Melatonin downregulates BimEL protein by COCs or FSH-mediated, activating the ERK pathway in porcine primary granulosa cells. (A) Phosphorylated ERK level increased in porcine primary granulosa cells treated with 10−9 M melatonin (Mel) in the presence of COCs for 24 h. (B) Inhibition of ERK phosphorylation by 20 μM U0126 prevented the decrease in BimEL level induced by melatonin and COCs, coinciding with the decrease in phosphorylated ERK. (C) phosphorylated ERK level increased in porcine primary granulosa cells treated with 10−9 M melatonin in the presence of FSH for 24 h. (D) Inhibition of ERK phosphorylation by 20 μM U0126 prevented the decrease in BimEL level induced by melatonin and FSH, coinciding with the decrease in phosphorylated ERK. (E) There was an inverse relationship between levels of BimEL and phosphorylated ERK in porcine granulosa cells from healthy or atretic follicles. (F) Melatonin concentration decreased in follicles with progressive atresia. H, healthy follicles (arrows); SA, slightly atretic follicle (arrowhead); A, atretic follicles (asterisks). Data are representative of three independent experiments. Values are expressed as the means ± S.D. of three separate experiments. * p < 0.05.