Patterns of oxytocin secretion during the oestrous cycle of the mare.

The research article explored how oxytocin levels change throughout the mare’s oestrous cycle, finding that oxytocin levels and their patterns of secretion fluctuate at different stages, potentially impacting the cycle’s regulation.

Study Details

• The study involved a sample group of 11 mares that were undergoing their regular oestrous cycles. Blood samples were collected at specific intervals – every three minutes for the first two hours and then every 15 minutes for the next six hours during four stages of the oestrous cycle.
• The researchers tracked oxytocin concentrations in the plasma at different points in the cycle and found that levels were highest 15 days after ovulation before decreasing again – strikingly higher than the days immediately after ovulation.
• Oxytocin was found to be secreted in a pulsed or rhythmic manner throughout the cycle. The study identified three different duration rhythms: short (0-29 minutes), medium (30-89 minutes) and long (over 90 minutes). However, the frequency of these pulses remained consistent regardless of where the mare was in her cycle.

Findings and Implications

• The pulse amplitudes for the short and medium duration rhythms were greatest on the 7th day post ovulation, significantly higher than on the day of ovulation, the 3rd day, and 15 days after. Interestingly, the base values for oxytocin during the 8-hour sampling period indicated a potential circadian rhythm, suggesting that there might be a time-of-day effect to oxytocin secretion as well.
• The researchers concluded these findings are in line with previous research indicating that oxytocin is secreted in a pulsed manner and might play a role in the regulation of the oestrous cycle.
• It is suggested that oxytocin may promote the breakdown of the corpus luteum (luteolysis) through inducing the synthesis and release of uterine PGF-2 alpha, a hormone known to regulate the luteal phase of the cycle. More research is needed to confirm these potential effects and explore the specifics of oxytocin’s role in the mare’s oestrous cycle.