Lipolysis and lipogenesis from glucose in human fat cells of different sizes

Abstract

A B S T R A C T Lipogenesis from glucose and lipolysisin human omental and subcutaneous fat cells were studied as functions of adipose cell size and number in adult females. Since subcutaneous fat cells were larger than those prepared from the greater omentum, a comparison could be made of the metabolism of different sizes of cells within individual subjects. Rates per cell of glyceride-glycerol and glyceride-fatty acid synthesis from glucose were similar in omental and subcutaneous fat cells incubated in the presence or absence of insulin. However, subcutaneous fat cells exhibited higher rates of basal lipolysis than omental fat cells and these differences were maintained when lipolysis was stimulated with theophylline. Different rates of lipolysis were not demonstrable after incubations with epinephrine, indicating that subcutaneous fat cells were less responsive to this hormone than smaller omental fat cells. Correlation and partial correlation analysis showed that differences in basal and theophylline-stimulated lipolysis between fat cells prepared from different subjects and between omental and subcutaneous fat cells could be accounted for A precise evaluation of the influence of adipose cell enlargement on its function requires that metabolic studies be performed on fat cells of different sizes prepared from the same fat depot. In the present investigation we have used an indirect approach to the problem, taking advantage of the fact that human subcutaneous fat cells are generally larger than those prepared from the greater omentum. It was thus possible to carry out paired comparisons in vitro of the metabolism of differently sized fat cells derived from a common in vivo internal environment. The data from different subjects were also examined to determine whether there was a correlation between the volume and metabolism of a fatThe Journal of Clinical Investigation Volume 49 1970 1213 cell independent of factors such as age and relative body weight. We reasoned that if both sets of analyses showed that adipose cell volume was the common factor in accounting for differences in cellular function within and between subjects, then this would be strong supportive evidence for an effect of cellular enlargement on metabolism. METHODSSource of adipose tissue. Samples of fat (8-12 g) were obtained from the subcutaneous tissues of the anterior abdominal wall and from the greater omentum of 31 subjects who were undergoing elective abdominal surgery. Operations were performed in the mornings after an overnight fast. Morphine and atropine or their derivatives were used for premedication. Anesthesia was induced with thiopentone sodium and maintained with nitrous oxide and halothane. Tissues were removed between 60 and 90 min after induction of anesthesia. On the basis of previous reports (9, 10) it has been assumed that variations in the duration and depth of anesthesia did not significantly affect the metabolism of subcutaneous and omental fat cells in vitro.Relevant clinical data as well and individual values for a...

Studies on Lipid and Carbohydrate Metabolism in the Rat

“…The finding of an increased rate of incorporation of glucose-U-"C into glyceride-glycerol in tissues containing large fat cells confirms previous reports on isolated epididymal fat cells from rats, guinea-pigs and hamsters (Girolamo and Mendlinger, 1969) and on isolated human subcutaneous fat eells (Goldrick and McLoughlin, 1970). Vinten and Gliemann (1970) obtained similar results with the incorporation of glucose-U-^^C into total glycerides in single rat epididymal fat cells of different sizes.…”

“…In this respect, the present findings are in agreement with previous studies on isolated fat cells (Goldrick and McLoughlin, 1970), but differ from the results obtained by Smith (1971) in human tissues and by Salans and Dougherty (1971) in rat epididymal fat cells. Whilst Smith's (1971) findings give rise to an entirely different interpretation, if the insulin effect is expressed not as a percentage increase above baseline but as an absolute increment, there is no satisfactory explanation for the discrepancy between our findings and those of Salans and Dougherty (1971).…”

“…That this is not the sole nor neeessarily the most important factor involved in influencing the rate of esterification can be seen from the variability of results obtained in rats of different ages and on different feeding programmes both in this study and that of Salans and Dougherty (1971). Finally, it should be noted that an increase in the rate of basal lipolysis proeeeds together with an increased rate of utilization of glucose for glyceride-glycerol synthesis as human subcutaneous fat cells enlarge (Goldrick and McLoughlin, 1970). A similar relationship between adipose cell size and basal glycerol production has been reported in isolated rat epididymal fat cells (Hartman, Gohen, Richane and Hsu, 1971), isolated human subcutaneous fat cells (Smith, 1970) and in tissues from New Zealand obese mice (Herberg, Gries and Hesse-Wortmann, 1970).…”

Adipose tissue growth, distribution and cellularity in steers of two biological types

“…Hood and Allen (1978) also reported that the activities of the four NADPH-generating enzymes and the synthesis rate of fatty acids were directly related to adipose cell volume in four bovine intramuscular adipose samples. Similarly, in vitro experiments by Goldrick and McLoughlin (1970), Smith (1971b),…”

“…On the other hand, basal lipolysis also increased in larger fat cells (Goldrick and McLoughlin, 1970) suggest ing an increased turnover rate of glyceride-glycerol in the enlarged fat cells. This may be one of the reasons for the increased rate of glucose incorporation into the larger cells (Smith, 1971b).…”