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 enhances currents mediated by GABA(A) and serotonin receptors. While a quantitative assay would aid in determining the role of oleamide in physiological processes, most of the available assays are lacking in sensitivity. We now describe 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 (¹³C₁₈ oleamide) was added to known concentrations of oleamide, which were converted to the N- trimethylsilyl or N-tert-butyldimethylsilyl derivatives before analysis by GC/MS, yielding linear calibration curves over the range of 1-25 ng of oleamide when monitoring the m/z 338/356 fragments. Using this technique, oleamide levels were determined following solvent extraction of normal rat cerebrospinal fluid and plasma to be 44 and 9.9 ng/ml, respectively. This technique constitutes a sensitive and reliable method for determining low nanogram quantities of oleamide in biological fluids.