PARENT SESSION
TRAINEE RESEARCH COMPETITION

REAL-TIME CHANGES IN THE LOCAL ANGIOTENSIN SYSTEM AND PROSTAGLANDIN PRODUCTION IN THE REGRESSING CORPUS LUTEUM IN THE COW.

Hayashi, Kanako¹, Acosta, Tomas¹, Berisha, Bajram², Kobayashi, Shu-ichi¹, Ozawa, Takahiro¹, Fukuda, Rie¹, Kojima, Ana¹, Ohtani, Masayuki¹, Schams, Dieter², Miyamoto, Akio¹, ^{1 2}

ABSTRACT- Prostaglandin (PG) F₂ decreases progesterone (P) production and causes regression of the corpus luteum (CL)in cattle. There is evidence that the vasoconstrictive peptide, angiotensin (Ang) II, regulates ovarian function. Moreover, Ang II has been shown to regulate CL function in vitro through paracrine/autocrine actions. To evaluate the impact of Ang II in the cascade of luteolysis, an in vivo microdialysis system (MDS) was used to characterize the relationship between the angiotensin system and luteal PGs in the regressing CL. Six cows were implanted with a microcapillary dialysis membrane of the MDS into the CL between Days 8-9 (Day 0=estrus), and PGF₂ analogue was injected i.m. to induce luteolysis. An increase in Ang II release (P<0.05) into the MDS was detected between 0-8 h after a luteolytic PG injection. Ang II concentration in ovarian venous plasma (OVP) was temporarily (between 0-24 h) higher than that of the jugular venous plasma (JVP: P<0.01). An acute increase in intraluteal release (MDS) of PGF₂ and PGE₂ were observed during the first 4 h, followed by a drop for the next 8 h. Intraluteal release (MDS) of both PGs gradually increased again between 48-72 h (P<0.05). PGF₂ concentration in OVP was higher than that of JVP by 4-100 times (p<0.001) during the experimental period. The RT-PCR analysis revealed that Ang-converting enzyme mRNA expression increased at 12 and 24 h (P<0.05). Also, cyclooxygenase-2 mRNA expression increased at 2 and 24 h (P<0.05). There were no significant changes in Ang type1 and 2 receptor mRNAs expression during induced-CL regression. The present results demonstrate real-timely in vivo local changes in angiotensin system of the bovine CL during PG-induced luteolysis. In addition, both PGF₂ and PGE₂ release increased in the regressing CL. The overall results support the concept that Ang II together with endothelin-1 are involved in the cascade of luteolysis in the cow. Supported by JSPS and DFG grants.

KEY WORDS: angiotensin, prostaglandin, luteolysis, cow