Preferential decarboxylation of L-threo-3,4-dihydroxyphenylserine in rat renal tissues

1. Administration of L-threo-3,4-dihydroxyphenylserine (L-threo-DOPS; 3, 10 and 30 mg/kg, i.p.) produced a dose-dependent increase in the tissue levels of both noradrenaline and its deaminated metabolite 3,4-dihydroxyphenylglycol (DOPEG) in the rat jejunum, liver and renal cortex, but not in the left ventricle. 2. The accumulation of noradrenaline and DOPEG after the administration of L-threo-DOPS (30 mg/kg, i.p.) was also found to be a time-dependent effect, reaching its maximum 15 min after the injection and then declining progressively. 3. The accumulation of noradrenaline and DOPEG after L-threo-DOPS (30 mg/kg, i.p.) was found to be similar in control and 6-OHDA treated rats and completely prevented by previous treatment with benserazide. 4. Administration of L-threo-DOPS (30 mg/kg) produced an increase in plasma levels of noradrenaline and DOPEG; this effect was maximum, for both noradrenaline (6.2-fold increase) and DOPEG (3.4-fold increase), at 30 min after the injection of L-threo-DOPS. 5. The results presented here support the view that most L-threo-DOPS is decarboxylated into noradrenaline by non-neuronal AAAD, a reaction occurring predominantly in renal tissues.