Polyunsaturated fatty acids (PUFA) are crucial for proper functioning of cell membranes, particularly in brain. Biologically important PUFA include docosahexaenoic acid (n-3 series) and arachidonic acid (n-6 series) which can be formed from their respective dietary essential precursors, alpha-linolenic acid (ALA) and linoleic acid (LA). Steroid hormones are thought to modulate PUFA synthesis in humans but whether they regulate PUFA status in brain and/or in neural membranes is unknown. In human neuroblastoma SH-SY5Y cells, we compared the effect of estradiol, testosterone, and progesterone on PUFA synthesis. Cells were incubated with ALA and/or LA 7 microM in combination with estradiol, testosterone, or progesterone at 10 nM without serum. The fatty acid composition was determined by gas chromatography and the mRNA expression of genes involved in PUFA metabolism by real-time RT-PCR. Estradiol affected both the n-3 and the n-6 PUFA conversion, the n-3 PUFA pathway being more sensitive to the estradiol treatment. In ALA-supplemented cells, estradiol increased while testosterone decreased the long-chain n-3 PUFA content (+17% and -15%, respectively) and the mRNA expression of the Delta5-desaturase (+11% and -9%), these two events being strongly correlated. Progesterone did not affect the PUFA composition. The positive effect of estradiol was blocked by the estrogen receptor antagonist ICI-182,780. We conclude that steroids have differential effects on PUFA synthesis and that their mode of action could involve the modulation of the Delta5-desaturase mRNA expression in neuroblastoma cells. These results help our understanding of the regulation of brain PUFA metabolism by steroid hormones.