In vitro maturation of porcine oocytes with retinoids improves embryonic development

In the present study, the effects of retinoid metabolite administration during in vitro maturation (IVM) on oocyte maturation, parameters of in vitro fertilisation (IVF) and embryo development were examined. Varying concentrations of 9-cis retinoic acid (RA; 0, 5, 50 and 500 nM; Experiment 1) and all-trans retinol (ROH; 0, 125, 1250 and 12 500 nM; Experiment 2) were included in the maturation medium. Cumulus-oocyte complexes were matured in vitro and inseminated with frozen-thawed spermatozoa. Presumptive zygotes were cultured for 16 h to assess IVF parameters or for 7 days to assess embryo development and quality. In Experiment 1, the oocyte maturation rate to metaphase II was significantly decreased (P < 0.001), with values below 5%, in the presence of the highest concentration of RA (500 nM). However, 5 and 50 nM RA had no effect compared with control. Treatment with 5 nM RA improved the blastocyst development rate (P < 0.001). In Experiment 2, the oocyte maturation rate did not differ between 125 and 1250 nM ROH treatment groups and control. However, treatment with 12 500 nM ROH was deleterious because no matured oocytes were observed following the treatment. The penetration rate was lower in the group treated with 1250 nM ROH compared with the 125 nM ROH-treated and control groups, but the blastocyst formation rate did not differ among the three groups. In conclusion, 5 nM RA in the IVM medium significantly increased the blastocyst formation rate, suggesting that RA may play an important role during IVM.