Oxytocin induction of pulses of a prostaglandin metabolite and luteolysis in mares.

The research investigates the role of oxytocin (OT) in prompting a prostaglandin metabolite (PGFM) pulse that simulates the one in luteolysis (degradation of the corpus luteum) in mares. The study determines that oxytocin can play a role in luteolysis in mares, similarly to other species.

OT Administration and PGFM Response

• The research develops a method for administering oxytocin (OT) to mares on Day 13 post-ovulation to stimulate a burst of PGFM, a metabolite of Prostaglandin F2α, which mimics a natural PGFM pulse during the luteal phase.
• Despite attempts using different doses, a bolus dose of oxytocin doesn’t produce the same response as a natural PGFM pulse. The maximum response was different, occurring approximately 4 minutes after administration.
• However, a two-hour infusion of oxytocin at doses of 1.25, 2.5, or 5 IU/100 kg induces a PGFM pulse similar to those reported in nature.

Peak Induced PGFM Levels

• The peak of an OT-induced PGFM pulse (260-380 pg/mL) turned out to be fairly similar to the natural peaks (200-300 pg/mL), as per the assay system in use. The interval from nadir to nadir was about 6.6 ± 0.2 hours.

Decrease in Progesterone Concentration

• There was a significant decrease in progesterone (P4) within 8 hours following OT infusion at doses of 1.25, 2.5 or 5IU/100kg, more than that observed in the control group. This indicates that OT infusion somehow stimulated a decrease in P4 levels.
• Flunixin meglumine treatment, a cyclooxygenase inhibitor, also led to decline in P4 concentration. But interestingly, this pretreatment didn’t prevent the OT-induced PGFM pulses nor the decrease in P4 concentration.

Conclusion

• The research concludes that an OT infusion, but not a bolus, can simulate a PGFM pulse. The pulse then induces a decrease in P4 that isn’t prevented by a cyclooxygenase inhibitor. This signals the idea that OT in mares could have the same role as in other species in relation to luteolysis.
• The results obtained from this research could be an important breakthrough in animal reproduction biology, shedding light specifically on the role of oxytocin in the luteal phase of the reproductive cycle.