Effects of different doses of E2 on cell proliferation of cultured PC12 by flow cytometric analysis. (A) The first red peak, the arc-shaped hatched portion in the middle and the second red peak represent G1 phase, S phase and G2 phase of cell cycle, respectively. (B) 10 nM and 20 nM E2 treatment did not induce a significant increase in the percentage of the S phase cells of the cell cycle, but induced a significant increase in the percentage of cells in S + G2 phase. 10 μM and 20 μM E2 treatments significantly decreased the percentage of cells in both S phase and S + G2 phase of the cell cycle (*p < 0.01 v.s. the control and DMSO groups, #p < 0.05 v.s. the control and DMSO groups). Dip: diploid.