Inhibition of TPA-induced PGE2 synthesis by phytosphingosine. Mouse peripheral mononuclear leukocytes were treated with TPA (16 nM) and indomethacin (1 nM and 10 nM), phytosphingosine (PS, 5 µM), or troglitazone (TGZ, 5 µM) for 16 h. PGE2 released into culture media was analyzed by enzyme immunoassay. Data represent the mean ± SD of 3 independent experiments. *Significant at P < 0.05. **Significant at P < 0.01.