Adaptive changes in enzyme activity and metabolic pathways in adipose tissue from meal-fed rats

A number of metabolic factors and the activity of a number of enzymes were determined in meal-fed (animals fed a single daily 2 hr meal) and nibbling (ad libitum-fed) rats. The dependency of the observed adaptive changes on the ingestion of carbohydrate was studied by feeding diets high in carbohydrate or fat. Glucose-6-phosphate dehydrogenase and NADP-malic dehydrogenase were more active in adipose tissue from high carbohydrate meal-fed rats than in tissue from ad libitum-fed rats. The activity in adipose tissue of isocitric dehydrogenase, 6-phosphogluconate dehydrogenase, and NAD-malic dehydrogenase did not increase significantly in response to meal-feeding the high carbohydrate diet. No increase in lipogenesis or enzyme activity could be demonstrated in adipose tissue from rats meal-fed a high fat diet. Lipase activity of adipose tissue was increased by high carbohydrate meal-feeding and decreased by feeding a high fat diet. The in vitro uptake of palmitate-1-(14)C by adipose tissue was depressed by a high fat diet and enhanced in rats meal-fed a high carbohydrate diet. Diaphragm or slices of liver from high fat-fed rats oxidized palmitate-1-(14)C more rapidly than did tissue from ad libitum-fed animals. Evidence is presented for the quantitative importance of citrate as a source of extramitochondrial acetyl CoA in adipose tissue of meal-eating and ad libitum-fed rats. The relationship of extramitochondrially formed citrate to the NAD-malic dehydrogenase-malic enzyme system in adipose tissue is discussed.     

Development of intra- and intermuscular adipose tissue in growing large white and Meishan pigs

Lipogenic enzyme activities of porcine intra- and intermuscular adipose tissues were determined in growing lean (Large White) and fat (Meishan) pigs. The activities of acetyl-CoA-carboxylase (ACX), malic enzyme (ME) and glucose-6-phosphate dehydrogenase (G6PDH) were compared in both breeds and at both adipose sites. All three enzyme activities were much lower in the intramuscular adipose tissue than in the intermuscular site. Although the lipogenic activity of the intramuscular adipose site was low, it appeared, however, to possess adequate levels of enzymes for in situ lipid synthesis. The highest differences in lipogenic enzyme activities between Meishan and Large White pigs were found in intramuscular adipose tissue, and essentially concerned the activity of malic enzyme which was much higher in Meishan pigs. A close relationship between ME activity and lipid content of intramuscular adipose tissue was observed in both breeds. It was concluded that ME appeared to be a major factor affecting the incidence of higher intramuscular fat in the pig.     

Development of hepatic and adipose tissue lipogenic enzymes and insulinemia during suckling and weaning on to a high-fat diet in Zucker rats

This study was designed to monitor the developmental changes in insulinemia and lipogenic enzyme activities in both inguinal adipose tissue and liver during suckling (7, 9, 14, and 17 days of age) and weaning (22 and 30 days of age) on to either a low-fat or a high-fat diet in lean (Fa/fa) and obese (fa/fa) rats. Tissues were removed through surgery and genotypes were retrospectively determined. During suckling, there was no difference in liver enzyme activities between the two groups. In contrast, adipose tissue fatty acid synthetase was increased by 50% and citrate cleavage enzyme and malic enzyme by 30% by 9 days of age. By 17 days of age, there was a threefold elevation in these enzyme activities and 6-phosphogluconic dehydrogenase and a twofold increase in glucose-6-phosphate dehydrogenase per inguinal fat pad in fa/fa versus Fa/fa. Consistent with these results, fat pad weight was increased by 20%, 50%, and 100% at 9, 14, and 17 days of age, respectively, in obese as compared to lean pups. However only by 17 days of age could a slight but significant increase in insulin level be detected in obese pups. Enlargement of inguinal fat pad accelerated after weaning on to a low-fat diet and still more after weaning on to a high-fat diet. Weaning on to a low-fat diet elicited an induction of hepatic lipogenic enzymes two or three times greater in fa/fa than in lean pups, while weaning on to a high-fat diet blunted the differences between genotypes. The lipogenic enzyme activities displayed per total inguinal fat were three to ten times greater in obese than in lean pups, regardless of the diet. However, adipose tissue lipogenic enzyme activities were much lower after weaning on to a high-fat than on to a low-fat diet in obese pups. The high-fat diet was as effective as the low-fat diet in triggering hyperinsulinemia in obese pups. The increased adipose tissue capacity for lipogenesis, starting during the suckling period, could play an important etiologic role in the development and maintenance of obesity in the Zucker rat.-Bazin, R., and M. Lavau. Development of hepatic and adipose tissue lipogenic enzymes and insulinemia during suckling and weaning on to a high-fat diet in Zucker rats.     

Thyroid hormone stimulates adipocyte differentiation of 3T3 cells

Triiodothyronine added at 0.1 nM to 3T3-F442A cells cultured in adipogenic medium having endogenous hormone concentrations similar to those of hypothyroid serum stimulated adipose conversion; activities of both lipogenic enzymes, glycerophosphate dehydrogenase and malic enzyme, increased with hormone treatment. The number of adipocytes was also augmented by L-T3 addition but the number of fat cell clusters remained the same as compared to non-treated cultures, suggesting that thyroid hormone increased the number of adipocytes probably through stimulating selective multiplication of precursor adipose cells. Hormone addition to cells cultured with non-adipogenic medium did not promote conversion showing that L-T3 is not an adipogenic factor by itself. Triiodothyronine added at concentrations similar to those found in hyperthyroidism, from 10 nM up to 10 µM, also increased the proportion of adipocytes without changing the number of fat cell clusters, but they decreased the activity of both lipogenic enzymes and lipid accumulation in mature adipocytes. It can be concluded that during 3T3-F442A differentiation into adipocytes L-T3 increases the number of differentiated adipocytes and, at low concentrations, also enhances lipogenic enzyme activities, whereas at the hyperthyroid hormone levels these enzyme activities are significantly reduced, remaining at levels similar to those of cells cultured with hypothyroid medium. This cloned cell line seems to be a useful model to study thyroid hormone action at both molecular and cellular level.     

The Influence of Hydrocortisone (HC) on Differentiation of Adipose Tissue is Dependent on Fetal Age

Elevated serum hydrocortisone (HC) levels are associated with larger fat cells and elevated levels of Iipogenic and associated enzymes in late term pig fetuses from genetically obese dams. We have investigated the influence of HC status per se on these and other adipose tissue traits by chronically treating pig fetuses hypophysectomized (hypox) on day 70 with HC between either day 70 and 90 or 90 and 105 of gestation. Treatment with HC during both periods increased serum HC levels (P<.05) and increased fat cell size (P<.05) in the perirenal (PERI) and subcutaneous (SQ) depots, but failed to influence body weights, insulin-like growth factor-1 and insulin levels. Quantitative analysis of sections of PERI and SQ adipose tissue indicated that HC increased lipoprotein lipase (LPL), esterase and glucose-6-phosphate dehydrogenase (G6PDH) activities. The degree of esterase and G6PDH, but not LPL response to HC, was greater during the 90- to 105-day period than during the earlier period. HC significantly increased lipid accretion only in the SQ depot between 90 and 105 days. Overall, HC significantly augmented hypox-induced alterations in cellular and metabolic traits of developing adipose tissue. The general increase in fat cell size (21%) with moderate (SQ-105d) or no (PERI-90, 105d; SQ-90d) increase in lipid accretion indicates that HC either did not influence or decreased apparent fat cell number. Regardless, these data indicate that changes in serum HC per se may account for adipose tissue traits that characterize fetuses from genetically obese dams.     

Early development of adipose cell lipogenesis and glycerol utilization in Zucker obese rats.

A study of adipose cell metabolism was made at ages 5, 7, 10, and 14 wk of age in genetically obese Zucker rats. Adipose samples were surgically removed and used for in vitro adipose cell incubations and for characterization of enzyme patterns. Lipogenic capacity from glucose and enzymes normally associated with lipogenesis (malic enzyme, citrate cleavage enzyme and glucose-6-PO4 dehydrogenase) followed the same pattern of development. At 5 wk of age, the adipose cells of obese animals had a greater capacity for fat synthesis than the lean rats. At all other ages lipogenic activity and enzyme levels were either similar or less than the pair-fed lean littermates. Glycerol utilization by isolated fat cells was similar; however, adipose tissue glycerokinase was elevated in obese rats at 14 wk of age. It was concluded that there was no apparent change in specific lipogenic capacity of fat cells from the obese rat when compared to its lean littermate. It was also concluded that increased adipose glycerokinase activity in obese rats represented a secondary shift in metabolism.     

Analysis of lines of mice selected for fat content. 2. Correlated responses in the activities of enzymes involved in lipogenesis

Estimates of the activities (Vmax) of six enzymes involved in de novo fat synthesis were made in replicated lines of mice differing in fat content. These lines had been selected high and low for 20 generations with three replicates each of Fat, Control and Lean lines and for a further eight generations high and low as an unreplicated line. The activities of ATP-citrate lyase (ACL), acetyl-CoA carboxylase (ACC), fatty acid synthetase (FAS), cytoplasmic malate dehydrogenase (MDH), malic enzyme (ME) and pyruvate kinase (PK) were determined in vitro in both liver and gonadal fatpad tissues taken at ages five and ten weeks. The activities of ACL, ACC, FAS and ME were significantly higher in the Fat than the Lean lines, and the differences were more pronounced at the earlier age and in the gonadal fatpad where activities in the Fat lines were higher by factors of 3.5, 2.4, 2.5 and 3.5 respectively. The activity of PK was unchanged in each tissue. MDH activity was significantly lower in adipose tissue in the Fat lines than the Lean lines at age ten weeks but not at age five weeks or in liver tissue. Results from replicates indicated that random genetic drift affected enzyme activities but nevertheless significant changes in activity were associated with the direction of selection. The changes in enzyme activity reported here are similar to those known to be associated with major mutations causing obesity in mice.     

Expression and activity of steroid aldoketoreductases 1C in omental adipose tissue are positive correlates of adiposity in women

We examined expression and activity of steroid aldoketoreductase (AKR) 1C enzymes in adipose tissue in women. AKR1C1 (20alpha-hydroxysteroid dehydrogenase; 20alpha-HSD), AKR1C2 (3alpha-HSD-3), and AKR1C3 (17beta-HSD-5) are involved mainly in conversion of progesterone to 20alpha-hydroxyprogesterone and inactivation of dihydrotestosterone to 5alpha-androstane-3alpha,17beta-diol. Abdominal subcutaneous and omental adipose tissue biopsies were obtained during abdominal hysterectomies in seven women with low visceral adipose tissue (VAT) area and seven age- and total body fat mass-matched women with visceral obesity. Women with elevated VAT areas were characterized by significantly higher omental adipose tissue 20alpha-HSD and 3alpha-HSD-3 mRNA abundance compared with women with low VAT accumulations (1.4- and 1.6-fold differences, respectively; P < 0.05). Omental and subcutaneous adipose tissue 3alpha-HSD activities were significantly higher in women with high vs. low VAT areas (P < 0.05 for both comparisons). Total and visceral adiposities were positively associated with omental 20alpha-HSD mRNA level (r = 0.75, P < 0.003 for fat mass; r = 0.57, P < 0.04 for VAT area) and omental 3alpha-HSD-3 mRNA level (r = 0.68, P < 0.01 for fat mass; r = 0.74, P < 0.003 for VAT area). Enzyme activities in both depots were also positively correlated with adiposity measures. Omental adipose tissue enzyme expression and activity were positively associated with omental adipocyte size and LPL activity. In conclusion, mRNA abundance and activity of AKR1C enzymes in abdominal adipose tissue compartments are positive correlates of adiposity in women. Increased progesterone and/or dihydrotestosterone reduction in abdominal adipose tissue may impact locally on fat cell metabolism.     

Activity of selected gluconeogenic and lipogenic enzymes in bovine rumen mucosa, liver and adipose tissue

The activities of phosphoenolpyruvate carboxykinase, ;malic enzyme', citrate-cleavage enzyme and glucose 6-phosphate dehydrogenase were assayed in homogenates of rumen mucosa, liver and adipose tissue of cattle. Rumen mucosa cytoplasm contained activities of ;malic enzyme' approximately sevenfold those of phosphoenolpyruvate carboxykinase, suggesting that the conversion of propionate into lactate by rumen mucosa involves ;malic enzyme'. Neither starvation for 8 days nor feeding with a concentrate diet for at least 3 months before slaughter produced enzyme patterns in the tissues different from those in cattle given only hay, except that the all-concentrate diet caused increased activities of glucose 6-phosphate dehydrogenase and ;malic enzyme' in adipose tissues. Rumen mucosa, liver and adipose tissue contained phosphoenolpyruvate carboxykinase activity. ;Malic enzyme' was absent in liver. Citrate-cleavage enzyme activity was present in liver and adipose tissue but was quite low in rumen mucosa. Liver contained much less glucose 6-phosphate dehydrogenase activity than rumen mucosa or adipose tissue.     

Comparative lipoplasty analysis of in vivo-treated adipose tissue

A comparative histologic and chemical analysis was undertaken of adipose tissue treated in vivo with traditional, ultrasound-assisted, and external ultrasound-assisted lipoplasty. A series of six healthy women undergoing elective liposuction according to the superwet technique using a 1:1 infiltration ratio with the estimated quantity of fat to be removed was included in the study. Four separate regions on each patient were treated independently in vivo with traditional liposuction, internal ultrasound-assisted liposuction, or external ultrasound-assisted liposuction for 7 minutes. External massage was used as a control. Four separate specimens of adipose tissue from each patient were assessed for cellular disruption using blinded histologic evaluation. The remainder of tissue was centrifuged to separate the aqueous phase from the cellular components and then spectrophotometrically analyzed for creatinine kinase and glycerol 3-phosphate dehydrogenase activity as markers of cellular disruption. Histologic analysis confirmed 70 to 90 percent cellular disruption with internal ultrasound-assisted liposuction. Suction-assisted and external ultrasound-assisted liposuction showed 5 to 25 percent disruption, whereas massage controls showed only 5 percent. Only internal ultrasound-assisted liposuction showed 5 to 20 percent thermal liquefaction. Absorbance analysis showed creatine kinase activity (sigma units) greatest in ultrasound-exposed tissue. Both external and internal ultrasound-assisted liposuction gave creatine kinase levels 28 to 33 percent greater than suction-assisted liposuction, which varied only 10 percent from controls. Glycerol 3-phosphate dehydrogenase activity was 44 percent greater for internal ultrasound-assisted liposuction than that detected with suction-assisted liposuction. Glycerol 3-phosphate dehydrogenase activity with external ultrasound-assisted liposuction and massage did not vary much from each other, at only 14 percent and 11 percent activity compared with internal ultrasound-assisted liposuction, respectively. Histologic and enzyme analysis of the different types of liposuction and their effect on adipocyte cellular disruption revealed no significant effect of external ultrasound or massage on the adipocytes. Further experimental studies are necessary to evaluate the role and efficacy of alternative techniques for body contouring.     

Regulation of glucose-6-phosphate dehydrogenase activity during caloric restriction in human adipose tissue

Glucose-6-phosphate dehydrogenase activity was significantly lower in adipose tissue of human subjects after 7 days of severe caloric restriction on low-carbohydrate diets and had returned to normal values 4 days after the subjects resumed normal diets. Three other enzyme activities (malate-NADP dehydrogenase, oxaloacetate decarboxylating; ATP-citrate lyase and 6-phosphofructokinase) were not significantly affected by these dietary changes. These results are consistent with separate control of glucose-6-phosphate dehydrogenase activity versus other 'lipogenic' enzyme activities in human adipose tissue.     

The stromal‐vascular fraction of adipose tissue contributes to major differences between subcutaneous and visceral fat depots

Adipose tissue represents a complex tissue both in terms of its cellular composition, as it includes mature adipocytes and the various cell types comprising the stromal‐vascular fraction (SVF), and in relation to the distinct biochemical, morphological and functional characteristics according to its anatomical location. Herein, we have characterized the proteomic profile of both mature adipocyte and SVF from human visceral adipose tissue (VAT) and subcutaneous adipose tissue (SAT) fat depots in order to unveil differences in the expression of proteins which may underlie the distinct association of VAT and SAT to several pathologies. Specifically, 24 proteins were observed to be differentially expressed between SAT SVF versus VAT SVF from lean individuals. Immunoblotting and RT‐PCR analysis confirmed the differential regulation of the nuclear envelope proteins lamin A/C, the membrane‐cytoskeletal linker ezrin and the enzyme involved in retinoic acid production, aldehyde dehydrogenase 1A2, in the two fat depots. In sum, the observation that proteins with important cell functions are differentially distributed between VAT and SAT and their characterization as components of SVF or mature adipocytes pave the way for future research on the molecular basis underlying diverse adipose tissue‐related pathologies such as metabolic syndrome or lipodystrophy.     

Prenatal developmental changes in glucose transporters, intermediary metabolism and hormonal receptors related to the IGF/insulin-glucose axis in the heart and adipose tissue of bovines

Glucose transporter ontogenesis is likely to play a key role in glucose uptake by foetal tissues in order to satisfy their energy requirements. We thus investigated developmental changes in the bovine heart and perirenal adipose tissue in two glucose transporter isoforms, namely GLUT1 and GLUT4, the latter being responsible for the regulation of glucose uptake by insulin. Other key players of the glucose/insulin axis were also assessed. Plasma glucose concentration in the foetus was lower at 8 and 8.5 months of age than previously. In the heart, GLUT1 protein level markedly decreased between 3 and 4 months of age, whereas the number of insulin and IGF-I binding sites continually decreased, especially between 7 and 8 or 8.5 months of age. On the contrary, the GLUT4 level increased until 8 months of age and remained high until 2 weeks after birth. The activities of enzymes of glucose metabolism (namely phosphofructokinase [PFK] and lactate dehydrogenase [LDH]) increased throughout gestation and reached a plateau at 6 and 8.5 months of age for PFK and LDH, respectively. The activities of enzymes involved in fatty acid metabolism increased especially at birth. In perirenal adipose tissue, high mitochondrial activity was detected before birth which is a characteristic of brown adipose tissue. Furthermore, lipoprotein lipase activity and GLUT4 protein level markedly increased to reach a maximum at 6-7 and 8 months of age, and sharply decreased thereafter, whereas GLUT1 protein level increased between 6 and 7 months of age. In conclusion, considerable changes in the regulation of the insulin/glucose axis were observed from 6 months onwards of foetal development in both the heart and adipose tissue of cattle, which probably alters the potential of these tissues to use glucose or fat as energy sources.     

The major plant-derived cannabinoid Δ(9)-tetrahydrocannabinol promotes hypertrophy and macrophage infiltration in adipose tissue

Synthetic cannabinoid receptor agonists activate lipoprotein lipase and the formation of lipid droplets in cultured adipocytes. Here we extend this work by examining whether Δ(9)-tetrahydrocannabinol (THC), a major plant-derived cannabinoid, increases adipocyte size in vivo. Further, possibly as a consequence of hypertrophy, we hypothesize that THC exposure promotes macrophage infiltration into adipose tissue, an inflammatory state observed in obese individuals. Rats repeatedly exposed to THC in vivo had reduced body weight, fat pad weight, and ingested less food over the drug injection period. However, THC promoted adipocyte hypertrophy that was accompanied by a significant increase in cytosolic phosphoenolpyruvate carboxykinase (PEPCK-C) expression, an enzyme important in packaging triglycerides. We also showed that THC induced macrophage infiltration and increased expression of the inflammatory cytokine tumor necrosis factor alpha (TNF-α) in adipose tissue but did not induce apoptosis as measured by TUNEL staining. That THC increased adipocyte cell size in the absence of greater food intake, body weight and fat provides a unique model to explore mechanisms underlying changes in adipocyte size associated with a mild inflammatory state in fat tissue.     

The effect of dietary and hormonal conditions on the activities of glycolytic enzymes in rat epididymal adipose tissue

1. Measurements were made of the activities of nine glycolytic enzymes in epididymal adipose tissues obtained from rats that had undergone one of the following treatments: starvation; starvation followed by re-feeding with bread or high-fat diet; feeding with fat without preliminary starvation; alloxan-diabetes; alloxan-diabetes followed by insulin therapy. 2. In general, the activities of the glycolytic enzymes of adipose tissue, unlike those of liver, were not greatly affected by the above treatments. 3. The ;key' glycolytic enzymes, phosphofructokinase and pyruvate kinase, were generally no more adaptive in response to physiological factors than other glycolytic enzymes such as glucose phosphate isomerase, fructose diphosphate aldolase, triose phosphate isomerase, glycerol 3-phosphate dehydrogenase, phosphoglycerate kinase and lactate dehydrogenase. 4. Adiposetissue pyruvate kinase did not respond to feeding with fat in a manner similar to the liver enzyme. 5. Glyceraldehyde phosphate dehydrogenase had a behaviour pattern unlike the other eight glycolytic enzymes studied in that its activity was depressed by feeding with fat and was not restored to normal by re-feeding with a high-fat diet after starvation. These results are discussed in relation to the requirements of adipose tissue for glycerol phosphate in the esterification of fatty acids. 6. A statistical analysis of the results permitted the writing of linear equations describing the relationships between the activities of eight of the enzymes studied. 7. Evidence is presented for the existence of two constant-proportion groups amongst the enzymes studied, namely (i) glucose phosphate isomerase, phosphoglycerate kinase and lactate dehydrogenase, and (ii) triose phosphate isomerase, fructose diphosphate aldolase and pyruvate kinase. 8. Mechanisms for maintaining the observed relationships between the activities of the enzymes in the tissue are discussed.     

Adipose tissue intracrinology: potential importance of local androgen/estrogen metabolism in the regulation of adiposity.

The present article summarizes some of the studies available on steroid hormone conversion through the specific expression of steroidogenic enzymes in adipose tissue (adipose tissue intracrinology) and discusses the potential impact of local adipose tissue steroid metabolism on the regulation of adipocyte function and other metabolic parameters. Several studies have demonstrated significant steroid hormone uptake and conversion by adipose tissues from various body sites and in various cell fractions. Activities and/or mRNAs of aromatase, 3beta-hydroxysteroid dehydrogenase (HSD), 3alpha-HSD, 11beta-HSD, 17beta-HSD, 7alpha-hydroxylase, 17alpha-hydroxylase, 5alpha-reductase and UDP-glucuronosyltransferase 2B15 have been detected in adipose tissue or adipose cells. These studies have demonstrated potentially important roles for these enzymes in obesity, central fat accumulation, and the metabolic syndrome. Future studies on adipose tissue intracrinology will contribute further to our understanding of steroid action in adipocytes.     

The effect of immunocastration on adipose tissue deposition and composition in pigs

Immunocastrated pigs (IC) exhibit intensive fat deposition after immunisation, but the underlying mechanisms of intensified fat metabolism and deposition are not yet fully understood. Moreover, there is also a lack of comparative studies performed on IC, entire males (EM) and surgical castrates (SC). The main objective of our research was, therefore, to characterise the adipose tissue from the quantitative, histo-morphological and biochemical perspectives in IC 5 weeks after their immunisation in comparison to EM and SC. Immunocastrated pigs had an intermediate position in carcass fatness traits between EM (the leanest) and SC (the fattest). The histo-morphological traits of the subcutaneous adipose tissue of IC were similar to those of SC and differed from those of EM; i.e., they exhibited larger adipocytes in the outer backfat and a larger lobulus surface area in both backfat layers than EM. Intensive fat tissue development in IC was corroborated with higher activities of lipogenic enzymes (i.e., fatty acid synthase, malic enzyme, glucose 6-phosphate dehydrogenase, citrate cleavage enzyme), which was especially pronounced in the subcutaneous adipose tissue of IC (1.5- to 2.7-fold higher activity than in EM or SC). The fatty acid composition of the backfat in IC was similar to that in EM pigs. Both IC and EM exhibited less saturated and more polyunsaturated fatty acids than SC. In contrast, the fatty acid composition of the intramuscular fat of longissimus dorsi muscle in IC pigs was more similar to SC than to EM (higher monounsaturated and lower polyunsaturated fatty acid content in IC and SC than EM). In this study, it was demonstrated that immunocastration notably influenced lipid metabolism. This was shown by increased quantity of lipid depots and with changes in adipose tissue cellularity compared to EM, with changes in the fatty acid composition of the intramuscular fat and enhanced lipogenic activity compared to both EM and SC. These results provide new insights into the specificity of adipose tissue development and deposition in IC compared to EM and SC.     

The anatomy of adipose tissue in captive Macaca monkeys and its implications for human biology

In a sample of 31 sedentary, ad libitum-fed monkeys, most specimens had less than 5% adipose tissue by weight. Total fatness correlated closely with the number of adipocytes per kilogram lean body mass, but not at all with mean adipocyte volume, except in specimens below 5% fat. The total number of adipocytes per kilogram of lean body mass increased more than tenfold in the most obese specimens. These data suggest that, like humans but in contrast to laboratory rodents, adipocyte proliferation, not adipocyte enlargement, is the chief mechanism of adipose tissue expansion except in very lean monkeys. Adipose tissue was found in all the typical mammalian depots and in the superficial abdominal paunch, which enlarged disproportionately in obese specimens, forming an almost continuous layer over most of the body. Site-specific differences in the activities of some glycolytic enzymes were similar to those of other mammals. Adipocytes in the paunch depot showed biochemical properties in common with those in the groin depots. The distribution and cellularity of adipose tissue in normal humans were similar to those of exceptionally obese monkeys. Many of the interspecific and sex differences can be attributed to the much greater abundance of adipose tissue in humans, and may not be associated with hair reduction or aquatic habits. Some minor changes in the size or shape of certain adipose depots may have arisen recently under sexual selection. The relevance of laboratory rodents as animal models of human obesity is assessed from comparison of the cellular structure, anatomical distribution and enzyme profiles of adipose tissue in monkeys with those of human and other mammals.     

Lipoprotein lipase and lipogenic enzyme activities in adipose tissue from rats fed different lipid sources

This work was designed to study the effect of different lipid sources on the activities of lipoprotein lipase and lipogenic enzymes in adipose tissue from rats fedad libitum or energy-controlled diets. Male Wistar rats were fed diets containing 40% of energy as fat (olive oil, sunflower oil, palm oil or beef tallow), for 4 wk. Underad libitum feeding no differences were found among dietary fat groups in final body weight, adipose tissue weights and total body fat. Under energy-controlled feeding, despite isoenergetic intake, rats fed the beef tallow diet gained significantly less weight than rats fed the other three diets. Beef tallow fed rats showed the lowest values for adipose tissue weights and total body fat. When rats had free access to food no effect of dietary lipid source on lipogenic enzyme activities was found. In contrast, under energy-controlled feeding rats fed the beef tallow diet showed significantly higher activities of glucose-6-phosphate dehydrogenase and fatty acid synthase than rats fed the other three diets. Heparin-releasable lipoprotein lipase activity in perirenal and subcutaneous adipose tissues was not different among rats fed olive oil, safflower oil, palm oil or beef tallow. When comparing both adipose tissue anatomical locations, significantly higher activities were found in subcutaneous than in perirenal fat pad independently of dietary fat. In conclusion, under our experimental protocol, lipogenesis in rat adipose tissue does not seem to be affected by dietary fat type.