Protective effects of melatonin on the in vitro developmental competence of bovine oocytes.

The present study investigated the effects of melatonin on bovine oocyte maturation and subsequent embryonic development in vitro. Results showed that the nuclear and cytoplasmic maturation, characterized by first polar body extrusion, normal distribution of cortical granules and mitochondria, as well as increased mitochondrial membrane potential, were significantly improved in 10-9  mol/L melatonin-treated oocytes. Melatonin supplementation reduced intracellular reactive oxygen species level and enhanced glutathione production. Meanwhile, the presence of melatonin (10-9  mol/L) during oocyte maturation resulted in a decreased early apoptotic rate in oocytes. After in vitro fertilization, oocytes receiving melatonin supplementation exhibited a significantly higher blastocyst formation rate and yielded a markedly lower number of apoptotic cells. Mechanistic explorations showed that addition of 10-9  mol/L melatonin to in vitro maturation media significantly attenuated the transcript level of caspase-3, while the expressions of BCL-2, XIAP, CAT and HSP70 were significantly reinforced in the resultant embryos. Taken together, melatonin ameliorates bovine oocyte maturation potential, and the beneficial effects can affect subsequent embryonic development. The protective role of melatonin may be due to its anti-apoptotic and anti-oxidative activities.