Melatonin may accelerate the expenditure of porcine intramuscular preadipocytes by increasing mitochondrial biogenesis. Measurement of the OCRs of intramuscular preadipocytes in control, 1 mM of melatonin, and 1 mM of melatonin + 10 μM of 4-P-PDOT [Quantitative (A), basal OCR (B), and maximum respiratory rate (C)]. D: Relative ATP level in porcine intramuscular preadipocytes treated with 1 mM of melatonin and 1 mM of melatonin + 10 μM of 4-P-PDOT. E: Mitochondrial contents were evaluated by measuring the ratio of mtDNA:nDNA (n = 3 per treatment). F–K: The expression levels of mitochondrial biogenesis (PGC-1α, TFAM, CPT-1β), thermogenesis genes (UCP3), and browning genes (CIDEA, PRDM16) were measured by RT-qPCR. The results are represented as the mean ± SEM (*P < 0.05; **P < 0.01; ***P < 0.001; n = 3).