This study investigated the mechanistic effect of transforming growth factor-beta1 (TGFbeta1) on the endothelial mediators: endothelin-1 (ET-1), prostacyclin (PGI(2)) and nitric oxide (NO) in the endothelial cell line 1G11. Endothelial cells were incubated with increasing concentrations of TGFbeta1 in the presence and absence of growth medium (deprived) or various inhibitors. In deprived cells, TGFbeta1 increased the release of PGI(2) (6-keto-PGF1alpha) concomitantly to an increase in COX-2 expression, whereas the production of ET-1 and NO metabolites was not affected. Either the removal of prior serum and heparin deprivation or NO synthase inhibition by L-NAME unmasked an inhibitory effect of TGFbeta1 on ET-1 production. Indomethacin abolished the TGFbeta1 inhibitory action on L-NAME-increased ET-1 production. These results show that TGFbeta1 induces an increase in production of PGI(2) that is consecutive to an induction of COX-2 in endothelial cells. This increase in PGI(2) partly accounts for the inhibitory action of TGFbeta1 on ET-1 secretion.