Chlorotriazines interact with undifferentiated PC12 cells in vitro to modulate catecholamine synthesis and release, but the mechanism(s) responsible for this effect had not been determined. In this study we evaluated the effect of atrazine, simazine and cyanazine on the protein expression of the enzymes responsible for the synthesis of dopamine [tyrosine hydroxylase (TH)] and norepinephrine [dopamine-beta-hydroxylase (DbetaH)]. We also examined the possible intracellular pathway associated with chlorotriazine-induced changes in catecholamine synthesis and release. Incubating PC12 cells in the presence of 100 microM atrazine and simazine decreased intracellular dopamine (DA), norepinephrine (NE) concentration and NE release, and the protein expression of TH (approximately 20%) and DbetaH (approximately 50 and 25%, respectively) after 12-24 h exposure. In contrast, cyanazine (100 microM) stimulated intracellular and released NE concentration, and the protein expression of TH (approximately 20%) and DbetaH (approximately 225%) after 12-36 h exposure. Simultaneous exposure to the essential TH co-factors (iron and tetrahydrobiopterine) was ineffective in altering cellular DA. Agents known to enhance TH and DbetaH transcription, phosphorylation or activity (e.g., 8-bromo cAMP, forskolin or dexamethasone) reversed the inhibitory effects of atrazine and simazine on the NE. Again, in contrast to atrazine and simazine, cyanazine attenuated catecholamine-depleting effect of alpha-Methyl-p-tyrosine (alphaMpT) on NE. Both DA and NE synthesis can be altered by the chlorotriazines and suggest these occur via an alteration of the synthetic enzymes TH and DbetaH.