Claude Wodon

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

Abstract 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- 14 C]-cetate or [1- 14 C]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.

Influence of Litter Size on Lipid Composition in Infant Mice

The amount of milk available to each member of the litter was varied by adjusting the number of mice pups to 4, 8 or 12 per dam. The total fatty acid content of the carcass of the young increased for 2 weeks, and there was more in the well-fed groups. The fatty acid contents decreased thereafter transiently in all groups until weaning. The milk diet contributed major quantities of lauric and myristic acids to peripheral tissues but not to the liver. Undernourishment during neonatal life was associated with a relative reduction in palmitoleic, oleic and linoleic acids in lipids of the carcass. In contrast the carcass of the progeny subjected to overall dietary abundance showed relative increase in palmitoleic, oleic and linoleic acids at the expense of stearic acid.

EFFECTS OF LYSINE DEFICIENCY ON THE EPIDIDYMAL ADIPOSE TISSUE OF YOUNG RATS

The small amount of very active enzymic and structural proteins, present in the epididymal adipose tissue of male rats, is under nutritional and hormonal control, both in uivo and in vitro (Christophe & Wodon, 1964). I t has been shown that young rats receiving ad libitum a diet deficient in lysine suffer from a loss of liver, pancreatic and muscle proteins (Vandermeers & Christophe, 1964; Vandermeers-Piret & Christophe, 1964; Sidransky & Baba, 1960), and it seemed worthwhile to see whether the kwashiorkor-like disease found in these malnourished animals had also some effect on the protein metabolism of their epididymal adipose tissue. The differences in the results between adipose tissue metabolism in lysine-deficient rats and control rats were moderate, while the differences in the results between adipose tissue metabolism in rats kept on the lysine-poor diet and rats recovering from their deficiency were striking. It will also be shown in this paper that an acute state of amino acid imbalance artificially created in uitro can already result in a degradation of protein metabolism in adipose tissue.

7-day time study of lipid metabolism in normal and obese-hyperglycemic Bar Harbor mice. Qualitative and quantitative aspects

Summary o 1. Lipid metabolism was followed for 7 days in lean and obese-hyperglycemic 11-week old Bar Harbor mice by measuring the incorporation of a single dose (90 μC) of [1-14C] acetate in the liver and extrahepatic tissues. 2. In the liver of control animals, microsomes were more active than supernatant with respect to lipogenesis at time 10 min. They were also more efficient in desaturating labelled 18 : 0 than 16 : 0. A portion of unlabelled fatty acid was elongated with [1-14C] acetate. The radioactivity of liver glycerides decreased rapidly because of the secretion of lipoproteins rich in labelled 18 : 1. The turnover at the 2-position in triglycerides remaining in the liver appeared to be slower than at positions 1 and 3. 3. In the adipose tissue, the renewal of 1–2 diglycerides was very rapid. The labelling of 1–3 diglycerides in this tissue suggests the existence of a monoglyceride pathway operative in vivo. Triglycerides were better labelled in muscle than in adipose tissue. 4. In all tissues, the secondary alterations in the structure of « precursortriglycerides and phospholipids during the 7-day period indicate that a sizeable proportion was submitted to either complete or partial lipolysis. Transfers of 14C by elongation and/or desaturation occurred in the newly released fatty acids before acyl rearrangements, as a result the divergences between 14C distribution and lipid structures observed at time 10 min were slowly reduced. 5. In obese-hyperglycemic mice twice as much of the radioactivity offered was incorporated into total body lipids. The liver was the chief lipogenetic site, with microsomes as well as supernatant overloaded with radioactive triglycerides. The microsomal 9,10 dehydrogenase was very active, and the 2-position of triglycerides was dominated by labelled 18 : 1 throughout the experiment. 6. Both, the renewal of adipose tissue 1–2 diglycerides and the radioactivity of muscle triglycerides were higher than in lean littermates.