Estrogen and its receptors influence growth and differentiation by stimulating the production and secretion of growth factors. Our previous studies indicate an increased expression of ER and decreased growth factor synthesis in the olfactory bulb of reproductive senescent female rats as compared to young animals. The present study tests the hypothesis that abnormal overexpression of ER contributes to decreased growth factor synthesis. We developed the HeLa-Tet-On cell line stably transfected with ER (HTER) that expresses increasing amounts of ER with increasing doses of doxycycline (Dox). Increasing doses of Dox had no effect on VEGF secretion in HTER cells. However, in the presence of 40nM 17-estradiol, VEGF secretion increased in low-dose Dox exposed HTER cultures, which was attenuated by the ER antagonist, MPP. However, at high-dose Dox, and consequently, high ER levels, estradiol failed to increase VEGF. In the HeLa X6 cell line where the Tet-On construct is upstream of an unrelated gene (Pitx2A), estradiol failed to induce VEGF at any Dox dose. Furthermore, in the HTER cell line, estradiol selectively down regulates phospho-ERK2 and phospho-Akt at high ER expression. This study clearly demonstrates that the "dose" of receptor critically mediates estradiol's ability to regulate growth factors and survival kinases. The present data also support the hypothesis that 17-estradiol treatment to an ER over-expressing system, such as the senescent brain, could reverse the normally-observed beneficial effect of estrogen.