Effect of aromatase inhibition on follicular development, blood flow, ovulation and ovulation rate in the mare

Abstract

Letrozole inhibits aromatase which is responsible for estrogen synthesis. This aromatase inhibitor has been successfully used in women, cattle and rats. However, it has never been tested in cyclic mares. The effect of treatment with letrozole prior to follicle deviation (e 20mm) will be evaluated in 40 cyclic mares during a complete estrous cycle. Animals will be divided in four groups (n=10 mares/group): Letrozole-Aspiration and Control-Aspiration in which will be performed follicular aspiration and Letrozole-US and Control-US in which will be performed B-mode and Doppler ultrasonography of follicles daily. All treatments will be done every other day intravenously (500 mg of letrozole) or intramuscularly (10 mL NaCl 0.9%) starting prior to follicle deviation (diameter e20 mm) until ovulation. Blood samples will be collected daily to measure FSH, LH, estradiol and progesterone. Mode-B ultrasonography will be performed daily to determine number of follicles present in the preovulatory follicle wave, day of deviation, interval from deviation to ovulation, interovulatory interval, number of preovulatory follicles and uterine edema. Doppler ultrasonography will be done daily to evaluate follicular wall hemodynamics. Additionally, follicular fluid will be collected by transvaginal aspiration of pre-ovulatory follicles (e35 mm) to measure progesterone. (AU)