17alpha-E-2, a weak estrogen exhibited both agonistic and antagonistic effects, and caused a time- and dose-dependent induction of VEGF-A mRNA expression in GH3 rat pituitary tumor cells. This effect was unaffected by the presence of the pure estrogen receptor antagonist ICI 182.780 but was specifically blocked by a protein synthesis inhibitor puromycin. Inhibition of phosphati-dylinositol-3 kinase (P13K) activity by wortmannin decreased the effect of 17alpha-E-2 on VEGF-A mRNA expression, This inhibitor also blocked the increase in phosphorlation of Akt induced by exposure to l7alpha-E-2. In contrast. exposure to the MAP kinase inhibitor, U0126, had no impact on 17alpha-E-2-induced VEGF-A mRNA expression. Taken together, these studies indicate that like potent estrogens 17alpha-E-2 up-regulates VEGF-A mRNA expression in estrogen responsive GH3 rat pituitary tumor cells, but this induction is not mediated through a classical estrogen receptor pathway. P13K-Akt signaling path ay is required for the induction of VEGF-A mRNA in GH3 cells by 17alpha-E-2. (C) 2002 Elsevier Science (USA). All rights reserved.