Release and metabolism of dopamine in a clonal line of pheochromocytoma (PC12) cells exposed to fenthion

The effects of an organophosphate (OP) pesticide, fenthion (FEN), on the release and metabolism of dopamine were evaluated in a clonal line of rat pheochromocytoma (PC12) cells. HPLC was used to determine media concentrations of DA and the DA metabolites norepinephrine (NE), 3,4-dihydroxyphenylacetic acid (DOPAC), and homovanillic acid (HVA). The FEN formulation solvent did not significantly affect DA metabolism. In the first study, cultures were treated with 10 −5 or 10 −6 m FEN or 10 −5 m neostigmine, a non-OP acetylcholinesterase inhibitor. Concentrations of both catecholamines were elevated in cultures treated with 10 −5 m FEN by 2.8-fold for DA and 3.5-fold for NE. Neostigmine effects were of smaller magnitude and DA was decreased after 24 hr. Cultures were also treated with depolarizing levels of K +, but the effect of FEN was not altered, suggesting that FEN does not act by increasing DA release. In the second study, the effect of 10 −6 m FEN was evaluated in cultures treated with the DA uptake inhibitor benztropine, the monoamine oxidase (MAO) inhibitor pargyline, or the catechol- O-methyltransferase (COMT) inhibitor tropolone. Inhibitor effects were consistent with their known mechanisms of action. In all cultures treated with FEN, the ratio HVA DOPAC was decreased after 3 and 6 hr of exposure. A decrease in HVA DOPAC was also observed in cultures treated with neostigmine and tropolone. In combination with pargyline, FEN decreased DA in contrast to its usual effect of increasing DA. Neither the stimulation of DA release nor the inhibition of DA uptake affected the observed action of FEN in PC12 cultures. Results were supportive of the ability of FEN to inhibit the catabolism of DOPAC to HVA, with a subsequent increase in DA levels.