FAST GAS-CHROMATOGRAPHIC MASS-SPECTROMETRIC METHOD FOR THE EVALUATION OF PLASMA FATTY-ACID TURNOVER USING [1-C-13]PALMITATE

(T)urnover of plasma free fatty acids (FFAs) can be determined from the palmitate enrichment of plasma after administration of analogues labeled with stable isotopes. We studied the conditions to measure both the concentration and the C-13 enrichment of plasma palmitate by gas chromatography-mass spectrometry (GC-MS) using crude extracts. The method used plasma extraction after addition of heptadecanoic acid as internal standard and methylation with diazomethane. Subsequently the samples were analyzed by GC-MS. Plasma palmitate levels determined with this simplified method did not differ statistically from those obtained by a more ''classical'' procedure using FFA separation from other plasma lipids. Palmitic acid turnover rates (R(a)) were evaluated in the steady-state period, in two normal subjects after 90 min infusion with [1-C-13]palmitate bound to human albumin. The rate of appearance (R(a)) was found to be 0.92 and 1.08 mmol kg(-1) min(-1), which is in good agreement with the turnover rate previously reported for normal subjects. Sample preparation and GC-MS analysis by the proposed procedure are simple and rapid and thus the method appears to be particularly useful in clinical studies where numerous samples have to be analyzed.