Increased Plasma Free Fatty Acid Research Articles

Profiling gene transcription in vivo reveals adipose tissue as an immediate target of tumor necrosis factor-alpha: implications for insulin resistance.

Despite extensive studies implicating tumor necrosis factor (TNF)-alpha as a contributing cause of insulin resistance, the mechanism(s) by which TNF-alpha alters energy metabolism in vivo and the tissue specificity of TNF-alpha action are unclear. Here, we investigated the effects of TNF-alpha infusion on gene expression and energy metabolism in adult rats. A 1-day TNF-alpha treatment decreased overall insulin sensitivity and caused a 70% increase (P = 0.005) in plasma levels of free fatty acids (FFAs) and a 46% decrease (P = 0.01) in ACRP30. A 4-day TNF-alpha infusion caused insulin resistance and significant elevation of plasma levels of FFAs and triglycerides and reduction of ACRP30. Plasma glucose concentration was not altered following TNF-alpha infusion for up to 4 days. As revealed by oligonucleotide microarrays, TNF-alpha evoked major and rapid changes in adipocyte gene expression, favoring FFA release and cytokine production, and fewer changes in liver gene expression, but favoring FFA and cholesterol synthesis and VLDL production. There was only a moderate repressive effect on skeletal muscle gene expression. We demonstrate that TNF-alpha antagonizes the actions of insulin, at least in part, through regulation of adipocyte gene expression including reduction in ACRP30 mRNA and induction of lipolysis resulting in increased plasma FFAs. TNF-alpha later alters systemic energy homeostasis that closely resembles the insulin resistance phenotype. Our data suggest that blockade of TNF-alpha action in adipose tissue may prevent TNF-alpha-induced insulin resistance in vivo.

Relationship between plasma free fatty acids and uncoupling protein-3 gene expression in skeletal muscle of obese subjects: in vitro evidence of a causal link.

To investigate whether skeletal muscle uncoupling protein-2 (UCP2) and uncoupling protein-3 (UCP3) gene expression is altered in massive obesity and whether it correlates with in vivo insulin sensitivity and with metabolic and hormonal status. Quantification of UCP2 and UCP3 gene expression in skeletal muscle of obese and lean subjects displaying different degrees of insulin sensitivity. Fourteen obese and 10 age- and sex-matched healthy control subjects with a mean body mass index (BMI) of 43.6 +/- 1.4 and 22.8 +/- 1.8 (+/- SEM), respectively. Insulin sensitivity by glucose clamp, body composition by bio-impedance, fasting plasma glucose, insulin, leptin and free fatty acids (FFA). Skeletal muscle UCP2 and UCP3 mRNA levels by quantitative reverse transcription polymerase chain reaction (RT-PCR). No significant differences in UCP2 or UCP3 mRNA levels were found between obese and control subjects. No significant correlation was observed, in both groups, between UCP2 or UCP3 mRNA levels and both anthropometrical and metabolic parameters. In contrast, a highly significant correlation was observed between skeletal muscle UCP3, but not UCP2, mRNA levels and plasma FFA in the obese, but not in the lean, group. Furthermore, exposure of human myocytes to FFA for 24 h strongly induced both UCP3 and peroxisome proliferator-activated receptor-gamma (PPARgamma) but not UCP2 gene expression. FFA levels correlate strongly with skeletal muscle UCP3 mRNA levels in obese, but not in lean, subjects; in addition, in human myocytes, high FFA concentrations promote UCP3 expression. Our studies therefore provide evidence that supports a role for increased plasma FFA concentrations in the regulation of human skeletal muscle UCP3 gene expression.

Prevention Conference VI: Diabetes and Cardiovascular disease: Writing Group I: epidemiology.

In patients with diabetes, a high priority must be given to modification of the major risk factors for cardiovascular disease (CVD). There is growing evidence that control of these risk factors will reduce the likelihood of developing CVD and its complications in patients with diabetes.1 In clinical management of patients with diabetes, attention must be given to the following risk factors: smoking, hypertension, prothrombotic state, low-density lipoprotein (LDL) cholesterol and diabetic dyslipidemia, hyperglycemia, overweight/obesity, physical inactivity, and adverse nutrition. Specific considerations of Writing Group IV will be reviewed. They will be discussed in light of current recommendations for management of risk factors in diabetes as presented by the American Diabetes Association (ADA), the American Heart Association (AHA), and the national education programs sponsored by the National Heart, Lung, and Blood Institute (NHLBI).2–11⇓⇓⇓⇓⇓⇓⇓⇓⇓ These recommendations are summarized in the Table. View this table: Table 1107395. Goals for Risk Factor Management in Patients With Diabetes In addition to being a cause of many forms of cancer and chronic lung disease, cigarette smoking is a major cardiovascular risk factor. When a smoking patient also has diabetes, this patient is doubly at risk for CVD. Thus, every effort must be made to convince patients with diabetes who smoke to give up the smoking habit. This need is strongly reinforced by a position statement from the ADA.10 Elevated blood pressure is a major independent risk factor for multiple cardiovascular end points: coronary heart disease (CHD), stroke, chronic renal failure, and heart failure.11 Patients with diabetes have an increased prevalence of hypertension.12 Multiple factors undoubtedly contribute to hypertension in patients with diabetes, eg, obesity, insulin resistance, hyperinsulinemia, and renal disease. Systolic hypertension appears to be the main blood pressure–related risk factor in patients with diabetes.13 …

Effect of ultrasound application on fat mobilization

The aim of this experimental trial was to study the effect of ultrasound application on the lipolysis in adipose tissue. Rats were administered to pentobarbital (Nembutal) anesthesia and their abdomens were shaved. Rat abdomen was subjected to 24 kHz–1 MHz ultrasound for 10 min to investigate frequency and power-intensity dependency for fat mobilization. Blood was taken from the tail vein to estimate plasma free fatty acids (FFA). For frequency dependency two regions around 100 kHz and 300–500 kHz were effective for fat mobilization. For power-intensity dependency, effective regions were found to be from 24 to 1090 kHz. In the effective regions on frequency and power-intensity, application of ultrasound caused increases in plasma FFA and norepinephrine concentration of extra-cellular fluid of perirenal adipose tissue. These results suggest that ultrasound application stimulates fat mobilization through a local increase in norepinephrine secretion under the conditions of effective frequency and intensity.

Plasma free fatty acid levels and the risk of ischemic heart disease in men: prospective results from the Québec Cardiovascular Study

Insulin resistance, through numerous related disturbances in glucose and lipoprotein-lipid metabolism, is associated with an increased risk of ischemic heart disease (IHD). The purpose of the present study was to examine the relationship between increased plasma free fatty acid (FFA) concentrations, as a feature of the insulin resistance syndrome, and the risk of IHD in men. Analyses were carried out in a nested, case-control sample of men selected from a population of 2103 individuals without IHD at baseline among whom 114 developed IHD during a 5-year follow-up period. Incident IHD cases were matched with controls for age, body mass index, smoking habits and alcohol intake. Analyses were performed while excluding (88 cases and 98 controls) and including (103 cases and 99 controls) patients with type 2 diabetes. Among non-diabetic individuals, elevated plasma FFA concentrations (3rd tertile of the distribution) yielded a twofold increase in the risk of IHD (odds ratio [OR] 2.1, P=0.05) compared with lower plasma FFA levels (lowest tertile) after adjusting for non-lipid risk factors. Further adjustment for insulin, triglycerides, apolipoprotein B, HDL cholesterol and small dense LDL attenuated significantly the relationship between plasma FFA concentrations and the risk of IHD. High plasma FFA levels showed no synergism with selected features of the insulin resistance syndrome in determining the risk of IHD. Inclusion of diabetic subjects in the study did not improve FFA independent prognostic value to the risk of IHD. These results suggest that elevated plasma FFA concentrations are associated with an increased risk of IHD. However, a single fasting measurement of plasma FFA levels does not appear to improve our ability to predict IHD onset in men when information on other risk factors is considered.

Effects of free fatty acids on hepatic glycogenolysis and gluconeogenesis in conscious dogs.

The aim of this study was to determine the effect of high levels of free fatty acids (FFA) and/or hyperglycemia on hepatic glycogenolysis and gluconeogenesis. Intralipid was infused peripherally in 18-h-fasted conscious dogs maintained on a pancreatic clamp in the presence (FFA + HG) or absence (FFA + EuG) of hyperglycemia. In the control studies, Intralipid was not infused, and euglycemia (EuG) or hyperglycemia (HG) was maintained. Insulin and glucagon were clamped at basal levels in all four groups. The arterial blood glucose level increased by 50% in the HG and FFA + HG groups. It did not change in the EuG and FFA + EuG groups. Arterial plasma FFA increased by approximately 140% in the FFA + EuG and FFA + HG groups but did not change significantly either in the EuG or HG groups. Arterial glycerol levels increased by approximately 150% in both groups. Overall (3-h) net hepatic glycogenolysis was 196 +/- 26 mg/kg in the EuG group. It decreased by 96 +/- 20, 82 +/- 16, and 177 +/- 22 mg/kg in the HG, FFA + EuG, and FFA + HG groups, respectively. Overall (3-h) hepatic gluconeogenic flux was 128 +/- 22 mg/kg in the EuG group, but it was suppressed by 30 +/- 9 mg/kg in response to hyperglycemia. It was increased by 59 +/- 12 and 56 +/- 10 mg/kg in the FFA + EuG and FFA + HG groups, respectively. In conclusion, an increase in plasma FFA and glycerol significantly inhibited hepatic glycogenolysis and markedly stimulated hepatic gluconeogenesis.

Atherogenesis: Historical Perspective, Biochemical Mechanism, and Current Status

Collation and integration of diverse multidisciplinary research reports into a compatible sequence of biochemical reactions in atherosclerosis defines a primary dysfunctional site residing in the metabolic processing of acetyl Co-A in oxidative phosphorylation. This site, subject to dysfunctional gene expression in the later phase of the mammalian life process, is also subject to evolutionary genetic speciation events defined by orthologous genes. Depressed processing of acetyl Co-A in the citric acid-oxidative phosphorylation cycle can account for increased plasma free fatty acid (FFA), depressed clearing of alimentary lipemia, chylomicrons, increased uploading of plasma protein with lipid (LDL), increased plasma triglycerides and cholesterol, all of which serve as historical biochemical indices of atherosclerosis. Depressed function of this citric acid-oxidative phosphorylation sequence of biochemical reactions embraces multiple sequentially related reaction sites including deficient biosynthesis and transfer of methyl groups, deficient heparin induced lipoprotein lipase, declining rate of albumin biosynthesis, declining generation of high energy phosphate (ATP), increased generation or mobilization of FFA, increased thrombin, depressed activation of plasminogen and increased biosynthesis and turnover of fibrinogen into polymerized fibrin atheroma.

PATHOGENESIS OF TYPE 2 DIABETES: Insulin Resistance

This article addresses the role of insulin resistance in the pathogenesis of type 2 diabetes. The major causes of acquired insulin resistance including aging, pregnancy, lack of physical activity, and obesity are discussed briefly. The role of free fatty acids (FFAs) as a link between obesity and insulin resistance/type 2 diabetes is discussed in detail. Evidence is provided showing that increased plasma FFA levels produce insulin resistance dosage dependently, acutely, and chronically. Mechanisms by which FFA can cause insulin resistance are outlined. Lastly, normalizing plasma FFA levels is proposed as a new approach to reducing insulin resistance and the risk for type 2 diabetes mellitus, and atherosclerotic vascular disease.

Effects of acute changes of plasma free fatty acids on intramyocellular fat content and insulin resistance in healthy subjects.

The reason for the 3- to 4-h delay between a rise in plasma free fatty acid (FFA) levels and the development of insulin resistance remains unknown. In the current study, we have tested the hypothesis that the delay may be caused by the need for plasma FFAs to first enter muscle cells and to be re-esterified there before causing insulin resistance. To this end, we have determined intramyocellular triglyceride (IMCL-TG) content with proton nuclear magnetic resonance ((1)H-NMR) spectroscopy in healthy volunteers before and 4 h after lowering of plasma FFAs (with euglycemic-hyperinsulinemic clamping) or after increasing plasma FFAs (with lipid plus heparin infusions). Increasing plasma FFAs (from 516 to 1,207 micromol/l or from 464 to 1,857 micromol/l, respectively) was associated with acute increases in IMCL-TG from 100 to 109 +/- 5% (P < 0.05) or to 133 +/- 11% (P < 0.01), respectively, and with a significant increase in insulin resistance (P < 0.05 after 3.5 h). Lowering of plasma FFAs from 560 to 41 micromol/l was associated with a tendency for IMCL-TG to decrease (from 100 to 95 +/- 3%). Changes in plasma FFAs correlated linearly with IMCL-TG (r = 0.74, P < 0.003). The demonstration that acute changes in plasma FFAs were accompanied by corresponding changes in IMCL-TG and with the development of insulin resistance, taken together with previous reports of a close correlation between IMCL-TG and insulin resistance, supported the notion that accumulation of IMCL-TG is a step in the development of FFA-induced insulin resistance.

Role of free fatty acids on cardiac autonomic nervous system in noninsulin-dependent diabetic patients: effects of metabolic control.

Decreased heart rate variability (HRV) is a risk factor for cardiovascular mortality. Elevated plasma free fatty acid (FFA) levels decrease HRV in healthy subjects. Thus, we investigated the effect of changes in plasma FFA levels on HRV, in non-insulin-dependent diabetes (NIDDM) patients. Thirty NIDDM patients free from diabetic neuropathy volunteered for a study made by two phases. In study A, changes in HRV along a 10% lipid emulsion infusion + heparin (n = 15) or saline infusion (control study; n = 15) were investigated. In study B, all patients (n = 30) underwent further determination of HRV after 3 months of improved metabolic control achieved by intensified insulin treatment. In study A, lipid emulsion infusion increased plasma FFA (P < 0.001) and catecholamine concentrations (P < 0.005), mean arterial blood pressure (P < 0.005), low frequency/high frequency (LF/HF) ratio (P < 0.001). Delta plasma FFA levels correlated with delta LF/HF ratio (r = 0.57; P < 0.02). Along with saline infusion, metabolic and cardiovascular parameters remained unchanged throughout the test. In study B, improved metabolic control lowered fasting plasma glucose (P < 0.005), FFA (P < 0.001), norepinephrine (P < 0.02), epinephrine (P < 0.04), and glycosylated hemoglobin levels (P < 0.001), mean arterial blood pressure(P < 0.05), and LF/HF ratio (P < 0.001). Again percent decline in plasma FFA correlated with the percent change in LF/HF ratio (r = 0.72; P < 0.001). In a multivariate analysis, percent changes in LF/HF ratio were associated with percent changes in plasma FFA independently of gender and percent changes in body mass index, waist/hip ratio, plasma norepinephrine, epinephrine, glycosylated hemoglobin, and daily insulin therapy. Our study demonstrates that changes in plasma FFA levels may have a parallel effect on cardiac sympathetic/parasympathetic nervous system balance in NIDDM patients.

TIME COURSE OF A 40 HOUR FAST ON PYRUVATE DEHYDROGENASE ACTIVATION AND KINASE EXPRESSION IN HUMAN SKELETAL MUSCLE

Pyruvate dehydrogenase (PDH) activity controls the entry of carbohydrate into the tricarboxylic cycle and is regulated by PDH kinase (PDK) which phosphorylates and inactivates the enzyme and PDH phosphatase which removes phosphate and returns the enzyme to its active from (PDHa). These enzymes are acutely controlled by allosteric regulators and over the longer term by changes in the stable activity of PDK. This study was designed to examine the effects of fasting on the gene expression of the four PDK isozymes (1–4) and resting PDHa activity. Seven healthy adults fasted for 40 hr after a standard meal (25% fat, 60% carbohydrate, 15% protein) with blood and muscles samples taken at 3, 15, and 40 hr post meal. Fasting increased plasma free fatty acid, glycerol and β-hydroxybutyrate and decreased glucose and insulin concentrations. PDHa activity decreased from 0.91 ± 0.14 mmol acetyl-CoA/min/kg wet muscle at 3 hr to 0.55 ± 0.11 and 0.36 ± 0.06 mmol/min/kg wm following 15 and 40 hr of fasting. PDK2 and 4 mRNA were the most abundant isoforms in human skeletal muscle. PDK2 was unaffected by the 40 hr fast. PDK4 was also unaffected after 15 hr, but increased 13-fold after 40 hr of fasting. The abundance of PDK1 and 3 mRNA was ∼200 and 300 fold lower than PDK2, respectively, and not affected by fasting. The results suggest that the decreased PDHa activity following 15 hr of fasting was due to allosteric regulation and independent of gene expression. The decreasing insulin concentration may have reduced the activation of PDH phosphatase and caused the lower PDHa activity. Following 40 hr of fasting, the large increase in PDK4 mRNA expression suggested that a stable increase in PDK activity had occurred, which also contributed to the low PDHa activity in resting human skeletal muscle.

Effects of Free Fatty Acids on Gluconeogenesis and Autoregulation of Glucose Production in Type 2 Diabetes

Effects of endogenously derived free fatty acids (FFAs) on rates of gluconeogenesis (GNG) (determined with 2H2O), glycogenolysis (GL), and endogenous glucose production (EGP) were studied in 18 type 2 diabetic patients and in 7 nondiabetic control subjects under three experimental conditions: 1) during an 8-h fast (from 16-24 h after the last meal), when plasma FFA levels increased slowly; 2) during 4 h (from 16-20 h) of nicotinic acid (NA) administration (fasting plus NA), when plasma FFAs decreased acutely; and 3) during 4 h (from 20-24 h) after discontinuation of NA (FFA rebound), when plasma FFAs increased acutely. During fasting, FFAs increased from 636 to 711 micromol/l in type 2 diabetic patients and from 462 to 573 micromol/l in control subjects (P < 0.04), but GNG did not change in diabetic patients (6.9 vs. 6.5 micromol x kg(-1) x min(-1), P > 0.05) or in control subjects (5.1 vs. 5.4 micromol x kg(-1) x min(-1), P > 0.05). During fasting plus NA, FFAs decreased in diabetic patients and control subjects (from 593 to 193 and from 460 to 162 micromol/l, respectively); GNG decreased (from 6.1 to 4.2 and from 4.7 to 3.5 micromol x kg(-1) x min(-1)), whereas GL decreased in diabetic patients (from 5.3 to 4.4 micromol x kg(-1) x min(-1)) but increased in control subjects (from 5.4 to 7.2 micromol x kg(-1) min(-1)). During the FFA rebound, FFAs increased in diabetic patients and control subjects (from 193 to 1,239 and from 162 to 1,491 micromol/l, respectively); GNG increased (from 4.2 to 5.4 and from 3.4 to 5.3 micromol x kg(-1) x min(-1) respectively), and GL decreased (from 4.4 to 3.4 and from 7.3 to 4.3 micromol x kg(-1) x min(-1), respectively). In summary, during an extended overnight fast, increasing plasma FFA levels stimulated GNG, whereas decreasing FFA levels inhibited GNG in both diabetic and control subjects; 20 h after the last meal, approximately one-third of GNG in both diabetic and control subjects was dependent on FFAs; and autoregulation of EGP by GL in response to decreasing GNG was impaired in diabetic patients.

A Sequence Variation in the Mitochondrial Glycerol-3-Phosphate Dehydrogenase Gene Is Associated with Increased Plasma Glycerol and Free Fatty Acid Concentrations among French Canadians

FAD-dependent glycerol-3-phosphate dehydrogenase (mGPD) enzyme is located in the mitochondrial inner membrane where it catalyzes irreversible oxidation reactions. Type 2 diabetes mellitus (DM) is a multifactorial disorder associated with physiological abnormalities in the glycerol and free fatty acids (FFA) metabolic pathways. In the present study, we have evaluated the association among the mGPD H264R sequence variation and postabsorptive plasma FFA and glycerol concentrations in a sample of French Canadians with and without type 2 DM. A sample of 81 recently diagnosed type 2 DM and 318 nondiabetic, nonobese, normotriglyceridemic French Canadians were screened for the presence of the mGPD H264R genetic variant using a PCR-RFLP-based method. The 318 nondiabetic subjects were free of known type 2 DM covariates (fasting glucose <7.0 mmol/L, body mass index <29 kg/m2, fasting glycerol <2.0 mmol/L and absence of the N288D sequence variation in the glycerol kinase gene, fasting triglyceride <2.5 mmol/L). The association of mGPD H264R sequence variation with plasma FFA and glycerol concentrations was assessed in different regression models. Among non-DM individuals, the R allele (HR and RR genotypes) was associated with increased plasma FFA and glycerol concentrations (P < 0.05). However, the mean plasma FFA and glycerol concentrations were not affected by the H264R genotype in the type 2 DM sample. Overall, mean plasma FFA concentrations in non-DM RR homozygotes reached values that were similar to those achieved in patients with type 2 diabetes (0.87 ± 0.63 vs 0.90 ± 0.48 mmol/L). After controlling for age, gender, body mass index, fasting glucose, and fasting triglyceride concentrations, the relative odds of having fasting plasma FFA levels above the 90th percentile (0.9 mmol/L) in the absence of DM was increased by twofold in H264R heterozygotes (P = 0.04) and fourfold among R264 homozygotes (P = 0.009) compared to noncarriers. In the absence of DM, the mGPD R allele was also associated with higher plasma glycerol concentrations (P < 0.05). Results in non-DM individuals suggest that the mGPD R allele is associated with DM intermediate phenotypes. The absence of a relation between mGPD genotype and DM is in accordance with the view that DM is a complex phenotype in which increased plasma FFA or glycerol concentrations result from metabolic alterations which might obscure the effect of the mGPD polymorphism.

The effect of an increased free fatty acid concentration on thermogenesis and substrate oxidation in obese and lean men

To examine whether a certain increase in plasma free fatty acid (FFA) concentration leads to similar increases in lipid oxidation and energy expenditure in obese and lean men. The study protocol consisted of a 30 min baseline period after which subjects received an i.v. bolus of 1000 IE heparin. Then consecutive infusions of 4.9, 9.8 and 19.6 microl/kg fat-free mass (FFM).min of a lipid heparin mixture were started, each infusion for 30 min. Eleven obese and 13 lean men with a mean body mass index (BMI) of 34.2+/-1.0 (+/-s.e.m.) and 23.9+/-0.5 kg/m(2) and age 46.0+/-1.0 and 42.6+/-1.5 y, respectively. Energy expenditure, respiratory exchange ratio (RER) and carbohydrate and lipid oxidation were continuously measured by indirect calorimetry. At the end of each infusion period, a blood sample was taken for FFA, glycerol, insulin, beta-hydroxybutyrate, noradrenaline and adrenaline determination. At baseline, plasma FFA levels were comparable in both groups. Lipid heparin infusion increased plasma FFA concentration by 301+/-47 micromol/l and 332+/-27 micromol/l in obese and lean men. Energy expenditure increased similarly in obese and lean men (0.34+/-0.08 vs 0.40+/-0.08 kJ/min, NS) during lipid heparin infusion, whereas RER decreased similarly in both groups. Lipid oxidation rates were comparable at baseline and increased similarly in obese and lean men (19+/-5 vs 13+/-4 mg/min, NS). Baseline plasma insulin levels were higher in the obese, but did not change during lipid heparin infusion. Plasma beta-hydroxybutyrate concentrations were similar at baseline, but increased significantly less in the obese during lipid heparin infusion. Baseline noradrenaline and adrenaline concentrations did not differ significantly between groups. During lipid heparin infusion, plasma noradrenaline levels decreased significantly, but plasma adrenaline levels remained unchanged in both groups. A certain increase in plasma FFA concentration leads to similar increases in lipid oxidation and energy expenditure in obese and lean men. The accumulation of fat in obese subjects may therefore be more likely to be due to a defect in adipose tissue lipolysis than a defect in lipid oxidation. International Journal of Obesity (2001) 25, 33-38

Increased production of very-low-density lipoproteins in transgenic mice overexpressing human apolipoprotein A-II and fed with a high-fat diet

We investigated the mechanisms that lead to combined hyperlipidemia in transgenic mice that overexpress human apolipoprotein (apo) A-II (line 11.1). The 11.1 transgenic mice develop pronounced hypertriglyceridemia, and a moderate increase in free fatty acid (FFA) and plasma cholesterol, especially when fed a high-fat/high-cholesterol diet. Post-heparin plasma lipoprotein lipase and hepatic lipase activities (using artificial or natural autologous substrates), the decay of plasma triglycerides with fasting, and the fractional catabolic rate of the radiolabeled VLDL-triglyceride (both fasting and postprandial) were similar in 11.1 transgenic mice and in control mice. In contrast, a 2.5-fold increase in hepatic VLDL-triglyceride production was observed in 11.1 transgenic mice in a period of 2 h in which blood lipolysis was inhibited. This increased synthesis of hepatic VLDL-triglyceride used preformed FFA rather than FFA of de novo hepatic synthesis. The 11.1 transgenic mice also presented reduced epididymal/parametrial white adipose tissue weight (1.5-fold), increased rate of epididymal/parametrial hormone-sensitive lipase-mediated lipolysis (1.2-fold) and an increase in cholesterol and, especially, in triglyceride liver content, suggesting an enhanced mobilization of fat as the source of preformed FFA reaching the liver. Increased plasma FFA was reverted by insulin, demonstrating that 11.1 transgenic mice are not insulin resistant. We conclude that the overexpression of human apoA-II in transgenic mice induces combined hyperlipidemia through an increase in VLDL production. These mice will be useful in the study of molecular mechanisms that regulate the overproduction of VLDL, a situation of major pathophysiological interest since it is the basic mechanism underlying familial combined hyperlipidemia.

Central injections of noradrenaline and adrenaline differentially affect plasma free fatty acid and glucose in conscious pigeons (Columba livia).

The possible involvement of central noradrenergic and/or adrenergic circuits in central mechanisms controlling free fatty acids and glucose levels was investigated in conscious pigeons. The effects of intracerebroventricular injections of noradrenaline (80 nmol) or adrenaline (80 nmol) on plasma free fatty acids and glucose concentrations were examined. The possible role of the autonomic nervous system, of sympathetic terminals and of pituitary hormone release in the metabolic responses induced by intracerebroventricular injections of adrenaline and noradrenaline was investigated by systemic pretreatment with a ganglionic blocker (hexamethonium, 1 mg/100 g), guanethidine (5 mg/100 g), and somatostatin (15 microg/100 g), respectively, 15 min before intracerebroventricular administration of adrenaline, noradrenaline or vehicle. Intracerebroventricular noradrenaline injections strongly increased plasma free fatty acid concentration but evoked no change in blood glucose levels, while adrenaline treatment increased glycemia without affecting free fatty acid levels. Hexamethonium did not block the increase in plasma free fatty acids induced by noradrenaline, while somatostatin pretreatment abolished noradrenaline-induced lipolysis during the experimental period. Adrenaline-induced hyperglycemia was blocked by systemic injections of somatostatin, hexamethonium and guanethidine. The present results suggest that: (1) adrenergic and noradrenergic mechanisms may participate in central control of blood glucose and free fatty acids, respectively, as observed in mammals. (2) noradrenaline-induced lipolysis may be mediated by pituitary mechanisms, and (3) postganglionic sympathetic fibers, possibly innervating the endocrine pancreas, may be involved in adrenaline-induced hyperglycemia.

Elevation of plasma fatty acids by ten-hour intralipid infusion has no effect on basal or glucose-stimulated insulin secretion in normal man

There is controversy over the effect of free fatty acids (FFAs) on insulin secretion. Previous studies have shown opposite effects of short- and long-term exposure to elevated concentrations of FFAs. We studied 8 normal subjects (mean age, 30 years; mean body mass index, 23.4 kg/m2) on 2 occasions. Each had a 10-hour overnight infusion of Intralipid 20% (Pharmacia, Milton Keynes, UK) with simultaneous infusion of heparin (0.4 U/kg body weight/min) or a control infusion of saline (150 mmol/L). Insulin secretion was assessed immediately after completion of the 10-hour infusion by an intravenous glucose tolerance test. Results were analyzed using paired ttests. Intralipid infusion caused an increase in plasma FFAs of more than 9-fold (P < .01), with a simultaneous increase in glycerol (P < .01) and hydroxybutyrate (P < .01). There was no difference in blood glucose concentrations during the infusion or intravenous glucose tolerance test. Similarly, insulin secretion was not significantly different during Intralipid infusion or in the intravenous glucose tolerance test (peak insulin achieved in glucose tolerance test, P = .51; total insulin secretion during intravenous glucose tolerance test, P = .27). In conclusion, after increasing plasma FFA concentrations over 9-fold during a 10-hour infusion of Intralipid and heparin, we found no difference in basal or glucose-stimulated insulin secretion.

The hormonal regulation of premigratory fat deposition and winter fattening in red-winged blackbirds

Glucagon is a highly potent lipolytic agent in birds and a candidate for regulating premigratory and winter fattening. The seasonal role of glucagon in fat metabolism was determined by monitoring plasma glucagon, fatty acids and glucose in two groups of red-winged blackbirds; one group exposed to outside environmental conditions (September to May) and a second group maintained at summer conditions with respect to day length and temperature. The results of this investigation demonstrate significantly lower plasma glucagon (480.1 pg/ml) in birds exposed to outdoor conditions than in birds maintained at summer conditions (734.6 pg/ml) during September/October. The data are consistent with the view that low plasma glucagon in outdoor birds ensures the preservation of fat stores for autumn migration. Lower plasma free fatty acid (FFA) levels (0.35 mEq/l) in outdoor birds (vs. 0.54 mEq/l in indoor birds) in autumn may reflect the rapid transport of FFA to adipose tissue for lipogenesis resulting in a steady increase in body weight from September to January. The sharp decline in plasma FFA in indoor birds from 0.54 mEq/l in September/October to 0.28 mEq/l in January/February may be attributed to a marked decrease in food consumption, rather than a dramatic change in the rate of lipid transport from blood to muscle or adipose tissue. Glucagon injections caused a 600% increase in plasma FFA and a more modest (50%) increase in plasma glucose. This confirms the major role of glucagon in fat mobilization. Its lipolytic effects, however, can vary seasonally by way of down regulation of glucagon receptors. Down regulation of glucagon receptors in adipose tissue and the associated reduced sensitivity of adipocytes to the lipolytic action of glucagon would account for the progressive increase in weight of the birds throughout November/December when plasma glucagon levels were significantly higher (578.9 pg/ml) in outdoor birds as compared to indoor birds (436.9 pg/ml). Lower plasma glucagon levels (405.5 pg/ml) in outdoor birds in January/February (vs. 638.6 pg/ml in indoor birds) may reflect the same physiological conditions prevailing in September/October favoring the preservation of fat stores.

Metabolic control analysis of insulin-stimulated glucose disposal in rat skeletal muscle.

Metabolic control analysis was used to calculate the distributed control of insulin-stimulated skeletal muscle glucose disposal in awake rats. Three separate hyperinsulinemic infusion protocols were performed: 1) protocol I was a euglycemic (approximately 6 mM)-hyperinsulinemic (10 mU. kg(-1). min(-1)) clamp, 2) protocol II was a hyperglycemic ( approximately 11 mM)-hyperinsulinemic (10 mU. kg(-1). min(-1)) clamp, and 3) protocol III was a euglycemic (approximately 6 mM)-hyperinsulinemic (10 mU. kg(-1). min(-1))-lipid/heparin (increased plasma free fatty acid) clamp. [1-13C]glucose was administered in all three protocols for a 3-h period, during which time [1-13C]glucose label incorporation into [1-13)]glycogen, [3-13C]lactate, and [3-13C]alanine was detected in the hindlimb of awake rats via 13C-NMR. Combined steady-state and kinetic data were used to calculate rates of glycogen synthesis and glycolysis. Additionally, glucose 6-phosphate (G-6-P) was measured in the hindlimb muscles with the use of in vivo 31P-NMR during the three infusion protocols. The clamped glucose infusion rates were 31.6 +/- 2.9, 49.7 +/- 1.0, and 24.0 +/- 1.5 mg. kg(-1). min(-1) at 120 min in protocols I-III, respectively. Rates of glycolysis were 62.1 +/- 10.3, 71.6 +/- 11.8, and 19.5 +/- 3.6 nmol. g(-1). min(-1) and rates of glycogen synthesis were 125 +/- 15, 224 +/- 23, and 104 +/- 17 nmol. g(-1). min(-1) in protocols I-III, respectively. Insulin-stimulated G-6-P concentrations were 217 +/- 8, 265 +/- 12, and 251 +/- 9 nmol/g in protocols I-III, respectively. A top-down approach to metabolic control analysis was used to calculate the distributed control among glucose transport/phosphorylation [GLUT-4/hexokinase (HK)], glycogen synthesis, and glycolysis from the metabolic flux and G-6-P data. The calculated values for the control coefficients (C) of these three metabolic steps (C(J)(GLUT-4/HK) = 0.55 +/- 0.10, C(J)(glycogen syn) = 0.30 +/- 0.06, and C(J)(glycolysis) = 0.15 +/- 0.02; where J is glucose disposal flux, and glycogen syn is glycogen synthesis) indicate that there is shared control of glucose disposal and that glucose transport/phosphorylation is responsible for the majority of control of insulin-stimulated glucose disposal in skeletal muscle.

Free fatty acid-induced insulin resistance is associated with activation of protein kinase C theta and alterations in the insulin signaling cascade.

To examine the mechanism by which free fatty acids (FFAs) induce insulin resistance in vivo, awake chronically catheterized rats underwent a hyperinsulinemic-euglycemic clamp with or without a 5-h preinfusion of lipid/heparin to raise plasma FFA concentrations. Increased plasma FFAs resulted in insulin resistance as reflected by a approximately 35% reduction in the glucose infusion rate (P < 0.05 vs. control). The insulin resistance was associated with a 40-50% reduction in 13C nuclear magnetic resonance (NMR)-determined rates of muscle glycogen synthesis (P < 0.01 vs. control) and muscle glucose oxidation (P < 0.01 vs. control), which in turn could be attributed to a approximately 25% reduction in glucose transport activity as assessed by 2-[1,2-3H]deoxyglucose uptake in vivo (P < 0.05 vs. control). This lipid-induced decrease in insulin-stimulated muscle glucose metabolism was associated with 1) a approximately 50% reduction in insulin-stimulated insulin receptor substrate (IRS)-1-associated phosphatidylinositol (PI) 3-kinase activity (P < 0.05 vs. control), 2) a blunting in insulin-stimulated IRS-1 tyrosine phosphorylation (P < 0.05, lipid-infused versus glycerol-infused), and 3) a four-fold increase in membrane-bound, or active, protein kinase C (PKC) theta (P < 0.05 vs. control). We conclude that acute elevations of plasma FFA levels for 5 h induce skeletal muscle insulin resistance in vivo via a reduction in insulin-stimulated muscle glycogen synthesis and glucose oxidation that can be attributed to reduced glucose transport activity. These changes are associated with abnormalities in the insulin signaling cascade and may be mediated by FFA activation of PKC theta.