Effect of aging and cellularity on lipolysis in isolated mouse fat cells

The effects of age and cellularity on lipolysis have been investigated in isolated epididymal fat cells from both Swiss albino mice and Sprague-Dawley rats. No significant lipolytic response to glucagon could be demonstrated with adipocytes from either young or old mice, while glycerol output was increased by this hormone with fat cells from young rats. Larger adipocytes from older mice showed significantly greater isoproterenol-stimulated lipolysis than those from younger animals if the glycerol output was expressed on a per cell basis. However, the lipolytic response per cell appeared to be equivalent in young and old rat adipocytes with either isoproterenol or ACTH-(1-24). In a complete aging study, relationships between body weight, epididymal fat pad weight and cellularity were examined covering the life span of the mouse. ACTH-(1-24)- and dibutyryl cyclic AMP-stimulated lipolysis increased with age and cell size but fell at senescence when adipocyte size diminished. Although an effect of aging per se cannot be ruled out with the experimental techniques used in the present study, a dominant influence of adipocyte size on the lipolytic process was demonstrated.     

Lipolysis and beta-adrenergic receptor binding on adipocytes of spontaneously hypertensive rats

Adipocytes from spontaneously hypertensive rats demonstrated a blunted lipolytic response to isoproterenol and dibutyryl cyclic AMP. (-)-[3H]Dihydroalprenolol binding was examined in adipocytes from normotensive and spontaneously hypertensive rats. Increasing concentrations of isoproterenol decreased total (-)-[3H]dihydroalprenolol binding to intact cells from normotensive rats, and the efficacy of competition was decreased in adipocytes from spontaneously hypertensive rats. Scatchard analysis indicated that the number of (-)-[3H]dihydroalprenolol binding sites and the affinity of dihydroalprenolol binding were comparable between normotensive and spontaneously hypertensive rats. Isoproterenol- and Gpp(NH)p-stimulated adenylate cyclase activity was consistently depressed in adipocyte membranes from spontaneously hypertensive rats as compared to normotensive rats. No difference in fluoride-stimulated adenylate cyclase activity was observed. The blunted lipolytic and cyclic AMP response to isoproterenol in these cells suggest a postreceptor lesion of the lipolytic pathway (possibly the guanine nucleotide regulatory protein) in adipocytes from spontaneously hypertensive rats. The blunted lipolytic response to dibutyryl cyclic AMP suggests defective regulation of lipolytic enzymes at the protein kinase-hormone-sensitive lipase level.     

Effect of cell size, age and anatomical location on the lipolytic response of adipocytes

Studies were conducted on the norepinephrine (NE) stimulated lipolytic sensitivity of adipocytes from epididymal (Epi), perirenal (PR), subcutaneous (SC) and mesentric (M) depots from young (7–8 wk.) and adult (14–16 wk.) male rats. In the young rats dose response curves to NE were similar for Epi, PR and M depots whereas adipocytes from the SC depot showed a diminished effect over the mid-portion of the curve. This difference could not be ascribed to differences in cell size. In the adult rats glycerol release in the Epi depot in response to NE was identical to the younger rats which was in marked contrast to the other depots in which glycerol release was decreased in comparison to the younger animals. This decreased responsiveness was probably largely a result of age and not changes vn adipocyte size within a given depot. In these older rats, glycerol release was greatest in the Epi cells, least in the SC and M depots, and intermediate in PR. When young rats were subjected to a 72-hour fast, loss of triglyceride per cell was the same in all depots as predicted by the $\text{in vitro}$ data whereas in old rats (610 g), triglyceride loss was proportional to cell size with Epi ≥ PR > SC ≥ M. This was also essentially in agreement with the $\text{in vitro}$ lipolytic data from adult rats. These data demonstrate lipolytic differences between depots that are minimal in young rats and which are accentuated with age.     

Enhanced lipolysis is not evident in adipocytes from exercise-trained SHR

Adipocytes from spontaneously hypertensive rats (SHR) are not as responsive to isoproterenol or dibutyryl adenosine 3',5'-cyclic monophosphate (cAMP) stimulation compared with Sprague-Dawley or Wistar-Kyoto rats. Lipolytic activity in adipocytes from trained normotensive rats was enhanced in response to 1 microM isoproterenol and 0.5 mM dibutyryl cAMP but not in adipocytes from trained SHR. Decreases in isoproterenol-stimulated (1 microM) cAMP accumulation were evident in adipocytes from trained normotensive rats but not in adipocytes from trained SHR. Basal and agonist-induced lipolysis in fat cells isolated from both normotensive rats and SHR immediately following a 60-min run was increased in both sedentary and trained rats. Adenylate cyclase activity in fat cell membranes was blunted in sedentary and trained SHR both in the absence and presence of 100 microM 5'-guanylyl imidophosphate. No apparent differences existed in antagonist affinity of binding sites for the antagonist dihydroalprenolol in normal rats or SHR. Evidence for a change in affinity of agonist isoproterenol might be indicated based on the enhanced potency of isoproterenol to stimulate lipolysis in trained normal rats. beta-Adrenergic receptor density and antagonist affinity were not different in normotensive rats and SHR in response to training. However, displacement of [3H]dihydroalprenolol in adipocytes from SHR required greater concentrations of isoproterenol compared with adipocytes from normotensive rats, further suggestive of increased agonist affinity of binding sites in normal rats. These data suggest a postreceptor lesion of the lipolytic pathway in adipocytes from spontaneously hypertensive rats, possibly at the guanine nucleotide regulatory protein level.(ABSTRACT TRUNCATED AT 250 WORDS)     

Metabolism of isolated fat cells from various tissue sites in the rat: influence of hemorrhagic hypotension

The in vitro lipolytic response to norepinephrine by rat adipocytes from epididymal, subcutaneous, perirenal, mesenteric, and omental tissue sites was studied in control and hypotensive animals. Lipolysis per millimole of triglyceride was found to be three to four times higher in mesenteric and omental fat cells than in adipocytes of the other sites sampled. The high lipolytic activity of mesenteric and omental adipocytes was partly attributable to their smaller cell size; however, lipolysis per cell was also higher. Hemorrhagic hypotension caused a 50-60% decrease in lipolytic activity at four of the five sites studied. Adipocytes of omental origin maintained their lipolytic activity at the prehypotensive level, however, indicating that the metabolic adjustments brought about by hemorrhagic hypotension are not uniform at all adipose tissue sites.     

Glucose metabolism in isolated fat cells: enhanced response of larger adipocytes from older rats to epinephrine and adrenocorticotropin.

The effects of insulin and of two lipolytic hormones (epinephrine and ACTH1) on the rate and pattern of glucose metabolism were compared during incubation of isolated fat cells, obtained from epididymal fat pads of rats of varying age and degrees of adiposity. Glucose metabolism and the intracellular free fatty acid levels were expressed on a per cell basis and in relation to adipocyte size. The data for total glucose metabolism show that, in contrast to the declining insulin effect observed with adipocyte enlargement, the stimulation of glucose uptake and metabolism by these lipolytic hormones was significantly greater in the larger fat cells from the older fatter rats than in the smaller ones from the younger leaner rats. Lipolytic hormones suppressed, whereas insulin enhanced, fatty acid synthesis; moreover the lipolytic hormones stiumlated glucose ce effect of epinephrine on the intracellular free fatty acid levels was greater in the small fat cells than in the large ones; this effect of epinephrine was markedly curtained by the presence of glucose in the incubation medium, making it unlikely that acceleration of glucose metabolism by the lipolytic stimulus was mediated by an elevation of the intracellular free fatty acid level. The present results show a markedly enhanced capacity of the large adipocytes to accelerate glucose metabolism in response to these liplytic hormones. Thus, in contrast to prevailing notions of declining hormonal responsiveness with expanding fat cell size in older and more obese animals, this study documents an instance of increased hormonal response in enlarged adipocytes and points to the need for a more comprehensive reevaluation of the various hormonal effects in adipocytes of different size.     

Comparison of the Lipolytic Effects of Norepinephrine and BRL 37344 in Rat Brown and White Adipocytes

The lipolytic effects of norepinephrine (a non-selective β-agonist) and BRL 37344 (a selective β₃-agonist) were compared in isolated rat brown and white adipocytes. Norepinephrine and BRL 37344 maximally stimulated lipolysis in brown and white adipocytes, approximately 10 times above basal values. However, adipocyte sensitivity for BRL 37344 was greater than that for norepinephrine, particularly in brown adipocytes [the EC₅₀ values (nM) for BRL 37344 and norepinephrine were 5 ± 1 and 103 ± 31 in brown adipocytes (P <0.01) versus 56 ± 9 and 124 ± 17 in white adipocytes (P <0.05), respectively]. On the other hand, the lipolytic effects of norepinephrine were totally blocked by 20–40 times superior concentrations of propranolol or bupranolol in brown as well as in white adipocytes. In contrast, the lipolytic effects of BRL 37344 were fully inhibited by concentrations of propranolol or bupranolol that were 200–1000 superior to the β₃ agonist concentration. The results demonstrate that: (1) the (β₃-agonist BRL 37344 is as effective as norepinephrine for maximally stimulating lipolysis in rat brown and white adipocytes, (2) both adipocyte types are more sensitive to the lipolytic effects of BRL 37344 than to those of norepinephrine, (3) although bupranolol is a better antagonist than propranolol on BRL 37344-stimulated lipolysis, it cannot be considered as a specific β₃-antagonist, (4) brown adipocytes are 10 times more sensitive than white adipocytes to the lipolytic effects of BRL 37344, suggesting an important role of β₃-receptors in brown adipose tissue.     

Effects of cold acclimation on adipose tissue lipolysis and cellularity in the hypophysectomized rat

The study investigated the effects of hypophysectomy and cold acclimation on cellularity and lipolytic capacity of adipose tissue. Hypophysectomized rats (H) were compared to age matched or weight matched controls. Rats were exposed to either 28 degrees C or 15 degrees C ambient temperature for five weeks. In H, despite the inhibition of body growth, it was observed that the growth of epididymal adipose tissue is not entirely inhibited. In comparison with weight matched controls, increase in tissue weight is found to be due to an adipocyte hypertrophy without changes in cell number. No effect of cold acclimation on adipose tissue weight, cellularity and insulinemia were observed in the H group. The in vitro lipolysis effect of norepinephrine was suppressed in 28 degrees C H; a partial recovery of this effect was observed after cold acclimation. This fact is not dependent on adipocyte size, but possibly on structural or metabolic modifications.     

Possible mechanisms of weight loss of Siberian hamsters (Phodopus sungorus sungorus) exposed to short photoperiod

Several weeks of short day photoperiod (SD) exposure promote a dramatic decrease of white adipose tissue (WAT) mass in Siberian hamsters(Phodopus sungorus sungorus). This slimming effect is accompanied by changes in the adipocyte responsiveness to adrenergic stimulation that are still under debate. We investigated whether possible changes in the antilipolytic responses, and/or lipogenic activities could be involved in such lipid deposition/mobilisation imbalance. Male Siberian hamsters were exposed for 11 weeks to SD or long day photoperiod and basal or stimulated lipolytic and lipogenic activities were measured on white adipocytes. As expected, the body mass of SD-animals was decreased. Besides a slight reduction in the basal lipolysis and in the maximal response to dibutyryl-cAMP, the responses to adrenergic and non-adrenergic lipolytic agents (forskolin, adenosine deaminase) were similar in both groups. Fat mass loss was likely not resulting from changes in the lipolytic responses of adipocytes to biogenic amines (e.g. octopamine), which were unaltered, or to a direct lipolytic stimulation by melatonin or histamine, which were inactive. Antilipolytic responses to insulin or tyramine were slightly decreased in SD-adipocytes. Basal or insulin-stimulated lipid accumulation in WAT, measured by glucose incorporation into lipids, did not change after SD-exposure. However, a significant decrease in the lipoprotein lipase activity was observed in the WAT of SDanimals. Despite the observed changes, the weight loss of SD-exposed Siberian hamsters was likely not resulting only from impaired antilipolytic orde novo lipogenic activities in white adipocytes, but either from other dramatic changes occurring during seasonal photoperiod-sensitive body weight regulation.     

Impairment in insulin sensitivity after early androgenization in the post-pubertal female rat

A link is known to exist between hyperandrogenicity and insulin resistance in mammals. We explored whether androgenization, early in reproductive life, in the female rat has any impact on later peripheral insulin sensitivity and parametrial (PM) fat function. Female, 60 day-old, rats were injected (i.m.) with 100 mul of sterile corn oil either alone (CT) or containing 2 mg of testosterone propionate (TP); rats were then used for experimentation at age 120 days. Daily food intake and body weight were recorded. Different groups of CT and TP rats were subjected to a high glucose load test or 24 h fasting for evaluation of changes in circulating levels of several metabolites and body composition. In vitro experiments were run to study the impact of androgenization on isolated PM adipocyte response to insulin. Finally, the direct effect of testosterone on insulin-induced leptin secretion by normal PM adipocytes was also evaluated. Androgenization induced a significant increase in daily food intake and body weight for the first 20 days after treatment. In vivo experiments indicate that TP rats released more (P<0.05) insulin than CT animals after high glucose load in order to maintain similar circulating glucose levels, a characteristic accompanied by decreased (P<0.05) overall corticoadrenal response in TP rats. Several metabolic responses to fasting were similar in both groups, although impaired adrenal response and changes in body composition were observed only in TP rats. Interestingly, cultured PM adipocytes from TP rats were less (P<0.05) sensitive than CT cells to insulin-induced leptin secretion. Also, we found that 48 h exposure of normal PM adipocytes to high testosterone concentration also impaired adipocyte endocrine function. Our study strongly supports that development of insulin resistance, in the female gender, can be established after an early, even transient, hyperandrogenemia.     

Adipose tissue cellularity in hypo-and hyperthyroid rats

To determine adipose tissue cellularity in hypo- and hyperthyroidism, male rats were thyroidectomized after weaning (T) and injected daily with either 0, 0.1, 1.8 or 25 microgram of L-thyroxine/100 g body weight for 40 days. They were compared with intact controls (C). Both epididymal fat-pad weight and adipocyte diameter were reduced in T+0, T+0.1 and T+25 animals. When corrected per unit of body weight, the diameters of adipocytes from T+0 and T+0.1 animals were larger than in the other groups. Those same animals have reduced absolute adipocyte number but not when corrected per unit of body weight. The fat-pad protein concentration varied conversely with the fat cell diameter. These findings indicate that thyroid hormone deficiency reduces the proliferation of fat cells in parallel with body growth while hyperthyroidism causes reduction in the size, but not the number, of fat cells which corresponds to its depletion of fat storage.     

Adipogenic and lipolytic effects of chronic glucocorticoid exposure

Glucocorticoids have been proposed to be both adipogenic and lipolytic in action within adipose tissue, although it is unknown whether these actions can occur simultaneously. Here we investigate both the in vitro and in vivo effects of corticosterone (Cort) on adipose tissue metabolism. Cort increased 3T3-L1 preadipocyte differentiation in a concentration-dependent manner, but did not increase lipogenesis in adipocytes. Cort increased lipolysis within adipocytes in a concentration-dependent manner (maximum effect at 1-10 μM). Surprisingly, removal of Cort further increased lipolytic rates (～320% above control, P < 0.05), indicating a residual effect on basal lipolysis. mRNA and protein expression of adipose triglyceride lipase and phosphorylated status of hormone sensitive lipase (Ser563/Ser660) were increased with 48 h of Cort treatment. To test these responses in vivo, Sprague-Dawley rats were subcutaneously implanted with wax pellets with/without Cort (300 mg). After 10 days, adipose depots were removed and cultured ex vivo. Both free fatty acids and glycerol concentrations were elevated in fed and fasting conditions in Cort-treated rats. Despite increased lipolysis, Cort rats had more visceral adiposity than sham rats (10.2 vs. 6.9 g/kg body wt, P < 0.05). Visceral adipocytes from Cort rats were smaller and more numerous than those in sham rats, suggesting that adipogenesis occurred through preadipocyte differentiation rather than adipocyte hypertrophy. Visceral, but not subcutaneous, adipocyte cultures from Cort-treated rats displayed a 1.5-fold increase in basal lipolytic rates compared with sham rats (P < 0.05). Taken together, our findings demonstrate that chronic glucocorticoid exposure stimulates both lipolysis and adipogenesis in visceral adipose tissue but favors adipogenesis primarily through preadipocyte differentiation.     

Influence of development and reduction of fat stores on the antilipolytic alpha 2-adrenoceptor in hamster adipocytes: comparison with adenosine and beta-adrenergic lipolytic responses

The response of the hamster adipocyte to various lipolytic (beta-adrenergic) and antilipolytic (alpha(2)-adrenergic and adenosine-dependent) stimuli was studied during the development and after cold-induced regression of fat stores. Alpha(2)-adrenergic binding ([(3)H]clonidine binding sites) was also investigated. Adipocytes came from young animals (4-5 weeks), adults (20-25 weeks), and adults submitted to a 6-week cold exposure (6 degrees C) that promoted a large decrease in fat stores and in fat cell size. The lipolytic response induced by isoproterenol (beta-agonist) was equivalent in the different groups. Adenosine and alpha(2)-adrenergic antilipolytic effects were estimated through the inhibition of theophylline-induced lipolysis by phenylisopropyladenosine and clonidine, respectively. The adenosine effect was unchanged in all the groups. In contrast, the alpha(2)-adrenergic effect, which was not present in young hamsters, increased simultaneously with fat cell size, was fully effective in adult hamsters, and had completely disappeared in small adipocytes from cold-exposed hamsters. In fat cell ghosts, alpha(2)-adrenoceptors ([(3)H]clonidine binding sites), followed similar modifications: they increased with fat cell enlargement and disappeared after cell size reduction following cold exposure. These results suggest that: 1) the increased alpha(2)-adrenergic antilipolytic response which is concomitant with fat cell enlargement could partly explain the growth-related decrease in the previously reported lipolytic effect of epinephrine; 2) the alpha(2)-receptivity of the adipocyte seems to be strictly fat cell size-dependent while the beta-adrenergic and adenosine responses are unaffected; and 3) the regulation in the adipocytes of the adenosine, alpha(2)- and beta-receptors seems to be unrelated.-Carpene, C., M. Berlan, and M. Lafontan. Influence of development and reduction of fat stores on the antilipolytic alpha(2)-adrenoceptor in hamster adipocytes: comparison with adenosine and beta-adrenergic lipolytic responses.     

A low-protein, high-carbohydrate diet increases the adipose lipid content without increasing the glycerol-3-phosphate or fatty acid content in growing rats

The amount of triacylglycerol (TAG) that accumulates in adipose tissue depends on 2 opposing processes: lipogenesis and lipolysis. We have previously shown that the weight and lipid content of epididymal (EPI) adipose tissue increases in growing rats fed a low-protein, high-carbohydrate (LPHC) diet for 15 days. The aim of this work was to study the pathways involved in lipogenesis and lipolysis, which ultimately regulate lipid accumulation in the tissue. De novo fatty acid synthesis was evaluated in vivo and was similar for rats fed an LPHC diet or a control diet; however, the LPHC-fed rats had decreased lipoprotein lipase activity in the EPI adipose tissue, which suggests that there was a decreased uptake of fatty acids from the circulating lipoproteins. The LPHC diet did not affect synthesis of glycerol-3-phosphate (G3P) via glycolysis or glyceroneogenesis. Glycerokinase activity - i.e., the phosphorylation of glycerol from the hydrolysis of endogenous TAG to form G3P - was also not affected in LPHC-fed rats. In contrast, adipocytes from LPHC animals had a reduced lipolytic response when stimulated by norepinephrine, even though the basal adipocyte lipolytic rate was similar for both of the groups. Thus, the results suggest that the reduction of lipolytic activity stimulated by norepinephrine seems essential for the TAG increase observed in the EPI adipose tissue of LPHC animals, probably by impairment of the process of activation of lipolysis by norepinephrine.     

High lipolytic activity and dyslipidemia in a Spontaneous Hypertensive/NIH Corpulent (SHR/N-cp) rat: a genetic model of obesity and type 2 diabetes mellitus

In order to better understand the link between obesity and type 2 diabetes, lipolysis and its adrenergic regulation was investigated in various adipose depots of obese adult females SHR/N-cp rats. Serum insulin, glucose, free fatty acids (FFA), triglycerides (TG) and glycerol were measured. Adipocytes were isolated from subcutaneous (SC), parametrial (PM) and retroperitoneal (RP) fat pads. Total cell number and size, basal lipolysis or stimulated by norepinephrine (NE) and BRL 37344 were measured in each depot. Obese rats were hyperinsulinemic and hyperglycemic, suggesting high insulin resistance. They presented a marked dyslipidemia, attested by increased serum FFA and TG levels. High serum glycerol levels also suggest a strong lipolytic rate. Obese rats showed an excessive development of all fat pads although a more pronounced effect was observed in the SC one. The cellularity of this depot was increased 8 fold when compared to lean rats, but these fat cells were only 1.5 to 2-fold larger. SC adipocytes showed a marked increase in their basal lipolytic activity but a lack of change in responsiveness to NE or BRL 37344. The association between high basal lipolysis and increased cellularity yields to a marked adipose cell lipolytic rate, especially from the SC region. SHR/N-cp rats were characterized by a hyperplasic type of obesity with an excessive development of the SC depot. The dyslipidemia, attested by an altered serum lipid profile could be attributed to excessive lipolysis that contributes to increased FFA levels, and to early development of insulin resistance through a lipotoxicity effect.     

Pmch-Deficiency in Rats Is Associated with Normal Adipocyte Differentiation and Lower Sympathetic Adipose Drive

The orexigenic neuropeptide melanin-concentrating hormone (MCH), a product of Pmch, is an important mediator of energy homeostasis. Pmch-deficient rodents are lean and smaller, characterized by lower food intake, body-, and fat mass. Pmch is expressed in hypothalamic neurons that ultimately are components in the sympathetic nervous system (SNS) drive to white and interscapular brown adipose tissue (WAT, iBAT, respectively). MCH binds to MCH receptor 1 (MCH1R), which is present on adipocytes. Currently it is unknown if Pmch-ablation changes adipocyte differentiation or sympathetic adipose drive. Using Pmch-deficient and wild-type rats on a standard low-fat diet, we analyzed dorsal subcutaneous and perirenal WAT mass and adipocyte morphology (size and number) throughout development, and indices of sympathetic activation in WAT and iBAT during adulthood. Moreover, using an in vitro approach we investigated the ability of MCH to modulate 3T3-L1 adipocyte differentiation. Pmch-deficiency decreased dorsal subcutaneous and perirenal WAT mass by reducing adipocyte size, but not number. In line with this, in vitro 3T3-L1 adipocyte differentiation was unaffected by MCH. Finally, adult Pmch-deficient rats had lower norepinephrine turnover (an index of sympathetic adipose drive) in WAT and iBAT than wild-type rats. Collectively, our data indicate that MCH/MCH1R-pathway does not modify adipocyte differentiation, whereas Pmch-deficiency in laboratory rats lowers adiposity throughout development and sympathetic adipose drive during adulthood.     

Sympathetic and metabolic correlates of hypoxic moderation of spontaneous hypertension in the rat

Exposure to hypobaric hypoxia (H; simulated altitude = 3658 m) was initiated in 5-week-old, male spontaneously hypertensive (SHR) and Wistar-Kyoto (WKy) normotensive rats while normoxic controls (N) for both groups were maintained under laboratory conditions. Significant attenuation of systolic arterial blood pressure was evident in SHR-H relative to SHR-N (125 +/- 6 vs 145 +/- 5 mm Hg; P less than 0.05) but not in WKy-H relative to WKy-N (WKy-H, 116 +/- 2 vs WKy-N, 117 +/- 5 mm Hg). Hypoxia significantly decreased metabolic efficiency in both normotensive and hypertensive rats, although being both more severe and accompanied by significantly impaired growth rate in SHR-H. Urinary excretion of norepinephrine in the SHR was elevated relative to WKy, irrespective of altitude treatment, while hypoxia elicited similar increases in urinary excretion of norepinephrine in both SHR and WKy. Myocardial and adrenal contents of norepinephrine were significantly reduced following 3 days of simulated altitude exposure in both strains of rats. Tissue contents of norepinephrine in hypoxic rats returned to normoxic levels by 21 days of simulated altitude. Both urine and tissue indices provided consistent indirect evidence that changes in sympathetic neuronal activity in response to hypoxia were similar in normotensive and hypertensive rats. These findings suggest that prior reports of reduced alpha-adrenergic responsiveness in vasculature from hypoxia-exposed SHR reflect a postsynaptic event that is regulated independently of norepinephrine release from sympathetic nerve terminals.     

Relationships among serum triacylglycerol, fat pad weight, and lipolysis in iron-deficient rats

We studied the relationships among serum triacylglycerol (TG), fat pad weight, and lipolytic response to norepinephrine (NE) in iron-deficient rats. We used male Sprague-Dawley International Golden Standard rats. The rats were randomly divided into four groups: two iron-adequate groups for 1 week (1A) and 5 weeks (5A), and two iron-deficient groups for 1 week (1D) and 5 weeks (5D), based on the AIN-93G diet. Iron-deficient treatment caused a significant decrease in hemoglobin (Hb) and hematocrit (Hct) values and an increase in relative heart weight in 1D and 5D rats. Although serum TG was not affected by the 1-week iron-deficient treatment, it was significantly increased by 5-week iron-deficient treatment. The 1-week iron-deficient treatment significantly decreased the relative weight of the retroperitoneal fat pads, but not that of the epididymal fat pads. On the other hand, the 5-week iron-deficient treatment significantly decreased the relative weight of both fat pads; the degree of decrease was 41% and 32% for retroperitoneal and epididymal fat pads, respectively. Basal lipolysis significantly decreased in the epididymal adipocytes from 1D rats, whereas lipolytic response to NE markedly increased. No effect due to the 5-week treatment on basal lipolysis was observed in either retroperitoneal or epididymal adipocytes. In addition, lipolytic response to NE significantly increased in the retroperitoneal, but not the epididymal adipocytes. These results demonstrate that the effects of an iron-deficient diet on fat pad weight are different, depending on the duration of the treatment and the location of fat pads. In addition, iron deficiency-caused hypertriacylglycerolmia may be predominantly related to the increase in lipolysis in retroperitoneal rather than in epididymal adipocytes. The data further show that the increase in lipolysis of epididymal adipocytes occurs in the earlier stage prior to a severe iron-deficient state.     

Grape pomace extract induced beige cells in white adipose tissue from rats and in 3T3-L1 adipocytes

This study investigated the effects of a grape pomace extract (GPE) rich in phenolic compounds on brown-like adipocyte induction and adiposity in spontaneously hypertensive (SHR) and control normotensive Wistar–Kyoto (WKY) rats fed a high-fat diet (HFD). HFD consumption for 10 weeks significantly increased epididymal white adipose tissue (eWAT) in WKY but not in SHR rats. Supplementation with GPE (300 mg/kg body weight/day) reduced adipocyte diameter and increased levels of proteins that participate in adipogenesis and angiogenesis, i.e., peroxisome-proliferator activated receptor gamma (PPARγ), vascular endothelial grow factor-A (VEGF-A) and its receptor 2 (VEGF-R2), and partially increased the uncoupling protein 1 (UCP-1) in WKY. In both strains, GPE attenuated adipose inflammation. In eWAT from SHR, GPE increased the expression of proteins involved in adipose tissue “browning,” i.e., PPARγ-coactivator-1α (PGC-1α), PPARγ, PR domain containing 16 (PRDM16) and UCP-1. In primary cultures of SHR adipocytes, GPE-induced UCP-1 up-regulation was dependent on p38 and ERK activation. Accordingly, in 3T3-L1 adipocytes treated with palmitate, the addition of GPE (30 μM) activated the β-adrenergic signaling cascade (PKA, AMPK, p38, ERK). This led to the associated up-regulation of proteins involved in mitochondrial biogenesis (PGC-1α, PPARγ, PRDM16 and UCP-1) and fatty acid oxidation (ATGL). These effects were similar to those exerted by (−)-epicatechin and quercetin, major phenolic compounds in GPE. Overall, in HFD-fed rats, supplementation with GPE promoted brown-like cell formation in eWAT and diminished adipose dysfunction. Thus, winemaking residues, rich in bioactive compounds, could be useful to mitigate the adverse effects of HFD-induced adipose dysfunction.     

Effect of the beta-adrenoblocker propranolol on adrenaline-stimulated lipolysis in the adipose tissue of spontaneously hypertensive rats

The effect of the beta-adrenoblocker propranolol on adrenaline-stimulated lipolysis was studied in the adipose tissue of spontaneously hypertensive rats (SHR) and control rats. The lipolytic activity was estimated from the increase in glycerol concentration in the incubation medium in vitro. The adipose tissue of SHR responded to adrenaline similarly to that of control rats, but the concentration of adrenaline inducing the half-maximum response (KA) was 2 times less for SHR than KA for normotensive controls. Under propranolol effect this parameter was increased more significantly in SHR than in controls. These data indicate higher sensitivity of SHR adipose tissue to propranolol that may well be relative to alteration of the properties of beta-adrenergic receptors of adipose tissue in this form of hypertension.