“…Melatonin (N-acetyl-5-methoxytryptamine) is a hormone secreted from vertebrate pineal gland and regulates homeostasis of reproductive tissues such as ovary and placenta [ 22 ] through receptor-mediated signaling pathways [ 23 ]. Recent studies have reported that melatonin plays a critical role in the cryopreservation of sperm [ 24 , 25 , 26 , 27 , 28 , 29 , 30 , 31 , 32 , 33 , 34 , 35 , 36 , 37 , 38 , 39 ], oocytes [ 40 , 41 , 42 , 43 , 44 , 45 , 46 ], and embryos [ 47 , 48 , 49 , 50 , 51 ] in various species. In addition, melatonin is an antioxidant that acts as a free radical scavenger and affects G-protein-coupled receptor-related signaling transduction [ 23 , 52 ].…”