The effects of exercise and dietary restriction on the activities of hexokinase and phosphofructokinase in superficial, intra-abdominal and intermuscular adipose tissue of guinea-pigs

1. The activities per gram of adipose tissue of hexokinase and phosphofructokinase were higher in the centre two intermuscular adipose depots of guinea-pigs than in any of the seven superficial and intra-abdominal depots studied. 2. The capacity for glucose utilization was reduced following about 3 months of regular exercise in all adipose depots studied except in the popliteal depot. The proportion of lipid decreased, and that of protein increased, in this intermuscular depot following regular, strenuous exercise, but it did not enlarge disproportionately. 3. We suggest that certain intermuscular adipose depots may act as a local energy source for adjacent muscles. The anatomical relations of adipose tissue to muscle may be an integral part of its physiological function.     

Comparative aspects of hexokinase and phosphofructokinase activity in intermuscular adipose tissue

1. The gross mass, mean adipocyte volume and activities of hexokinase (HK) and phosphofructokinase (PFK) were measured in adipose tissue from precisely identified intermuscular, superficial and intra-abdominal depots of 56 randomly collected wild and captive mammals and one bird. 2. In all intermuscular depots studied except that medial to the trapezius muscle, the activities of HK and PFK per adipocyte in adipose tissue in the centre of the depot were greater than in superficial and intra-abdominal depots of the same specimen. 3. These data are consistent with the suggestion that intermuscular adipose tissue may act as a local energy supply for adjacent muscles.     

Differential Response of Obese Gene Expression from Fasting in Bovine Adipose Tissues

To understand the molecular mechanism for intramuscular fat deposition, the expression of the obese gene was examined in response to fasting. Food deprivation for 48 h induced a decrease in the level of obese mRNA in pooled adipose tissues (abdominal, perirenal, subcutaneous, intermuscular and intramuscular). The expression of obese mRNA was examined for individual adipose tissue from several fat depots. It was highly expressed in perirenal adipose tissue, but fasting did not affect its expression level in this tissue. Moderate levels were detected in subcutaneous and intermuscular adipose tissues, and a fasting-induced decrease in obese mRNA was apparent in these tissues. The expression level of the obese gene in intramuscular adipose tissue was very low and did not respond to fasting.     

Differential response of obese gene expression from fasting in bovine adipose tissues

To understand the molecular mechanism for intramuscular fat deposition, the expression of the obese gene was examined in response to fasting. Food deprivation for 48 h induced a decrease in the level of obese mRNA in pooled adipose tissues (abdominal, perirenal, subcutaneous, intermuscular and intramuscular). The expression of obese mRNA was examined for individual adipose tissue from several fat depots. It was highly expressed in perirenal adipose tissue, but fasting did not affect its expression level in this tissue. Moderate levels were detected in subcutaneous and intermuscular adipose tissues, and a fasting-induced decrease in obese mRNA was apparent in these tissues. The expression level of the obese gene in intramuscular adipose tissue was very low and did not respond to fasting.     

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.     

Depot specific differences during adipogenesis of porcine stromal-vascular cells

Recently a role of adipose tissue as an endocrine organ secreting factors involved in the regulation of whole-body energy homeostasis has emerged. Preadipocytes in different fat depots have distinct adipogenic potential and the metabolic activity differs between mature adipocytes of different depot origins. Here we describe the proliferation and differentiation of stromal-vascular cells derived from subcutaneous and visceral fat depots of adult pigs. We demonstrate that subcutaneous porcine preadipocytes proliferate more actively and that individual subcutaneous adipocytes have a more rapid accumulation of triacylglycerols than visceral cells. During differentiation, subcutaneous and visceral preadipocytes showed similar gene expression patterns with increased expression of adiponectin (APM1), adipocyte-specific fatty acid binding protein (FABP4), catalase (CAT), and peroxisome proliferator-activated receptor gamma 2 (PPARG2). Furthermore, initial data showing depot-originated effects on the expression of CAT, carnitine palmitoyl transferase 1B (CPT1B) and FABP4 suggest possible depot specific differences in the function and metabolism of mature porcine adipocytes.     

Tissue leptin and plasma insulin are associated with lipoprotein lipase activity in severely obese patients

The development of metabolic complications of obesity has been associated with the existence of depot-specific differences in the biochemical properties of adipocytes. The aim of this study was to investigate, in severely obese men and women, both gender- and depot-related differences in lipoprotein lipase (LPL) expression and activity, as well as the involvement of endocrine and biometric factors and their dependence on gender and/or fat depot. Morbidly obese, nondiabetic, subjects (9 men and 22 women) aged 41.1+/-1.9 years, with a body mass index (BMI) of 54.7+/-1.7 kg/m(2) who had undergone abdominal surgery were studied. Both expression and activity of LPL and leptin expression were determined in adipose samples from subcutaneous and visceral fat depots. In both men and women, visceral fat showed higher LPL mRNA levels as well as lower ob mRNA levels and tissue leptin content than the subcutaneous one. In both subcutaneous and visceral adipose depots, women exhibited higher protein content, decreased fat cell size and lower LPL activity than men. The gender-related differences found in abdominal fat LPL activity could contribute to the increased risk for developing obesity-associated diseases shown by men, even in morbid obesity, in which the massive fat accumulation could mask these differences. Furthermore, the leptin content of fat depots as well as plasma insulin concentrations appear in our population as the main determinants of adipose tissue LPL activity, adjusted by gender, depot and BMI.     

Adipose tissue,the immune system and exercise fatigue: how activated lymphocytes compete for lipids

Adipose depots that contain lymph nodes, and probably intermuscular fat in skeletal and cardiac muscle, are specialized to provision adjacent tissue in a paracrine mode. Perinodal adipocytes respond selectively to various cytokines and incorporate proportionately more polyunsaturated fatty acids. Lipolysis in the adipocytes of node-containing depots can be stimulated via inflammation of the enclosed lymph nodes. Repeated immune stimulation elicits properties characteristic of perinodal adipocytes in those elsewhere in the same depot, and hours later in other node-containing depots, but not in nodeless depots. Such site-specific properties of adipose tissue enable partitioning of dietary and metabolic supplies of fatty acids between competing tissues. Local interactions emancipate the peripheral immune system from competing with other tissues for lipids during immune responses, and may be especially important during periods of high demand, such as strenuous exercise. Biopsies of subcutaneous adipose tissue from sites remote from lymph nodes do not adequately represent the composition of fatty acids available to the immune system in situ, and perhaps that supplied to other tissues. Intermuscular fat in skeletal and cardiac muscle may also indicate paracrine relationships between adipocytes and "end-user" tissues. The concept of paracrine interactions between certain adipocytes and "user" tissue may account for the widespread contiguity between these tissues in vivo.     

Organization of white adipose tissue in lemuridae

The gross anatomy of white adipose tissue was studied in seven carcasses representing three lemurid species (Lemur catta, Eulemur fulvus, E. mongoz) to validate in vivo methods of assessing fatness, and to contribute to a comprehensive database on the organization of adipose tissue in Mammalia. During the years preceding their deaths, subjects had been either caged or semi-provisioned under semi-captive conditions, and their body masses had been recorded several times annually. All specimens were as fat or fatter than anthropoid primates maintained for long periods under comparable conditions. At least eight superficial, four intra-abdominal, and two intermuscular adipose depots were described, all of which were comparable to those described previously for macaques and humans. All typical mammalian depots were present. Many superficial depots adhered tightly to the skin and/or underlying muscles. The superficial “paunch” depot on the outer ventral wall of the abdomen, characteristic of anthropoid primates, was found in all specimens. The existence of this depot in lemurs suggests that it evolved early in Primates. As in monkeys and humans, the paunch was very variable in size, massive in obese specimens but almost absent in moderately lean ones, confirming that extensive accumulation and selective depletion of adipose tissue at this depot is a special feature of Primates. In some obese specimens, adipose tissue on the ventral and lateral thorax and on the inner dorsal wall of the abdomen, extending around the kidneys and into the pelvic canal, was also massive. The investigation allowed for improvement of protocols for external measurement in ongoing research on growth, mass, and fatness in ringtailed and redfronted lemurs. Comparisons of subjects' ranges of body mass change during adult life with masses of adipose tissue found upon dissection suggested that much of lemurs' predictable seasonal change in body mass is due to changes in the mass of white adipose tissue. © 1995 Wiley-Liss, Inc.     

Retinoids and retinoid-binding protein expression in rat adipocytes.

Adipose tissue has been reported to contain relatively high levels of the specific mRNA for retinol-binding protein (RBP) (Makover A., Soprano, D.R., Wyatt, M. L., and Goodman, D.S. (1989) J. Lipid Res. 30, 171-180). Studies were conducted to explore retinoid and retinoid-binding protein storage and metabolism in adipose tissue. In these studies, we measured RBP and cellular retinol-binding protein (CRBP) mRNA levels and retinoid levels in 6 adipose depots in male rats. Total RNA was isolated from inguinal, dorsal, mesenteric, epididymal, perinephric, and brown adipose tissue, and average RBP and CRBP mRNA levels were determined by Northern blot analysis. The relative levels of RBP mRNA in these 6 anatomically different adipose depots averaged, respectively, 6.3, 6.7, 16, 34, 37, and 21% of the level in a rat liver RNA standard. Retinoid levels in the 6 depots were similar and averaged approximately 6-7 micrograms of retinol eq/g of adipose tissue. Since adipose tissue contains several cell types, the cellular localizations of RBP and CRBP expression and retinoid storage were examined. RNA was prepared from isolated rat adipocytes and stromal-vascular cells. Cellular levels of the mRNAs for RBP, CRBP, apolipoprotein E (apoE), lipoprotein lipase, adipocyte P2, and adipsin were measured by Northern blot analysis. RBP was expressed almost exclusively in the adipocytes and only weakly in the stromal-vascular cells. Both CRBP and apoE mRNA levels were relatively high in the stromal-vascular cell preparations and only very low mRNA levels were found in the adipocytes. Lipoprotein lipase, adipsin, and adipocyte P2 mRNAs were found in substantial levels in both the adipocytes and stromal-vascular cells, but with higher levels present in the adipocytes. Cultured adipocytes synthesized RBP protein and secreted it into the medium. Only adipocytes (not stromal-vascular cells) contained retinol, at levels between 0.65-0.8 micrograms of retinol eq/10(6) cells. These studies demonstrate that adipocytes store retinoid and synthesize and secrete RBP, and suggest that rat adipocytes may be dynamically involved in retinoid storage and metabolism.     

Effects of fasting on lipoprotein lipase activity in different depots of white and brown adipose tissues in diet-induced overweight rats

The aim of the present study was to evaluate the effects of 24 hours of starvation on lipoprotein lipase (LPL) activity in various depots of white and brown adipose tissues in control rats and in rats with two different degrees of overweight, both induced by dietary treatment. In control rats, no changes in LPL immunoreactive mass were observed in either white or brown adipose tissues after fasting, whereas the effects of food deprivation on enzyme activity were opposite in white versus brown adipose tissues. The LPL activity response to fasting was impaired by obesity: White adipose depots of cafeteria obese rats showed a lower ability to downregulate LPL during fasting and the increased LPL activity induced by fasting in brown adipose depots was less intense in the obese rats compared with control animals. When the degree of overweight was reduced, the differences between obese and control rats were also attenuated.     

Adipose tissue in the mammalian heart and pericardium: structure, foetal development and biochemical properties

1. The occurrence and relative abundance of adipose tissue around the heart and in the pericardium of wild and domesticated mammals are reviewed and some new data reported. 2. For macaque monkeys and a wide range of other adult mammals, the mean volume of epicardial adipocytes is constant at about half the average of that of other depots, although the relative mass of this depot is unrelated to the abundance of adipose tissue in the rest of the body. 3. In young adult guinea-pigs, the maximum rate of fatty acid synthesis is significantly higher in epicardial adipose tissue than that in the pericardial, perirenal and popliteal depots. 4. The rate of fatty acid release by epicardial adipose tissue is approximately twice that of the pericardial and perirenal depots. 5. The protein contents of guinea-pig epicardial and pericardial adipose tissue are similar, and are significantly higher than those of the perirenal and popliteal adipose tissue and there are no site-specific differences in the abundance of mitochondria. 6. In adult Macaca monkeys, the capacity of the epicardial adipose tissue for glucose utilization is about half that of the intra-abdominal depots. 7. The principal difference between epicardial adipose tissue and that elsewhere in the body is its greater capacity for fatty acid release. 8. It is suggested that cardiac adipose tissue may act as a local energy supply for adjacent myocardium and/or as a buffer against toxic levels of free fatty acids.     

Metallothionein gene expression and secretion in white adipose tissue

White adipose tissue (WAT) has been examined to determine whether the gene encoding metallothionein (MT), a low-molecular-weight stress response protein, is expressed in the tissue and whether MT may be a secretory product of adipocytes. The MT-1 gene was expressed in epididymal WAT, with MT-1 mRNA levels being similar in lean and obese (ob/ob) mice. MT-1 mRNA was found in each of the main adipose tissue sites (epididymal, perirenal, omental, subcutaneous), and there was no major difference between depots. Separation of adipocytes from the stromal-vascular fraction of WAT indicated that the MT gene (MT-1 and MT-2) was expressed in adipocytes themselves. Treatment of mice with zinc had no effect on MT-1 mRNA levels in WAT, despite strong induction of MT-1 expression in the liver. MT-1 gene expression in WAT was also unaltered by fasting or norepinephrine. However, administration of a beta(3)-adrenoceptor agonist, BRL-35153A, led to a significant increase in MT-1 mRNA. On differentiation of fibroblastic preadipocytes to adipocytes in primary culture, MT was detected in the medium, suggesting that the protein may be secreted from WAT. It is concluded that WAT may be a significant site of MT production; within adipocytes, MT could play an antioxidant role in protecting fatty acids from damage.     

Level of Preadipocyte Growth Factor in Rat Adipose Tissue which Specifically Permits the Proliferation of Preadipocytes Is Affected by Restricted Energy Intake

We previously reported the presence of a protein growth factor in rat adipose tissue which specifically permits the proliferation of 3T3-L1 and Obl771 preadipocytes [Biochem. Biophys. Res. Commun. 1990;171:905–912, ref. 1] and which is hereinafter referred to as PAGF (preadipocyte growth factor). In this study, the effects of long-term restricted energy intake on the PAGF activity in rat epididymal and perirenal adipose tissue toward 3T3-L1 preadipocytes were investigated. When rats were subjected to restricted energy intake for three weeks, PAGF activity increased with energy intake. The body weight, epididymal and perirenal fat depot weights and glycerol 3-phosphate dehydrogenase activity also increased with the energy intake, whereas the lactate dehydrogenase activity remained almost constant in all energy intake groups. These results suggest that the PAGF in fat depots functions in response to energy intake and contributes to the de novo formation of adipocytes and the growth of adipose tissue. This factor may provide a useful tool for further elucidation of the relationship between energy storage in adipose tissue and adipose tissue development.     

Effect of adipose tissue site, animal size, and fasting on lipolysis in bovine adipose tissue in vitro.

1. Lipolytic rates expressed as mumol glycerol released per mg protein increased with body weight in Holstein steers. 2. Lipolytic rates were greatest in both inner and outer back fat and lowest in omental, perirenal, and intermuscular fat depots. 3. Epinephrine stimulated overall glycerol release 3-5-fold. 4. Fasting resulted in greater basal lipolytic rates but epinephrine-stimulated rates tended to be greater for nonfasted steer adipose tissue. 5. Lipolytic activity in adipose tissue seems to increase with growth and fattening, and differences in lipolytic rates between various depots diminish with growth.     

Structural and histochemical aspects of perirenal adipose tissue in fetal pigs: relationships between stromal-vascular characteristics and fat cell concentration and enzyme activity

Samples of perirenal adipose tissue were obtained from four fetuses from each of seven crossbred gilts at each of three stages of gestation: 70, 90, and 110 days. Samples were routinely prepared for histochemistry and histology. At each age, the largest fat cell clusters were consistently located near points where large blood vessels entered the loose connective tissue. Cell-cluster size decreased with distance from the entry points of large blood vessels. Fat cells proximal to entry points of large arterioles and fat cells distal to entry points of large arterioles were the same size. Enzyme cytochemistry disclosed that reactions for glucose-6-phosphate dehydrogenase (G6PDH), lipoprotein lipase (LPL) and NADH-TR enzymes were reduced in distal (relative to entry points of large arterioles) adipocytes compared with proximal adipocytes. Reactions for succinate dehydrogenase (SDH) and lactate dehydrogenase (LDH) in adipocytes were not influenced by location within the tissue. Small fat cell clusters with sparse capillary beds surround arterioles in distal areas of sections from fetuses at 70, 90, and 110 days of gestation. In the proximal areas of sections from 110-day-old fetuses, arterioles were surrounded by large fat cell clusters with dense capillary beds. These characteristics serve to distinguish perirenal depots from subcutaneous depots in the fetus.     

Regulation of haptoglobin gene expression in 3T3-L1 adipocytes by cytokines, catecholamines, and PPARgamma

Factors which regulate expression of the haptoglobin (acute phase reactant) gene in adipocytes have been examined using 3T3-L1 cells. Haptoglobin expression was observed by Northern blotting in each of the major white adipose tissue depots of mice (epididymal, subcutaneous, mesenteric, and perirenal) and in interscapular brown fat. Expression occurred in mature adipocytes, but not in the stromal-vascular fraction. In 3T3-L1 cells, haptoglobin mRNA was detected from day 4 after the induction of differentiation into adipocytes. Lipopolysaccharide and the cytokines, TNFalpha and interleukin-6, resulted in substantial increases in haptoglobin mRNA in 3T3-L1 adipocytes; the increase (7-fold) was highest with TNFalpha. Increases in haptoglobin mRNA level were also induced by dexamethasone, noradrenaline, isoprenaline, and a beta3-adrenoceptor agonist. In contrast, haptoglobin mRNA was reduced by nicotinic acid and the PPARgamma agonist, rosiglitazone. RT-PCR showed that the haptoglobin gene was expressed in human adipose tissue (subcutaneous, omental). It is concluded that haptoglobin gene expression in adipocytes is stimulated by inflammatory cytokines, glucocorticoids, and the sympathetic system, while activation of the PPARgamma nuclear receptor is strongly inhibitory.     

Effect of acute exercise on tissue free fatty acids in untrained rats.

The effects of a single bout of swimming on free fatty acids (FFA) in adipose tissue, heart, skeletal muscle, and serum were examined. Surprisingly, in previously untrained rats, FFA were elevated (P less than 0.001) in epididymal, inguinal, and retroperitoneal adipose depots 48 h after a 2-h swim. FFA in the three fat depots returned to resting levels 96 h after exercise. In heart, soleus, and fast-red fibers of the quadriceps, FFA remained elevated (P less than 0.01) for as long as 72 h after the 2-h swim. Serum FFA were still elevated (P less than 0.001) 96 h after swimming but not after 168 h. These results provide evidence that the rise in FFA is an acute effect of exercise and not a cellular adaptation resulting from daily episodes of lipolysis induced by exercise training. In a separate experiment, involving the adaptive response to endurance exercise, adipocytes from epididymal, inguinal, and retroperitoneal depots were reduced in size (P less than 0.001) to approximately the same degree. These results provide evidence that adipocytes from each depot contribute equally in meeting the energy needs of muscle during repeated bouts of endurance exercise.     

The distribution of lipoprotein lipase in rat adipose tissue. Changes with nutritional state engage the extracellular enzyme

Lipoprotein lipase (LPL) acts at the vascular endothelium. Earlier studies have shown that down-regulation of adipose tissue LPL during fasting is post-translational and involves a shift from active to inactive forms of the lipase. Studies in cell systems had indicated that during fasting LPL might be retained in the endoplasmic reticulum. We have now explored the relation between active/inactive and intra/extracellular forms of the lipase. Within adipocytes, neither LPL mass nor the distribution of LPL between active and inactive forms changed on fasting. Extracellular LPL mass also did not change significantly, but shifted from predominantly active to predominantly inactive. To explore if changes in secretion were compensated by changes in turnover, synthesis of new protein was blocked by cycloheximide. The rates at which intra- and extracellular LPL mass and activity decreased did not change on fasting. To further explore how LPL is distributed in the tissue, heparin (which detaches the enzyme from the endothelial surface) was injected. Tissue LPL activity decreased by about 10% in 2 min and by 50% in 1 h. Heparin released mainly the active form of the lipase. There was no change of LPL activity or mass within adipocytes. The fraction of extracellular LPL that heparin released and the time course were the same in fed and fasted rats, indicating that active, extracellular LPL was distributed in a similar way in the two nutritional states. This study suggests that the nutritional regulation of LPL in adipose tissue determines the activity state of extracellular LPL.     

Isomers of conjugated linoleic acid decrease plasma lipids and stimulate adipose tissue lipogenesis without changing adipose weight in post-prandial adult sedentary or trained Wistar rat

The respective effects and interactions of supplementation with two conjugated linoleic acid (CLA) isomers and exercise on plasma metabolic profile, activity of lipogenic enzymes and cellularity in two adipose tissue sites, those of the liver and heart, were examined in adult Wistar rats. Rats that were either sedentary or exercise-trained by treadmill running were fed one of four diets: a diet without CLA; a diet with either 1% cis 9, trans 11 CLA or 1% trans 10, cis 12 CLA; or a mixture of both isomers (1% of each) for 6 weeks. We observed that the exercise decreased lipogenic enzyme activities in epididymal and perirenal adipose tissue. Plasma cholesterol, insulin, and leptin concentrations were lower in exercise-trained rats than in sedentary rats. The ingestion of either CLA mixture or the trans 10, cis 12 CLA increased lipogenic enzyme activities in epididymal tissue and more markedly in perirenal adipose tissue, especially in sedentary rats, and without affecting adipose tissue weight or cellularity. A similar effect of trans 10, cis 12 CLA was observed in regard to malic enzyme activity in the liver. In addition, this isomer decreased plasma lipid and urea concentrations and increased plasma 3-hydroxybutyrate levels. The ingestion of cis 9, trans 11 CLA increased fatty acid synthase activity in perirenal adipose tissue in sedentary rats and decreased plasma cholesterol and leptin concentrations. These results show that isomers of CLA decrease plasma lipids and stimulate adipose tissue lipogenesis without changing adipose weight in adult sedentary or exercise-trained rat, thus suggesting a stimulation of adipose tissue turnover.