DISTRIBUTION OF APOMORPHINE ENANTIOMERS IN PLASMA, BRAIN-TISSUE AND STRIATAL EXTRACELLULAR FLUID

Steady-state concentrations of apomorphine enantiomers were measured i n the extracellular fluid collected from rat brain striatum by microdi alysis. The foe and total concentrations of both enantiomers were also measured in plasma as well as the total concentrations in different b rain regions (striatum, cortex and cerebellum). We noticed no regional difference in the total concentrations of the two enantiomers. The ex tracellular concentrations were much lower, amounting to 8% for R(-)-a pomorphine and 4% for S(+)-apomorphine, of the total brain tissue conc entrations. The microdialysis samples contained 12 times more (R(-)-ap omorphine and 5 times more S(+)-apomorphine than the free apomorphine measured in plasma. The extracellular concentrations of R(-)-apomorphi ne (129 +/- 20 pmol/ml) were significantly higher (P = 0.001, n = 6), than those of S(+)-apomorphine (70 +/- 10 pmol/ml). These results indi cate that both enantiomers of apomorphine concentrate equally in brain cells, and that a stereoselective uptake system could operate for R(- )-apomorphine at the blood-brain barrier level. (C) 1997 Elsevier Scie nce B.V.