The effects of morphine on the accumulation of homovanillic and 5-hydroxyindoleacetic acids in the choroid plexus of rats.

1 Choroid plexus obtained from the lateral ventricles of the rat actively accumulated homovanillic acid (HVA) and 5-hydroxyindoleacetic acid (5-HIAA). 2 Morphine 5 X 10(-6) M to 5 X 10(-4)M potentiated 5-HIAA accumulation but did not affect HVA accumulation. Levorphanol and dextorphan had little effect. 3 Naloxone at high concentrations inhibited both HVA and 5-HIAA accumulation. 4 Glutamic acid, glycine, and arginine also decreased 5-HIAA accumulation, but lysine, tryptophan, and aspartic acid had no effect. 5 Probenecid, naloxone, arginine, glycine, and tryptophan blocked the increase of 5-HIAA accumulation induced by morphine. 6 Acute or chronic morphine treatment did not increase the accumulation of 5-HIAA. 7 These results suggest that the increase of 5-HIAA or HVA in brain by morphine is not due to the inhibition of the elimination of these metabolites from the choroid plexus.