Development under the control of insulin of lipogenic enzymes, lipoprotein lipase, isoproterenol and glucagon sensitivity in differentiating rat preadipocytes in primary culture.

In preadipose cellular fractions (I, II and III) isolated by density gradient centrifugation from the inguinal tissue of young rats, we followed the activity of fatty acid synthetase, ATP citrate lyase and lipoprotein lipase during differentiation in culture. 1.5 nM insulin when added at confluence markedly induced the activity of ATP citrate lyase and fatty acid synthetase in the cells derived from the lighter fractions (I and II). The magnitude of this response was 25-50-fold the initial value 15 days after plating. In the cells of the heaviest fraction (III) both enzymes exhibited low activity which was slightly stimulated by the presence of insulin, VLDL and heparin. In contrast, the activity of lipoprotein lipase appeared before confluence in cells from all three fractions and peaked at day 6 after plating. This early emergence was independent of the addition of insulin to the medium. However, insulin slightly enhanced the peak activity in post-confluent cells. The development of cAMP production in response to isoproterenol (100 microM) and to glucagon (0.3 microM) was determined in the cells of fraction II in the same culture conditions. The responsiveness to isoproterenol was present very early in these cells and rose rapidly during the exponential growth phase, reaching a peak value at day 8 after plating. In contrast, the development of glucagon sensitivity occurred only during late differentiation. The stimulatory effect of glucagon was enhanced when VLDL and heparin were added with insulin to the medium.

Effects of cycles of food restriction followed by ad libitum refeeding on body composition and energy expenditure in obese rats.

Male Wistar rats rendered obese by a cafeteria diet were subjected to three successive cycles alternating food restriction with ad libitum cafeteria-diet feeding (WC rats). Body composition, energy intake, energy required for maintenance, and oxygen consumption were studied. Results were compared with those for rats fed a standard stock diet (CON rats) or a cafeteria diet (CAF rats). The rate of weight loss or regain was independent of the number of cycles. WC rats were fatter than CON rats and as fat as CAF rats after the third cycle. Cost of maintenance of WC rats decreased; their oxygen consumption decreased in the lean state, increased again in the fat state, but remained lower than that of CON and CAF rats. We conclude that the practice of successive restriction and refeeding did not result in resistance to weight loss, but rather in a defect in the utilization of energy intake, facilitating the development of obesity.

Massive overfeeding and energy balance in men: the Guru Walla model.

To determine the magnitude of the thermogenic response to a massive long-term overfeeding, an energy-balance study was carried out in nine lean, young Cameroonian men participating in a traditional fattening session: the Guru Walla. Food intake, body weight, body composition, activity, and metabolic rates were recorded during a 10-d baseline period and over the 61-65 d of fattening. Total energy expenditure (TEE) was measured by using doubly labeled water during the baseline period and the final 10 d of Guru Walla. Cumulative overfeeding consisted of 955 +/- 252 MJ (chi +/- SD) mainly as carbohydrate. Body-weight increase was 17 +/- 4 kg, 64-75% as fat. Metabolic rates increased but TEE did not. However, when accounting for the reduction in physical activity, substantial thermogenesis was observed but its amplitude was not greater than that observed under less extreme carbohydrate-overfeeding conditions. If luxuskonsumption does exist, it is not related to the magnitude of the cumulative overfeeding.

Effects of slimming and composition of diets on VO2 and thyroid hormones in healthy subjects.

Oxygen consumption and plasma thyroid hormone concentrations are modified by both low- and high-calorie diets. It has been suggested that the trigger may be changes in weight ("adipostatic" hypothesis involving the difference between the actual weight and the "set point") or changes in amount of carbohydrate in the diet ("carbohydrate" hypothesis). Two experiments were performed in order to test both hypotheses. Fourteen young healthy volunteers were studied: 1) at their spontaneous stable weight; 2) while losing weight rapidly on a calorically restricted diet; 3) and then at their stable new weight when consuming a refeeding diet. The calorie restricted diet resulted in decrease of VO2, and T3, and an increase of rT3; the refeeding diet resulted in values of VO2, T3, and rT3 intermediate between those of the spontaneous diet and those of the restricted diet. Another group of nine subjects were studied at their spontaneous caloric and proteic levels, comparing a diet containing only protein and carbohydrate with a diet containing only protein and fat. During the low carbohydrate diet rT3 increased and T3 decreased but they remained unchanged during the carbohydrate-rich diet. Thus neither the adipostatic hypothesis nor the carbohydrate hypothesis is sufficient alone to explain the observed changes in serum T3 and rT3.

Lowering of HDL2-cholesterol and lipoprotein A-I particle levels by increasing the ratio of polyunsaturated to saturated fatty acids.

The protective role of high-density lipoproteins (HDLs) has been attributed to the subfractions HDL2 (according to the density) and lipoprotein A-I (LpA-I) (according to the composition in apolipoproteins). We investigated the effect of a high ratio of polyunsaturated to saturated fatty acids (P:S) on these subfractions in a homogeneous group of young adult males. Two prescribed diets were consumed successively at the subjects' homes for 3 wk each in a random order; one diet contained 70 g butter (P:S 0.2, diet B), the other contained 70 g sunflower margarine (P:S 1.1, diet M). Total calorie, fat, and cholesterol intakes were similar for the two diets. Cholesterol and apolipoprotein B in serum and in low-density lipoproteins (LDLs) were lower with diet M than with diet B. However, significant decreases in protective subfractions of HDL, HDL2, and LpA-I were observed. This undesirable effect of the diet with a high P:S could cancel the benefits of lowering the LDL-cholesterol concentrations.

n-3 polyunsaturated fatty acids raise low-density lipoproteins, high-density lipoprotein 2, and plasminogen-activator inhibitor in healthy young men.

The effects of a moderate supplementation in n-3 polyunsaturated fatty acids (PUFAs) were investigated in 36 young healthy adult males. Factors investigated were lipoprotein (including HDL subfractions and apolipoproteins) and hemostasis indexes, assessed by platelet aggregation and plasminogen-activator-inhibitor (PAI) activity. Fat-controlled diets were prescribed, one with and one without a fish-oil supplement (control diet), successively during 3 wk in random order. Total calorie, fat, and cholesterol intakes were similar in the two diets. Triglycerides in serum and very-low-density lipoproteins were lower and high-density-lipoprotein 2 cholesterol was higher with the n-3 PUFA-supplemented diet. These effects as well as a significant decrease in platelet aggregation can be considered beneficial in terms of cardiovascular risk. However, significant increases in low-density-lipoprotein cholesterol and PAI activity occurred and were correlated. This latter effect could be detrimental.

Effects of ovarian steroids on energy balance in rats fed a highly palatable diet.

The effects of progesterone and estradiol on body weight, energy intake, energy expenditure, body composition, and brown adipose tissue activity were investigated in female rats fed a highly palatable diet (association of chow and full milk with sugar), which, by itself, induced an increase in food intake and energy expenditure. Progesterone and estradiol were administered in the form of implants. Ovariectomized animals were used in the estradiol studies. Energy expenditure was assessed through oxygen consumption, body composition through carcass analysis, brown adipose tissue activity through measurements of uncoupling-protein, guanosine diphosphate (GDP) binding capacity, and assay of uncoupling-protein mRNA. Body weight and food intake were increased by progesterone and decreased by estradiol. Energy expenditure was not altered by progesterone. Indirect evidence showed that estradiol increased energy expenditure, but direct measurements showed no modification. Changes in body weight under progesterone or under estradiol were not due to brown adipose tissue activity. The results indicate that ovarian hormones act on energy balance mainly by altering food intake, and possibly in the case of estradiol by increasing energy expenditure. These effects persist in rats fed a highly palatable diet, despite increases in energy intake and expenditure induced by the diet alone.

Tritium dilution space measurement is not modified by a doubling in fluid intake.

The purpose of this study was to examine the effects of a doubling in water intake on the total body water measured by the tritium dilution technique. Overdrinking was obtained by presenting tap water and sweet water to the rats. Total body water was measured twice, tritium dilution vs. dessication. Body water volumes differed between the two methods but not between the two groups. Thus the isotopic dilution technique can be used to measure total body water regardless of the flux of fluid through the subject.

A kappa opiate agonist, U50,488H, enhances energy expenditure in rats.

The effect of U50,488H (a selective kappa opiate agonist) on oxygen consumption was measured in either resting and free-moving rats. In both states, U50,488H provokes an increase in oxygen consumption. In resting rats, the increase occurs at lower doses than in free-moving rats. The explanation could be that in the free-moving rats the drug results in an increase in energy expenditure, partially compensated by a decrease in activity.

Effects of severe diet restriction on the oxygen consumption of obese women during exercise.

Eleven moderately obese, but otherwise healthy, young women were studied for three days while being fed their normal, unrestricted diet and then again for a two week period while being fed an energy-restricted, high-protein diet--220 kcal (0.92 MJ)/day as casein. Oxygen consumption (VO2) was measured 32 times for each subject, both at rest and during bicycle exercises. For each subject oxygen consumption was significantly lower, at rest and during moderate exercise, when the subjects were being fed the restricted diet. There was no significant difference among the diet treatments at the highest activity levels. The explanation proposed (though without experimental proof) is that, during the restricted diet, the increased reverse triiodothyronine (rT3) would result in a decrease of the aerobic glycolysis and no change in the anaerobic glycolysis.

Measure of total body water, using infrared spectrometry of heavy water.

The total body water can be assayed by the measurement of the diffusion space of heavy water. A well reproducible and inexpensive method is the infrared spectrometry, using two differential comparisons.

A method for separating cultured preadipocytes according to their density: application to stromal cells from overfed suckling rats.

The stroma vascular fraction of adipose tissue consists of a heterogeneous cell population; not all the cells in this compartment undergo adipose conversion in primary culture. A density gradient centrifugation procedure was used to separate cultured cells on the basis of their triglyceride content. This method was applied to both stroma vascular cells from rat adipose tissue and to a 3T3 F442A preadipose cell line as a reference. Comparison of the results obtained from these two cell types suggests that this separation procedure can lead to a quantification of adipose differentiation in the heterogeneous stromal cell population. Separation procedures were applied to cultured stromal cells derived from young rats during the onset of nutritional obesity induced by overfeeding in early life. Results show that early overfeeding induced an increase in the stromal cell differentiation capacity which is expressed in vitro.

Relationship between plasma insulin, the size and number of adpocytes and habitual calory intake in a group of 186 obese women.

In a group of 186 obese women, no correlation was found between post-glucose load insulinemia, measured at 13:00 hrs, and the degree of overweight, nor between post-glucose insulinemia and mean adipocyte diameter. Significant correlations were found between post-glucose insulinemia and daily caloric intake, and between post-protein insulinemia and mean adipocyte diameter. Post-glucose and post-protein load insulinemia were interrelated.

Increased lipoprotein lipase content in the adipose tissue of suckling and weaning obese Zucker rats.

The aim of this study was to determine whether the increase in lipoprotein lipase activity displayed by the adipose tissue of obese (fa/fa) rats as compared with that of lean (Fa/fa) rats could be ascribed to a change in the content or in the catalytic properties of the enzyme. The question was addressed in rats of two ages: in 7-day-old suckling and in 30-day-old post-weaning pups. Inguinal fat-pads were removed surgically (7 days of age) or after killing (30 days of age), and acetone-extract powders were prepared. The relative quantity of enzyme was assessed by immunotitration using an antiserum raised in goat against purified lipoprotein lipase from rat adipose tissue. The results indicate that increases in enzyme activity in obese animals were strictly paralleled by increases in the amount of enzyme in suckling as well as in post-weaning pups. Moreover, the apparent Km values of lipoprotein lipase for its substrate triacylglycerol were identical in the two genotypes. In conclusion, the genotype-mediated increase in lipoprotein lipase activity in adipose tissue of obese Zucker rats was fully accounted for by an increase in the content of the enzyme. In addition, this work documents the mechanism of the increase in lipoprotein lipase activity during weaning, which is mediated mainly through changes in the adipose-tissue enzyme content.

Genetic approach of family obesity: study of HLA antigens in 10 families and 86 unrelated obese subjects.

HLA A and B typing was performed in 86 unrelated obese subjects and in 10 families including at least one parent and one obese sibling. The results in the series of unrelated subjects show no significant difference in antigen frequencies as compared to the control series. However in the 10 families studied, a group of 5 families is characterized by a high penetrance of obesity. In this group, inheritance of obesity seems to be transmitted through a dominant mode, and antigen B 18 appeared 4 times out of 5. The possible existence of a genetic form of obesity is considered in the discussion.

Circadian and ultradian rhythms in the feeding behaviour and nutrient intakes of oil refinery operators with shift-work every 3--4 days.

Seven healthy adult men, five shift-workers and two non-shift-workers (from 21 to 36 years; mean = 26.4) volunteered to record what and when they ate, both at work and at home, every day, during eight consecutive weeks (Oct. - Dec. 1974). 1) All the subjects maintained the timing of main-meal (lunch and supper) during all shifts. 2) The major intake of protein and lipid was concentrated on the two main meals during all shifts. 3) Only the pattern of carbohydrate intake was modified by the shift-work: e.g. night-shift is associated with nibbling behaviour. 4) However, shift-work and in particular the occurence of nibbling behaviour did not result in change either in the mean 24 h caloric intake, or in the percentage of protein calories. 5) The comparison between the constancy of the timing of major meals and the shift of the timing of circadian rhythm acrophases of the 5 shift-workers leads to conclude that meal timing had a poor synchronizing effect, if any.

Abnormal fatty acid utilization by cultured cardiac cells from 7-day-old obese Zucker rats.

Fatty acid utilization by muscle and nonmuscle heart cells in culture has been investigated in the 7-day-old Zucker rat to determine if this tissue could contribute to the lower energy expenditure reported in obese rats at the onset of obesity. The partitioning of oleate to oxidation and esterification products and the effect of genotype on this partitioning according to cell types were studied. Results showed that the fatty acid beta-oxidation and its esterification in neutral lipid was decreased by 30% in beating muscle cells from obese animals when compared with those from lean animals. In contrast, nonmuscle cells exhibited a decreased beta-oxidation alone. A similar fatty acid composition of the phospholipids was found in non-muscle cells of obese animals and their lean litter mates. In muscle cultures, palmitic and oleic acids are lower in cells of obese rats than in those of lean rats. The present study indicates that a defect in energy metabolism could be found in heart cells at the onset of obesity, suggesting that this defect is determined by intrinisic factor(s).

[Lipid metabolism in rats fed a diet rich in various carbohydrates. I. Results after I.P. injection of lipogenic precursors]. / Métabolism lipidique chez le rat recevant un régime riche en certains glucides. I. Résultats obtenus après injection I.P. de précurseurs lipogéniques

Male rats, Wistar CF strain, weighing 120 g at the beginning of the experiment, were fed during 7 months with one of the following diets, containing 72 p. 100 (w/w) carbohydrate: starch, fructose, glucose and sucrose. These diets were about 18% (w/w) in protein content and were conveniently balanced with respect to vitamins and mineral nutrients. After an overnight fast, the animals received by the i.p. way, 30 mn before their killing, one of the following lipogenic precursors: glucose (considered as the control treatment), fructose ethanol or acetate, thus forming 16 experimental groups. In their liver, heart and blood were determined the concentrations of 6 lipid compounds: triglycerides, non-esterified fatty acids, free, esterified and total cholesterol, phospholipide. a. The sucrose diet gave the heaviest animals, with a liver and heart which were the richest in triglyceride content. They had also the highest liver and blood cholesterol, but their blood phospholipid was the lowest. The starch diet also increased, compared to the glucose diet, liver and heart triglycerides and liver cholesterol. As regards the fructose diet, it had the same effects than the sucrose one in elevating liver weight, blood triglycerides and cholesterol; conversely, it lowered liver and chiefly heart triglycerides and increased blood phospholipide. The glucose diet was for almost all parameters the one which displayed the lowest values. b. Relative to the glucose injection, other ones increased liver triglycerides, cholesterol and phospholipids and non-esterified fatty acids of the 3 assayed tissues. We observed that some differences between the effects of two given injections varied according to the previous diet, e.g. the sucrose-fed rats had more liver triglycerides and cholesterol, more heart and blood cholesterol after i.p. fructose than after i.p. glucose, which was not the case for the starch-fed animals. The importance of liver esterification reactions, which are increased with a long-term administration of a fructose-containing diet, is emphasized in the discussion. However dietary fructose could not be able to display its lipogenic effets in the absence of dietary glucose and that is why sucrose is more efficient than glucose in promoting a net lipid synthesis.

Evidence of enhanced storage capacity in adipose tissue of genetically fat chickens.

The storage capacity for plasma triglyceride in abdominal adipose tissue has been investigated in two lines of chickens selected for either high or low adiposity (fat line and lean line, respectively). Adipose tissue cellularity and lipoprotein lipase (LPL) activity were estimated in 2- and 5-wk-old birds. In 2-wk-old birds, cellularity and LPL and glycerophosphate dehydrogenase (GPDH) activity were evaluated in the stromavascular fraction. At both ages studied, the fat line exhibited a twofold increase in mature fat cell number and a marked hypertrophy. LPL activity per cell did not differ with genotype, regardless of the nutritional state; however, LPL activity per whole fat pad was higher in fat birds. In 2-wk-old fat chickens, the stromavascular fraction was characterized by an increase in cell number and a decrease in LPL activity, while GPDH was unchanged. Finally, adipocyte hyperplasia in the fat line appeared to reflect an excessive proliferation of precursor cells. The higher LPL activity in fat birds resulted mainly from cell hyperplasia, rather than from a greater intrinsic activity of adipocytes. Consequently, enhanced fatty acid uptake by adipose tissue represents a major factor in determination of adiposity in the chicken.