Secretion patterns of oxytocin and PGF2alpha-metabolite in response to cervical dilatation in cyclic mares.

This study explores the influence of cervical dilation on the estrous cycle in mares, particularly its impact on progesterone and oxytocin levels. It found that dilation shortens the cycle and produces a marked increase in oxytocin levels, but doesn’t significantly alter PGF2alpha-metabolite concentrations.

Research Design and Methods

• This study employed six healthy Haflinger mares, and utilized a Latin square design to administer three different treatments: control (no intervention), insertion, and dilation. These procedures were conducted on Days 5 and 7 of the mares’ cycles in varied orders to ensure data reliability.
• Dilatation was achieved by gradually inflating a balloon catheter every 30 seconds using warm physiological saline until a maximum of 50ml. The resulting size of the balloon was 4.5cm in diameter and 6cm in length.

Findings and Implications

• The researchers found a significant decrease in the length of the estrous cycles of the mares that underwent dilation, compared to those in the control and insertion groups.
• Progesterone concentrations on Days 10, 12, and 14 post-ovulation were markedly lower in the dilation group. This lower progesterone secretion was also observed when calculating the Area Under Curve (AUC) from Day 7 to Day 12.
• Oxytocin levels saw a remarkable increase following both cervical insertion and dilation. This was noted from the basal levels (1.0-6.1 pg/ml) that soared to maximum levels (insertion: 125.5 pg/ml and dilatation: 305.2 pg/ml). The oxytocin AUC was significantly higher for insertion and dilation compared with the controls.
• Dilation did not cause considerable changes in the plasma concentrations of the PGF2α metabolite, indicating that dilation did not trigger any immediate PGF2α release. Hence, the luteolytic pathway, which is involved in the breakdown of the corpus luteum, is unlikely to be the factor shortening the length of diestrus and the estrous cycle.
• This led the team to hypothesize that the consistent rise in oxytocin levels could be responsible for the shortening of the luteal phase post-cervical manipulation. The luteal phase is the part of the estrous cycle where the body prepares for potential pregnancy post-ovulation, and its alteration may have significant reproductive implications.