Effects of ovarian input on GnRH and LH secretion immediately postovulation in pony mares.

This research investigates how the presence or absence of ovaries in pony mares influences the post-ovulation levels of GnRH and LH, hormones critical for reproductive function. It suggests that the decline in LH after ovulation requires feedback from the ovaries and that the removal of the ovaries disrupts the secretion of GnRH, effectively preventing the decline of LH post-ovulation.

Research Approach and Methodology

• The study was performed on two groups of pony mares: one group had their ovaries intact (Group 1, n=3), and the other was ovariectomized (Group 2, n=3) within 12 hours of ovulation.
• The mares’ blood was collected every 10 minutes over a 6-hour period during estrus (the period when mares are sexually receptive) and 8 days post-ovulation. The blood was drawn from the jugular vein (JV) and intercavernous sinus (ICS) for detailed analysis of LH and GnRH.
• Further, JV blood samples were collected twice a day at 12-hour intervals for 30 days to analyze LH and progesterone (P4) levels.

Primary Findings

• The study found significant differences in the plasma LH concentrations between the two groups. LH concentrations decreased in the intact mares but remained elevated in ovariectomized mares, indicating that ovarian factors play a significant role in regulating postovulation LH levels.
• A further rise was observed in LH levels in ovary-removed mares by Day 8 post-ovariectomy. This increase could be attributed to an elevated LH episode amplitude.
• Analyses of the GnRH hormone showed a decrease from estrus to Day 8 in both groups, indicating that the sampling period could influence GnRH levels. Moreover, GnRH episode amplitude declined in the ovariectomized mares from estrus to Day 8 but remained relatively stable in the control group.

Conclusion

• This research illustrated the role of ovarian feedback in the decline of LH after ovulation. It also emphasized that the removal of ovaries alters the dynamics of GnRH secretion, thus impeding the postovulatory decline in LH concentrations, which instead tend to further increase with time after ovary removal.