PARENT SESSION
OVARY - C

Wednesday, August 4, 2004
10:30 AM–12:30 PM
Buchanan Courtyard

(796) ENDOGENOUS LH SURGE DECIDES THE FATE OF CORPUS LUTEUM FORMATION AFTER ASPIRATION OF THE DOMINANT FOLLICLE IN COWS.

Hayashi, Ken-Go¹, Matsui, Motozumi¹, Acosta, Tomas¹, Ohtani, Masayuki¹, Miyamoto, Akio¹, ¹ Department of Agricultural and Life Science, Obihiro, Japan

ABSTRACT- The LH surge initiates the final stages of ovarian follicle maturation and luteinization, and finally induces ovulation. It is known that active angiogenesis is taking place during corpus luteum (CL) formation, and that the blood flow in the CL well reflects CL development in the cow. Thus, we aimed to investigate the direct effect of endogenous LH surge on CL formation in cows, particularly focused on the changes in the local blood flow. For this purpose, the follicular fluid (FF) of dominant follicle (DF) was removed by ultrasound-guided follicular aspiration during different stage of estrous cycle. Normally cycling Holstein cows were divided into three groups based on the timing of follicular aspiration as follows; 1) luteal phase (n=5); a DF was aspirated on Day 7 after the estrus, 2) pre-LH surge (n=5); a DF was aspirated 42 h after PGF ₂ injection during mid luteal phase, and 3) post-LH surge (n=4); a DF was aspirated 24 h after GnRH injection following PGF ₂. The observation of morphological changes of the aspirated follicle using a color Doppler ultrasonography as well as blood collection for progesterone (P) determination was performed every three days beginning on the day of follicular aspiration (Day 0) until Day 12. The CL formation following aspiration of DF was induced only in post-LH surge group. In both luteal phase and pre-LH surge groups, however, all cows showed neither local blood flow at the aspirated point from Day 3 nor CL formation. In post-LH surge group, plasma P level increased from Day 3. Intra-luteal blood flow area, CL volume and plasma P level in the post-LH surge group were not different from that in the cows ovulated spontaneously. Moreover, an injection of luteolytic dose of PGF₂ on Day 14 in post-LH surge group showed a typical decrease in plasma P level, showing the occurrence of normal luteolysis. Our results clearly demonstrated that only DF exposed to an endogenous LH surge develops active angiogenesis and differentiates into the functional CL. The data also showed that removal of FF without follicle rupture induced normal CL formation, suggesting that a structural breakdown with inflammatory activation in the follicular wall may not be essential event for CL formation. Supported by JSPS and the 21 ^st century COE program (A - 1).

KEY WORDS: corpus luteum, cow, LH surge, blood flow