Development of Technology for Regulating Reproductive Efficiency by Controlling Corpus Luteum Function in Cows

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The ovarian function is controlled by vascular functions in various local phenomena including ovulation, corpus luteum (CL) development and regression. This study was conducted to develop a basic as well as applicable technology to activate CL angiogenesis and function thereby improving the conception rate by keeping high progesterone level in the cow. At the same time, a local secretion by a microdialysis system together with a local blood flow by a color Doppler ultrasonography observation of ovulatory follicle and CL during development and regression was examined in detail in vivo. From the series of experiments, the following points were clarified for the first time.1. A LH surge activates a complex of local secretion of PG and vasoactive peptides that induces an acute increase in the local blood flow within the preovulatory follicular wall, but not within the atretic follicles. These changes are essential process to ovulation. Consequently, we proposed the existence of endothelin- … More angiotensin-ANP system in the preovulatory follicles.2. The active angiogenesis occurring immediately after ovulation directly relates to the formation of CL and its function (progesterone secretion), and this local mechanism involves secretory function of PG, angiotensin and ANP, but not for endothelin. Particularly, a luteolytic factor PGF2α produced in the developing CL play a role as a luteotropic rather than luteolytic factor. This unique mechanism may directly correlate with anti-luteolytic characteristic of developing CL.3. Once the CL matures, PGF2α can induce luteolysis in which other vasoactive peptides such as endothelin and angiotensin are highly active and luteolytic. This local mechanism induces a serious inhibition of local blood flow within the CL so that a cascade of luteolysis is accelerated further.4. A single injection of hCG to the cow one day after ovulation effectively activates the CL formation as well as plasma progesterone level, possible by promoting angiogenesis in the CL. To confirm the impact of this treatment on the conception rate after artificial insemination and embryo transfer, the field studies are also on going. Less