Melatonin (N-acetyl-5-methoxytryptamine) is a derivative of tryptophan which is produced and secreted mainly by the pineal gland and regulates a variety of important central and peripheral actions.To examine the potential effects of melatonin on the proliferation and differentiation of bovine intramu scular preadipocytes (BIPs),BIPs were incubated with different concentrations of melatonin.Melatonin s upplementation at 1 mM significantly increased peroxisome proliferator-activated receptory (PPARy),CCA AT/enhancer-binding protein (C/EBP)β,and C/EBPα expression and promoted the differentiation of BIPs into adipocytes with large lipid droplets and high cellular triacylglycerol (TAG) levels.Melatonin also significantly enhanced lipolysis and up-regulated the expression of lipolytic genes and proteins,including hormone sensitive lipase (HSL),adipocyte triglyceride lipase (ATGL),and perilipin 1 (PLIN1).Moreov er,melatonin reduced intracellular reactive oxygen species (ROS) levels by increasing the expression lev els and activities of superoxide dismutase 1 (SOD1) and glutathione peroxidase 4 (GPX4).Finally,the positive effects of melatonin on adipogenesis,lipolysis,and redox status were reversed by treatment wit h luzin dole,an antagonist of nonspecific melatonin receptors 1 (MT1) and 2 (MT2),and 4-phenyl-2-pr opionamidotetraline (4P-PDOT),a selective MT2 antagonist.These results reveal that melatonin promote s TAG accumulation via MT2 receptor during differentiation in BIPs.