Effetto dell’acido okadaico sulla maturazione in vitro di oociti di cane di differente diametro

This study was designed to determine the effect of okadaic acid (OA) on meiotic
resumption and progression of canine oocytes with different diameter. Oocytes were collected from
ovaries of bitches at various stages of the oestrus cycle. Only healthy-looking cumulus complexes
were used for in vitro maturation and were divided in three groups based on diameter : < 11 O, 11 O
to< 120; > 120 J.lm. Oocyes were pre-incubated for l h in TCM 199 + 20% SCE + cisteamine + OA
(0.5J.!M) and thereafter cultured for 48h in the same medium without OA. Moreover a group >
120J.!m oocytes was denuded from cumulus cells, incubated with or without OA and matured as
described above. Finally, we tested the possibility to induce, before exposition to OA, a prematuration
of < 120 J.lm oocytes by incubation with follicular cells from bitch at proestrus stage.
Results showed that OA induces a higher rate of meiotic resumption (GVBD-MI-MII) in the
oocytes < 110 J.lm and 110 to < 120J.!m compared to the contro! group. In the > 120J.!m OA group
percentages of meiotic resumption were similar to the contro l, but a significantly higher number of
oocytes progressed to MII (51.3% vs 16.7%). A low number of oocyte were able to resume
meiosis also after stimulation with OA in absence of cumulus cells. Results also evidenced a
negative effect of the bi-phasic culture system suggesting the need to find appropriate conditions to
increase meiotic competence ofbitch oocytes< 120 J.lm diameter.