A gas chromatographic-mass spectral assay for the quantitative determination of oleamide in biological fluids

Oleamide is a putative endogenous sleep-inducing lipid which potently enhan ces currents mediated by GABA(A) and serotonin receptors, While a quantitat ive assay would aid in determining the role of oleamide in physiological pr ocesses, most of the available assays are lacking in sensitivity. We now de scribe a quantitative assay for measuring low nanogram amounts of oleamide in biological fluids using GC/MS in the selective ion-monitoring mode. The internal standard (C-13(18) oleamide) was added to known concentrations of oleamide, which were converted to the N-trimethylsilyl or N-tert-butyldimet hylsilyl derivatives before analysis by GC/MS, yielding linear calibration curves over the range of 1-25 ng of oleamide when monitoring the m/z 338/35 6 fragments. Using this technique, oleamide levels were determined followin g solvent extraction of normal rat cerebrospinal fluid and plasma to be 44 and 9.9 ng/ml, respectively. This technique constitutes a sensitive and rel iable method for determining low nanogram quantities of oleamide in biologi cal fluids.