Effect of a high fat diet on rat adipocyte lipolysis: responses to epinephrine, forskolin, methylisobutylxanthine, dibutyryl cyclic AMP, insulin and nicotinic acid

Effects of dietary supplementation of different oils and conjugated linoleic acid on the reproductive and metabolic aspects of male mice

The present study was carried out to examine first, if diets enriched with 320 g of the base diet with common dietary oils including fish oil, olive oil, hydrogenated sunflower seed (H-SFS) oil, flaxseed oil and sunflower seed oil (SFS) could induce weight gain and alter reproductive and metabolic characteristics of male mice. Second, whether the addition of conjugated linoleic acid (CLA, 10% of the diet) could ameliorate any negative effects. In this cross-sectional study, 90 four-week-old male NMRI mice were used in two consecutive experiments. A high level of dietary oils negatively affected some reproductive and metabolic characteristics of male mice (p < 0.05), specifically, sunflower seed oil enrichment resulted in higher HDL levels and apoptosis of germinal epithelial cells. An olive oil-enriched diet caused an increase in plasma triglyceride concentrations and germinal cell apoptosis, as well as a decrease in sperm concentration and perturbed spermatogenesis. When CLA was fed in conjunction with dietary oils it successfully mitigated some of the negative reproductive and metabolic characteristics. We conclude that male reproductive processes are affected by high dietary oils, even before signs of obesity are evident. Inclusion of dietary CLA may provide some benefit to offset negative effects, although further studies are required.

High-fat diets: modeling the metabolic disorders of human obesity in rodents

RESEARCH METHODS AND PROCEDURES

High-fat (HF) diet feeding can induce obesity and metabolic disorders in rodents that resemble the human metabolic syndrome. However, this dietary intervention is not standardized, and the HF-induced phenotype varies distinctly among different studies. The question which HF diet type is best to model the metabolic deterioration seen in human obesity remains unclear. Therefore, in this review, metabolic data obtained with different HF diet approaches are compiled. Both whole-body and organ-specific diet effects are analyzed.

RESULTS

On the basis of these results, we conclude that animal fats and omega-6/omega-9-containing plant oils can be used to generate an obese and insulin-resistant phenotype in rodents, whereas fish oil-fed animals do not develop these disorders.

DISCUSSION

Looking at the present data, it does not seem possible to define an ideal HF diet, and an exact definition of diet composition and a thorough metabolic characterization of the HF diet effects in a researcher's specific laboratory setting remains essential for metabolic studies with this model.

Adenylyl cyclase inhibitory pathway is differentially modified in rat white and brown fat by high-energy diets

Incubation of white adipose tissue (WAT) adipocytes from rats fed a high-energy diet (Exp group) with antilipolytic Gi-coupled adenylyl cyclase inhibitory agonists, nicotinic acid (Nic) and N8-(L-2-phenylisopropyl)adenosine (PIA), resulted in lower cellular adenosine 3',5'-cyclic monophosphate (cAMP) levels than in stimulated adipocytes from rats fed a nutritionally balanced diet (Con group). In contrast to WAT, incubation of brown adipose tissue (BAT) adipocytes with Nic yielded higher cAMP levels in the Exp vs. Con rats. In both WAT and BAT adipocytes, pertussis toxin treatment abolished the differences in Nic- and PIA-inhibited cAMP formation between Exp and Con animals. Immunoblotting of adipocyte membranes indicated a lower content of Gi alpha but not Gs alpha in BAT membranes of Exp vs. Con animals after 6 and 10 wk of feeding. No such differences were found in the Gs alpha or Gi alpha contents of WAT membranes. Thus the inhibitory pathway of adenylyl cyclase is proposed to be sensitized in WAT and desensitized in BAT of rats fed high-energy diets. These modifications in sensitivity are in line with reduced cAMP and lipolysis in WAT and increased cAMP and thermogenesis in BAT during obesity.

Dietary fat and adipose tissue metabolism in ruminants, pigs, and rodents: a review

Effects of dietary fat on dairy cows are reviewed. Dietary fat did not affect gain in BW or body condition score after peak lactation but tended to increase BW loss during early lactation and body fat deposition in growing cattle. Dietary fat decreased de novo fatty acid synthesis in adipose tissue. Basal FFA release from adipose tissue in vitro and beta-adrenergic lipolytic responses were increased by protected polyunsaturated fatty acids. Dietary fat increased body fat in growing pigs and decreased BW loss in lactating sows. Dietary fat decreased de novo fatty acid synthesis and basal glycerol release in adipose tissue and tended to increase simultaneously beta-adrenergic lipolytic responses to increased membrane fluidity. Dietary fat increased body fat in rats. Polyunsaturated fatty acids were sometimes less efficient than saturated ones in increasing body fat. Lipoprotein lipase activity in adipose tissue generally decreased. Hepatic fatty acid synthesis was decreased sharply by polyunsaturated fatty acids, and adipose tissue response was less important. beta-Adrenergic-stimulated lipolysis decreased, and fatty acid esterification increased, particularly from saturated fatty acids. A trend toward insulin resistance, which was more marked with saturated fatty acids, occurred in adipose tissue.

Differential post-receptor responses of adenylate cyclase in white and brown adipose tissue membranes of rats fed high-energy diets

1. Adenylate cyclase activity was determined in membranes of white and brown adipose tissue (WAT and BAT, respectively) from rats fed a high-energy diet (EXP group) vs those fed a nutritionally balanced one (CON group). 2. The isoproterenol- and guanine nucleotide-induced adenylate cyclase activity in WAT membranes of EXP rats was lower than that in CON rats. 3. Relative adenylate cyclase activity in like treated BAT membranes was higher in EXP than in CON rats. 4. It is concluded that feeding high-energy diets to rats induces similar post-receptor modifications of adenylate cyclase as found in genetic obese rodents.

Duodenal rapeseed oil infusion in early and midlactation cows. 4. In vivo and in vitro adipose tissue lipolytic responses

In vitro glycerol and FFA releases from adipose tissue were studied in early (wk 3, trial 1) and midlactation (wk 19 to 26, trial 2) multiparous Holstein Friesian cows receiving a duodenal rapeseed oil infusion (1.0 to 1.1 kg/d). In trial 2, in vitro basal FFA release, basal FFA: glycerol ratio, and isoproterenol-stimulated FFA and glycerol releases were higher in perirenal adipose tissue from oil-infused cows. Plasma FFA concentration also was higher in oil-infused cows before and after intravenous isoproterenol injection. In trail 1, basal and stimulated glycerol and FFA releases from perirenal (but not subcutaneous) adipose tissue tended to be lower in oil-infused cows. This was probably linked to a lower milk production potential of oil-infused than of control cows which introduced a bias in energy balance. The basal FFA:glycerol ratio tended to be higher in oil-infused cows in both adipose tissues, suggesting a lower rate of reesterification inducted by oil, as was the case in trial 2. The alpha 2-agonist clonidine decreased perirenal adipose tissue glycerol release in cows and treatments in which the responses to 4 x 10(-7) M isoproterenol were higher. In vivo and in vitro lipolytic responses were lower in trial 2 than in trial 1, except the in vitro maximally stimulated lipolytic rate, which probably reflected a long lasting teleophoretic adaptation to ensure energy needs of lactation. This study indicated that oil infusion affected both beta- and alpha 2-adrenergic responses and that postpartum lipid mobilization did not seem to be reduced by the exogenous unsaturated fatty acid supply.

In vivo incorporation of lauric acid into rat adipose tissue triacylglycerols

An in vivo approach was taken to examine fatty acid esterification in adipose tissue using a coconut oil-enriched diet. Rats were fed a diet containing coconut oil (50% lauric acid) for six weeks. Triacylglycerols from perirenal adipose tissue were fractionated by silver nitrate-thin layer chromatography and, then, preparative gas chromatography. The distribution of 169 triacylglycerol types accounting for 97% of total triacylglycerols was determined. There was evidence for a very high content of mixed triacylglycerols composed of intermediate (12:0 and 14:0) and long acyl moieties. No significant differences were observed between the experimental distribution of triacylglycerol types and the random distribution, calculated from the total fatty acid composition. This indicated that most long chain triacylglycerols stored before coconut oil feeding would have been rearranged after the six weeks of coconut oil feeding. The experimental proportion of trilauroylglycerol reached 2%, as expected from its random proportion, and the proportions of dilauroylacylglycerols were slightly higher than the random values. Present results were compared with those previously obtained from triacylglycerols of adipose tissue of rats fed a low-fat standard diet. From our results and those of other authors, it is suggested that lauric acid is a good substrate for sn-glycero-3-phosphate acyltransferase and diacylglycerol acyltransferase in rat adipose tissue.