Role of luteinizing hormone in follicle deviation based on manipulating progesterone concentrations in mares.

The study examines the role of hormones in the growth of follicles in mares, revealing that high doses of progesterone suppresses follicle growth, while intermediate doses of the same do not affect Follicle Stimulating Hormone (FSH) levels but lead to a decrease in Luteinizing Hormone (LH) levels prior to the deviation in growth rate observed in the control group.

Study Approach and Methodology

• The researchers explored the impact of varying doses of progesterone on FSH and LH concentrations in order to understand their influence on the deviation of growth rates involving the two largest follicles.
• The mares were given daily doses of progesterone according to four categories: 0 mg (as a control group), 30 mg (low dose), 100 mg (intermediate dose), and 300 mg (high dose).
• Ablation was performed on all follicles greater or equal to 6 mm in size on day 10, with the day of ovulation being referred to as Day 0. This method set forth a new follicular wave.
• They also induced luteolysis using prostaglandin F(2alpha), and progesterone was administered from Days 10 to 24.

Study Findings and Results

• The low dose of progesterone did not result in any significant changes to the ovarian or gonadotropin end points.
• High doses reduced FSH concentrations and in turn, this caused a reduction in the growth of the two largest follicles, making them smaller than in the control group.
• The intermediate dose did not affect FSH concentrations but led to an initial increase in LH concentrations followed by a decrease to pretreatment levels.
• The decrease in LH in the intermediate group occurred two days prior to the growth rate deviation observed in the control group.
• The decrease in the size of the largest follicle in the intermediate group was statistically significant compared to the control group, while the size of the second-largest follicle remained the same across both groups.

Conclusions and Implications

• The research revealed that high levels of progesterone suppress the growth of follicles by through FSH depression.
• Intermediate levels of progesterone caused a decrease in LH levels before a deviation in growth rates, but this didn’t delay the onset of deviation.
• From these findings, the researchers suggested that LH was not involved in the initiation of dominance (where the largest follicle inhibits the growth of other follicles) but was required for sustained growth of the dominant follicle after or concurrently with its initial expression of dominance.