Effects of Melatonin Addition to the Cold Storage Medium on Cumulus Oocyte Complex Apoptosis, Viability and In Vitro Maturation Rates of Cat Oocytes

Usage of oocytes obtained from ovaries after long-term cold storage for in vitro embryo production is a promising tool for the protection of wildlife and endangered animal species. Mammalian oocytes are susceptible to oxidative stress with regard to the high lipid content of plasma membranes. Melatonin is known as a powerful antioxidant and anti-apoptotic agent due to its ability to eliminate toxic oxygen derivatives and reduce the formation of reactive species. This study was performed to verify the optimal environmental conditions for long-term preservation of cat ovaries (Felis domesticus) by adding different concentrations of melatonin (500, 750 and 1000 mu M) to the storage medium (0.9% NaCl) as an antioxidant to be preserved at 4 degrees C for 24 h. To determine the effect of melatonin on cat oocytes collected from stored ovaries, the anti and pro-apoptotic gene levels in cumulus oophorus, the in vitro maturation rates, the cell membrane and oocytes viability were evaluated. In all melatonin added groups regardless of whether they are stored in the cold; Pro-apoptotic gene levels (BAX) were determined to be upregulated however, anti-apoptotic gene levels (BCL-2) were downregulated in cumulus cells (P<0.05). The cell membrane stability and cell viability rates of oocytes began to deteriorate in parallel with the rate of melatonin increase. In parallel with these findings, in vitro maturation rates of oocytes were negatively affected as the amount of melatonin increased (P <= 0.001). In conclusion the results showed that adding melatonin (500,750 or 1000 mu M) to the ovarian transport and storage medium had negative effect on in vitro maturation rate, viability and cell membrane structure of cat oocytes.