Antioxidants stimulate meiosis resumption, but inhibit mitogen-activated protein kinase phosphorylation and further cell cycle progression in porcineoocytes

In the present study the effects of two cell-permeant antioxidants, 2(3)-te rt-butyl-4-hydroxyanisole (BHA) and nordihydroguaiaretic acid (NDGA), on po rcine oocyte meiosis resumption, chromatin behaviour and spindle assembly w ere investigated. The antioxidants BHA and NDGA stimulated meiosis resumpti on in a dose-dependent manner in both cumulus-enclosed and denuded porcine oocytes. After in vitro culture for 8 h, few oocytes underwent germinal ves icle breakdown (GVBD) in control groups, whereas GVBD occurred in high perc entages of oocytes treated with BHA or NDGA at concentrations that inhibit GVBD in rodent oocytes, although mitogen-activated protein (MAP) kinase was not phosphorylated as revealed by Western immunoblots. Orcein staining and fluorescein isothiocyanate-anti-alpha -tubulin labelling showed that chrom osome and spindle formation, respectively, and further meiosis progression were inhibited 20 and 25 h after culture. Instead, chromatin was highly con densed or existed in scattered condensed clusters. Correspondingly, MAP kin ase phosphorylation was inhibited by both BHA and NDGA in a dose-dependent manner. The inhibitory effects of BHA on meiosis completion and MAP kinase phosphorylation was reversible. These results suggest that, unlike in roden t oocytes, antioxidants stimulate GVBD in the absence of MAP kinase activat ion, but inhibit MAP kinase phosphorylation, meiotic apparatus formation an d thus the further progression of the meiosis of porcine oocytes.