Effects of Different Activation Regimens on Pronuclear Formation and Developmental Competence of In Vitro–Matured Porcine Oocytes After Intracytoplasmic Sperm Injection

To improve the activation protocol for in vitro–maturated porcine oocytes after intracytoplasmic sperm injection (ICSI), we examined the combined effect of U0126, a specific inhibitor of mitogen‐activated protein kinase kinases, and an electrical pulse on pronuclear formation and developmental competence. Two approaches were tested: (i) 6‐h treatment of ICSI oocytes with U0126 applied at different intervals (0, 2, 3 or 4 h) after the electrical pulse and (ii) treatment of ICSI oocytes with U0126 applied 4 h after the electrical pulse over an additional 4, 6 or 8 h. Another protein kinase inhibitor, 6‐dimethylaminopurine, was used as a chemical activator in control experiments. The highest rates of diploid embryo formation, normal fertilization and blastocyst formation were observed after 6 h of exposure to U0126 starting 4 h after the electrical pulse. Therefore, U0126 can be used as an activating agent for porcine oocytes fertilized by ICSI.