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Spectrum of fatty acids synthesized in situ and metabolic heterogeneity of free fatty acids and glycerides within isolated rat adipocytes

par Winand, Jacques ;Furnelle, Jacques ;Wodon, Claude ;Christophe, Jean
Référence Biochimica et biophysica acta. L, Lipids and lipid metabolism, 239, 2, page (142-153)
Publication Publié, 1971-07

Article révisé par les pairs

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Résumé :

1. 1. Lipid metabolism was explored in isolated rat adipose cells incubated in the presence of 10 mM glucose and a low concentration (0.05-0.2 mM) of a labelled pre-cursor ([1-14C]-cetate or [1-14C]palmitate). Six lipid classes were partitioned by thin-layer chromatography and their fatty acids were analyzed by radio gas-liquid chromatography. 2. 2. Since the specific activity of free fatty acids was always lower intracellularly than in the medium, it follows that the intracellular pool of free fatty acids was heterogeneous. Free fatty acids labelled in vitro with acetate left the cells first, while the relatively large amount of free fatty acids derived from bulk triglycerides was esterified more quickly. 3. 3. The specific activity of diglycerides was very high after incubation with both precursors when compared with their concentration. Therefore, it is probable that a portion of recently synthesized diglycerides was very susceptible to lipolytic breakdown. The 1,3-diglycerides were often as well labelled as the 1,2-diglycerides. Theophylline and dibutyryl cyclic AMP increased the total concentration of diglycerides by 50%. They made the fatty acid composition of diglycerides more comparable to the triglycerides (i.e. richer in unsaturated fatty acids) and reduced their labelling sharply. 4. 4. Myristate, palmitate and palmitoleate labelled with acetate were preferentially esterified into triglycerides and stearate was concentrated into phospholipids. 5. 5. The in vitro differences between mass and radioactivity distribution of fatty acids may be due to the heterogeneity of the lipogenetic process (2-carbon elongation and monodesaturation) and/or to the previous in vivo supply to adipose cells of lipids of hepatic origin rich in unlabelled stearate and oleate. Lipolytic agents increased the relative porportion of myristate labelled with acetate. © 1971.