Intraluteal release of prostaglandin F_2α and E₂ during corpora lutea development in the cow

It is well known that prostaglandin (PG) F_2α and PGE ₂ are actively produced by bovine early corpus luteum (CL) at higher levels than in the CL of later stages. However, there is no in vivo information about the local secretion of PGs within bovine developing CL so far. Thus, the objective of the present study was to determine in detail the real-time changes in PGF_2α and PGE₂ secretion within developing CL. A microdialysis system (MDS) was surgically implanted into the newly formed CL of 6 cows on Day 3 after GnRH administration (about 1.5 days after ovulation) to induce superovulation following FSH treatment. Both PGF_2α and PGE₂ release were high during the first 24 h within developing CL but decreased thereafter. These profiles were well reflected in the PG concentrations in ovarian venous plasma. Furthermore, reverse transcription polymerase chain reaction analysis using CL from other animals independent from the MDS study revealed that the level of cyclo-oxyganase-2 mRNA expression in early CL was higher than that of later luteal phases. The present results provide the first direct in vivo evidence that active PGs production in CL occurs up to Day 4 after estrus in the cow.