Postnatal changes in fatty acids composition of brown adipose tissue

It has been demonstrated that thermogenic activity of brown adipose tissue (BAT) is higher during the early postnatal period, decreasing towards a low adult level. The present study examined postnatal changes in the lipid composition of BAT. BAT from pre-weaning rats at 4 and 14 days old showed the following differences in lipid composition compared to that from adults of 12 weeks old. (i) Relative weight of interscapular BAT to body weight was markedly greater. (ii) BAT-triglyceride (TG) level was lower, while BAT-phospholipid (PL)level was higher. (iii) In TG fatty acids (FA) polyunsaturated fatty acids (PU; mol %), arachidonate index (AI), unsaturation index (UI) and PU/saturated FA (SA) were higher; rare FA such as eicosadienoate, bishomo--linolenic acid and lignoceric acid in mol % were also higher. (iv) In PL-FA monounsaturated FA (MU) in mol % was lower; PU mol %, AI and UI were higher. These features in BAT of pre-weaning rats resembled those in the cold-acclimated adults, suggesting a close relationship of the PL-FA profile to high activity of BAT.     

Respiratory rate and thermal sensitivity of brown fat and other tissues from Jaculus orientalis and rat

In vitro oxygen consumption of brown adipose tissue (BAT) was compared to that of brain. heart, muscle, diaphragm and intestine from rat and Jaculus orientalis, a hibernating desert rodent. Eleven assay temperatures between 5 and 44°C were used. BAT from Jaculus orientalis showed the highest oxygen consumption and was temperature independent between 15 and 40°C. For other tissues there was little difference betwee the two species with the exception of higher transition temperatures for certain tissues from jerboa.     

Characteristics of diet-induced brown adipose tissue growth and thermogenesis in rats

The characteristics of regional brown (BAT) and white adipose tissue (WAT) growth and of thermogenesis following experimental overfeeding were studied in groups of male Sprague-Dawley rats fed lab chow or cafeteria diets for 8 weeks postweaning. Regional BAT and WAT growth was determined by dissection and weighing, and thermogenesis was characterized by measurements of resting and norepinephrine (NE)-stimulated oxygen consumption, of serum thyroid hormone concentrations, and of 24-hour urinary NE excretion levels. Cafeteria feeding resulted in a 113% increase in total BAT, with the most prominent increases in the interscapular, thoracic, and perirenal regions. Retroperitoneal, epididymal, and omental WAT were significantly greater in cafeteria than in chow-fed rats. Resting oxygen consumption of cafeteria-fed rads increased by 10% and NE excretion by 64% compared to chow-fed controls, while serum T₃ concentrations were nearly doubled in the cafeteria-fed rats. The thermogenic response to NE injection in cafeteria-fed rats was 102% of their resting levels, compared to a 51% increase in the chow-fed controls. The results indicate that increased BAT growth occurs in all primary BAT depots following cafeteria-feeding in rats, and that the greater BAT mass is qualitatively proportional to their greater capacity for non-shivering thermogenesis. Also, the increased NE excretion and greater serum T₃ concentration are consistent with increased sympathetic and thyroidal activity and may in part explain the thermogenic response to diet in the rat.     

Shc depletion stimulates brown fat activity in vivo and in vitro

Adipose tissue is an important metabolic organ that integrates a wide array of homeostatic processes and is crucial for whole‐body insulin sensitivity and energy metabolism. Brown adipose tissue (BAT) is a key thermogenic tissue with a well‐established role in energy expenditure. BAT dissipates energy and protects against both hypothermia and obesity. Thus, BAT stimulation therapy is a rational strategy for the looming pandemic of obesity, whose consequences and comorbidities have a huge impact on the aged. Shc‐deficient mice (ShcKO) were previously shown to be lean, insulin sensitive, and resistant to high‐fat diet and obesity. We investigated the contribution of BAT to this phenotype. Insulin‐dependent BAT glucose uptake was higher in ShcKO mice. Primary ShcKO BAT cells exhibited increased mitochondrial respiration; increased expression of several mitochondrial and lipid‐oxidative enzymes was observed in ShcKO BAT. Levels of brown fat‐specific markers of differentiation, UCP1, PRDM16, ELOVL3, and Cox8b, were higher in ShcKO BAT. In vitro, Shc knockdown in BAT cell line increased insulin sensitivity and metabolic activity. In vivo, pharmacological stimulation of ShcKO BAT resulted in higher energy expenditure. Conversely, pharmacological inhibition of BAT abolished the improved metabolic parameters, that is the increased insulin sensitivity and glucose tolerance of ShcKO mice. Similarly, in vitro Shc knockdown in BAT cell lines increased their expression of UCP1 and metabolic activity. These data suggest increased BAT activity significantly contributes to the improved metabolic phenotype of ShcKO mice.     

Dietary lipid quality and mitochondrial membrane composition in trout: responses of membrane enzymes and oxidative capacities

To examine whether membrane fatty acid (FA) composition has a greater impact upon specific components of oxidative phosphorylation or on overall properties of muscle mitochondria, rainbow trout (Oncorhynchus mykiss) were fed two diets differing only in FA composition. Diet 1 was enriched in 18:1n-9 and 18:2n-6 while Diet 2 was enriched in 22:6n-3. The FA composition of mitochondrial phospholipids was strongly affected by diet. 22:6n-3 levels were twice as high (49 %) in mitochondrial phospholipids of fish fed Diet 2 than in those fed Diet 1. 18:2n-6 content of the phospholipids also followed the diets, whereas 18:1n-9 changed little. All n-6 FA, most notably 22:5n-6, were significantly higher in fish fed Diet 1. Nonetheless, total saturated FA, total monounsaturated FA and total polyunsaturated FA in mitochondrial phospholipids varied little. Despite a marked impact of diet on specific FA levels in mitochondrial phospholipids, only non-phosphorylating (state 4) rates were higher in fish fed Diet 2. Phosphorylating rates (state 3), oxygen consumption due to flux through the electron transport chain complexes as well as the corresponding spectrophotometric activities did not differ with diet. Body mass affected state 4 rates and cytochrome c oxidase and F ₀ F ₁ ATPase activities while complex I showed a diet-specific effect of body mass. Only the minor FA that were affected by body mass were correlated with functional properties. The regulated incorporation of dietary FA into phospholipids seems to allow fish to maintain critical membrane functions even when the lipid quality of their diets varies considerably, as is likely in their natural environment.     

Hepatic and adipose tissue lipogenic enzyme mRNA levels are suppressed by high fat diets in the rat

Small changes in lipogenic enzyme activity induced by dietary fats of different composition may, over the long term, have significant impact on the development of obesity. We have investigated the effect of high fat diets (45% of calories as fat) on abundance of mRNA encoding fatty acid synthetase (FAS) and glycerophosphate dehydrogenase (GPDH) in male Sprague-Dawley rats. When caloric intake was equal, the relative amount of hepatic FAS mRNA was greater in rats fed a saturated compared to a polyunsaturated fat diet. This difference could not be attributed to diet-induced changes in plasma insulin concentration. However, both fat diets suppressed hepatic FAS mRNA compared to a sucrose diet. Close correlation between FAS specific activity and the relative amount of mRNA suggested that regulation was mainly at a pre-translational level. Adipose tissue FAS mRNA was suppressed by the two fat diets equally while GPDH mRNA was unaffected by dietary composition. Retroperitoneal fat pads were significantly larger in rats fed saturated compared to those fed polyunsaturated fat for 26 weeks. We concluded that dietary saturated fats fail to suppress hepatic de novo lipogenesis as effectively as polyunsaturated fats, which may have implications for the prevention of obesity in humans.     

Adaptive modification of membrane phospholipid fatty acid composition and metabolic thermosuppression of brown adipose tissue in heat-acclimated rats

Thermogenesis, especially facultative thermogenesis by brown adipose tissue (BAT), is less important in high ambient temperature and the heat-acclimated animals show a lower metabolic rate. Adaptive changes in the metabolic activity of BAT are generally found to be associated with a modification of membrane phospholipid fatty acid composition. However, the effect of heat acclimation on membrane phospholipid fatty acid composition is as yet unknown. In this study, we examined the thermogenic activity and phospholipid fatty acid composition of interscapular BAT from heat-acclimated rats (control: 25±1°C, 50% relative humidity and heat acclimation: 32±0.5°C, 50% relative humidity). Basal thermogenesis and the total thermogenic capacity after noradrenaline stimulation, as estimated by in vitro oxygen consumption of BAT (measured polarographically using about 1-mm³ tissue blocks), were smaller in the heat-acclimated group than in the control group. There was no difference in the tissue content of phospholipids between the groups when expressed per microgram of DNA. The phospholipid fatty acid composition was analyzed by a capillary gas chromatograph. The state of phospholipid unsaturation, as estimated by the number of double bonds per fatty acid molecule, was similar between the groups. The saturated fatty acid level was higher in the heat-acclimated group. Among the unsaturated fatty acids, heat acclimation decreased docosahexaenoic acid and oleic acid levels, and increased the arachidonic acid level. The tissue level of docosahexaenoic acid correlated with the basal oxygen consumption of BAT (r=0.6, P<0.01) and noradrenaline-stimulated maximum values of oxygen consumption (r=0.5, P<0.05). Our results show that heat acclimation modifies the BAT phospholipid fatty acids, especially the n-3 polyunsaturated fatty acid docosahexaenoic acid, which is possibly involved in the metabolic thermosuppression. Received: 9 August 1999 / Revised: 8 November 1999 / Accepted: 24 November 1999     

Fatty acid composition of brown adipose tissue in genetically heat-tolerant FOK rats

The phospholipid fatty acid composition of brown adipose tissue (BAT) was examined in inbred heat-tolerant FOK rats and compared with that in conventional Wistar rats not previously exposed to heat. The FOK rats showed higher unsaturation states, as indicated by higher levels of polyunsaturated fatty acids and a higher unsaturation index and polyunsaturated fatty acids/saturated fatty acids ratio. This higher level of unsaturation was characterized by the higher amount of polyunsaturated fatty acids such as linoleic acid, arachidonic acid and docosahexaenoic acid. It may be concluded that the increased docosahexaenoic acid level in BAT phospholipids brings about the hyperplasia of BAT, causing an enhancement of its in vivo thermogernic activity as well as the systemic non-shivering thermogenesis observed in heat-tolerant FOK rats. Received: 17 May 2000 / Revised: 21 August 2000 / Accepted: 21 September 2000     

Effect of diet on the weight of brown adipose tissue in rodents

Interscapular brown adipose tissue (BAT) weighed more in rats given access to a solution of sucrose in addition to a nutritionally complete basal diet than in rats eating only a basal diet. This incremental effect of drinking sucrose solution occurs across a variety of dietary conditions. In the first experiment, rats were fed diets containing either 9%, 18%, 27% or 36% casein. Rats given access to a sucrose solution had significantly larger brown fat pads than controls when the diets contained 9 or 18% casein, but not when diets contained either 27% or 36% casein. The second experiment examined the weight of brown adipose tissue as a function of the type of protein and the percentage of fat in the diet. Animals given a sucrose solution had significantly more BAT than animals not given sucrose. Neither the type of protein (casein or soy protein) nor the percentage of fat (14.5% or 36.4%) in the diet influenced the weight of BAT. Animals given access to either a sucrose solution or a glucose solution had significantly heavier BAT than animals given access to a fructose solution, granulated sucrose or water.     

Dehydroepiandrosterone alters Zucker rat soleus and cardiac muscle lipid profiles

High levels of serum free fatty acids (FFA) and lower proportions of polyunsaturated (PU) FAs, specifically arachidonic acid (AA), are common in obesity, insulin resistance (IR), and type 2 diabetes mellitus. Dehydrepiandrosterone (DHEA) decreases body fat content, dietary fat consumption, and insulin levels in obese Zucker rats (ZR), a genetic model of human youth onset obesity and type 2 diabetes. This study was conducted to investigate DHEA's effects on lean and obese ZR serum FFA levels and total lipid (TL) FA profiles in heart and soleus muscle. We postulated that DHEA alters serum FFA levels and tissue TL FA profiles of obese ZR so that they resemble the levels and profiles of lean ZR. If so, DHEA may directly or indirectly alter tissue lipids, FFA flux, and perhaps lower IR in obese ZR. Lean and obese male ZR were divided into six groups with 10 animals in each: obese ad libitum control, obese pair-fed, obese DHEA, lean ad libitum control, lean pair-fed, and lean DHEA. All animals had ad libitum access to a diet whose calories were 50% fat, 30% carbohydrate, and 20% protein. Only the diets of the DHEA treatment groups were supplemented with 0.6% DHEA. Pair-fed groups were given the average number of calories per day consumed by their corresponding DHEA group, and ad libitum groups had 24-h access to the DHEA-free diet. Serum FFA levels and heart and soleus TL FA profiles were measured. Serum FFA levels were higher in obese (approximately 1 mmol/L) compared to lean (approximately 0.6 mmol/L) ZR, regardless of group. In hearts, monounsaturated (MU) FA were greater and PU FA were proportionally lower in obese compared to the lean rats. In soleus, saturated and MU FA were greater and PU FA were proportionally lower in the obese compared to the lean rats. DHEA groups displayed significantly increased proportions of TL AA and decreased oleic acid in both muscle types. Mechanisms by which DHEA alters TL FA profiles are a reflection of changes occurring within specific lipid fractions such as FFA, phospholipid, and triglyceride. This study provides initial insights into DHEA's lipid altering effects.     

Fatty acid mobilization in voles--model species for rapid fasting response and fatty liver

Factors regulating fatty acid (FA) composition of small herbivores are poorly known. Because of the fast response to food deprivation, the tissue FA profiles of voles could be rapidly modified. The selectivity of incorporating dietary FA into tissue total lipids and mobilizing tissue FA was examined in two Microtus vole species either fed or fasted for 12-18 h. The FA composition of the tissues reflected the dietary lipids, but FA were selectively incorporated depending on their structure. The FA profiles of white and brown adipose tissues were different and contained more saturated and monounsaturated FA and less polyunsaturated FA (PUFA) than the diet. The essential PUFA precursors with smaller tissue percentages were likely converted into longer-chain derivatives for structural lipids. The FA composition of the vole tissues was selectively modified by food deprivation. The preferences for retention or loss were tissue-specific and related to the FA structure. Livers displayed steatosis with characteristic accumulation of triacylglycerols, while FA prevalent in membrane phospholipids decreased in proportion. Hepatic FA could be partly derived from lipids hydrolyzed in fat depots. The FA profiles of the vole tissues reflect the dietary lipids and are rapidly and selectively modified by food deprivation.     

Tissue fatty acid composition of pigs fed different fat sources

Dietary fat influences the physico-chemical properties of meat, and fatty acid (FA) composition may have implications on human health. The objectives of the experiment were to study tissue FA partitioning and the effect of dietary fat source on tissue FA composition. Seventy crossbred gilts (61.8 ± 5.2 kg BW average) were fed one of seven treatments: a diet containing a very low level of fat (no fat (NF)) and six fat-supplemented diets (10%: tallow (T), high-oleic sunflower oil (HOSF), sunflower oil (SFO), linseed oil (LO), fat blend (FB: 55% tallow, 35% SFO, 10% LO) and fish oil blend (FO: 40% fish oil, 60% LO). Differential tissue FA depositions were observed, with flare fat being the most saturated, followed by intermuscular, and subcutaneous being the least saturated. Monounsaturated fatty acid (MUFA) deposition showed an opposite tissue pattern. Subcutaneous fat showed the highest MUFAs, intermuscular fat showed intermediate values and flare fat showed the lowest MUFAs. Intramuscular polyunsaturated fatty acid (PUFA) content was less susceptible to dietary treatment modifications compared with other depots. Significant tissue FA modifications were observed due to dietary treatments, mainly in diets rich in PUFA. The saturated fatty acids (SFA) were high in NF-fed and low in HOSF-fed animals, MUFA were high in HOSF-fed and low in SFO-, LO- and FO-fed animals, while PUFA were high in SFO- and LO-fed and low in HOSF-, T- and NF-fed animals. Pigs fed LO and FB showed detectable levels of EPA, which depended on the linolenic content of the diet. The only effective way to increase tissue DHA contents was to add DHA in the diet through FO feeding. Araquidonic acid was high in SFO diets and low in LO and FB diets, and also high in intramuscular fat compared with other tissues. EPA and DHA were also high in intramuscular fat compared with other fat depots. The deposition of oleic and linoleic acids depended on the composition of dietary fat, as their deposition varied between diets, even at similar levels of intake of each FA. The NF diet resulted in the greatest proportion of SFAs (palmitic and stearic) of all treatments tested. SFAs were less susceptible to modification than MUFA in response to the different PUFA levels supplemented in the diet. T resulted in less fat deposition in some of the fat depots and more in others, suggesting that T could partition fat differently among fat depots.     

Canola Oil in Lactating Dairy Cow Diets Reduces Milk Saturated Fatty Acids and Improves Its Omega-3 and Oleic Fatty Acid Content

To produce milk that is healthier for human consumption, the present study evaluated the effect of including canola oil in the diet of dairy cows on milk production and composition as well as the nutritional quality of this milk fat. Eighteen Holstein cows with an average daily milk yield of 22 (± 4) kg/d in the middle stage of lactation were used. The cows were distributed in 6 contemporary 3x3 Latin squares consisting of 3 periods and 3 treatments: control diet (without oil), 3% inclusion of canola oil in the diet and 6% inclusion of canola oil in the diet (dry matter basis). The inclusion of 6% canola oil in the diet of lactating cows linearly reduced the milk yield by 2.51 kg/d, short-chain fatty acids (FA) by 41.42%, medium chain FA by 27.32%, saturated FA by 20.24%, saturated/unsaturated FA ratio by 39.20%, omega-6/omega-3 ratio by 39.45%, and atherogenicity index by 48.36% compared with the control treatment. Moreover, with the 6% inclusion of canola oil in the diet of cows, there was an increase in the concentration of long chain FA by 45.91%, unsaturated FA by 34.08%, monounsaturated FA by 40.37%, polyunsaturated FA by 17.88%, milk concentration of omega-3 by 115%, rumenic acid (CLA) by 16.50%, oleic acid by 44.87% and h/H milk index by 94.44% compared with the control treatment. Thus, the inclusion of canola oil in the diet of lactating dairy cows makes the milk fatty acid profile nutritionally healthier for the human diet; however, the lactating performance of dairy cows is reduce.     

Thermogenesis in brown adipose tissue of genetically obese, diabetic (KKAY) mice

Thermogenesis of brown adipose tissue (BAT) of genetically obese mice, KKAY mice, was examined by measuring the BAT mitochondrial guanosine diphosphate (GDP) binding as an index of thermogenesis and comparing it with that of normal C57BL mice. No great difference in GDP binding was observed in KKAY and C57BL mice fed a stock diet. However, when they were given a sucrose solution, the increase in BAT mitochondrial GDP binding of KKAY mice (+22%) was much lower than that of C57BL mice (+106%). A high fat diet increased BAT mitochondrial GDP binding in KKAY mice to the same extent (+82%) as in C57BL mice. When the mice were fasted for 48 h, BAT mitochondrial GDP binding of C57BL mice decreased by 70%, while that of KKAY mice showed no change. Both acute exposure to cold and norepinephrine injections increased GDP binding in KKAY mice by 90% and 131%, respectively. These results indicate that low BAT thermogenesis in response to sucrose intake may be a cause of obesity in KKAY mice, and this may be brought about by defects in the central nervous system.     

Congruence of individual responsiveness to dietary cholesterol and to saturated fat in humans

Previous experiments have shown that differences between humans in the response of serum cholesterol to dietary cholesterol are at least partly reproducible and stable over a prolonged period. In this study it was investigated whether enhanced sensitivity to dietary cholesterol and saturated fat go together. The subjects had also participated in three or four experiments dealing with the reproducibility of the effect on blood cholesterol of either adding cholesterol to the diet in normal subjects (NORM-EGG group; n = 23) or of cessation of egg consumption in subjects with a high habitual egg intake (HAB-EGG group; n = 24). In the present experiment the NORM-EGG subjects were fed a mixed natural diet providing 21% of energy as polyunsaturated and 11% as saturated fat (P/S2 ratio, 1.9) for 3 weeks, and one providing 5% of energy as polyunsaturated fat and 23% as saturated fat (P/S ratio, 0.2) for the next 3 weeks. The HAB-EGG group was fed the same diets in reverse order. The serum cholesterol concentrations were higher on the low P/S diet than on the high P/S diet (on average 23% in normal subjects and 16% in habitual egg eaters). The correlation coefficient between each subject's serum cholesterol response to fatty acids and his or her average response to dietary cholesterol in the dietary cholesterol experiments was 0.62 for the normal subjects (P less than 0.01) and 0.15 for the HAB-EGG group. We conclude that modest differences in responsiveness of serum cholesterol to dietary saturated fat do exist in humans, and that, in people of normal cholesterol intake, responsiveness to dietary cholesterol and to saturated fat tend to go together.     

Mitochondrial activity,hemocyte parameters and lipid composition modulation by dietary conditioning in the Pacific oyster Crassostrea gigas

Several parameters can affect membrane lipid composition in bivalves, including diet. Although two fatty acids (FA) 22:6n-3 and 20:5n-3 are essential membrane components, they are sparingly synthesized by bivalves and must be obtained from their diet. Here, effects of dietary modifications of membrane lipid composition were studied at both cellular and subcellular levels in the oyster Crassostrea gigas. To this end, we compared oysters fed two monoalgal diets that differed markedly in their FA composition and a mix of both. As expected, algae impacted phospholipids, in particular 22:6n-3 and 20:5n-3, reflecting differences of dietary microalgae FA composition. Meantime, total saturated FA, total monounsaturated FA, total polyunsaturated FA and total non-methylene-interrupted FA varied little and phospholipid class composition was only slightly affected by diets. Measures made in hemocytes indicated that only mitochondrial membrane potential was affected by diets. Total ROS production as well as mitochondrial superoxide production did not differ with diet. There was no difference in phosphorylating (state 3) and non-phosphorylating (state 4) rates of oxygen consumption rates or in cytochrome c oxidase activity of mitochondria isolated from gills between the three diets. Similarly, neither cytochromes a, b, c or c ₁ content nor citrate synthase activities were changed, suggesting that number and morphology of mitochondria were not affected by dietary treatment. These results suggest that oysters could possess high homeostatic capabilities, at both cellular and subcellular levels, to minimize the effect of dietary FA and related membrane lipid FA modifications on mitochondrial functions. These capabilities could be a means to face variations in diet composition in their natural environment and to preserve important oyster physiological functions such as growth and reproduction.     

Comparison of blood leptin and vitamin E and blood and adipose fatty acid compositions in wild and captive populations of critically endangered Vancouver Island marmots (Marmota vancouverensis)

Vancouver Island marmots (Marmota vancouverensis) (VIMs) are a critically endangered species of fat-storing hibernators, endemic to Vancouver Island, British Columbia, Canada. In addition to in-situ conservation efforts, a captive breeding program has been ongoing since 1997. The captive diet is mostly pellet-based and rich in n−6 polyunsaturated fatty acids (PUFAs). In captivity, overall length of hibernation is shortened, and marmots have higher adipose tissue reserves compared to their wild-born counterparts, which may be a risk factor for cardiovascular disease, the leading cause of mortality in captive marmots. To investigate differences in lipid metabolism between wild and captive populations of VIMs, blood vitamin E, fatty acid (FA) profiles and leptin, and white adipose tissue (WAT) FA profiles were compared during the active season (May to September 2019). Gas chromatography, high-performance liquid chromatography, and multiplex kits were used to obtain FA profiles, α-tocopherol, and leptin values, respectively. In both plasma and WAT, the concentration of the sum of all FA in the total lipids was significantly increased in captive VIMs. The n−6/n−3 ratio, saturated FAs, and n−6 PUFAS were higher in captive marmots, whereas n−3 PUFAs and the HUFA score were higher in wild marmots. Serum concentrations of α-tocopherol were greater by an average of 45% in captive marmots, whereas leptin concentrations did not differ. Results from this study may be applied to improve the diet and implement weight management to possibly enhance the quality of hibernation and decrease the risk of cardiovascular and metabolic diseases of captive VIMs.     

The different molecular structure and glycerol-to-fatty acid ratio of palm oils affect their nutritive value in broiler chicken diets

The aim of this study is to assess how the fat molecular structure and its glycerol-to-fatty acid ratio (G : FA) affect the fatty acid (FA) apparent absorption of palm oils in broiler chickens. The experimental diets were the result of a basal diet supplemented with 6% of different palm oils. Native palm oil (N), rich in triacylglycerols, was the positive control (T1), and acid palm oil (A), rich in free FA, was the negative control (T2). In order to improve the nutritive value of A, two different nutritional strategies were performed. The first strategy was achieved by adding increasing amounts of free glycerol (G) (4% (T3), 8% (T4) and 16% (T5)) to A, and the second one by adding increasing amounts of mono- (MAG) and diacylglycerols (DAG), coming from re-esterified palm oil (E) (40% (T6), 70% (T7), and 100% (T8)) to A. As a result, eight dietary treatments were formulated with a G : FA ratio ranging from 0.04 to 0.67. These treatments were randomly assigned to 192 one-day-old female broiler chickens (Ross 308), distributed in 48 cages. The results showed how, by keeping the G : FA ratio constant (0.33 mol/mol), the diet with a high MAG and DAG content (T7) achieved higher saturated FA apparent absorption values than did the diet with a high triacylglycerol content (T1) and this, in turn, more than did the diet with a high free FA content (T4). The behavior of oils with high or low G : FA ratio was dependent on whether G was in a free state or esterified as part of acylglycerol molecules. Thus, increasing amounts of G to A did not enhance the total FA apparent absorption, but rather quite the opposite, even impairing the absorption of mono- and polyunsaturated FA. However, increasing amounts of E (rich in MAG and DAG) to A (rich in FFA) did enhance total FA apparent absorption, primarily due to the increased absorption of saturated FA. In conclusion, the greater the G : FA ratio of a palm oil, the greater the absorption of total FA, as long as G is esterified as part of acylglycerol molecules. Thus, the re-esterification process for obtaining E makes sense in order to give added value to A, achieving even greater digestibility values than does its corresponding N.     

Brown adipose tissue cell respiration in hypo- and hyperthyroidism after stimulation with selective and non selective beta-adrenergic agonists.

Brown adipocyte respiration was measured in isolated cells from hypothyroid, hyperthyroid and euthyroid Sprague-Dawley male rats. Hypothyroidism was induced by providing drinking water containing methimazole and hyperthyroidism was induced by addition of thyroid powder to the diet. Brown adipose tissue (BAT) cells were isolated by collagenase digestion and oxygen consumption (VO2) was measured by Clark type oxygen electrodes. BAT cell respiration was stimulated by selective and nonselective beta-adrenergic agonists: BRL 35135A (BRL) and Isoprenaline (ISO). Basal BAT cells respiration did not differ according to thyroid status. Maximal VO2 responses of BAT adipocytes from hypothyroid rats were significantly lower than in euthyroidism after ISO and BRL. The reduced response was more marked for ISO than for BRL. The thermogenic sensitivity was significantly greater in euthyroid than is hypothyroid cells for ISO, but not for BRL. The euthyroid-hyperthyroid differences were not significantly different. These results suggest: basal respiration of BAT cells in hypo- and hyperthyroidism does not reflect the overall changes in whole body metabolism; the decreased thermogenic response in hypothyroidism might be due to decreased beta-adrenoceptor numbers and/or decreased intracellular thyroxine-triiodothyronine conversion; changes in sensitivity to ISO and BRL in vitro reflect the changes seen in VO2 in vivo.