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Hereditary argininemia manifests as neurological disturbance and mental retardation, features not observed in other amino acidemias. The cytotoxic effect of a high concentration of L-arginine (L-Arg) was investigated using NB9 human neuroblastoma cells (NB9), which express neuronal nitric oxide synthase (nNOS). When the concentration of L-Arg in the medium increased from 50 microM to 2 mM after incubation for 48 hr, the intracellular concentration of L-Arg increased from 68.0 +/- 1 pmol/10(6) cells to 1310.0 +/- 5 pmol/10(6) cells and that of L-citrulline (L-Cit) from undetectable levels to 47.1 +/- 0.2 pmol/10(6) cells (mean +/- SD of three independent analyses). This increase in intracellular L-Arg levels caused a decrease in NOS activity by approximately 71%. Flow cytometric analysis showed that reactive oxygen species (ROS) are produced in NB9 exposed to 2 mM L-Arg. The production of ROS was abolished by a NOS inhibitor, NG-nitro-L arginine-methylester. Production of ROS was also observed when NB9 were treated with L-Cit for 48 hr. To investigate the effect of L-Cit on the activity of NOS, a kinetic study on nNOS was conducted using cellular extracts from NB9. The apparent Km value of nNOS for L-Arg was 8.4 microM, with a Vmax value of 8.2 pmol/min/mg protein. L-Cit competitively inhibited NOS activity, as indicated by an apparent Ki value of 65 nM. These results suggest that L-Cit formed by nNOS in L-Arg-loaded neuronal cells inhibits NOS activity and nNOS in these L-Arg-loaded cells functions as a NADPH oxidase to produce ROS, which may cause neurotoxicity in argininemia.

Comme la constriction du muscle lisse induite par lea agonistes ~x l-adr$nergiques d~pend de la r~ponse du phosphatidylinositol (PI), cette ~tude vise ?l v~rifier sur des' tranches d'aone de rat si le thiamylal et le fentanyl affectent la r$ponse du PI induite par la nor~pin~phrine (NE). Cellesci sont incub$es dans une solution de Krebs-Henseleit contenant 5 m M de LiCI, du [3 I-IJ myo-inositol et diffe'rentes concen-

Peripheral nerve injury often leads to neuropathic pain, which might involve sympathetic postganglionic nerve fiber sprouting in the dorsal root ganglion. Recent studies suggest the effectiveness of ropivacaine in blocking neuropathic pain. To determine if ropivacaine affects sympathetic sprouting, we used pheochromocytoma (PC-12) cells, which differentiate into neurons on exposure to nerve growth factor (NGF). PC-12 cells were precultured in the presence of 50 ng/mL of NGF for 4 days. Neurite outgrowth was quantified as neurite extension after 24-, 48-, and 72-h exposure to ropivacaine at doses ranging from 10 to 200 microg/mL. Ropivacaine inhibited the neurite outgrowth in a dose-dependent manner. The inhibitory effect of ropivacaine was completely reversible because the NGF-stimulated neurite outgrowth was recovered to control level after washing out ropivacaine. Ropivacaine, therefore, may exert its therapeutic action on neuropathic pain, at least in part, by suppressing sympathetic sprouting.