Luteinizing hormone receptor formation in cumulus cells surrounding porcine oocytes and its role during meiotic maturation of porcine oocytes

We investigated the formation of LH receptor (LHR) in cumulus cells surrounding porcine oocytes and the role of LHR in meiotic maturation of oocytes. At least three splice variants of LHR mRNA were detected in cumulus cells, in addition to the full-length form. Low levels of three types of products were seen in cumulus cells from cumulus oocytes complexes (COCs), whereas the full-length form was significantly increased by 12-h cultivation with FSH. The addition of FSH also significantly increased the binding level of biotinylated hCG to COCs. The formation of LHR in FSH-stimulated cumulus cells was not affected by additional 0.5 mM phosphodiesterase inhibitor, 3-isobutyl-1-methylxanthine (IBMX), and the oocytes were synchronized to the germinal vesicle (GV) II stage by exposure to 0.5 mM IBMX and FSH for 20 h. The binding of LH to its receptor induced a further increase in cAMP level and progesterone production and acceleration of meiotic progression to the metaphase I stage. The oocytes cultured with LH for 24 h following cultivation with FSH and IBMX were used for in vitro fertilization. At 6 days after in vitro fertilization, blastocyst rate in oocytes matured under these conditions was significantly higher than that of oocytes cultured in the absence of LH. Treatment of oocytes with FSH and 0.5 mM IBMX to express LH receptor in cumulus cells while holding oocytes at the GV II stage is a very beneficial way to produce in vitro-matured oocytes, which have high developmental competence.