PARENT SESSION
FUNCTION AND REGULATION OF THE CORPUS LUTEUM
Laurel
7:30 AM-10:00 AM

(459) LOCAL CHANGES IN THE BLOOD FLOW WITHIN THE PREOVULATORY FOLLICLE WALL AND EARLY CORPUS LUTEUM IN THE COW: EFFECT OF LH SURGE.

Acosta Ayala, Tomas^1,2, Hayashi, Ken-GO¹, Hayashi, Misato¹, Masayuki, Ohtani¹, Miyamoto, Akio¹, ¹ Dept of Animal Science, Obihiro, Japan² Dept de Fisiologia, San Lorenzo, Paraguay

ABSTRACT- Hemodynamic changes are involved in the cyclic remodeling of ovarian tissue that occurs during ovulation and the new corpus luteum (CL) development. Therefore, this study aimed to characterize the real-time changes in the blood flow within the follicle wall associated with the LH-surge, ovulation and CL development in the cow. Normally cycling cows with an spontaneous LH-surge (n = 5) or an induced-LH surge by a GnRH analogue injection (n = 5) were examined by transrectal color and pulsed Doppler ultrasonography to determine the blood flow area and the time-averaged maximum velocity (TAMXV) of the preovulatory follicle and the early CL. Ultrasonographic examinations began 48 h after a luteolytic injection of PGF₂. The cows with spontaneous-LH surge were scanned at 6 h intervals until ovulation occurred. Cows with induced-LH surge were scanned just before GnRH injection (0 h), 0.5, 1, 2, 6, 12, 24 h, and then at 24 h intervals up to Day 5. Blood samples were collected at the same time points for estradiol (E), LH, and progesterone (P) determinations. Cows with both spontaneous- and induced-LH surge showed a clear rise in the plasma levels of LH (LH-surge) followed by ovulation at 26-34 h later. In the color Doppler image of the preovulatory follicle, before LH-surge the blood flow was detectable only in a small area in the base of the follicle. An acute increase in the blood flow velocity (TAMXV) was detected at 0.5 h, synchronously with the initiation of the LH-surge. At 12 h after the LH-surge the plasma concentrations of E decreased to basal levels. The blood flow area in the follicular wall further increased toward ovulation. The TAMXV remained unchanged after the initial increase until ovulation and decreased on Day 2 (12-24 h after ovulation). In the early CL, the blood flow gradually increased in parallel with the increase in CL volume, plasma P concentration, and TAMXV from Day 2 to Day 5, indicating active angiogenesis and normal luteal development. During Days 3-4, the blood flow and the volume of early CL increased 2-3-fold. Collectively, the present results indicate that the spontaneous as well as induced-LH surge induces an acute increase in the blood flow within the preovulatory follicle wall. This initial increase in the blood flow may trigger the cascade of ovulation in the cow. Supported by JSPS grants

KEY WORDS: ovulation, corpus luteum, luteinizing hormone, blood flow