Determination of m-nitrophenol and nipecotic acid in mouse tissues by high-performance liquid chromatography after administration of the anticonvulsant m-nitrophenyl-3-piperidinecarboxylate hydrochloride

The nipecotic acid ester m-nitrophenyl-3-piperidinecarboxylate (MNPC) possesses anticonvulsant activity. In the present study, the metabolites m-nitrophenol and nipecotic acid were determined in mouse blood and brain tissue after administration of MNPC. This determination was used as an indication of the distribution of the parent compound MNPC and to provide information regarding the differences in distribution between the enantiomers of MNPC, the times of onset, and effectiveness when (±)MNPC was administered by subcutaneous (sc) and intraperitoneal (ip) routes. m-Nitrophenol was determined by a previously reported high-performance liquid chromatography (HPLC) method. There was no significant difference in m-nitrophenol distribution after sc administration of (+)MNPC and (−)MNPC (400 mg/kg each). This similar pattern of distribution is in agreement with the earlier reported equi-effectiveness of the enantiomers of anticonvulsants. Peak m-nitrophenol levels in blood, which occurred at 15min, were three times greater when (±)MNPC was administered by ip injection as compared with sc injection. This significant difference is most likely due to enhanced absorption and the peripheral metabolism of MNPC by the liver when the ip route is employed. A novel HPLC assay for the determination of nipecotic acid in mouse brain was developed, based on a modification of a reported amino acid analysis procedure. The results of the brain distribution studies showed that nipecotic acid brain levels peaked at 30min after sc administration of (−)MNPC. These findings correlate with m-nitrophenol distribution in the blood and the previously reported onset of the anticonvulsant effect of MNPC. The HPLC assays used in this study are simple, rapid, and sensitive. Furthermore, the HPLC brain assay for nipecotic acid can be used to examine the distribution of other esters of nipecotic acid reported to possess anticonvulsant activity.