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The effect of ethanol on the concentration of the aberrant dopamine metabolite, tetrahydropapaveroline (THP), in brains of L-dopa-treated rats has been evaluated. THP was isolated from rat brain extract by a newly developed multiple stage separation technique that is highly specific for the alkaloid. THP, dopa, and dopamine were assayed by high-performance liquid chromatography with electrochemical detection. THP was not found in brains of untreated animals. However, levels of 0.42 pmol THP per g brain were observed in animals that received L-dopa (200 mg/kg) by intraperitoneal injection (IP) 90 min before decapitation. Administration of ethanol (3g/kg) IP to L-dopa-treated animals at time intervals ranging from 60 to 240 min before decapitation resulted in significant increases in brain levels of THP as compared to L-dopa-treated animals. Maximum levels of THP (4.02 to 4.82 pmol/g brain) were observed when ethanol was given at time intervals ranging from 80 to 180 min before the animals were killed. Administration of ethanol and L-dopa, as compared to the administration of L-dopa only, markedly increased brain levels of dopa and dopamine. Maximum brain levels of THP, dopa, and dopamine in animals administered ethanol plus L-dopa as compared with L-dopa-treated animals represented a 1048%, 325%, and 84% increase, respectively. These results strongly support the concept that the concentration of THP in the brain of intact animals can be enhanced by ethanol administration.

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