| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
|
|
|
|||||||
|
|||||||||
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
1Faculty of Applied Health Sciences, Brock University, St. Catharines, Ontario; and 2Department of Medicine, McMaster University, Hamilton, Ontario, Canada
Submitted 13 June 2007 ; accepted in final form 10 October 2007
 |
ABSTRACT |
|---|
 TOP ABSTRACT METHODSRESULTSDISCUSSIONGRANTSREFERENCES |
|---|
300 g saturated (SFA) or n-6 polyunsaturated fatty acid (PUFA) fat over the course of 5 h. Following this, participants cycled at 65% of their maximum oxygen uptake for 15 min. Muscle biopsies were taken before and following fat loading and at 1 min exercise. Plasma free fatty acids increased from 0.15 ± 0.07 to 0.54 ± 0.19 mM over 5 h with SFA and from 0.11 ± 0.04 to 0.35 ± 0.13 mM with n-6 PUFA and were significantly lower throughout the n-6 PUFA trial. PDHa activity was unchanged following fat loading but increased at the onset of exercise in the SFA trial, from 1.18 ± 0.27 to 2.16 ± 0.37 mmol·min–1·kg wet wt–1. This effect was negated in the n-6 PUFA trial (1.04 ± 0.20 to 1.28 ± 0.36 mmol·min–1·kg wet wt–1). PDH kinase was unchanged in both trials, suggesting that the attenuation of PDHa activity with n-6 PUFA was a result of changes in the concentrations of intramitochondrial effectors, potentially intramitochondrial NADH or Ca2+. Our findings suggest that attenuated PDHa activity contributes to the preferential oxidation of n-6 PUFA during moderate-intensity exercise. active fraction of pyruvate dehydrogenase; carbohydrate oxidation; moderate-intensity exercise; saturated fatty acids; polyunsaturated fatty acids; n-6 fatty acids
Different types of dietary fat also seem to have an effect on fuel oxidation during exercise. At moderate intensities, following a single fat load, an increase in fat oxidation is seen throughout exercise with primarily n-6 PUFA compared with both an SFA load and control (46). In this study there was also a decrease in CHO oxidation with PUFA compared with SFA. While it is evident that different types of fat behave differently with respect to oxidation, the mechanism(s) have not yet been elucidated.
Pyruvate dehydrogenase (PDH) is a rate-limiting, multienzyme complex responsible for the irreversible decarboxylation of pyruvate to produce acetyl coenzyme A (acetyl CoA). Acetyl CoA can then be oxidized in the tricarboxylic acid (TCA) cycle or used for fatty acid (in adipose tissue and liver) or cholesterol (in liver) synthesis. In skeletal muscle, the PDH complex occupies a pivotal role in fuel selection and regulation of CHO oxidation. During times of high CHO availability, PDH activation is increased, increasing CHO flux into the TCA cycle. When CHO availability is low, PDH activity decreases, thus sparing CHO for use in other areas of the body (35). Both acute and chronic (or adaptive) regulation of the PDH complex occurs via two intrinsic regulatory enzymes, a family of PDH kinases (PDK1–4; inhibitory) and a pair of PDH phosphatases (PDP1 and -2; stimulatory) (14, 40). Of the four isoforms of PDK, PDK2 and PDK4 are the most abundant in skeletal muscle. The PDKs phosphorylate up to three serine residues on the E1
subunit of the PDH complex, and although site 1 is sufficient for complete inactivation of the complex, increased occupancy of sites 2 and 3 renders the complex less sensitive to activation by PDP (40). PDK4 has been shown to be most responsive to alterations in diet (12, 27, 28) and has a higher affinity for site 2 as a substrate than PDK2 (40).
Research has demonstrated that only 24 h of a high-fat/low-CHO diet will increase PDK activity and consequently decrease PDH activity in human skeletal muscle (27). However, it is not yet known whether this adaptive increase in PDK activity would be observed in a shorter time period. In addition, recent studies have suggested that the type of dietary fat may influence the partitioning of fat between oxidation and storage (30, 46) and may specifically alter the magnitude of adaptive changes in the PDH complex (43).
The purpose of the present study, therefore, was to determine the metabolic effects of 5 h of high-fat feeding, rich in either SFA or n-6 PUFA fat, at rest and at the onset of moderate-intensity exercise. Specifically, the effects of short-term oral loading of differential fats on PDK activity and the activation of the PDH complex (PDHa activity) in human skeletal muscle were examined. We hypothesized that a 5-h fat load would be long enough to elicit a significant increase in PDK activity. This would result in attenuated PDHa activity at rest and at the onset of exercise with PUFA but not SFA (due to increased fat oxidation with n-6 PUFA).
|
METHODS |
|---|
|
TOPABSTRACTMETHODSRESULTSDISCUSSIONGRANTSREFERENCES |
|---|
Study design. Before beginning the experimental trials, participants recorded their diets for 3 days, including two week days and one weekend day. They also recorded their diet and all physical activity for 3 days leading up to the first trial day. Participants were asked to follow this exact dietary and exercise regime for 3 days before each experimental trial to reduce variability in results based on prior dietary consumption.
The participants reported to the laboratory on four occasions. Participants arrived on the first day 2–4 h following a normal meal and performed an incremental ride to exhaustion on a load-adjusted cycle ergometer (Lode Excalibur, Groningen, The Netherlands) to determine maximal oxygen uptake (
O2 max). On the second visit, subjects arrived at the same time of day as the first visit, 2–4 h after the same breakfast meal. This visit was at least 3 days after the first visit, to allow recovery from the O2 max test. At this time, they performed a 15-min practice trial on the cycle ergometer to determine the workload that would elicit 65% of their O2 max. Gas measurements were the only analyses performed during the first and second visits.
A workload of 65% O2 max was chosen to increase the subjects' reliance on fat oxidation as previously described (48), as well as to enable us to compare the results of the present study with those of previous studies using similar workloads (13, 23, 24). The level of resistance determined during the practice trial was used for both experimental trials. The workload was consistent between trials (oxygen consumption: SFA = 68.7 ± 0.4% of the O2 max; PUFA = 68.0 ± 0.4% of O2 max).
On the third and fourth visits, participants arrived at the laboratory following a 12-h fast for the two randomized experimental trials. The participants were given a breakfast low in fat (whole wheat bagel with cream cheese). The breakfast meal contained 392 calories and was composed of 61% CHO, 25% fat [14% SFA; 7% monounsaturated fatty acid (MUFA); 2% PUFA; 2% other fat], and 14% protein. The purpose of the breakfast meal was to suppress adipose tissue lipolysis and lower plasma triglyceride (TG) and free fatty acid (FFA) concentrations, thereby reducing the dilution of the plasma FFA with endogenous fatty acids (9). This would enhance the likelihood that the composition of the plasma fatty acids would reflect the composition of the fat consumed during the fat loading.
Two hours following the breakfast meal, a resting blood sample (5 ml) was drawn into a heparinized tube from the antecubital vein. Two resting muscle biopsies were taken from the vastus lateralis muscle under local anesthetic as previously described (3). One sample was extracted fresh for mitochondria that were subsequently used to measure PDK activity and the other was frozen immediately in liquid nitrogen for analysis of PDHa activity and metabolites. Participants then consumed the first experimental meal (either SFA or PUFA) 5 h before exercise (time = 0 min) (see Experimental meals). Experimental meals were consumed at 30-min intervals for 300 min (total of 10 meals = 850 ml). At 300 min (5 h after first experimental meal), subjects cycled at 65% O2 max for 15 min (Fig. 1). Gas analysis was performed throughout exercise using a metabolic cart (Quinton Q-Plex2, Quinton Institute, Seattle, WA). Blood samples were taken every 30 min during the rest phase and every 5 min during the exercise phase. Two more resting muscle biopsies were taken after the rest phase (300 min). One muscle sample was taken at 1 min of exercise (301 min) and frozen immediately for determination of PDHa activity and metabolites.
|
Blood analyses. One portion of whole blood (100 µl) was deproteinized with 6% perchloric acid (500 µl of 0.6 N HClO4), and centrifuged. The supernatant was removed for analysis of β-hydroxybutyrate, glucose, lactate, and glycerol (2). The plasma sample was also analyzed for individual plasma nonesterified fatty acids (NEFA) using gas chromatography (outlined below) and total FFA using a Wako NEFA C test kit (Wako Chemicals, Richmond, VA). An aliquot of the remaining plasma was used for radioimmunoassay analysis of insulin, using a Coat-a-Count insulin test kit (Diagnostics Products, Los Angeles, CA). Another aliquot of the remaining plasma was used for analysis of plasma TGs, using a kit (Sigma, St. Louis, MO).
Determination of individual plasma NEFA. Plasma NEFAs were methylated as previously described (20). The methyl esters were redissolved in 10 µl of methylene chloride, and 0.1 µl was injected into the gas chromatograph (Trace GC Ultra, Thermo Electron, Milan, Italy) fitted with a split/splitless injector, a fast flame ionization detector (FFID), and Triplus AS autosampler. Fatty acid methyl esters were separated on a UFM RTX-WAX analytical column (Thermo Electron) using helium as a carrier gas. The column temperature was initially 120°C, raised to 200°C at 30°C/min, held at 200°C for 30 s, then raised to 225°C at 10°C/min, and held at 225°C for 1 min. Fatty acids were identified by comparison of retention times with those of a known standard solution (Supelco 37 component FAME mix, Supelco, Bellefonte, PA). Absolute amounts of individual fatty acids were calculated with the aid of an internal standard, heptadecanoic acid (17:0), added to the plasma samples immediately before the methylation process. Preliminary analyses indicated no detectable endogenous 17:0 in the samples analyzed.
Processing of muscle samples. Any visible blood and connective tissue were removed from the fresh biopsies, and then the sample was immediately processed for the extraction of intact mitochondria (21, 29). An aliquot of the intact mitochondria was used to measure PDK activity and citrate synthase activity.
The remaining biopsy samples were immediately frozen and stored in liquid nitrogen. A 5- to 15-mg piece was chipped from the frozen biopsy sample for determination of PDHa. The frozen sample was later analyzed for total homogenate citrate synthase which was used to determine mitochondrial recovery.
Mitochondrial extraction. Differential centrifugation was utilized to obtain intact mitochondria from fresh muscle, as previously described (21, 29). Recovery of the mitochondrial preparations was determined by citrate synthase activity in extramitochondrial and total mitochondrial fractions as described previously (29, 39). The recovery of the mitochondrial preparations was 17 ± 1.1%.
PDK activity. Total PDK activity was determined as previously outlined (7, 29, 45). Briefly, the mitochondrial pellet was suspended in a phosphate buffer containing 30 mM KH2PO4, 5 mM EGTA, 5 mM dithiothreitol, 25 µg/ml oligomycin B, 1.0 mM tosyl-lysyl-chloro-methyl-ketone, 0.1% Triton, and 1% BSA (pH 7.0), and freeze-thawed twice to ensure that all of the mitochondria were ruptured. Magnesium-ATP (0.3 mM) was added to the remaining suspension and further warmed to 30°C. At timed intervals, samples were removed and diluted 1:1 in a buffer containing 200 mM sucrose, 50 mM KCl, 5 mM MgCl2, 5 mM EGTA, 50 mM Tris·HCl, 50 mM NaF, 5 mM dichloroacetate, and 0.1% Triton (pH 7.8) and stored on ice for later radioscopic analysis of PDH activity as previously described (4, 5, 34). NaF in the buffer inhibited PDP and dichloroacetate inhibited PDK to effectively "lock" the complex in the active form (PDHa), sampled at each time point. PDK activity is reported as the apparent first-order rate constant of the inactivation of PDH (min–1), which is the slope of ln[%(PDHa activity with ATP addition)/(total PDH without ATP addition)] vs. time (7, 45).
PDHa activity.
A small piece of frozen wet muscle (10–15 mg) was removed from each biopsy under N2 for the determination of PDHa as previously described (5, 34). Total creatine (Cr) content was measured in the PDHa homogenates (2) and used to correct PDHa activity to the highest Cr content in a set of biopsies from a given subject. PDHa activity was expressed as millimoles acetyl-CoA per minutes per kilogram wet muscle.
Muscle metabolites. The remainder of the frozen muscle was freeze-dried, powdered, and dissected of all visible blood, connective tissue, and fat. Muscle metabolites were measured using standard enzymatic methods. Phosphocreatine (PCr), Cr, ATP, and lactate were measured spectrophotometrically on perchloric acid extracts (2); pyruvate was measured fluormetrically (25); and acetyl-CoA and acetylcarnitine were determined radioisotopically (4). Muscle metabolites were corrected to the highest total Cr content from a given subject's biopsies.
Calculations. Whole body CHO oxidation rate was estimated as 4.585 x carbon dioxide production – 3.226 x oxygen consumption (26). The regression equation for dynamic exercise was used to determine [H+], as outlined by Sahlin et al. (37). These values were then used in the near-equilibrium creatine kinase and adenylate kinase reactions equations to determine free ADP (ADPf) and AMP (AMPf), respectively, as described by Lawson and Veech (18).
Data analysis and statistics. Meals and diets were analyzed for caloric and nutrient content using Data Analysis Plus nutritional software (Thomson-Nelson; Scarborough, Ontario, Canada). Muscle and blood data were analyzed using a two-way ANOVA (type of fat load x time) with repeated measures over time using SigmaStat software (Port Richmond, CA). Fisher protected post hoc analysis was used to determine differences between means where significant F-values were found. Significance was accepted at P < 0.05.
|
RESULTS |
|---|
|
TOPABSTRACTMETHODSRESULTSDISCUSSIONGRANTSREFERENCES |
|---|
O2 max of 45.2 ± 4.7 ml·kg–1·min–1 (range = 39.7–50.5 ml·kg–1·min–1). Mean height and weight of the subjects were 183 ± 3 cm and 85 ± 11 kg, respectively. The diets before the two experimental trials were unaltered. Content was 3,322 ± 751 kcal (CHO 63.5 ± 6%, protein 18 ± 2%, total fat 19 ± 5%, SFA 5 ± 1%, PUFA 3.5 ± 1.8%) and 2,926 ± 815 kcal (CHO 58 ± 7%, protein 23 ± 4%, total fat 19 ± 5%, SFA 5 ± 1%, PUFA 3.3 ± 2.2%) for SFA and PUFA trials, respectively. Experimental meals. The total caloric value of the trial meals consumed over the 5 h was well matched at 2,811 kcal (SFA) and 2,947 kcal (PUFA). The SFA and PUFA diets were similar with respect to protein, CHO, total fat, and MUFA content, with the only difference being the amount of SFA (mainly 14:0, 16:0, and 18:0) and PUFA (mainly 18:2 n-6; Table 1).
|
12% reduction in energy derived from CHO during the PUFA trial. Blood parameters. Total plasma FFA increased 2.6-fold from 0.15 ± 0.03 to 0.54 ± 0.08 mM over 5 h with SFA (P < 0.001) and 2.2-fold, from 0.11 ± 0.02 to 0.35 ± 0.05 mM, with PUFA (P < 0.001; Fig. 2). These increases in total plasma FFA were mainly due to increases in 14:0, 16:0, 18:1, and total SFA with SFA diet, and 18:1, 18:2 n-6, and total n-6 PUFA with PUFA diet (Table 2, Fig. 3), which correspond to the predominant fatty acids found in the respective meals (Table 1). During exercise, total plasma FFA decreased significantly from 0.54 ± 0.08 to 0.30 ± 0.04 mM with SFA (P < 0.001) and 0.35 ± 0.05 to 0.24 ± 0.02 mM with PUFA (P < 0.05). Overall, total plasma FFAs were significantly higher throughout SFA vs. PUFA (P < 0.05).
|
|
|
|
Muscle enzyme activity. PDHa activity increased significantly in the first minute of exercise in the SFA trial from 1.29 ± 0.24 to 2.16 ± 0.37 mmol·min–1·kg wet wt–1 (P < 0.05), whereas there was no change in PDHa activity with exercise during the PUFA trial (Fig. 4). PDHa activity was significantly higher in SFA compared with PUFA at the onset of exercise (SFA 2.16 ± 0.37 mmol·min–1·kg wet wt–1; PUFA 1.28 ± 0.36 mmol·min–1·kg wet wt–1; P < 0.05).
|
|
|
Calculated ADPf and AMPf increased at the onset of exercise, but no differences were observed between the two trials (P < 0.001; Table 4).
|
DISCUSSION |
|---|
|
TOPABSTRACTMETHODSRESULTSDISCUSSIONGRANTSREFERENCES |
|---|
Plasma FFA and TGs. It has been shown in previous work, and in several different models, that dietary n-6 PUFAs are oxidized at a higher rate than SFAs (6, 16, 17, 30, 46). SFAs are more commonly stored as TGs, whereas n-3 PUFAs are often used by the cells to build lipid membranes, and n-6 PUFAs are preferentially oxidized (6). In the present study, an increase in plasma FFA concentration ([FFA]) was seen throughout 5 h consumption of SFA compared with an n-6 PUFA load. Plasma TG increased in both trials to a similar extent, which was expected with the similar fat content in the loads.
Although the increased plasma [FFA] with SFA could suggest decreased gastrointestinal absorption with PUFA, this is unlikely since plasma TGs increased equally with both trials. Orally consumed TGs must be broken down to glycerol and fatty acid components to allow the FFAs to cross the intestinal membrane, then reassembled for release into the bloodstream (11). Since the TG levels in the blood were similar between the two trials, it is probable that the difference in plasma [FFA] was not due to decreased TG absorption with PUFA but likely due to increased uptake and removal of plasma FFA by muscle and other organs.
In this circumstance, a decrease in plasma [FFA] with PUFA relative to SFA may suggest an increased uptake of FFA by the cells for oxidation, further suggesting that n-6 PUFA was preferentially taken up and oxidized by the cells compared with SFA. This agrees with the findings of Vukovich et al. (46), who saw increased fat oxidation throughout 60 min of moderate-intensity exercise (60% O2 max) with an intralipid infusion (>85% n-6 PUFA; mainly composed of 18:2 n-6 linoleic acid) compared with a SFA meal (whipping cream, >90% SFA). It is important to note that Vukovich et al. (46) administered the two types of fat using different methods, the n-6 PUFA being infused directly into the blood and the SFA being taken orally as a single bolus load (500 ml whipping cream), making comparisons between treatments difficult. In addition, no muscle measurements were taken in this study, and thus potential mechanism(s) of increased fat oxidation with n-6 PUFA were not determined. However, we also observed an increase in whole body fat oxidation throughout the 15 min of moderate exercise following consumption of n-6 PUFA compared with SFA, as determined by RER. Taken together, these results indicate an increased reliance on fat oxidation during moderate-intensity exercise with n-6 PUFA compared with SFA, regardless of the method of fat administration.
PDHa and PDK activity. Correlated with the observed decrease in whole body CHO oxidation and increased fat oxidation, there was an attenuation of PDHa activity with n-6 PUFA compared with SFA at the onset of exercise. However, contrary to our hypothesis, this attenuation was not accompanied by a chronic or adaptive increase in PDK activity or an attenuation of PDHa activity at rest.
The increase in PDHa activity following the SFA load at 1 min of exercise is comparable to that seen when subjects exercised 2–3 h after a mixed meal. Howlett et al. (13) saw a similar increase in PDHa activity by 1 min exercise at 65% O2 max without prior fat loading (2.6 mmol·min–1·kg wet wt–1 compared with 2.2 ± 0.4 mmol·min–1·kg wet wt–1 seen in the present study). Similar results were also observed by Odland et al. (23) at 1 min of exercise at 65% O2 max (2.8 mmol·min–1·kg wet wt–1). Therefore, even with an excess of available saturated fat after 5 h SFA loading, skeletal muscle appears to behave as if no fat were consumed, increasing CHO oxidation when the cell is challenged by contraction. The opposite effect was seen with n-6 PUFA, as PDHa did not increase significantly at 1 min of exercise. The modest but not significant change in PDHa activity from rest to exercise is consistent with what has been observed previously at 1 min of exercise following primarily n-6 PUFA intralipid/heparin infusion (24).
PDK activity did not increase in this study in response to either 5 h of n-6 PUFA or SFA fat loading. Previous studies have demonstrated increased PDK activity with short-term perturbations that result in an increased reliance on fat oxidation. For example, small but significant increases in PDK activity have been observed with as little as 24 h consumption of a high-saturated-fat diet (28) and also after 4 h of prolonged exercise (47). With a short-term high-fat diet, changes in PDK4 protein and mRNA were observed (28); however, only a change in PDK activity (without changes in the PDK proteins) was observed during prolonged exercise (47). Although there is evidence that changes in PDK4 gene expression can occur with very short term perturbations that are less than or equal to 24 h (27, 28, 31, 32, 33, 38, 42), few studies have measured PDK4 protein or PDK activity (28, 47). Some studies have measured increased PDK4 mRNA in response to 4–5 h intralipid/heparin infusions (33, 42), but our results might suggest that this does not necessarily translate into increased PDK activity in the same time frame. However, recently Pilegaard et al. (33) demonstrated increased phosphorylation of the E1 subunit of the PDH complex at both site 1 and site 2 after 4 h of intralipid/heparin (predominantly n-6 PUFA) infusion. This may seem difficult to reconcile in the face of our inability to detect increases in total PDK activity in our subjects. However, their data do help to explain the observation that PDHa activity is attenuated at the onset of exercise with n-6 PUFA. It is possible that while maximal PDK activity is not significantly altered with either intralipid/heparin or n-6 PUFA-feeding, the in vivo specific activity of the PDK enzyme could have been acutely altered through changes in mitochondrial effectors. Additionally, it is possible that adaptive decreases in PDP activity could explain the attenuation of PDHa activity with n-6 PUFA, but there is little known about adaptive regulation of human skeletal muscle PDP activity. Long-term nutritional perturbations (such as 48 h starvation and drug-induced diabetes) cause decreased PDP activity in heart and liver tissues (15), and recently it has been demonstrated that starvation decreases skeletal muscle PDP activity and PDP2 expression in resting rat skeletal muscle (19). Thus it is possible that stable changes in PDP activity may have contributed to the differential regulation of PDH activity during exercise following the two different fat loads.
Acutely, the PDH complex is regulated through the effects of hormonal influences or the accumulation of intramitochondrial effectors on PDK and/or PDP activity. PDP2 is upregulated by insulin (1, 40), but plasma insulin levels were consistent between the SFA and n-6 PUFA trials. Thus this regulation is unlikely to be a factor in the attenuation of PDHa activity after n-6 PUFA loading. PDP1 activity is upregulated by Ca2+ released from the sarcoplasmic reticulum at the onset of exercise (14). In the present study, the subjects exercised at the same intensity in both trials, and therefore intramuscular [Ca2+] should have been similar between the trials. However, recent studies have shown that dietary PUFAs may decrease Ca2+ release from the sarcoplasmic reticulum (22, 41). This group demonstrated that eicosapentaenoic acid (20:5, n-3) decreases Ca2+ release through direct inhibition of the sarcoplasmic reticulum Ca2+-release channel/ryanodine receptor in intact cells. This inhibition was not seen with saturated fatty acids (41). Although these experiments were done with n-3 and not n-6 fatty acids, earlier work has demonstrated an inhibition of labeled ryanodine binding to the sarcoplasmic reticulum with arachidonic acid, an n-6 PUFA (44, 49). Although this potential mechanism has not been fully elucidated, it is possible that the dietary n-6 PUFAs in the present study allowed downregulation of PDHa activity at the onset of exercise via a decreased release of Ca2+ from the sarcoplasmic reticulum compared with the SFA trial, even at the same exercise workload. This would result in the higher PDHa activity observed in the SFA condition at the onset of exercise.
PDHa activity is acutely upregulated by mitochondrial concentrations of pyruvate and downregulated by increasing acetyl-CoA-to-CoA ratio, energy charge (ATP-to-ADP ratio), and mitochondrial redox (NADH-to-NAD+ ratio) (1, 40). Pyruvate and acetyl-CoA were not different between the PUFA and SFA trials and may not account for the differences in PDHa activity. However, the effects of the ratio of NADH/NAD+ on PDHa activity during exercise have proven elusive, due to difficulties in accurately measuring the redox state in the mitochondria during exercise. An increase in this ratio causes increased PDK activity and, in turn, decreased PDHa activity. As in the case of pyruvate oxidation, NAD+ is also a substrate of the PDH reaction; therefore an increase in NAD+ would also help increase flux through the enzyme. It is possible that n-6 PUFA loading caused an increase in intramitochondrial NADH as a result of elevated FFA oxidation compared with SFA. Increased NADH in the n-6 PUFA condition would be expected to increase binding of PDK to the E2 core of the PDH complex (36), increasing PDK specific activity and attenuating PDHa activation. However, further experiments would be necessary to fully explore the role of intramitochondrial effectors such as Ca2+ and NADH in the differential activation of PDHa following n-6 PUFA and SFA loading.
Summary. This study examined the metabolic effects of differential dietary fatty acids at rest and the onset of moderate-intensity exercise. As hypothesized, an attenuation of PDHa activity was seen at the onset of exercise following an n-6 PUFA load compared with an SFA load, facilitating decreased CHO oxidation and increased oxidative disposal of the consumed n-6 PUFA load. This was accompanied by a decrease in circulating plasma FFA at rest and during exercise with n-6 PUFA as well as increased fat oxidation throughout 15 min of moderate-intensity exercise. Taken together, these data indicate a preference of skeletal muscle to oxidize fat with acute n-6 PUFA feeding compared with SFA, regulated, at least in part, by attenuation of PDHa activity.
There was no change in PDK activity between trials, suggesting the 5 h may be too short a time for a fat load to affect total PDK activity to any significant extent. Since changes in total PDK activity were not responsible for the alterations in PDHa activity at the onset of moderate-intensity exercise, it was most likely a result of changes in the concentrations of intramitochondrial effectors that were different between the trials, specifically intracellular Ca2+ or NADH.
|
GRANTS |
|---|
|
TOPABSTRACTMETHODSRESULTSDISCUSSIONGRANTSREFERENCES |
|---|
|
FOOTNOTES |
|---|
The costs of publication of this article were defrayed in part by the payment of page charges. The article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.
|
REFERENCES |
|---|
|
TOPABSTRACTMETHODSRESULTSDISCUSSIONGRANTSREFERENCES |
|---|
dephosphorylation and activation in human skeletal muscle during exercise: effect of intralipid infusion. Diabetes 55: 3020–3027, 2007.[Web of Science]
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
| Visit Other APS Journals Online |
). Two muscle biopsies (one fresh and one frozen) were taken before fat loading and after fat loading (
) and polyunsaturated fatty acid trial (PUFA; 
). 
Significant main effect for trials, SFA > PUFA (P < 0.05).
