THE EFFECTS OF MORPHINE ON THE ACCUMULATION OF HOMOVANILLIC AND 5‐HYDROXYINDOLEACETIC ACIDS IN THE CHOROID PLEXUS OF RATS

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Abstract
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 × 10−6 M to 5 × 10−4 M potentiated 5-HIAA accumulation but did not affect HVA accumulation. Levorphanol and dextrorphan 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.