Pharmacological characterization of dopamine sulfoconjugation by human platelets

Human platelets accumulate dopamine (DA) from the incubation medium in vitro and convert a significant percentage of the accumulated DA to dopamine sulfate (DAS). Platelet content of both DA and DAS increased linearly with incubation time and tissue concentration. Increasing the concentration of DA in the incubation medium also increased platelet content of both DA and DAS. However, after prolonged incubation times or in the presence of high concentrations of DA, the percentage conversion of DA to DAS decreased; this decrease was reversed at least partially by incubation in the presence of sodium sulfate, suggesting that sulfate availability may limit sulfoconjugation under some conditions. Incubation with fluoxetine produced a concentration-dependent decrease in both DA and DAS content of the platelets. In contrast, the agent 2,6-dichloro-4-nitrophenol, an inhibitor of the enzyme phenol sulfotransferase, did not interfere with DA uptake, but did inhibit DAS formation in a concentration-dependent manner. These studies suggest that the human platelet may represent a useful model system for the study of factors regulating DA sulfoconjugation.