Effect of GnRH-I and GnRH-II on the activation of ERK1/2. HEC1A cells were treated with GnRH-I or GnRH-II (100 nM) in a time-dependent manner. Phosphorylation of ERK1/2 was determined by Western blot analysis following treatment with GnRHs. The error bars represent the mean ± S.D. from three independent experiments. a, indicates p < 0.05 vs. control (cont).). The white bars indicate GnRH-I treatment while gray bars indicate GnRH-II treatment.