degenerates.
• A common progesterone threshold of about 2 ng/ml is identified as potentially having a negative effect on LH concentration, both at the beginning and end of the luteal phase. This suggests a critical balance between these two hormones in a mare’s cycle.

Fluctuations in Progesterone and LH Concentrations

The researchers noted the fluctuations in progesterone and luteinising hormone concentrations during the ovulation cycle.

• Progesterone and LH concentrations decrease at an equivalent rate from Day 6 onwards until the onset of luteolysis on Day 14. This shows a consistent correlation between the levels of these two hormones.
• This trend could also suggest a diminishing positive effect of LH on progesterone concentration during this period.

LH Concentration Increase and Estradiol Surge

The study details the rate and stages of LH increase during the ovulatory surge.

• The researchers identified two linear regression segments in the increase of LH concentration. From Day 14-22, the rate is 0.4 ng/ml/day, which then rises to 1.8 ng/ml/day from Day 22 until one day after the second ovulation.
• The end of the first increase segment and the beginning of the second come two days before ovulation, coinciding with the peak of the ovulatory estradiol surge. Estradiol is an estrogen steroid hormone and a primary female sex hormone. It surges at ovulation to prepare the reproductive tract for conception.