Anticonvulsant activity of di-n-propylacetate and brain monoamine metabolism in the rat

Selective effects of nitric oxide on the disposition of chlorzoxazone and dextromethorphan in isolated perfused rat livers

The rapid and direct effects of nitric oxide (NO) donors sodium nitroprusside (SNP) and isosorbide dinitrate (ISDN) on the hepatic and biliary disposition of chlorzoxazone (CZX), a marker of CYP2E1, and dextromethorphan (DEM), a marker of CYP2D1, were studied in a single-pass isolated perfused rat liver model. Livers (n = 30) were perfused with constant concentrations of NO donors (0-120 min) in addition to infusion of CZX or DEM (60-120 min), and periodical outlet and bile samples were collected. Both ISDN and SNP significantly reduced (30 and 60%, respectively) the hepatic extraction ratio of CZX and decreased (50 and 70%, respectively) the recovery of the CYP2E1-mediated metabolite, 6-hydroxychlorzoxazone, in the outlet perfusate and bile. As for DEM, both NO donors increased (up to 3.5-fold) the recovery of the CYP2D1-mediated metabolite dextrorphan (DOR) in the outlet perfusate. However, this was associated with a simultaneous decrease (50-75%) in the excretion of the metabolite into the bile, thus resulting in no change in the overall recovery of DOR as a result of NO donor treatment. The decrease in the biliary excretion of DOR was caused by NO-induced simultaneous reductions in both the conjugation of DOR and biliary clearance of DOR conjugate. Additionally, both SNP and ISDN significantly reduced the metabolism of DEM to 3-hydroxymorphinan, which is mostly regulated by CYP3A2. These studies in an intact liver model confirm the selectivity of the inhibitory effects of NO donors on cytochrome P450 enzymes, which was recently reported in microsomal studies, and expand these inhibitory effects to conjugation pathways.

Alterations of lidocaine and pentylenetetrazol-induced convulsions by manipulation of brain monoamines

The thresholds for pentylenetetrazol and lidocaine-induced clonic convulsions were significantly influenced by manipulation of brain biogenic amines. Pretreatment with inhibitors of monoamine synthesis, alpha-methyl-p-tyrosine and p-chlorophenylalanine, caused significant decreases in brain monoamine contents and pentylenetetrazol seizure threshold, while the threshold for lidocaine-induced convulsions was significantly increased by either treatment. Moreover, the inhibitor of dopamine-beta-hydroxylase, disulfiram, caused significant decrease in brain noradrenaline (NA) and significant increase in brain dopamine (DA) contents. The threshold for pentylenetetrazol-induced convulsions was decreased by treatment with disulfiram, while that of lidocaine was increased by the same treatment. Furthermore, treatment with L-dihydroxyphenylalanine (L-DOPA) caused significant increase in brain DA contents, while 5-hydroxytryptophan (5-HTP) treatment caused significant increase in brain 5-hydroxytryptamine (5-HT) contents, but the thresholds for lidocaine and pentylenetetrazol-induced convulsions were not influenced by either treatment. These results may suggest that the brain monoaminergic systems, different from their ability to inhibit control of pentylenetetrazol seizures, act to potentiate lidocaine-induced convulsions.

The effect of valproic acid on 5-hydroxytryptamine and 5-hydroxyindoleacetic acid concentration in hippocampal dialysates in vivo

The effect of valproic acid (100, 200 and 400 mg/kg i.p.) on extracellular 5-hydroxytryptamine (5-HT) and 5-hydroxyindoleacetic acid (5-HIAA) has been studied using intracerebral microdialysis of the ventral hippocampus. Valproate caused a dose-dependent increase in dialysate 5-HT, but in contrast no effect on 5-HIAA level was observed. These findings are considered with regard to a possible role of 5-HT in mediating the anticonvulsant action of valproate.