The influence of 3,4-dihydroxyphenylacetic acid on the accumulation of 5-hydroxyindoleacetic acid in the choroid plexus and kidney cortex slices of rats.

In vitro, the choroid plexus of rats accumulates 5-hydroxyindoleacetic acid (5-HIAA) by active transport. In the experiments presented here, the kidney cortex slices also showed active accumulation of this organic acid, which proved to be inhibited by most of the organic acids tested. In the choroid plexus 3,4-dihydroxyphenylacetic acid (DOPAC), a metabolite of dopamine, stimulated the accumulation of 5-HIAA, whereas in the kidney slices DOPAC was inhibitory. This stimulating effect of DOPAC was blocked by homovanillic acid and probenecid. Metabolic inhibitors such as 2,4-dinitrophenol and N-ethylmaleimide also blocked the stimulation, but sodium fluoride was ineffective. Omission of calcium, but not magnesium ion in the incubation medium depressed the accumulation of 5-HIAA. DOPAC still produced the stimulating action in calcium-free medium. The release of 5-HIAA from choroid plexus was retarded by DOPAC. These results suggest that the stimulating action of DOPAC may be due to a calcium-dependent active transport system and delay of 5-HIAA release.