Follicle suppression of circulating follicle-stimulating hormone and luteinizing hormone before versus after emergence of the ovulatory wave in mares.

The research article examines how the ovarian follicles in mares affect the plasma concentrations of two hormones, namely follicle-stimulating hormone (FSH) and luteinizing hormone (LH). The researchers observed the effects on these hormones before and after the emergence of the ovulatory follicular wave.

Study Design

• The investigation was carried out on a group of mares from Day 0 (the day of ovulation) to Day 18, in four designated groups of six mares each.
• Except for a control group, follicles greater than or equal to 6mm in diameter were removed or ‘ablated’ from the other three groups on Days 0.5, 6.5, or 12.5.
• This time structure was based on the observation that in the herd of mares studied, the ovulatory follicle typically emerged at about 6mm in size around Day 10.5 on average.

Results and Observations

• Analysis of plasma FSH concentrations revealed that the levels did not differ significantly in the groups with follicle ablation on Day-0.5 or Day-6.5 when compared to the control group. However, when follicles were ablated on Day 12.5, there was an immediate increase in FSH concentration.
• The LH response was different. The ablation of follicles on Day 0.5 had a particular pattern. There were notably lower LH concentrations on each of Days 15.5 to 18.0 compared to the control group. But, follicle ablation on Days 6.5 or 12.5 did not lead to a significant group effect or interaction.
• A distinct drop in testosterone concentration was observed on Day 2 in the group where follicles were ablated on Day0.5. This change was not seen in progesterone or estradiol concentrations.

Conclusions

• The researchers concluded that follicles do not contain adequate FSH suppressors on Days 0.5 and 6.5, suggesting that these suppressors appear only in the Day-12.5 ablation group or after the expected emergence of the ovulatory wave.
• The study supports the theory of an association between low postovulatory concentrations of an ovarian steroid and low concentrations of LH after Day 15.