Doppler sonography of the uterine and ovarian arteries during a superovulatory program in horses.

This study investigates how treatment with gonadotropins, to stimulate superovulation, affects the ovarian and uterine blood flow in horses, its relationship with steroid hormone levels, and the response of the ovary to the treatment. Using color Doppler sonography, it was discovered that the treatment causes a significant increase in uterine and ovarian perfusion, which is concurrent with the development of multiple follicles and an increase in estrogen levels. This increased blood flow seems to be related to how effectively the ovaries respond to the stimulation.

Study Methodology

• The study observed six mares over five cycles and examined them sonographically for 3 days (from t1 to t3) during the follicular development phase, and for 4 days in the preovulatory phase. These examinations started when a follicle size of ≥ 22 mm was observed.
• Following each examination, the levels of total estrogens and progesterone in the peripheral plasma were determined.
• The cycles alternated, such that the 1st, 3rd and 5th cycles were unstimulated, while the 2nd and 4th cycles were stimulated using eFSH.
• The mares were inseminated when in estrus at 12 and 24 hours after hCG administration. Embryo recovery was carried out 6.5 days post ovulation.
• Ovarian and uterine blood flow were quantified by observing the blood flow volume and the pulsatility index in their respective arteries.

Results from Study

• The mean number of ovulations and developing Corpus Luteum (CL) was 1.3 ± 0.4 in unstimulated cycles and 4.4 ± 3.1 in stimulated cycles with no difference between the ovaries within mares.
• No difference was observed in the uterine blood flow volume and pulsatility index during the follicular development phase between the unstimulated and stimulated cycles.
• However, during the preovulatory phase, the pulsatility index was lower and blood flow volume was higher in stimulated cycles than in unstimulated cycles.
• All uterine and ovarian blood flow parameters were related to the number of developing follicles in the stimulated cycles.
• The pulsatility index in both the uterine and ovarian arteries showed a negative correlation with the number of ovulations on t3, and with the number of collected embryos on different days.
• Progesterone levels were not positively correlated with the uterine blood flow volume.
• However, the estrogen levels and ovarian blood flow volume in the stimulated cycles showed a positive correlation.

Conclusion

The research found that treatment with gonadotropins to induce superovulation in mares resulted in a significant increase in uterine and ovarian blood flow. This increased blood flow was concurrent with the development of multiple follicles and an increase in estrogen levels, indicating a correlation between gonadotropin treatment, increased perfusion and steroid hormone levels. The results suggest that this increased blood flow may be related to the effectiveness of the ovarian response following stimulation, ultimately improving the outcome of superovulation.