Interrelationships of estradiol, inhibin, and gonadotropins during follicle deviation in pony mares.

The research study investigates the interplay between hormones such as FSH, LH, estradiol, and inhibin, and the growth of ovarian follicles within pony mares. It compares this masculine interdependence during the first and second ovulation waves as well as the last anovulatory wave. The research shows that the rise in estradiol as deviation starts is not essential for suppressing the FSH surge and starting the deviation.

Research Methodology

• The researchers studied the changes in circulating concentrations of FSH, LH, estradiol, and total inhibin related to the beginning of follicle diameter deviation.
• This study was conducted among the last anovulatory follicular wave of the year and the first and second ovulatory waves in pony mares. Seven mares were included in the sample.
• Follicle diameters and circulating hormone concentrations for each wave were normalized to the observed beginning of deviation (Day 0).

Key Research Findings

• The study found that follicle deviation occurred during the anovulatory wave as well as during the ovulatory waves, and the diameter of the future dominant follicle at the beginning of deviation was similar for the three waves (overall mean: 23.7+/-0.6 mm).
• The circulating estradiol concentrations did not increase during the last anovulatory wave but increased similarly for the two ovulatory waves, beginning near the onset of deviation.
• There were no differences among waves in concentrations of inhibin encompassing deviation.
• The FSH concentrations for the wave-stimulating FSH surge did not differ significantly among the three waves. Circulating LH did not increase during the last anovulatory wave but increased during the first and second ovulatory waves.

Research Conclusions

• The research concluded that an increase in circulating estradiol at the beginning of deviation was not required for suppression of the wave-stimulating FSH surge and the initiation of deviation.
• This conclusion was based on an observed estradiol increase in association with deviation during the ovulatory waves but not during the anovulatory wave.
• Concentrations of inhibin were similar among waves and thus, the similar suppression of FSH was attributed to inhibin.
• The later increase in LH before the first ovulation was not attributable to estradiol, evidenced by the similarity between the two ovulatory waves in the increasing estradiol concentrations.