White Adipose Tissue Depots Research Articles

Regional variations in metabolic responses of white adipose tissue to food restriction

The effects of food restriction (limited access to food for 2 h/day for 10 days) on lipoprotein lipase (LPL) activities and rates of fatty acid synthesis and glucose utilization in vivo in two superficial (interscapular and subcutaneous) and three deep abdominal white adipose tissue depots (parametrial, perirenal, and mesenteric) of adult female Wistar rats were examined before and at 2 h after a standard laboratory diet meal (5 g). Fasting LPL activities in perirenal (1.6-fold), mesenteric (5.9-fold), and subcutaneous (2.7-fold) adipose tissue, when expressed per unit of delipidated tissue, were increased in response to food restriction. This effect was retained (but not enhanced) after the meal. In contrast, muscle LPL activities were either unchanged or suppressed by food restriction. Stimulation of adipose tissue fatty acid synthesis and glucose utilization evoked by feeding in control rats was greatly enhanced by prior food restriction. There was no relationship between anatomical location and presence or absence of the response of adipose tissue LPL activity to food restriction, but the effect of food restriction to enhance the responses of fatty acid synthesis and glucose utilization to a meal was more marked in perirenal and parametrial adipose tissue than in the more superficial depots. The results thus demonstrate regional specificity in the response of adipose tissue functions to food restriction.

Nonshivering thermogenesis and obesity in the diabetic WKY/N-cp rat

Groups of lean and obese WKY/N-cp rats were fed a diet containing 54% carbohydrate, 20% protein, and 16% fat plus other essential nutrients from 1 until 8 months of age. Final body weights of obese were 1.7-fold > lean littermates. The greater BW were associated with marked increases in adipocyte size, number/depot, and fat pad mass in all major white adipose tissue depots. Interscapular brown adipose tissue (IBAT) mass of obese was 3-fold > lean, and represented a greater proportion of final body weight in obese than lean. The greater IBAT obese was due to greater lipid accretion and increased non-fat residue than occurred in lean rats. Resting thermogenesis (RMR) of lean > obese. The thermic response to norepinephrine was proportionately similar in both phenotypes, but the thermic response to cold (4°C) of lean > obese. Serum T4 concentrations and T4:T3 ratios of lean > obese, while serum T3 concentrations were similar in the two phenotypes. These results are consistent with a decreased capacity for NST in the obese phenotype of this stain, and suggest that the decreased NST may be due in part to alterations in BAT-mediated thermoregulation, in combination with impairments in other neuroendocrine or hormonal mediators of thermogenesis.

Transforming growth factor alpha and atrial natriuretic peptide in white adipose tissue depots in rats.

To detect the presence in adipose tissue of peptides known to affect tissue growth and to investigate potential regional differences, epididymal and perirenal adipose tissue depots from male Sprague-Dawley rats were separated into adipocyte and stroma-vascular fractions by collagenase digestion, sequential centrifugation and filtration. Identity and integrity of the fractions were demonstrated by light and electron microscopy, while dose-response curves for angiotensin-converting enzyme (ACE) were performed, revealing maintained functional capacity of the stroma-vascular fraction. ACE, atrial natriuretic peptide (ANP), and transforming growth factor-alpha (TGF-alpha) concentrations were significantly greater in epididymal than perirenal stroma-vascular tissue. Adipocyte fractions from both depots contained significant concentrations of ANP and TGF-alpha. There was no detectable ACE in the adipocyte fractions, indicating that no contaminating stromal-vascular cells were present in these fractions. These data show significant concentrations of peptides with effects on growth in subfractions of adipose tissue and demonstrate regional differences in concentrations between fat depots.

Regional and interspecific differences in the ligand binding properties of β-adrenergic receptors of individual white adipose tissue depots in the sheep and rat

The ligand binding of β-adrenergic receptors was characterized in the omental, subcutaneous and popliteal adipose tissue depots in the sheep, and the lumbar and parametrial depots in the rat. Displacement of [ 125I]iodocyanopindolol ([ 125I]ICYP) binding to sheep adipose tissue membranes by the β-adrenergic antagonists CGP 20712A and ICI 118,551 (β 1- and β 2-antagonists, respectively) suggested only a single ligand binding site predominantly β 2 in character in all three depots, but revealed differences in affinity for these ligands between depots. Lactation increased β-receptor ligand binding in subcutaneous and omental but not popliteal sheep adipose tissue depots, but had no effect on β-adrenergic receptor affinities for CGP 20712A and ICI 118,551 in the three sheep adipose tissue depots studied. In rat adipocyte membranes, displacement of [ 125I]ICYP by CGP 20712A and ICI 118,551 was biphasic, indicating high and low affinity sites; displacement profiles differed markedly between lumbar and parametrial depots, the former having a preponderance of β 1-like receptors and the latter a preponderance of β 2-like receptors. The properties of the β-adrenergic receptor binding site thus show species and depot specific differences.

Stimulatory effects of cold exposure and cold acclimation on glucose uptake in rat peripheral tissues

The effects of cold exposure on the net rates of 2-[3H]deoxy-D-glucose uptake (Ki) in rat peripheral tissues were investigated comparatively in warm- and cold-acclimated animals to determine whether cold acclimation induces regulatory alterations in glucose metabolism. Acute exposure of warm-acclimated (25 degrees C) rats to cold (48 h at 5 degrees C) markedly increased the Ki values in red and white skeletal muscles (2-5 times), in the heart (8 times), in several white adipose tissue (WAT) depots (4-20 times), and in brown adipose tissue (BAT) (110 times). After cold acclimation (3 wk at 5 degrees C), the Ki values further increased in the heart (15 times) and WAT (up to 29 times) but decreased in BAT (36 times). Remarkably, glucose uptake was still increased in muscles of cold-exposed/cold-acclimated animals (that do not shiver), demonstrating that enhanced glucose uptake may occur in muscles in the absence of shivering thermogenesis (or contractile activity). When cold-acclimated rats were returned to the warm for 18 h, the Ki values of all tissues, except WAT, returned to control levels. Cold exposure synergistically potentiated the stimulation of tissue glucose uptake induced by a maximal effective dose of insulin (0.5 U/kg iv) in warm- as well as in cold-acclimated animals.(ABSTRACT TRUNCATED AT 250 WORDS)

The influence of starvation and natural refeeding on the rate of triacylglycerol/fatty acid substrate cycling in brown adipose tissue and different white adipose sites of the rat in vivo. The role of insulin and the sympathetic nervous system.

Triacylglycerol/fatty acid substrate cycling was measured in vivo in brown adipose tissue (BAT) and white adipose tissue (WAT) of fed, starved and refed rats. Starvation (24h) significantly decreased the rate of cycling in BAT, and refeeding chow diet led to a rapid, 6-fold increase in cycling. Cycling rate in WAT was much lower than in BAT, and was not influenced by fasting or refeeding. Similar rates of cycling were found in epididymal, mesenteric, subcutaneous, and scapular WAT depots. Sympathetic denervation of interscapular BAT abolished the response of the tissue to refeeding, as did acute suppression of insulin secretion. Similarly, rats fasted for 3 days showed no acute increase in the activity of the cycle following refeeding.

Development of adipose tissues

Studies on the development of brown and white adipose tissues and their relationship to ordinary connective tissue are the subject of the present review, which is updated to the fall of 1985. Primordial entities described as "primitive organs" have been noted at sites of adipose tissue development by numerous investigators. These "primitive organs" are clearly delineated from surrounding connective tissue and possess a well-defined vascular network in the interstices of which cellular organization takes place. The precursor cells of brown and white adipocytes appear to acquire their distinctive cytogenetic properties at a very early stage in the embryo. These progenitor cells temporarily exhibit structural similarities to fibroblasts and endothelial cells. This resemblance has led to speculation that fibroblasts and/or endothelial cells may be ancestral to adipocytes. However, recent in vivo and in vitro observations suggest that the brown adipose precursor cell is morphogenetically distinct from the white adipose precursor cell on one hand, and from fibroblasts and endothelial cells on the other. In vitro studies have also shown that the pericytic elements present in both brown and white adipose tissue depots in the adult are quiescent precursor cells that may be recruited under certain circumstances. Areas for further inquiry by means of recently developed techniques are indicated.

Cold exposure potentiates the effect of insulin on in vivo glucose uptake.

The effects of cold exposure (48 h at 4 degrees C) and insulin injection (0.5 U/kg iv) on the rates of net 2-[3H]deoxyglucose uptake (Ki) in peripheral tissues were investigated in warm-acclimated rats (25 degrees C). Cold exposure and insulin treatment independently increased Ki values in skeletal muscles (soleus, extensor digitorum longus, and vastus lateralis), heart, white adipose tissue (subcutaneous, gonadal, and retroperitoneal), and brown adipose tissue (P less than 0.01). The effects of cold exposure were particularly evident in brown adipose tissue where the Ki increased greater than 100 times. When the two treatments were combined (insulin injection in cold-exposed rats), it was found that cold exposure synergistically enhanced the maximal insulin responses for glucose uptake in brown adipose tissue, all white adipose tissue depots, and skeletal muscles investigated. The results indicate that cold exposure induces an "insulin-like" effect on Ki that does not appear to be specifically associated with shivering thermogenesis in skeletal muscles, because that effect was observed in all insulin-sensitive tissues. The data also demonstrate that cold exposure significantly potentiates the maximal insulin responses for glucose uptake in the same tissues. This potentialization may result from an enhanced responsiveness of peripheral tissues to insulin, possibly occurring at metabolic steps lying beyond the insulin receptor and an increased tissue blood flow augmenting glucose and insulin availability and thereby amplifying glucose uptake.

Preferential utilization of brown adipose tissue lipids during arousal from hibernation in hamsters.

The participation of brown adipose tissue in the arousal process of golden hamsters was studied. The utilization of lipids in different depots of brown adipose tissue was followed gravimetrically. From both the interscapular and the cervical brown adipose tissue depots, 28 mg of lipid were lost during arousal; there was no measurable loss of lipid from the white adipose tissue depots. The total weight of eight identified depots of brown adipose tissue in nonhibernating, cold-acclimated hamsters was estimated to be 1,700 mg, of which 475 g were lipid. It is calculated that a total of 255 mg lipid disappeared from brown adipose tissue during arousal; this lipid is theoretically capable of giving rise to 2.4 kcal (9.9 kJ) of heat. It is concluded that the heat produced by the combustion of the lipid that disappeared from the brown adipose tissue during the arousal process could be the major source of the heat needed to rewarm the hamster from hibernating to euthermic body temperatures.

Tissue blood flow in control and cold-adapted hyperthyroid rats.

Chronic injections (once daily for 10-14 days) of triiodothyronine (T3) stimulated oxygen consumption by 50 and 15% in anaesthetized, control (24 degrees C), and cold-adapted (5 degrees C) rats, respectively, compared with euthyroid controls. Tissue blood flow, determined from the distribution of radioactive microspheres, was unaffected by T3 treatment in skeletal muscle, scrotum, brain, bone, skin, diaphragm, and brown adipose tissue (BAT) of rats housed at 24 degrees C, but was decreased in spleen (53% of control) and significantly increased in three white adipose tissue depots (average 267% increase) and liver (56%). Blood flow to epididymal fat and leg muscle of cold-adapted rats was increased by T3 treatment (100 and 138% increases, respectively), but other tissues were unaffected. Blood oxygen extraction and oxygen consumption in vivo by interscapular BAT was increased in hyperthyroid rats compared with euthyroid controls, but was reduced by T3 treatment in cold-adapted animals. These data show that BAT makes only a minor contribution (7%) to thyroid thermogenesis, but suggest that kidney, liver, gut, and particularly white adipose tissue may be involved.