Corpus luteal function in nonpregnant mares following intrauterine administration of prostaglandin E(2) or estradiol-17beta.

This study evaluated whether the intrauterine administration of prostaglandin E(2) or estradiol-17beta can extend the functioning of the corpus luteum in nonpregnant horses. The hormone prostaglandin E(2) was found to support this theory, unlike estradiol-17beta.

Objective

• The principal objective of the research was to determine if the intrauterine administration of the hormones prostaglandin E(2) (PGE(2)) or estradiol-17beta (E-17beta) could extend the function of the corpus luteum (CL) in nonpregnant mares.

Procedure

• Nonpregnant mares were continuously administered either 240 µg/d of PGE(2), 6 µg/d of E-17beta, or a vehicle (sham treatment).
• The administration took place from Days 10 to 16 following ovulation, using osmotic minipumps which were surgically placed into the uterine lumen on Day 10.
• Pregnant and nonpregnant mares were used as positive and negative controls, totaling to 11 per group.
• CL function was defined as extended if plasma progesterone remained above 2.5 ng/ml and if ovulation did not occur on Days 9 to 30.

Results

• CL function was extended until Day 30 for 1 out of 11 nonpregnant mares, 4 out of 11 sham-treated mares, 6 out of 11 E-17beta-treated mares, 8 out of 11 PGE(2)-treated mares, and all 11 pregnant mares.
• Statistically, the incidence of extended CL function in the nonpregnant and sham-treated mares was similar.
• The hypothesis that PGE(2) would extend CL function in nonpregnant mares was corroborated, as mares treated with PGE(2) had a higher incidence of extended CL function compared to nonpregnant mares and sham-treated mares, and a not significantly different incidence when compared with pregnant mares.
• The hypothesis that E-17beta would extend CL function was not confirmed, i.e., there was no notable difference in the incidence of prolonged CL function between E-17beta-treated mares and sham-treated mares, and the incidence was lower in E-17beta-treated mares compared to pregnant mares.

Conclusion

• The findings showed that intrauterine administration of a pharmacological dose of PGE(2) launched extended CL function in nonpregnant mares.
• The researchers suggested that additional studies are necessary to validate the role of conceptus secretion of PGE(2) in CL maintenance and to unravel the mechanism of action of PGE(2) within the equine reproductive tract.