Oleuropein aglycone enhances UCP1 expression in brown adipose tissue in high-fat-diet-induced obese rats by activating β-adrenergic signaling

Oleuropein is the pungent principle of raw olives. Oleuropein aglycone (OA) is a major phenolic compound in extra virgin olive oil and the absorbed form of oleuropein. We aimed to determine the mechanism underlying the nutritional effects of oleuropein and OA on interscapular brown adipose tissue (IBAT) in rats with high-fat (HF) diet-induced obesity by examining the agonistic activity of oleuropein and OA toward the transient receptor potential ankyrin 1 (TRPA1) and vanilloid 1 (TRPV1). Four-week-old male Sprague–Dawley rats were fed an HF (palm oil 30% wt:wt) diet alone or with oleuropein (HF-O, 1 g/kg diet) for 28 days. In rats fed HF-O compared to HF, urinary noradrenaline, adrenaline and UCP1 levels in IBAT were significantly higher, whereas plasma leptin levels and the total weight of the abdominal cavity adipose tissue were significantly lower. In anaesthetized 7-week-old male Sprague–Dawley rats, the OA (3.8 mg of intravenous injection)-induced increase in plasma noradrenaline secretion was suppressed by TRPA1 or TRPV1 antagonist and by a β2- or β3-adrenoceptor antagonist. Furthermore, OA-activated rat and human TRPV1s expressed on HEK293 cells at the same level as zingerone (pungent component in ginger). OA also activated humanTRPA1, and its potency was approximately 10-fold stronger than that for TRPV1. These findings suggest that OA is the agonist of both TRPA1 and TRPV1 and that OA enhances UCP1 expression in IBAT with a concomitant decrease in the visceral fat mass of HF-diet-induced obese rats through enhanced noradrenaline secretion via β-adrenergic action following TRPA1 and TRPV1 activation.     

Sex‐Dependent Dietary Obesity,Induction of UCPs,and Leptin Expression in Rat Adipose Tissues

Objective: The aim of this study was to determine the sex‐dependent differences in the response of key parameters involved in thermogenesis and control of body weight in brown adipose tissue (BAT) and white adipose tissue (WAT) in postcafeteria‐fed rats, a model of dietary obesity. Research Methods and Procedures: BAT and WAT were obtained from male and female control and postcafeteria‐fed Wistar rats. Postcafeteria‐fed rats were initially fed with cafeteria diet from day 10 of life until day 110 (cafeteria period) and with standard chow diet from then until day 180 of life (postcafeteria period). Body mass and energy intake were evaluated. Biometric parameters were analyzed in interscapular BAT (IBAT). Levels of uncoupling protein 1 (UCP1), α₂‐adrenergic receptor (AR), and β₃‐AR proteins and UCP1, UCP2, UCP3, β₃‐AR, and leptin mRNAs, in IBAT or WAT, were studied by Western blot and Northern blot analyses, respectively. Results: Rats attained 59% (females) and 39% (males) increase in body weight at the end of the cafeteria period. During the postcafeteria period, the rats showed a loss of body weight, which was higher in females. Postcafeteria‐fed female rats also presented higher activation of thermogenic parameters in IBAT, including UCP1, UCP2, and UCP3 mRNAs. Female control rats showed lower levels of both α2 and β₃‐ARs in BAT compared with male rats, but these levels in postcafeteria‐fed female and male rats were the same, because males tended to down‐regulate them. Levels of leptin mRNA in response to the postcafeteria state depended on gender and the specific WAT depot studied. Discussion: It is suggested that in postcafeteria‐fed female rats, BAT thermogenic capacity becomes more efficiently activated than in males. Female rats also showed a bigger weight loss. The parallel regulation of the levels of UCP2 and UCP3 mRNAs, with respect to UCP1 mRNA, with higher activation in female postcafeteria‐fed rats, suggests a possible role of both UCP2 and UCP3 in the regulation of energy expenditure and in the control of body weight. The distinct responses to overweight of α2 and β₃‐ARs—which were sex dependent—and leptin mRNA—which depended on both sex and WAT depot—also support the different response of thermogenesis‐related parameters between overweight males and females.     

TRPV1 Agonist Monoacylglycerol Increases UCP1 Content in Brown Adipose Tissue and Suppresses Accumulation of Visceral Fat in Mice Fed a High-Fat and High-Sucrose Diet

The administration of such a transient receptor potential vanilloid 1 (TRPV1) agonist as capsaicin, which is a pungent ingredient of red pepper, promotes energy metabolism and suppresses visceral fat accumulation. We have recently identified monoacylglycerols (MGs) having an unsaturated long-chain fatty acid as the novel TRPV1 agonist in foods. We investigated in this present study the effects of dietary MGs on uncoupling protein 1 (UCP1) expression in interscapular brown adipose tissue (IBAT) and on fat accumulation in mice fed with a high-fat, high-sucrose diet. The MG30 diet that substituted 30% of all lipids for MGs (a mixture of 1-oleoylglycerol, 1-linoleoylglycerol and 1-linolenoylglycerol) significantly increased the UCP1 content of IBAT and decreased the weight of epididymal white adipose tissue, and the serum glucose, total cholesterol and free fatty acid levels. The diet containing only 1-oleoylglycerol as MG also increased UCP1 expression in IBAT. MGs that activated TRPV1 also therefore induced the expression of UCP 1 and prevented visceral fat accumulation as well as capsaicin.     

Oleuropein supplementation increases urinary noradrenaline and testicular testosterone levels and decreases plasma corticosterone level in rats fed high-protein diet

The effects of oleuropein, a phenolic compound in extra virgin olive oil, on protein metabolism were investigated by measuring testicular testosterone and plasma corticosterone levels in rats fed diets with different protein levels. In Experiment 1, rats were fed experimental diets with different protein levels (40, 25 and 10 g/100 g casein) with or without 0.1 g/100 g oleuropein. After 28 days of feeding, the testosterone level in the testis was significantly higher and the plasma corticosterone level was significantly lower in rats fed the 40% casein diet with oleuropein than in those fed the same diet without oleuropein. The urinary noradrenaline level, nitrogen balance and hepatic arginase activity were significantly higher in rats fed the 40% casein diet with oleuropein supplementation than in those fed the 40% casein diet without oleuropein supplementation. In Experiment 2, the effects of oleuropein aglycone (a major phenolic compound in extra virgin olive oil and the absorbed form of oleuropein ingested in the gastrointestinal tracts) on the secretion of luteinizing hormone (LH) from the pituitary gland, which regulates testosterone production in the testis, were investigated in anesthetized rats. Plasma LH level increased dose dependently after the administration of oleuropein aglycone (P<.001, r= 0.691). These findings suggest that dietary supplementation with 0.1 g/100 g oleuropein alters the levels of hormones associated with protein anabolism by increasing urinary noradrenaline and testicular testosterone levels and decreasing plasma corticosterone level in rats fed a high-protein diet.     

Postprandial LDL phenolic content and LDL oxidation are modulated by olive oil phenolic compounds in humans

Olive oil phenolic compounds are potent antioxidants in vitro, but evidence for antioxidant action in vivo is controversial. We examined the role of the phenolic compounds from olive oil on postprandial oxidative stress and LDL antioxidant content. Oral fat loads of 40 mL of similar olive oils, but with high (366 mg/kg), moderate (164 mg/kg), and low (2.7 mg/kg) phenolic content, were administered to 12 healthy male volunteers in a cross-over study design after a washout period in which a strict antioxidant diet was followed. Tyrosol and hydroxytyrosol, phenolic compounds of olive oil, were dose-dependently absorbed (p<0.001). Total phenolic compounds in LDL increased at postprandial state in a direct relationship with the phenolic compounds content of the olive oil ingested (p<0.05). Plasma concentrations of tyrosol, hydroxytyrosol, and 3-O-methyl-hydroxytyrosol directly correlated with changes in the total phenolic compounds content of the LDL after the high phenolic compounds content olive oil ingestion. A 40 mL dose of olive oil promoted a postprandial oxidative stress, the degree of LDL oxidation being lower as the phenolic content of the olive oil administered increases. In conclusion, olive oil phenolic content seems to modulate the LDL phenolic content and the postprandial oxidative stress promoted by 40 mL olive oil ingestion in humans.     

Role of adipogenic and thermogenic genes in susceptibility or resistance to develop diet-induced obesity in rats

The aim of the present work was to assess whether changes in adipose tissue gene expression related with adipogenesis and/or thermogenesis could be involved in the mechanism conferring susceptibility or resistance to develop obesity in high-fat fed outbreed rats. For this purpose, male Wistar rats were fed with standard laboratory diet (control group) or high fat diet. After 15 days, two groups of rats with significant differences on body weight gain in response to the high fat diet were characterized and identified as diet-induced obesity (DIO) and diet resistant (DR) rats. A significant increase in visceral white adipose tissue (WAT) PPARgamma and aP2 (p < 0.05) mRNA levels associated to a decrease in RARgamma expression (p < 0.05) was observed in DIO rats, suggesting an increase of adipogenesis. Furthermore, our data showed a marked increase in brown adipose tissue (BAT) of UCP1 mRNA in DIO animals (p < 0.01) (without affecting PGC-1alpha gene expression), whereas no changes were found in WAT UCP2 gene expression. All these data suggest that the variations found in the expression pattern of PPARgamma, aP2 and RARgamma by high-fat diet could be involved, at least in part, in the differences in body weight gain and adiposity observed between DR and DIO animals. The compensatory adaptations through the increase in energy expenditure by changes on the expression levels of UCP1 seem not to be enough to avoid the obesity onset in the DIO group.     

TRPV1 agonist monoacylglycerol increases UCP1 content in brown adipose tissue and suppresses accumulation of visceral fat in mice fed a high-fat and high-sucrose diet

The administration of such a transient receptor potential vanilloid 1 (TRPV1) agonist as capsaicin, which is a pungent ingredient of red pepper, promotes energy metabolism and suppresses visceral fat accumulation. We have recently identified monoacylglycerols (MGs) having an unsaturated long-chain fatty acid as the novel TRPV1 agonist in foods. We investigated in this present study the effects of dietary MGs on uncoupling protein 1 (UCP1) expression in interscapular brown adipose tissue (IBAT) and on fat accumulation in mice fed with a high-fat, high-sucrose diet. The MG30 diet that substituted 30% of all lipids for MGs (a mixture of 1-oleoylglycerol, 1-linoleoylglycerol and 1-linolenoylglycerol) significantly increased the UCP1 content of IBAT and decreased the weight of epididymal white adipose tissue, and the serum glucose, total cholesterol and free fatty acid levels. The diet containing only 1-oleoylglycerol as MG also increased UCP1 expression in IBAT. MGs that activated TRPV1 also therefore induced the expression of UCP 1 and prevented visceral fat accumulation as well as capsaicin.     

Effects of diet and phenotype on adipose cellularity and 5'-deiodinase activity of liver and brown adipose tissue of diabetic SHR/N-cp rats.

1. Groups of lean and obese male SHR/N-cp rats were fed isoenergetic diets containing 54% carbohydrate as cornstarch (CS) or sucrose (SU) plus other nutrients from 5 weeks of age, and measures of adiposity, thyroxine 5' deiodinase (T4-5'DI) activity, and tissue and plasma triiodothyronine (T3) content determined at 9.5 months of age. 2. Body weights (BW) of obese greater than lean, and were greater when fed the SU than CS diet in both phenotypes. Phenotype effects (obese greater than lean) were present for fat pad weights and adipose cellularity in most primary adipose tissue depots, and diet effects (SU greater than CS) were present for epididymal and retroperitoneal depots in both phenotypes. 3. Interscapular brown adipose tissue (IBAT) and IBAT:BW ratios of obese greater than lean, and diet effects (SU greater than CS) were present for lean but not obese rats. Liver T4-5'DI activity and plasma and tissue T3 of lean greater than obese, while IBAT 5'DI activity of obese greater than lean in the CS diet. 4. These results indicate that obesity occurs in the SHR/N-cp rat as the result of hypertrophy and hyperplasia of adipose tissue, and that isoenergetic substitution of simple for complex carbohydrate exaggerates fat accretion in lean but not obese rats. Moreover, the obesity occurs in spite of greater mass, cellularity, and T4-5'DI activity of IBAT, consistent with a thermogenic defect in the obese phenotype of this strain.     

Altered Brown Adipose Tissue and Na,K Pump Activities During Diet-Induced Obesity and Weight Loss in Rats

Brown adipose tissue (BAT) thermogenesis is an uncoupled ATPase-independent thermogenic mechanism. Ion transport by the Na,K pump is an ATPase- dependent thermogenic mechanism. Both have been proposed as mechanisms of altered energy expenditure during states of dietary energy surfeit and deficit. Our aim was to study these mechanisms during diet-induced obesity and weight loss. Over 36 weeks rats were fed lard- or tallow-based diets (63% energy as fat), or a control diet (12% energy as fat). During periods of restriction rats were fed 50% of the energy intake of controls in the form of a control diet. Several components of thermogenic response increased in rats eating high fat diets and decreased following dietary restriction. BAT activation occurred, particularly with a lard-based diet, as indicated by increased GDP binding and uncoupling protein (UCP) content. Na,K pump activity in thymocytes increased with the feeding of both high fat diets at some time points. Plasma T₃ level increased in rats eating the lard-based diet and decreased with dietary restriction regardless of previous diet. Resting metabolic rate (RMR) of the animals was unchanged despite increases in these thermogenic components and was decreased in all groups following dietary restriction. Our results indicate a lack of any major role for activated BAT thermogenesis in mitigating the extent of the obesity induced by the high fat diets. The reasons for the differences in response to the two different sources of saturated fat, lard, and tallow, are not clear.     

Influence of fasting and dopamine on the tissue catecholamines diurnal variations

To define the role of catecholamines (CA) in the metabolic adaptation to fasting we examined the effect of exogenous dopamine(DA) on heat production(HP) and CA content in the interscapular brown adipose tissue(IBAT) and adrenals of control-fed and 2-day fasted rats in the morning(M) and in the evening(E). DA stimulates HP in fed rats in the M by 45% but the thermogenic effect of this CA is markedly higher in the E. However, DA had no thermogenic effect in fasted rats. The tissue CA in fed rats fluctuates diurnally: in the IBAT noradrenaline(NA) was much higher in the E while adrenaline(A) in adrenals was lower. DA in fed rats did not change the adrenal A but reduced NA content both in the adrenals and in the IBAT all over the day. Fasting depleted A from adrenals but increased NA content both in the M and in the E. Unlike the adrenals in the IBAT fasting did not affect NA content. In the adrenal gland of fasted rats DA significantly increased the A content to the equal degree during the day, while this CA had no effect on NA content of the IBAT.     

Effects of the presence, absence, and overexpression of uncoupling protein-3 on adiposity and fuel metabolism in congenic mice

Uncoupling protein-3 (UCP3) is a poorly understood mitochondrial inner membrane protein expressed predominantly in skeletal muscle. The aim of this study was to examine the effects of the absence or constitutive physiological overexpression of UCP3 on whole body energy metabolism, glucose tolerance, and muscle triglyceride content. Congenic male UCP3 knockout mice (Ucp3-/-), wild-type, and transgenic UCP3 overexpressing (UCP3Tg) mice were fed a 10% fat diet for 4 or 8 mo after they were weaned. UCP3Tg mice had lower body weights and were less metabolically efficient than wild-type or Ucp3-/- mice, but they were not hyperphagic. UCP3Tg mice had smaller epididymal white adipose tissue and brown adipose tissue (BAT) depots; however, there were no differences in muscle weights. Glucose and insulin tolerance tests revealed that both UCP3Tg and Ucp3-/- mice were protected from development of impaired glucose tolerance and were more sensitive to insulin. 2-Deoxy-D-[1-3H]glucose tracer studies showed increased uptake of glucose into BAT and increased storage of liver glycogen in Ucp3-/- mice. Assessments of intramuscular triglyceride (IMTG) revealed decreases in quadriceps of UCP3Tg mice compared with wild-type and Ucp3-/- mice. When challenged with a 45% fat diet, Ucp3-/- mice showed increased accumulation of IMTG compared with wild-type mice, which in turn had greater IMTG than UCP3Tg mice. Results are consistent with a role for UCP3 in preventing accumulation of triglyceride in both adipose tissue and muscle.     

Short-term, increasing dietary protein and fat moderately affect energy expenditure, substrate oxidation and uncoupling protein gene expression in rats

Macronutrient composition of diets can influence body-weight development and energy balance. We studied the short-term effects of high-protein (HP) and/or high-fat (HF) diets on energy expenditure (EE) and uncoupling protein (UCP1-3) gene expression. Adult male rats were fed ad libitum with diets containing different protein-fat ratios: adequate protein-normal fat (AP-NF): 20% casein, 5% fat; adequate protein-high fat (AP-HF): 20% casein, 17% fat; high protein-normal fat (HP-NF): 60% casein, 5% fat; high protein-high fat (HP-HF): 60% casein, 17% fat. Wheat starch was used for adjustment of energy content. After 4 days, overnight EE and oxygen consumption, as measured by indirect calorimetry, were higher and body-weight gain was lower in rats fed with HP diets as compared with rats fed diets with adequate protein content (P<.05). Exchanging carbohydrates by protein increased fat oxidation in HF diet fed groups. The UCP1 mRNA expression in brown adipose tissue was not significantly different in HP diet fed groups as compared with AP diet fed groups. Expression of different homologues of UCPs positively correlated with nighttime oxygen consumption and EE. Moreover, dietary protein and fat distinctly influenced liver UCP2 and skeletal muscle UCP3 mRNA expressions. These findings demonstrated that a 4-day ad libitum high dietary protein exposure influences energy balance in rats. A function of UCPs in energy balance and dissipating food energy was suggested. Future experiments are focused on the regulation of UCP gene expression by dietary protein, which could be important for body-weight management.     

The enantioselective immunoaffinity extraction of an optically active ibuprofen-modified peptide fragment

Recent in vitro studies have demonstrated antioxidant properties of some virgin olive oil phenolic compounds. One of the prerequisites to extrapolate these data to an in vivo situation is the knowledge of their bioavailability in humans. In the present work we describe an analytical method which enables us to perform hydroxytyrosol and tyrosol quantitative determinations in human urine. This method was successfully used in bioavailability studies of both phenolic compounds after acute olive oil administration. Virgin olive oil was administered to healthy volunteers after a low phenolic diet. The dose administered of both phenolic compounds was estimated in reference to free forms of hydroxytyrosol and tyrosol present in virgin olive oil extracts before and after being submitted to hydrolytic conditions. These conditions mimic those occurring during digestion. Urine samples were collected before and after acute olive oil intake and analyzed by capillary gas chromatography-mass spectrometry. Hydroxytyrosol and tyrosol urinary recovery increased in response to olive oil administration, obtaining maximal values in the first 4 h. Our results further indicate that hydroxytyrosol and tyrosol are mainly excreted in conjugated form, since only 5.9 +/- 1.4% (hydroxytyrosol) and 13.8 +/- 5.4% (tyrosol) of the total amounts excreted in urine were in free form.     

The flavan-3-ol fraction of cocoa powder suppressed changes associated with early-stage metabolic syndrome in high-fat diet-fed rats

Aims

Previous epidemiological studies have suggested that ingestion of chocolate reduces the risk of cardiovascular disease. In the present study, we examined the effects of flavan-3-ols derived from cocoa on blood pressure, lipolysis, and thermogenesis in rats fed a high-fat diet and that showed early signs of metabolic syndrome.

Main methods

The rats were divided into three groups, and fed either normal diet (normal), 60% fat high-fat diet (HFD), or HFD containing 0.2% flavan-3-ols (HFD-flavan) for 4 weeks. At the end of the feeding period, blood pressure was measured and animals were sacrificed under anesthesia. Lipolysis and thermogenesis-related protein levels were measured in several tissues by Western blotting, and mitochondrial DNA copy number was measured by RT-PCR.

Key findings

Mean blood pressure and epididymal adipose tissue weight of HFD-flavan were significantly lower compared with those of HFD. Uncoupling protein (UCP)1 in brown adipose tissue and UCP3 in gastrocnemius of HFD-flavan were significantly increased compared with those of HFD group. Carnitine palmitoyltransferase (CPT) 2 levels in liver and medium-chain acyl-CoA dehydrogenase (MCAD) levels in gastrocnemius and liver were significantly increased by the supplementation of flavan-3-ols.

Significance

In addition to having hypotensive effects, flavan-3-ols enhance thermogenesis and lipolysis and consequently reduce white adipose tissue weight gain in response to high-fat diet feeding.     

Antioxidant defenses in the ground squirrel Citellus citellus. 1. A comparison with the rat

The antioxidant defenses of the liver, erythrocytes, blood plasma, and interscapular brown adipose tissue (IBAT) of male ground squirrels were compared with those of male rats kept under identical conditions and fed the same diet. Superoxide dismutase (SOD), ascorbate, vitamin E, catalase, glutathione, and enzymes of glutathione metabolism were measured. In general, antioxidant defenses in erythrocytes were lower in ground squirrels than in rats. The same was true in liver, except that catalase-specific activity was higher. In IBAT, ascorbate, vitamin E, catalase, and glutathione reductase were higher than in rat and more of the SOD activity present was cyanide-insensitive (MnSOD). It is suggested that IBAT in ground squirrels may need a relatively greater antioxidant defense because of its important role in thermogenesis, especially in reawakening from hibernation. No major differences in antioxidant defenses between male and female ground squirrels were observed, except that the SOD activity of IBAT was higher in females.     

Reduced lipogenesis in cafeteria-fed rats exhibiting diet-induced thermogenesis

Fatty-acid synthesis has been measured in vivo with³H₂O in cafeteria-fed rats exhibiting diet-induced thermogenesis. Synthesis was decreased in brown adipose tissue, the liver, white adipose tissue, and the carcass of the cafeteria-fed animals compared to rats fed the normal stock diet. Whole-body synthesis was also decreased in the cafeteria-fed group. Diet-induced thermogenesis, in contrast to cold-induced non-shivering thermogenesis does not lead to increased fatty-acid synthesis and this is presumably due to the inhibitory effects on lipogenesis of the high dietary fat intake characteristic of cafeteria diets. The results also indicate that the energy cost of body fat deposition in cafeteria-fed rats is lower than in animals fed a low-fat/high-carbohydrate stock diet.     

Sympatho-adrenal activity and metabolic responses in fasted rats--the role of interscapular brown adipose tissue

1. Sympatho-adrenal (SA) and metabolic responses to fasting were studied in sham-operated (SHAM) rats and in those with interscapular brown adipose tissue (IBAT) removed. 2. Fasting significantly increased adrenaline (A) excretion and serum free fatty acids (FFA), but decreased noradrenaline (NA) excretion and blood glucose level in SHAM rats. 3. IBAT removal did not change metabolic responses while it markedly altered the SA activity. Fasting in animals void of IBAT potentiated the activity of adrenal medulla, inhibited the FFA rise and prevented glucose reduction, which is normally observed in SHAM-fasted rats. 4. Results suggest the significance of IBAT in the regulation of the blood level of energy substrates in fasted rats and in maintaining the basal level of NA excretion.     

Zinc deficiency and the activities of lipoprotein lipase in plasma and tissues of rats force-fed diets with coconut oil or fish oil

The present study was performed to investigate the effect of zinc deficiency on the activities of lipoprotein lipase in postheparin serum and tissues of rats fed diets containing either coconut oil or fish oil as dietary fat, using a bifactorial experimental design. To ensure an adequate food intake, all the rats were force-fed by gastric tube. Experimental diets contained either 0.8 mg zinc/kg (zinc-deficient diets) or 40 mg zinc/kg (zinc-adequate diets). The effects of zinc deficiency on the activities of lipoprotein lipase in postheparin serum and postprandial triglyceride concentrations and distribution of apolipoproteins in serum lipoproteins depended on the type of dietary fat. Zinc-deficient rats fed the coconut oil diet exhibited a reduced activity of lipoprotein lipase in postheparin serum and adipose tissue, markedly increased concentrations of triglycerides in serum, and a markedly reduced content of apolipoprotein C in triglyceride-rich lipoproteins and high density lipoproteins compared with zinc-adequate rats fed coconut oil. By contrast, zinc-deficient rats fed the fish oil diet did not exhibit reduced activities of lipoprotein lipase in postheparin serum and adipose tissue and increased concentrations of serum lipids compared with zinc-adequate rats fed the fish oil diet. This study suggests that a reduced activity of lipoprotein lipase might contribute to increased postprandial concentrations of serum triglycerides observed in zinc-deficient animals. However, it also demonstrates that the effects of zinc deficiency on lipoprotein metabolism are influenced by dietary fatty acids.     

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.     

Uptake of glucose and release of fatty acids and glycerol by rat brown adipose tissue in vivo

The net in vivo uptake or release of free fatty acids glycerol, glucose, lactate, and pyruvate by the interscapular brown adipose tissue (IBAT) of barbital-anesthetized, cold-acclimated rats was determined from measurements of plasma arteriovenous concentration differences across IBAT and tissue blood flow. Measurements were made without stimulation of the tissue and also during submaximal and maximal stimulation by infused noradrenaline (NA), the physiological activator of BAT thermogenesis. There was no appreciable uptake of glucose or release of fatty acids and glycerol by the nonstimulated tissue. At both levels of stimulation there was significant uptake of glucose (1.7 and 2.0 mumol/min) and release of glycerol (0.9 and 1.2 mumol/min), but only at maximal stimulation was there significant release of fatty acids (1.9 mumol/min). Release of lactate and pyruvate accounted for 33% of the glucose taken up at submaximal stimulation and 88% at maximal stimulation. By calculation, the remainder of the glucose taken up was sufficient to have fueled about 12% of the thermogenesis at submaximal stimulation, but only about 2% at maximal stimulation. As estimated from the rate of glycerol release, the rate of triglyceride hydrolysis was sufficient at submaximal stimulation to fuel IBAT thermogenesis entirely with the resulting fatty acids, but it was not sufficient to do so at maximal stimulation when some of the fatty acid was exported. It is suggested that at maximal NA-induced thermogenesis a portion of lipolysis proceeded only to the level of mono- and di-glycerides with the result that glycerol release did not fully reflect the rate of fatty acid formation.(ABSTRACT TRUNCATED AT 250 WORDS)