Iloprost, a prostacyclin analogue, stimulates meiotic maturation and early embryonic development in pigs

Oviduct fluid contains various cytokines and growth factors that enhance the embryo development during the preimplantation period. In hatched embryos, prostacyclin (PGI₂) improves implantation, but its role during oocyte maturation and early embryo development remains contentious. Therefore, in the present study, we examined the effects of a PGI₂ analogue (iloprost) on meiotic maturation and early embryonic development in pigs, as well on the structural integrity, mitochondrial membrane potential and apoptosis in blastocysts. First, meiotic maturation in pig oocytes was examined in the presence of increasing concentrations of iloprost (1, 5 and 10 μM). After IVM, a higher proportion of iloprost-treated compared with untreated oocytes was in MII (90.0% v. 65.7%, respectively; P < 0.05). In addition, protein kinase A activity increased in iloprost-treated oocytes, indicating increased intracellular cAMP concentrations. After 22 h iloprost treatment (44 h total incubation time), western blotting demonstrated increased expression of extracellular signal-regulated kinase (ERK) 1/2, phosphorylated (p-) ERK1/2, cAMP response element-binding protein (CREB), p-CREB and cyclo-oxygenase-2, indicating activation of the mitogen-activated protein kinase and PGI ₂ pathways. In addition, the frequency of polyspermy decreased in iloprost-treated oocytes (19.9%) compared with control (35.8%), whereas the rate of blastocyst formation increased (P < 0.05). Terminal deoxynucleotidyl transferase-mediated dUTP nick-end labelling (TUNEL) showed that the number of nuclei containing fragmented DNA at the blastocyst stage decreased in the iloprost-treated group compared with control (1.2% v. 3.6%, respectively). In conclusion, iloprost appears to play a direct role in porcine oocyte maturation by enhancing blastocyst structure and survival.