Utilization Of Free Fatty Acids Research Articles

Relationships of aerobic capacity and percent body fat with plasma free fatty acid following walking

We investigated relationships of peak V̇o2 and percent body fat with postexercise plasma free fatty acid (FFA) and glycerol concentrations in 14 men using multiple-regression techniques. During 1 h of walking (36% of peak V̇o2), no significant differences in plasma-FFA response were attributed to either peak V̇o2 or percent body fat. However, individuals with higher peak V̇o2s tended to have greater elevations in plasma-glycerol concentration during exercise (p = 0.074). They also had greater peak FFA concentrations and FFA · glycerol−1-molar ratios immediately after exercise and faster subsequent clearing of excess FFA from the blood (p < 0.05). Percent fat was not related to postexercise plasma glycerol, FFA, FFA · glycerol−1 responses. Differing postexercise FFA responses, as related to peak V̇o2, were due, not to varying rates of lipolysis but rather to different rates of FFA mobilization and utilization.

Marathon fatigue: the role of plasma fatty acids, muscle glycogen and blood glucose.

The role of carbohydrate depletion in marathon fatigue was examined in 6 marathon runs. Four of the runs were potentially 'fast-time' marathons and culminated in fatigue. The utilization of carbohydrate, lipid and protein, and plasma concentrations of free fatty acids (FFA), glucose and lactate were measured at intervals throughout the runs. The contribution from protein to energy output was low (1-2%). The utilization of lipid was dependent upon plasma concentrations of FFA, which rose throughout the run. The utilization of carbohydrate mirrored that of FFA and thus fell throughout the run. Fatigue was characterized by a drop in running speed, a drop in carbohydrate utilization, an unchanging FFA utilization and a fall in blood glucose. The fall in blood glucose was not seen in the non-fatigued runners. These results are consistent with carbohydrate depletion being the cause of fatigue. The implications of these data are that lipid is the preferred fuel, but is rate-limiting, and that carbohydrate depletion, even though it causes fatigue, ensures an optimal-time marathon.

Stimulants and Athletic Performance (Part 1 of 2): Amphetamines and Caffeine.

In brief: Some athletes use amphetamines and caffeine to fight fatigue, but the effects of these substances on athletic performance are unclear. Both can be harmful. Amphetamines affect the central nervous system (CNS) and can cause tremulousness, anxiety, insomnia, and fever. Caffeine can increase free fatty acid utilization, mask fatigue through CNS stimulation, and increase the force of skeletal muscle contraction. The International Olympic Committee has banned the use of amphetamines altogether, and has banned caffeine when its values are greater than 15 μ g· ml(-1) in a urine test.

Effects of glucose-insulin-potassium on intestinal hemodynamics and substrate utilization during endotoxemia.

This study examined the effects of endotoxin on small intestinal hemodynamics and metabolism with and without an infusion of glucose-insulin-potassium (GIK). Glucose uptake and lactate release were determined by arteriovenous differences across a segment of canine ileum, which was vascularly isolated in vivo, and by the direct measurement of intestinal blood flow. Free fatty acid (FFA) utilization by intestinal tissue was assessed by the constant infusion of albumin-bound [14C]palmitate and [3H]oleate. Endotoxemic dogs showed a sustained reduction of mean arterial blood pressure (MABP) and intestinal blood flow. In contrast, endotoxemic dogs infused with GIK demonstrated a decreased intestinal vascular resistance and an increased blood flow (two-fold), whereas MABP was transiently improved. Intestinal glucose uptake was not different from control values in endotoxemic animals; however, a sixfold increase was seen in shocked dogs treated with GIK. The endotoxin-induced increase in the plasma lactate concentration and intestinal lactate release was similar between dogs infused with saline or GIK. After endotoxin, the arterial FFA concentration remained unchanged and whole-body FFA turnover was decreased. FFA uptake by the gut was reduced, but FFA oxidation was not altered. Similar changes in FFA metabolism were seen in endotoxemic animals infused with GIK. The metabolic pattern after endotoxin suggests an elevated rate of aerobic glycolysis by the gut that increases the availability of lactate to the liver. Compared with saline-infused endotoxemic animals, GIK produced an elevation in glucose uptake without a further increase in lactate output, suggesting an increased storage of glucose by this tissue.

Muscle triglyceride utilization during exercise: effect of training.

The respiratory exchange ratio (RER) is lower during exercise of the same intensity in the trained compared with the untrained state, even though plasma free fatty acids (FFA) and glycerol levels are lower, suggesting reduced availability of plasma FFA. In this context, we evaluated the possibility that lipolysis of muscle triglycerides might be higher in the trained state. Nine adult male subjects performed a prolonged bout of exercise of the same absolute intensity before and after adapting to a strenuous 12-wk program of endurance exercise. The exercise test required 64% of maximum O2 uptake before training. Plasma FFA and glycerol concentrations and RER during the exercise test were lower in the trained than in the untrained state. The proportion of the caloric expenditure derived from fat, calculated from the RER, during the exercise test increased from 35% before training to 57% after training. Muscle glycogen utilization was 41% lower, whereas the decrease in quadriceps muscle triglyceride concentration was roughly twice as great (12.7 +/- 5.5 vs. 26.1 +/- 9.3 mmol/kg dry wt, P less than 0.001) in the trained state. These results suggest that the greater utilization of FFA in the trained state is fueled by increased lipolysis of muscle triglyceride.

Reduced insulin secretion after short-term food deprivation in rats plays a key role in the adaptive interaction of glucose and free fatty acid utilization

The present study was undertaken to investigate the effects of short-term fasting periods up to 24 hr on insulin secretory responses of the B-cell to glucose and the consequences for FFA and glucose availability in the circulation. Conscious male rats provided with permanently implanted heart catheters received glucose infusions at midday, lasting for 20 min, in the nearly ad lib condition (i.e., 6 hr of non feeding during daytime) and after extending the fasting period to 12, 18 and 24 hr. Basal preinfusion insulin levels and insulin responses to glucose decreased gradually during these fasting periods. Basal blood glucose dropped only significantly after 24 hr of fasting whereas basal FFA levels increased gradually from 6 hr of fasting onwards. After prolonged fasting insulin released during glucose infusion became more effective in suppressing plasma FFA levels. While our data suggest that the sensitivity to the antilipolytic action of insulin is increased, the decreased responsiveness of the B-cell after moderate fasting periods may result in a drop of basal insulin levels. This facilitates the switch from glucose to FFA metabolism for most tissues already, when the first meals are missed. The results suggest that this physiological process is important to save the glycogen stores as long as possible as fuel for the central nervous system, and also to support basic energy requiring processes adequately.

Relation between myocardial substrate utilization, oxygen consumption and regional oxygen balance in the dog heartin vivo

The interaction between myocardial function, oxygen consumption and energy production was examined in the left ventricular myocardium during various physiological conditions. Myocardial function was measured by both LV dP/dTmax and by local contractile tension. Coronary blood flow was measured from the coronary sinus; regional coronary blood supply was recorded using a thermistor placed on the epicardial surface. Intracellular oxygen balance was estimated using NADH fluorescence. Myocardial oxygen consumption and utilization of glucose, pyruvate, lactate and free fatty acids were calculated from their concentrations in the arterial and coronary sinus blood. The effects of tachycardia at 180 and 240 bpm, noradrenaline infusion (25 micrograms kg-1 min-1), and increased coronary blood flow caused by hypopneic respiration were examined. During pacing, contractile force, coronary flow and NADH fluorescence increased. At 240 bpm, the lactate/pyruvate ratio increased from 5.98 +/- 0.92 to 8.76 +/- 1.41 and NADH fluorescence increased from 50 to 71.7 +/- 3.73 (as compared to control), indicating impairment of myocardial oxygenation. Hypopneic respiration produced a marked elevation of coronary blood flow. Both noradrenaline infusion and hypopnea produced a decrease in both NADH fluorescence and the lactate/pyruvate ratio. No significant difference was found between the FORCE/ATP, FORCE/MVO2 and ATP/MVO2 ratios during pacing and noradrenaline. However, during hypopnea, the amount of ATP apparently formed (as calculated by substrate utilization assuming the formation of 3 ATP molecules per oxygen) was disproportionately greater than contractile force and oxygen consumption. It is suggested that this discrepancy may be due to the uncoupling of oxidative phosphorylation.

Meal-induced increases in parasympathetic and sympathetic activity elicit simultaneous rises in plasma insulin and free fatty acids

The aim of this study was to investigate sympathetic and parasympathetic activity during food intake in rats by measuring plasma norepinephrine (NE), epinephrine (E), insulin, free fatty acids (FFA), glycerol and blood glucose. Therefore male Wistar rats were implanted with silastic jugular vein cannulas so that blood could be withdrawn from freely moving animals. Blood samples were frequently taken before, during and after intake of a test meal. The effects of the blood sampling procedure on above mentioned blood compounds was also determined. Insulin increased considerably within the first minutes of food intake before a rise in blood glucose which is mediated by a vagal mechanism. An increase in plasma NE could be observed during the whole period of ingestive behavior whereas E increased considerably only in the first minute. Plasma FFA level was augmented sharply during food intake and a few minutes afterwards, whereas plasma glycerol levels did not changes. After termination of food intake sympathetic activation disappeared and both plasma FFA and glycerol levels declined significantly below levels as observed in control rats. In contrast, plasma insulin and blood glucose increased considerably. It is concluded that food intake in rats causes a simultaneous increase in both sympathetic and parasympathetic activity and because of that a rise in plasma FFA and insulin respectively. It is argued that augmented sympathetic activity elicits a rise in plasma FFA levels, which is not mediated by increased lipolysis but by either decreased FFA utilization or reduced reesterification.

Influence of Age, Dietary Cholic Acid, and Calcium Levels on Performance, Utilization of Free Fatty Acids, and Bone Mineralization in Broilers

The effects of age on the utilization of dietary palmitic or a 50/50 mixture of palmitic and oleic acid at the 8% inclusion level in the absence or presence of .2% cholic acid and also in the presence of low (.8%) or high (1.2%) calcium were investigated using broiler chicks from 1 to 56 days of age.Significant interactions (P<.01) were observed between the type of fatty acid supplemented and the presence or absence of cholic acid on weight gain and feed efficiency. Supplementing diets with a mixture of equal weights of palmitic and oleic acid, reduced feed intake relative to control diets and diets supplemented with palmitic acid alone. There was an interaction between the age of the bird and the type of fatty acid supplemented on fat retention and metabolizable energy (ME) of diets (P<.01). There was also a significant interaction between the type of fatty acid supplemented and the addition of cholic acid on fat retention and ME of diets.While cholic acid reduced soap formation during the process of digestion (P<.05), increasing dietary calcium level increased the proportion of the digesta fat that was present as soap (P<.01). The proportion of digesta and excreta fat, present as soap, depended on the type of fatty acid supplemented. The addition of free fatty acids to broiler diets resulted in a decrease in bone ash and bone calcium content relative to those birds fed the control diet. It is concluded that the ability of broilers to utilize dietary free fatty acids depends on the age at which they are fed, although in all cases supplemental cholic acid enhances fatty acid utilization.

Function and regulation of hepatic and intestinal fatty acid binding proteins

Two structurally different fatty acid binding proteins (FABP) have been isolated from rat liver and small intestinal epithelium. hFABP is a 14 184 Da protein found in abundance in both liver and small intestine, whereas gFABP (15 063 Da) is abundantly present only in small intestine. This review discusses studies which have provided insight into the physiological functions of these proteins. These include analyses of endogenous and exogenous ligand binding to FABP in vitro; examination of the modulating effect of FABP preparations on enzyme activities in vitro; exploration of relationships between alterations in cytosolic FABP content in response to hormonal, pharmacological, and dietary manipulations and changes in the rates of cellular fatty acid uptake and utilization; and studies of hFABP turnover and the mechanisms of FABP regulation. These experiments provide compelling evidence for a broad role of the FABPs in the transport, utilization and cellular economy of free fatty acids in the liver and small intestine, and also in protecting several aspects of cellular function against the modulatory effects of fatty acids, fatty acyl-CoA esters, and other ligands. Studies of FABP regulation also suggest a role in long-term rather than short-term modulation .of hepatic fatty acid metabolism and indicate that hFABP and gFABP may perform different functions in the small intestine.

1793 FATTY ACID BINDING TO LUNG CYTOSOLIC PROTEINS

In tissues with a high rate of fatty acid utilization, intra-cellular free fatty acids are bound to a low molecular weight (12000 daltons) fatty acid binding protein (FABP). By differential binding of fatty acids, FABP may compartmentalize different fatty acid species and regulate cellular free fatty acid utilization. To determine if lung contains cytosolic proteins that bind free fatty acids, we prepared a 100,000xg supernatant of whole rabbit lung and incubated it with radiolabeled palmitate. After gel filtration on a calibrated Sephadex G-75 column, two peaks of radioactivity were noted. The first eluted in the void volume and probably represents high molecular weight aggregates of fatty acids. A second peak eluted at the volume calibrated to be approximately 12000 daltons. Similar studies on supernatants prepared from pure adult type II pneumocytes showed a similar elution profile. No peak in this region was observed following incubation of the cytosol with radiolabeled phospha-tidylcholine. Incubation with equimolar concentrations of radiolabeled oleate produced a smaller peak than observed with palmitate. These studies suggest that whole lung and pure type II cells contain an intracellular binding protein for fatty acids which may be similar to FABP. (Supported by a grant from the March of Dimes--Birth Defects Foundation 1–923).

Increased regional utilization of free fatty acids in liver cirrhosis

Increased regional utilization of free fatty acids in liver cirrhosis

Lipid metabolism in nephrotic rats induced by daunomycin injection

Lipid metabolism in the blood and liver of rats was investigated to clarify the mechanism of dyslipoproteinemia in the nephrotic syndrome. The nephrotic syndrome was induced in rats by a single injection of daunomycin. The serum total cholesterol, triglyceride, and phospholipid levels in nephrotic rats 14 days after the injection were increased 3.1-fold, 2-fold, and 2.7-fold, respectively, over the control values. The cholesterol, triglyceride, and phospholipid contents of high-density lipoprotein (HDL), low-density lipoprotein (LDL), and very-low-density lipoprotein (VLDL) were also increased, increase in VLDL lipids being the greatest. The serum HDL cholesterol level decreased gradually after day 14, returning to the normal level on day 37, whereas the LDL and VLDL cholesterol levels continued to increase until day 37. The mechanism of dyslipoproteinemia in the nephrotic syndrome was examined by comparing lipid metabolism in the liver of nephrotic rats induced by daunomycin with that of rats fed on high-cholesterol diet. The contents of total lipids, triglyceride, and cholesterol ester in the liver were significantly less in nephrotic rats than in controls. The contents of total lipids and cholesterol ester in the liver were much higher in rats fed on high-cholesterol diet than in controls. The contents of total lipids, triglyceride, cholesterol ester, and phospholipid in the liver were significantly lower in nephrotic rats fed on high-cholesterol diet than in normal rats fed on high-cholesterol diet. [1- 14C]Acetate incorporation into liver lipids was higher in nephrotic rats and lower in rats fed on high-cholesterol diet than in controls. [1- 14C]Palmitate incorporation into liver lipids was higher in nephrotic rats and rats fed on high-cholesterol diet than in controls. These data suggest that discharge of lipids, de novo synthesis of lipids, and utilization of preformed free fatty acids were all stimulated in the liver of rats with the nephrotic syndrome induced by daunomycin. However, although the utilization of preformed free fatty acids was stimulated, de novo synthesis of lipids was suppressed in the liver of rats fed on high-cholesterol diet.

Myocardial exchange of metabolites after nitroglycerin in patients with coronary artery disease

We studied the effects of sublingual nitroglycerin (dose range 0.5–1.0 mg) on cardiac metabolism in the resting state in 12 patients with chronic coronary artery disease. Seven patients with chronic coronary artery disease served as a control group. No patient from either of the groups experienced angina pectoris during the study. Reduced heart work after nitroglycerin was evident from a 34% decrease of oxygen uptake ( P < 0.001) and a 35% fall in coronary sinus blood flow ( P < 0.01). Nitroglycerin decreased lactate extraction by 30% ( P < 0.05), lactate uptake by 58% ( P < 0.025); glucose uptake by 47% ( P < 0.01) while net exchange of free fatty acids did not change. The aorto-coronary sinus difference of plasma citrate became increasingly negative (from −4 ± 3 μmol/l to −8 ± 2 μmol/l) ( P < 0.02) after nitroglycerin. In the control group coronary sinus blood flow and myocardial exchange of oxygen and substrates remained unchanged. Our results suggest a relatively increased myocardial utilization of free fatty acids compared with that of carbohydrates after nitroglycerin. This may in part be explained as an inhibition of glycolysis due to citrate accumulation. The study indicates that myocardial lipid-carbohydrate metabolism is disturbed in chronic coronary artery disease even in patients without clinical evidence of ischaemia in resting state and that nitroglycerin reverses this condition towards the metabolism of the normal heart.

Changes in myocardial substrate utilisation and protection of ischemic stressed myocardium by oxfenicine [(S)-4-hydroxyphenylglycine

Potential protective effects of oxfenicine [(S)-4-hydoxyphenylglycine] in ischemic stressed canine myocardium have been studied. This compound is characterized as a drug leading to metabolic inhibition of free fatty acid (FFA) metabolism. The drug (0.06 mmol . kg-1 body weight) caused no changes in hemodynamics or energy demand (Et) but depressed myocardial oxygen consumption (MVO2) by 11% (P less than 0.02). Significant changes in FFA and lactate metabolism were observed: lactate extraction (EX) increased from 22.5-37.1 mumol/Min, extraction ratio (EXR) from 16.5-30% and oxygen extraction ratio (OER) from 24.8-38%; EX of FFA decreased from 6900-5000 nmol/min, EXR from 48.2-31.4% and OER from 59.7-46.6%. Arterial concentrations of FFA and lactate remained unchanged. EX, EXR and OER of glucose were not affected under basic conditions. In the same collective, repeated ischemia (3 min) was produced by proximal occlusion of the left anterior descending artery (LAD). The efficiency of the drug was examined by (a) the amounts of ischemia metabolites released in the early reperfusion and (b) quantification of O2-debt and O2-repayment in the occlusion- and reperfusion periods. Compared to control occlusions, premedication led to a reduced O2-debt (P less than 0.01) combined with a reduced amount of oxygen additionally taken up in the early reperfusion (P less than 0.05). Furthermore, release of potassium increased (+7.1%; P less than 0.05); release of lactate (-32%, P less than 0.001) and inorganic phosphate (-34%, P less than 0.01) decreased. These data give support to the concept that a pharmacologically induced shift of cardiac metabolism with reduction of FFA utilisation may be favourable in circumstances with limited oxygen supply.

Fat deposition in Hereford and Friesian steers: 3. Growth efficiency and fat mobilization

SUMMARYFood utilization in relation to growth of body components, and fat mobilization and its hormonal control in vivo, were examined in 15 Hereford and 15 Friesian steers which were slaughtered at 20 months of age. Changes in body composition between 6 and 20 months were calculated from the body composition of these animals and from an additional four and two steers from each breed slaughtered at 6 and 13 months of age, respectively.The Friesians consumed more food overall (14%) and grew more rapidly (14%), but their intake in relation to metabolic body weight was not different from that of the Herefords. Although the Friesians deposited more protein in relation to lipid there was no breed difference in food conversion ratio, and maintenance requirement relative to empty-body weight0·75 was estimated to be 7% greater in the Friesians than the Herefords. Friesians therefore had a lower efficiency of conversion of food energy to body energy. It is speculated that the higher maintenance requirement of the Friesians was due to a faster rate of protein deposition and a higher proportion of visceral organs with an associated higher rate of protein turnover.Changes in plasma concentrations of free fatty acids (FFA), insulin, growth hormone (GH), adrenaline and noradrenaline were examined in response to fasting at 12 and 20 months of age. Inaddition plasma concentrations of glucose, thyroxine (T4) and triiodothyronine (T3) were measured at 20 months of age.At both ages, FFA concentration increased almost linearly with duration of fasting and was not different between breeds. It was therefore unrelated to fat partitioning and a poor index of breed differences in metabolic and body type. Within breeds, the rate at which FFA concentration increased during fasting was correlated with estimated maintenance requirement (r = 0·53). This suggests a different relationship between FFA utilization and maintenance requirement in the two breeds.During fasting at 12 months of age, Friesians had higher concentrations of plasma GH and noradrenaline. At 20 months of age they had higher concentiations of glucose, insulin and catecholamines. There was no obvious hormonal explanation for the observed differences in body composition or growth efficiency. Correlations between indices of fat partitioning and maintenance requirement were low, suggesting no direct link between the two traits.

Assessment of regional myocardial ischemia by positron-emission computed tomography

Positron-emission computed tomography (PCT) is a new means of studying regional myocardial metabolism. This new device permits quantitative, cross-sectional imaging of the tissue concentrations of positron-emitting tracers of blood flow and metabolism in the myocardium. To examine the potential value of PCT for evaluating regional alterations in myocardial metabolism, acute myocardial ischemia was induced by rapid atrial pacing in open-chest dogs with partial coronary stenoses. Regional myocardial glucose uptake and utilization of free fatty acids were examined with the glucose analog F-18 2-fluoro-2-deoxyglucose (FDG) and C-11-labeled palmitic acid. Myocardial blood flow was evaluated with N-13 ammonia. In the ischemic segment, uptake of C-11 paimitic acid was reduced in proportion to blood flow and its rate of clearance as an index of beta oxidation was delayed. There was a relative or absolute increase in FDG uptake (depending on the uptake of FDG in the normal myocardium). Similar observations were made in patients with ischemic heart disease and anginal symptoms at the time of study. The observed alterations in the regional distribution of positron-emitting tracers of metabolic substrates in ischemic myocardium are in agreement with previously reported animal experimental studies in which a fall in free fatty acid utilization associated with an increase in glycolytic flux was observed. These studies indicate that metabolic alterations associated with acute myocardial ischemia observed previously in destructive animal experiments do indeed occur in humans and can now be demonstrated noninvasively in humans by PCT.

Utilization of long-chain free fatty acids in white and red muscle of rats

Utilization of long-chain fatty acids was studied in white and red muscle slices prepared from quadriceps femoris muscle of rats, using radioactive palmitate and linoleate as precursors. After 2 h incubation, red muscle oxidized more palmitate to CO 2 (433%) and converted more of it to triacylglycerol (142%) and phospholipid (173%) compared with white muscle. The metabolic fate of palmitate incorporated into skeletal muscle fibers varied with muscle fiber types. Namely, in white muscle, 22% of incorporated palmitate was oxidized and 34% was converted to triacylglycerol and 43% to phospholipid. On the other hand, the percent distribution of radioactivity among CO 2, triacylglycerol and phospholipid in red muscle was 44%, 22% and 34%, respectively. Percent distribution of the radioactivity in phospholipids was similar in white and red muscle. Predominant labeling with radioactive palmitate was found in phosphatidylcholine (78–81%). Incubations with linoleate decreased the rates of oxidation and esterification of the fatty acid in both types of muscle compared with those with palmitate: CO 2 (−30 to −35%); triacylglycerol (−62 to −82%); and phospholipid (−58 to 67%). The labeling profiles of radioactivity in muscle phospholipids with radioactive linoleate differed from those with palmitate. Namely, more linoleate was incorporated into phosphatidylethanolamine, phosphatidylinositol, phosphatidylserine, cardiolipin and phosphatidylglycerol compared with palmitate. On the contrary, palmitate had faster rates of incorporation into phosphatidylcholine and sphingomyelin than linoleate. This study showed that (a) utilization of fatty acids depended on muscle fiber types and (b) each fatty acid was oxidized to CO 2 and esterified to the lipid esters to a different extent by skeletal muscles.

Oxidation of plasma free fatty acids in nonshivering thermogenesis of rats treated chronically with norepinephrine and thyroxine.

In rats treated chronically with norepinephrine and thyroxine, enhanced nonshivering thermogenesis was observed, with a concomitant increase in the utilization of plasma free fatty acids (FFA). The increased utilization of plasma FFA was characterized by a more preferential increment in the oxidation of FFA in tissues rather than that in the uptake of FFA by tissues. These biochemical findings were accompanied by an increased mitochondrial mass in red fibers of skeletal muscle. Both biochemical and morphological changes of a similar nature were found in cold-acclimated rats.

Free fatty acid utilization by skeletal muscle after endotoxin administration.

The effect of endotoxin administration on free fatty acid (FFA) utilization by skeletal muscle was investigated. Albumin bound [1-14C]palmitate was continuously infused into anesthetized dogs. Blood samples from the carotid artery and profunda femoris veins were obtained and blood flow through the thigh muscles was determined. After endotoxin, skeletal muscle blood flow decreased by 29%, reflecting the average decrease in cardiac output. Arterial FFA concentration in endotoxin-treated animals was significantly reduced relative to saline-treated animals. Whole-animal FFA turnover decreased up to 37% after endotoxin. FFA uptake was linearly correlated with arterial FFA concentration both preceding and following endotoxin and the slopes of the regression lines were identical. FFA uptake by skeletal muscle was significantly reduced during the early postendotoxin time period. Skeletal muscle FFA oxidation after endotoxin also tended to decrease. It is concluded that the changes in skeletal muscle FFA metabolism are most likely due to decreased arterial FFA levels after endotoxin rather than a direct effect of endotoxin on skeletal muscle.