In the present study, we investigated the effects of a specific Rho kinase (ROCK) inhibitor, Y-27632, on germinal vesicle breakdown (GVBD), changes of cytoskeletal organization, and the resumption of porcine oocyte maturation after its removal. In Experiment 1, cumulus-oocyte complexes (COCs) cultured in medium containing Y-27632 for 24 h showed GVBD of 98, 88, 84, and 4% (P<0.01) of the oocytes treated with 0, 1, 10, and 100 µM of the drug, respectively. In addition, Y-27632 treatment from 24 to 44 h of incubation significantly inhibited maturation of the oocytes. The metaphase II (MII) rates were 84, 78, 65, and 10% (P<0.01) for the corresponding groups, and 0, 2, 8, and 45% of the oocytes failed to show emission of the first polar body (PB1). In Experiment 2, resumption of meiotic maturation was examined after removal of Y-27632. COCs incubated with Y-27632 for 18 h and then cultured in Y-27632-free medium for an additional 44 h showed a significantly lower MII rate (86 vs. 33%, P<0.01). After the addition of Y-27632, cortical microfilaments of the oocytes decreased in density to approximately 40% of that of the controls. The present results suggest that Y-27632 inhibits GVBD and emission of PB1 in porcine oocytes and that ROCK inhibition for 18 h after the start of maturation incubation may be detrimental to and exert an irreversible effect on the progression of meiosis.
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