The uterus as a source of oxytocin in cyclic mares.

The research explores the role of oxytocin, a hormone, in the reproductive cycle of mares. The oxytocin appears to be secreted inside the uterus and encourages luteolysis, the disintegration of the corpus luteum that signals the end of a menstrual cycle.

Objective of the Research

The purpose of this research was to verify the role of oxytocin in the cyclical luteolysis observed in mare reproduction. Luteolysis refers to the process of breaking down and removing the corpus luteum from the uterus, leading to the end of a reproductive cycle or the onset of new one in these animals.

• Through their previous study, the researchers had established that continuous administration of oxytocin between day 8 and day 20 post-ovulation could prevent luteolysis in most mares.
• This earlier finding prompted further exploration into the links between oxytocin and the reproductive cycles of mares.

Methods Used in the Research

The authors of this paper used several scientific procedures to explore the relationship between oxytocin and mare luteolysis.

• They measured the concentration of oxytocin found in the uterine fluid of nine mares between days 14 and 18 following ovulation.
• They also administered oxytocin directly into the uterus of some mares to observe the effect on the concentration of 13,14-dihydro-15-keto PGF2alpha in their blood. This compound is produced naturally by the body in response to oxytocin and is involved in the process of luteolysis.

Findings of the Research

The outcomes of the measurements and the uterine administration of oxytocin assisted the researchers to draw conclusions about the role of this hormone in mare reproduction.

• The results from the oxytocin concentration measurements showed exceptionally higher quantities inside the uterus compared to the levels in the mare’s peripheral blood plasma. This finding indicates the uterus as a major source of oxytocin during certain stages of the mare’s reproductive cycle.
• The administration of oxytocin directly into the uterus led to a notable increase in the peripheral blood plasma levels of 13,14-dihydro-15-keto PGF2alpha. Despite the increase, there was no corresponding rise in plasma oxytocin levels, which hints at the secretion of oxytocin in the uterus in sizable amounts.
• These results indicate that oxytocin plays a significant part in luteolysis in mares’ reproductive cycles. It is secreted inside the uterus during the late dioestrus and early oestrus stages, where it promotes a release of PGF2alpha and ultimately leads to luteolysis.