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

(T)urnover of plasma free fatty acids (FFAs) can be determined from th e palmitate enrichment of plasma after administration of analogues lab eled with stable isotopes. We studied the conditions to measure both t he concentration and the C-13 enrichment of plasma palmitate by gas ch romatography-mass spectrometry (GC-MS) using crude extracts. The metho d used plasma extraction after addition of heptadecanoic acid as inter nal standard and methylation with diazomethane. Subsequently the sampl es were analyzed by GC-MS. Plasma palmitate levels determined with thi s simplified method did not differ statistically from those obtained b y a more ''classical'' procedure using FFA separation from other plasm a lipids. Palmitic acid turnover rates (R(a)) were evaluated in the st eady-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 a greement with the turnover rate previously reported for normal subject s. Sample preparation and GC-MS analysis by the proposed procedure are simple and rapid and thus the method appears to be particularly usefu l in clinical studies where numerous samples have to be analyzed.