High hydrostatic pressure treatment of porcine oocytes induces parthenogenetic activation

An innovative technique called high hydrostatic pressure (HHP) treatment has recently been reported to improve the cryosurvival of gametes and embryos in certain mammalian species, including the mouse, pig, and cattle. In the present study the parthenogenetic activation (PA) of pig oocytes caused by HHP treatment was investigated in different holding media with or without Ca(2+). The efficiency of activation was tested at different pressure levels and media including T2 (HEPES-buffered TCM-199 containing 2% cattle serum), and mannitol-PVA fusion medium with (MPVA + Ca(2+)) or without Ca(2+) and Mg(2+)(MPVA). The results showed that HHP cannot induce PA in T2, but only in MPVA + Ca(2+) with low Ca(2+) concentration and MPVA without Ca(2+). The highest activation efficiency was achieved with 10 min HHP treatment using 100 or 200 bars for oocytes in MPVA + Ca(2+) or MPVA, respectively. In the light of these results, the possible source of Ca(2+) during activation was investigated. It was found that even after a total of 30-min wash with TL-HEPES-PVA buffer without Ca(2+) before HHP treatment in MPVA, the oocytes could still be activated, indicating the possibility of an intracellular Ca(2+) source caused cytoplasmic free Ca(2+) elevation. In conclusion, parthenogenetic activation could be induced by HHP in certain holding media with low or zero Ca(2+) content. Further experiments are needed to identify the exact mechanisms of activation.