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Growth factors stimulate astroglial and neuronal proliferation and differentiation in culture. Estrogens markedly influence astroglia, and are key factors participating in neurodegeneration. The aim of the present study was to investigate interactions between estradiol (E2) and epidermal growth factor (EGF) during astroglia development, maturation and differentiation in culture. DNA or RNA labeling in 16 or 40 or 60 days in vitro (DIV) astrocyte cultures treated for 24 or 48 h with EGF and/or E2 was evaluated. A significant increase in DNA labeling in 16 DIV astrocyte cultures treated for 24 h with EGF (5 ng/ml) and E2 (1 nM) was found. EGF (5 or 10 ng/ml) addition in the last 24 h in 48 h E2 (1 or 5 nM)-treated astrocyte cultures at 16 DIV caused a slight, but significant increase in DNA labeling. No differences in RNA labeling were observed in 16 DIV astrocyte cultures treated for 24 or 48 h with EGF (5 or 10 ng/ml) in the presence of E(2) (1 or 5 nM). A significant stimulation in DNA labeling was shown in 40 DIV astrocyte cultures treated for 48 h with E2 (1 or 5 nM) in the presence of EGF (5 or 10 ng/ml) added in the last 24 h. In well differentiated astroglial cell cultures (60 DIV), DNA labeling was remarkably increased after 24 h treatment with 1 nM E2 or 5 ng/ml EGF. Co-addition of 1 nM E2 and 5 ng/ml EGF for 24 h reduced [methyl-(3)H]thymidine incorporation, when data are compared to E2- or EGF-treated cultures. Addition of EGF in the presence of E2 for 48 h or only in the last 24 h caused a significant decrease of [methyl-(3)H]thymidine incorporation in comparison with EGF-treated cultures at 60 DIV or with untreated cultures. Treatment of cultures for 24 h with EGF (5 or 10 ng/ml) alone or in combination with E2 (1 or 5 nM) induced a strong increase of RNA labeling in 60 DIV astrocyte cultures. Addition for 48 h of E2 (1 or 5 nM) or EGF (5 or 10 ng/ml) alone or in association stimulated significantly RNA labeling in astrocyte cultures at 60 DIV. When 60 DIV astrocyte cultures were treated for 48 h with E2 (1 or 5 nM) in the presence of EGF (5 or 10 ng/ml) added only in the last 24 h, a potentiating effect of RNA labeling was observed. The above results suggest that interaction between growth factors and estrogens may contribute to regulate astroglia development, maturation and differentiation.