Quantitative determination and regional distribution of pipecolic acid in rodent brain

A rapid and sensitive method for the quantitative determination of pipecolic acid (PA), one of the three cyclic secondary imino acids present in mammalian brain is described. The quantification and identification of PA are accomplished in rat and mouse brain using high performance liquid chromatography with electrochemical detection (LCEC) and nipecotic acid (NPA) as an internal standard. The cyclic imino acids are derivatized with 2,4-dinitrofluorobenzene (DNFB) to dinitrophenyl derivatives. The remaining time for LCEC analysis is less than 30 min and the limit of sensitivity is in the lower picomole range. The levels of PA found in rat and mouse brain are comparable to those reported using gas chromatography/mass spectrometry. The regional distribution of PA shows higher concentrations of PA in hypothalamus, pons-medulla oblongata and cerebellum. The present results demonstrate that LCEC is sensitive enough to determine endogenous levels of PA in mg amounts of rodent brain tissue. Due to its simplicity and rapidity, the technique represents an alternative to existing methods. This method can also be used for determination of PA in CSF, blood or urine of hyperpipecolic patients.