Tyrosine hydroxylation in the rat striatum after fentanyl and droperidol in vivo.

The effects of fentanyl, droperidol, and morphine on tyrosine hydroxylation in the rat striatum was measured after inhibition of aromatic amino acid decarboxylase with R04-4602. Any direct change in the product of hydroxylation (i.e.dopa) was supposed to reflect a change in enzyme activity. Fentanyl (0.1 mg/kg intraperitoneally) first (10 min) appears to slightly depress, and later (30 min) significantly activate tyrosine hydroxylation. Morphine (10 mg/kg i.p.) activates tyrosine hydroxylation to a much lesser degree than fentanyl. Droperidol (3 mg/kg i.p.) only slightly activates the in vivo activity of the enzyme.