Luteolysis following carotid or ovarian arterial injection of prostaglandin F2alpha in mares.

The research aimed to determine the effects of prostaglandin F2α (PGF2α), a hormone-like compound, on the reproductive cycles of mares when injected directly into the carotid artery or ovarian artery. Results showed that ovarian artery injection was more effective in inducing luteolysis, a process involving the breakdown of the corpus luteum resulting in decreased progesterone levels and quicker onset of estrus and ovulation.

Experiment Design

• The study was conducted using 20 pony mares which were randomly assigned to one of five groups.
• The mares underwent different injections on Day 7 of their ovulation cycle depending on the group they were in. The types of injections were either into the carotid artery (ICA) or the ovarian artery (IOA).
• The injections contained different amounts of PGF2α or were used as controls with only vehicle (a substance used as a medium to deliver the actual drug) injected.
• Researchers measured progesterone and LH (Luteinising Hormone) levels in the mares at various points in time post-treatment.
• The researchers also recorded the intervals (days) from treatment to the estrus and ovulation cycle stages.

Results and Interpretation

• The mares that received IOA injections of .125 mg or .250 mg PGF2α had significantly shorter intervals from treatment to estrus and ovulation. There was no significant change in these intervals in mares that received ICA injections of .125 mg PGF2α, suggesting that the effect is more prominent on an ovarian level.
• The progesterone levels in the mares differed based on the type of injection they received. For mares that received an IOA injection of .125 mg PGF2α, progesterone levels significantly reduced by 24 hours after treatment. These findings suggest that PGF2α administered in the ovarian artery effectively induces luteolysis, leading to reduced progesterone levels.
• In the .250 mg IOA group, the plasma LH concentration increased after treatment, meaning that PGF2α may also stimulate LH secretion.
• A significant correlation was found between progesterone and LH concentrations in the mares given .125 mg and .250 mg IOA, suggesting that the changes in these hormones are linked.

Conclusions

• The research concluded that the principal site of luteolytic action of exogenous PGF2α in the mare is at the ovarian rather than at the hypothalamic-pituitary level.
• The study provides valuable insights in terms of how hormones can be used to manipulate the reproductive processes in mares, which could find applications in horse breeding.