Superficial Vastus Lateralis Research Articles

Impact of supine versus upright exercise on muscle deoxygenation heterogeneity during ramp incremental cycling is site specific

PurposeWe tested the hypothesis that incremental ramp cycling exercise performed in the supine position (S) would be associated with an increased reliance on muscle deoxygenation (deoxy[heme]) in the deep and superficial vastus lateralis (VLd and VLs, respectively) and the superficial rectus femoris (RFs) when compared to the upright position (U).Methods11 healthy men completed ramp incremental exercise tests in S and U. Pulmonary dot{V}O2 was measured breath-by-breath; deoxy[heme] was determined via time-resolved near-infrared spectroscopy in the VLd, VLs and RFs.ResultsSupine exercise increased the overall change in deoxy[heme] from baseline to maximal exercise in the VLs (S: 38 ± 23 vs. U: 26 ± 15 μM, P < 0.001) and RFs (S: 36 ± 21 vs. U: 25 ± 15 μM, P < 0.001), but not in the VLd (S: 32 ± 23 vs. U: 29 ± 26 μM, P > 0.05).ConclusionsThe present study supports that the impaired balance between O2 delivery and O2 utilization observed during supine exercise is a regional phenomenon within superficial muscles. Thus, deep muscle defended its O2 delivery/utilization balance against the supine-induced reductions in perfusion pressure. The differential responses of these muscle regions may be explained by a regional heterogeneity of vascular and metabolic control properties, perhaps related to fiber type composition.

Unaltered V̇o2 kinetics despite greater muscle oxygenation during heavy-intensity two-legged knee extension versus cycle exercise in humans.

Relative perfusion of active muscles is greater during knee extension ergometry (KE) than cycle ergometry (CE). This provides the opportunity to investigate the effects of increased O2 delivery (Q̇o2) on deoxygenation heterogeneity among quadriceps muscles and pulmonary oxygen uptake (V̇o2) kinetics. Using time-resolved near-infrared spectroscopy, we hypothesized that compared with CE the superficial vastus lateralis (VL), superficial rectus femoris, and deep VL in KE would have 1) a smaller amplitude of the exercise-induced increase in deoxy[Hb + Mb] (related to the balance between V̇o2 and Q̇o2); 2) a greater amplitude of total[Hb + Mb] (related to the diffusive O2 conductance); 3) a greater homogeneity of regional muscle deoxy[Hb + Mb]; and 4) no difference in pulmonary V̇o2 kinetics. Eight participants performed square-wave KE and CE exercise from 20 W to heavy work rates. Deoxy[Hb + Mb] amplitude was less for all muscle regions in KE (P < 0.05: superficial, KE 17-24 vs. CE 19-40; deep, KE 19 vs. CE 26 μM). Furthermore, the amplitude of total[Hb + Mb] was greater for KE than CE at all muscle sites (P < 0.05: superficial, KE, 7-21 vs. CE, 1-16; deep, KE, 11 vs. CE, -3 μM). Although the amplitude and heterogeneity of deoxy[Hb + Mb] were significantly lower in KE than CE during the first minute of exercise, the pulmonary V̇o2 kinetics was not different for KE and CE. These data show that the microvascular Q̇o2 to V̇o2 ratio, and thus tissue oxygenation, was greater in KE than CE. This suggests that pulmonary and muscle V̇o2 kinetics in young healthy humans are not limited by Q̇o2 during heavy-intensity cycling.

Blood flow occlusion-related O2 extraction "reserve" is present in different muscles of the quadriceps but greater in deeper regions after ramp-incremental test.

It was recently demonstrated that an O2 extraction reserve, as assessed by the near-infrared spectroscopy (NIRS)-derived deoxygenation signal ([HHb]), exists in the superficial region of vastus lateralis (VL) muscle during an occlusion performed at the end of a ramp-incremental test. However, it is unknown whether this reserve is present and/or different in magnitude in other portions and depths of the quadriceps muscles. We tested the hypothesis that an O2 extraction reserve would exist in other regions of this muscle but is greater in deep compared with more superficial portions. Superficial (VL-s) and deep VL (VL-d) as well as superficial rectus femoris (RF-s) were monitored by a combination of low- and high-power time-resolved (TRS) NIRS. During the occlusion immediately post-ramp-incremental test there was a significant overshoot in the [HHb] signal ( P < 0.05). However, the magnitude of this increase was greater in VL-d (93.2 ± 42.9%) compared with VL-s (55.0 ± 19.6%) and RF-s (47.8 ± 14.0%) ( P < 0.05). The present study demonstrated that an O2 extraction reserve exists in different pools of active muscle fibers of the quadriceps at the end of a ramp exercise to exhaustion. The greater magnitude in the reserve observed in the deeper portion of VL, however, suggests that this portion of muscle may present a greater surplus of oxygenated blood, which is likely due to a greater population of slow-twitch fibers. These findings add to the notion that the plateau in the [HHb] signal toward the end of a ramp-incremental exercise does not indicate the upper limit of O2 extraction. NEW & NOTEWORTHY Different portions of the quadriceps muscles exhibited an untapped O2 extraction reserve during a blood flow occlusion performed at the end of a ramp-incremental exercise. In the deeper portion of the vastus lateralis muscle, this reserve was greater compared with superficial vastus lateralis and rectus femoris. These data suggest that the O2 extraction reserve may be dependent on the vascular and/or oxidative capacities of the muscles.

Near-infrared spectroscopy of superficial and deep rectus femoris reveals markedly different exercise response to superficial vastus lateralis.

To date our knowledge of skeletal muscle deoxygenation as measured by near‐infrared spectroscopy (NIRS) is predicated almost exclusively on sampling of superficial muscle(s), most commonly the vastus lateralis (VL‐s). Recently developed high power NIRS facilitates simultaneous sampling of deep (i.e., rectus femoris, RF‐d) and superficial muscles of RF (RF‐s) and VL‐s. Because deeper muscle is more oxidative with greater capillarity and sustains higher blood flows than superficial muscle, we used time‐resolved NIRS to test the hypotheses that, following exercise onset, the RF‐d has slower deoxy[Hb+Mb] kinetics with reduced amplitude than superficial muscles. Thirteen participants performed cycle exercise transitions from unloaded to heavy work rates. Within the same muscle (RF‐s vs. RF‐d) deoxy[Hb+Mb] kinetics (mean response time, MRT) and amplitudes were not different. However, compared with the kinetics of VL‐s, deoxy[Hb+Mb] of RF‐s and RF‐d were slower (MRT: RF‐s, 51 ± 23; RF‐d, 55 ± 29; VL‐s, 18 ± 6 s; P < 0.05). Moreover, the amplitude of total[Hb+Mb] was greater for VL‐s than both RF‐s and RF‐d (P < 0.05). Whereas pulmonary V˙O2 kinetics (i.e., on vs. off) were symmetrical in heavy exercise, there was a marked on‐off asymmetry of deoxy[Hb+Mb] for all three sites i.e., MRT‐off > MRT‐on (P < 0.05). Collectively these data reveal profoundly different O2 transport strategies, with the RF‐s and RF‐d relying proportionately more on elevated perfusive and the VL‐s on diffusive O2 transport. These disparate O2 transport strategies and their temporal profiles across muscles have previously been concealed within the “global” pulmonary V˙O2 response.

Muscle deoxygenation in the quadriceps during ramp incremental cycling: Deep vs. superficial heterogeneity.

Muscle deoxygenation (i.e., deoxy[Hb + Mb]) during exercise assesses the matching of oxygen delivery (Q̇O2) to oxygen utilization (V̇O2). Until now limitations in near-infrared spectroscopy (NIRS) technology did not permit discrimination of deoxy[Hb + Mb] between superficial and deep muscles. In humans, the deep quadriceps is more highly vascularized and oxidative than the superficial quadriceps. Using high-power time-resolved NIRS, we tested the hypothesis that deoxygenation of the deep quadriceps would be less than in superficial muscle during incremental cycling exercise in eight males. Pulmonary V̇O2 was measured and muscle deoxy[Hb + Mb] was determined in the superficial vastus lateralis (VL), vastus medialis (VM), and rectus femoris (RF-s) and the deep rectus femoris (RF-d). deoxy[Hb + Mb] in RF-d was significantly less than VL at 70% (67.2 ± 7.0 vs. 75.5 ± 10.7 μM) and 80% (71.4 ± 11.0 vs. 79.0 ± 15.4 μM) of peak work rate (WR(peak)), but greater than VL and VM at WR(peak) (87.7 ± 32.5 vs. 76.6 ± 17.5 and 75.1 ± 19.9 μM). RF-s was intermediate at WR(peak) (82.6 ± 18.7 μM). Total hemoglobin and myoglobin concentration and tissue oxygen saturation were significantly greater in RF-d than RF-s throughout exercise. The slope of deoxy[Hb + Mb] increase (proportional to Q̇O2/V̇O2) in VL and VM slowed markedly above 70% WR(peak), whereas it became greater in RF-d. This divergent deoxygenation pattern may be due to a greater population of slow-twitch muscle fibers in the RF-d muscle and the differential recruitment profiles and vascular and metabolic control properties of specific fiber populations within superficial and deeper muscle regions.

Greater Absolute Deoxygenation In Deep Versus Superficial Quadriceps Muscles At Vo2max During Cycle Ergometry

Skeletal muscle deoxygenation ([HHb]) during exercise is dependent on the ratio of oxygen utilization (Vo2) to oxygen delivery (Qo2). Assessment of regional muscle deoxygenation by near infrared spectroscopy (NIRS) has previously been limited technically to superficial muscles. PURPOSE: To use a new high-power Time Resolved (TR) NIRS to investigate deep and superficial muscle deoxygenation during exercise. Because deep muscle has a greater oxidative fiber expression and Qo2/Vo2, we hypothesized that deep quadriceps muscle would deoxygenate less during exercise than superficial muscle. METHODS: Deep and superficial [HHb] was measured by TR NIRS in eight men during incremental cycle ergometry in: superficial vastus lateralis (VL), superficial vastus medialis (VM), and superficial (RF-s) and deep rectus femoris (RF-d). Pulmonary Vo2 was measured breath-by-breath. RESULTS: Vo2max was 2.6±0.4 L/min. On average, for all muscle regions, [HHb] increased from 55±7 μM at baseline to 80±20 μM at peak exercise. [HHb] was less (P<0.05) in RF-d than superficial VL at 70% and 80% peak power, but greater (88±33 μM; P<0.05) than superficial VM (75±20 μM) and VL (77±18 μM) at peak power (Fig.). CONCLUSION: Compared with the superficial muscles, [HHb] was significantly less in deep muscles at submaximal high-intensity work rates: Likely reflecting better maintenance of Qo2/Vo2 in oxidative deep muscle fibers. At peak exercise however, greater [HHb] in deep muscle reveals a greater absolute capacity for O2 extraction compared to more glycolytic superficial muscles. High power NIRS has substantial potential to address important questions regarding vascular and muscle function during exercise. Supported by BBSRC UK, BB/I024798/1, JSPS-24247046

Nf Kappa B Inhibitor Attenuates Antioxidant Enzyme Activity: Effect Of Exercise Training

Gene regulation of antioxidant enzymes is known to be regulated via redox-sensitive signal transduction pathways involving nuclear factor (NF) kappaB and mitogenactivated protein kinases (MAPK). PURPOSE: The goal of this study is to examine whether the pharmacological agent pyrolidine dithiocarbamate (PDTC), a known NF kappaB inhibitor, or propranolol (PL), a beta-adrenergic blocker, affect basal levels of antioxidant enzymes activity due to interference with their signaling. We also investigated whether exercise training would alter the potential effects of these drugs. METHODS: Female Sprague-Dawley rats were injected (i.p.) daily with either PDTC (50 mg/kg body wt, N=16), PL (30 mg/kg, N=16) or saline (S, N=16). Half of each treatment group of rats participated in an 8-wk treadmill training regimen at 26 m/min, 15% grade for 1 h/day, 5 d/wk (T), whereas the other half group remained untrained (C). Heart, liver, deep (DVL) and superficial (SVL) vastus lateralis, soleus and gastrocnemius (Gas) muscles were harvested 24 h after the last exercise bout. RESULTS: Superoxide dismutase activity did not alter with PDTC, PL, or T. Glutathione peroxidase activity was decreased in DVL, SVL and Gas (P<0.05) of PDTC-C vs. S-C rats, whereas T restored these changes. PDTC rats showed lower heart catalase activity (P<0.01) vs. C rats. Malodialdehyde content was increased (P<0.05) with PDTC in heart, liver and SVL of C, and T attenuated the effects. CONCLUSIONS: These data suggest that impaired NF kappaB signaling by PDTC can affect antioxidant enzyme expression, whereas chronic exercise may protect against the drug-induced adverse effects and oxidative stress.

The Role Of Xanthine Oxidase In Muscle Oxidative Damage Caused By Repeated Sprinting Exercise

Xanthine oxidase (XO) plays an important role in generating reactive oxygen species (ROS) during organ ischemia-reperfusion. Activation of XO has been postulated to underlie the mechanism of tissue oxidative damage resulting from high-intensity muscular contraction. Purpose The purpose of this study was two-fold: (1) to investigate whether high-intensity sprinting exercise would generate ROS and elicit oxidative damage to the heart and skeletal muscle in rats; and (2) to examine whether administration of allopurinol (ALP), a XO inhibitor, would attenuate oxidative tissue damage. Methods Female Sprague-Dawley rats (age 4 mo) were randomly divided into three groups: (1) rested (R, N=9); (2) sprinting on treadmill at 35 m/min, 15% grade, for 3 min followed by 3 min rest, repeated until exhaustion (ST, N=9); and (3) receiving two i.p. injections of ALP (0.4 mmol/kg body wt each) 24 and 1 h prior to ST (ST+ALP, N=9). Heart and three types of skeletal muscle were collected immediately after rats were killed. Results Time of running to exhaustion was not different between ST (86.2 ± 6.6 min) and ST/ALP (89.2 ± 6.3 min). ROS generation measured with the 2',7'-dichlorofluorescein method in fresh homogenate was not different between R, ST and ST/ALP in the heart or skeletal muscle. ST decreased glutathione (GSH) content, increased glutathione disulfide (GSSG) content and lowered the GSH:GSSG ratio in the heart and superficial vastus lateralis (SVL) muscle, whereas ALP attenuated the ST-induced GSH disturbance. Lipid peroxidation measured by malondialdehyde content was increased in ST vs. R, but unchanged in ST/ALP vs. R. Conclusion High-intensity sprinting exercise imposes an oxidative stress to heart and glycolytic muscle fibers, which can be attenuated by ALP treatment. Whether the source of ROS originated from XO requires further investigation.

Muscle fiber‐specific apoptosis and TNF‐α signaling in sarcopenia are attenuated by life‐long calorie restriction

Increased tumor necrosis factor-alpha (TNF-alpha) levels have been found with age and are connected to muscle atrophy and cell loss, yet the signaling events that occur in vivo are unknown. Calorie restriction (CR), a robust intervention shown to repeatedly evade the physiological declines associated with aging, has been reported to reduce TNF-alpha and may assist in understanding the mechanisms of muscle sarcopenia. The effects of age and CR on muscle mass, myocyte area, fiber number, myocyte TNF-alpha expression, plasma TNF-alpha levels, and specific elements linked with the TNF-alpha signaling cascade (TNF-R1, IKKgamma, IkappaBalpha, p65, NF-kappaB binding activity, FADD, caspase-8, and DNA fragmentation) were investigated in soleus (predominately Type I fiber), and superficial vastus lateralis (SVL, predominately Type II fiber), of 6-month-old ad libitum fed (6AL), 26-month-old ad libitum fed (26AL), and 26-month-old calorie-restricted (26CR) male Fischer 344 rats (CR = 40% restriction compared with ad libitum). Plasma TNF-alpha was increased with age, and the age-associated rise was attenuated with life-long CR. In soleus muscle, we reported a greater capacity to cultivate inflammatory signaling through the transcription factor NF-kappaB compared with that detected in SVL with age. In contrast, in the SVL TNF-alpha stimulated apoptotic signaling with age to a much higher extent than was observed in the soleus. Moreover, a reduction in muscle mass, cross-sectional area, and fiber number in the SVL coincided with this age-linked elevation in apoptosis. In agreement with CR's ability, TNF-alpha stimulation of both inflammatory and apoptotic pathways were abrogated. Our results suggest that TNF-alpha signals transmitted to specific fiber types determine the decision of selecting life or death signaling pathways and are linked to the extent of fiber loss experienced in the aging muscle. Such a specific potential may constitute a major proponent in the pathogenesis of sarcopenia.

Control of muscle glucose uptake: test of the rate‐limiting step paradigm in conscious, unrestrained mice

The aim of this study was to test whether in fact glucose transport is rate-limiting in control of muscle glucose uptake (MGU) under physiological hyperinsulinaemic conditions in the conscious, unrestrained mouse. C57Bl/6J mice overexpressing GLUT4 (GLUT4(Tg)), hexokinase II (HK(Tg)), or both (GLUT4(Tg) + HK(Tg)), were compared to wild-type (WT) littermates. Catheters were implanted into a carotid artery and jugular vein for sampling and infusions at 4 month of age. After a 5-day recovery period, conscious mice underwent one of two protocols (n = 8-14/group) after a 5-h fast. Saline or insulin (4 mU kg(-1) min(-1)) was infused for 120 min. All mice received a bolus of 2-deoxy[(3)H]glucose (2-(3)HDG) at 95 min. Glucose was clamped at approximately 165 mg dl(-1) during insulin infusion and insulin levels reached approximately 80 microU ml(-1). The rate of disappearance of 2-(3)HDG from the blood provided an index of whole body glucose clearance. Gastrocnemius, superficial vastus lateralis and soleus muscles were excised at 120 min to determine 2-(3)HDG-6-phosphate levels and calculate an index of MGU (R(g)). Results show that whole body and tissue-specific indices of glucose utilization were: (1) augmented by GLUT4 overexpression, but not HKII overexpression, in the basal state; (2) enhanced by HKII overexpression in the presence of physiological hyperinsulinaemia; and (3) largely unaffected by GLUT4 overexpression during insulin clamps whether alone or combined with HKII overexpression. Therefore, while glucose transport is the primary barrier to MGU under basal conditions, glucose phosphorylation becomes a more important barrier during physiological hyperinsulinaemia in all muscles. The control of MGU is distributed rather than confined to a single rate-limiting step such as glucose transport as glucose transport and phosphorylation can both become barriers to skeletal muscle glucose influx.

Regulation of insulin-stimulated muscle glucose uptake in the conscious mouse: role of glucose transport is dependent on glucose phosphorylation capacity.

Previous work suggests that normal GLUT4 content is sufficient for increases in muscle glucose uptake (MGU) during hyperinsulinemia, because glucose phosphorylation is the more formidable barrier to insulin-stimulated MGU. It was hypothesized that a partial ablation of GLUT4 would not impair insulin-stimulated MGU when glucose phosphorylation capacity is normal but would do so when glucose phosphorylation capacity is increased. Thus, chow-fed C57BL/6J mice with a GLUT4 partial knockout (GLUT4(+/-)), hexokinase II overexpression (HK(Tg)), or both (HK(Tg) + GLUT4(+/-)) and wild-type littermates were studied. Carotid artery and jugular vein catheters were implanted for sampling and infusions at 4 months of age. After a 5-d recovery, 5-h fasted mice (n = 8-11/group) underwent a 120-min saline infusion or insulin clamp (4 mU/kg.min insulin with glucose maintained at 165 mg/dl) and received a 2-deoxy[(3)H]glucose bolus to provide an index of MGU (R(g)) for the soleus, gastrocnemius, and superficial vastus lateralis. Basal R(g) from all muscles studied from saline-infused mice were not changed by any of the genetic modifications. HK(Tg) mice had augmented insulin-stimulated R(g) in all muscles studied compared with remaining genotypes. Insulin-stimulated R(g) was not impaired in any of the muscles studied from GLUT4(+/-) mice. However, the enhanced insulin-stimulated R(g) created by HK overexpression was ablated in HK(Tg) + GLUT4(+/-) mice. Thus, a 50% reduction of normal GLUT4 content in the presence of normal HK activity does not impair insulin-stimulated MGU. However, when the glucose phosphorylation barrier is lowered by HK overexpression, GLUT4 availability becomes a limitation to insulin-stimulated MGU.

AMP kinase-induced skeletal muscle glucose but not long-chain fatty acid uptake is dependent on nitric oxide.

The purpose of this study was to examine the effects of AMP kinase (AMPK) activation on in vivo glucose and long-chain fatty acid (LCFA) uptake in skeletal muscle and to examine the nitric oxide (NO) dependence of any putative effects. Catheters were chronically implanted in the carotid artery and jugular vein of male Sprague-Dawley rats. After 4 days of recovery, rats were given either water or water containing 1 mg/ml nitro-l-arginine methylester (l-NAME) for 2.5 days. After an overnight fast, rats underwent one of five protocols: saline, 5-aminoimidazole-4-carboxamide-1-B-d-ribofuranoside (AICAR) (10 mg. kg(-1). min(-1)), l-NAME, AICAR + l-NAME, or AICAR + Intralipid (20%, 0.02 ml. kg(-1). min(-1)). Glucose was clamped at approximately 6.5 mmol/l in all groups, and an intravenous bolus of 2-deoxy[(3)H]glucose and [(125)I]-15-(p-iodophenyl)-3-R,S-methylpentadecanoic acid was administered to obtain indexes of glucose (K(g)) and LCFA (K(f)) uptake and clearance. At 150 min, soleus, gastrocnemius, and superficial vastus lateralis were excised for tracer determination. Both K(g) and K(f) increased with AICAR in all muscles studied. K(g) decreased with increasing muscle composition of type 1 slow-twitch fibers, whereas K(f) increased. In addition, AICAR-induced increases in K(g) but not K(f) were abolished by l-NAME in the majority of muscles examined. This shows that the mechanisms by which AMPK stimulates glucose and LCFA uptake are distinct.

Quinides of Roasted Coffee Enhance Insulin Action in Conscious Rats

Consumption of large amounts of coffee has been shown to decrease the incidence of type 2 diabetes. However, the specific compounds and mechanisms responsible for this effect are not known. The aim of this study was to determine the effects of a decaffeinated coffee extract and a synthetic quinide, representative of those found in roasted coffee, 3,4-diferuloyl-1,5-quinolactone, on insulin-stimulated glucose disposal and muscle glucose uptake. Experiments were performed on conscious rats during hyperinsulinemic, euglycemic clamps receiving gastric infusions of saline, a decaffeinated coffee extract (DECAF) (220 mg/kg), or 3,4-diferuloyl-1,5-quinide (DIFEQ) (110 mg/kg). Following treatment, rats received an intravenous bolus of deoxy-[2-3H] glucose to assess muscle glucose uptake (Rg, micromol x 100 g(-1) x min(-1)). Glucose infusions [mg/(kg x min)] required to maintain euglycemia during the tracer period were higher with DIFEQ (14.6 +/- 0.7) than with saline (10.8 +/- 0.7) and DECAF (11.5 +/- 1.1). Despite increased glucose requirements, Rg in skeletal (soleus, gastrocnemius, superficial vastus lateralis) and cardiac muscle were unchanged. DECAF or DIFEQ did not affect heart rate, blood pressure, plasma nonesterified fatty acids or liver aminotransferase activity. These results demonstrate that DIFEQ increases whole-body glucose disposal independently of skeletal muscle Rg.

Hexokinase II partial knockout impairs exercise-stimulated glucose uptake in oxidative muscles of mice.

Muscle glucose uptake (MGU) is distributively controlled by three serial steps: delivery of glucose to the muscle membrane, transport across the muscle membrane, and intracellular phosphorylation to glucose 6-phosphate by hexokinase (HK). During states of high glucose fluxes such as moderate exercise, the HK activity is of increased importance, since augmented muscle perfusion increases glucose delivery, and increased GLUT4 at the cell membrane increases glucose transport. Because HK II overexpression augments exercise-stimulated MGU, it was hypothesized that a reduction in HK II activity would impair exercise-stimulated MGU and that the magnitude of this impairment would be greatest in tissues with the largest glucose requirement. To this end, mice with a HK II partial knockout (HK+/-) were compared with their wild-type control (WT) littermates during either sedentary or moderate exercise periods. Rg, an index of glucose metabolism, was measured using 2-deoxy-[3H]glucose. No differences in glucose metabolism were detected between sedentary groups. The increase in Rg due to exercise was impaired in the highly oxidative heart and soleus muscles of HK+/- compared with WT mice (7 +/- 10 vs. 29 +/- 9 and 8 +/- 3 vs. 25 +/- 7 micromol. 100 g-1. min-1, respectively). However, the increase in Rg due to exercise was not altered in gastrocnemius and superficial vastus lateralis muscles in HK+/- and WT mice (8 +/- 2 vs. 12 +/- 3 and 5 +/- 2 vs. 8 +/- 2 micromol. 100 g-1. min-1, respectively). In conclusion, MGU is impaired by reductions in HK activity during exercise, a physiological condition characterized by high glucose flux. This impairment is critically dependent on the tissue's glucose metabolic rate and correlates with tissue oxidative capacity.

Superoxide dismutase gene expression is activated by a single bout of exercise in rat skeletal muscle.

The goal of this experiment was to examine contraction-mediated activation of superoxide dismutase (SOD) gene expression in rat superficial vastus lateralis (SVL, type IIb) and deep vastus lateralis (DVL, type IIa) muscles. Female Sprague-Dawley rats were randomly divided into exercise (E) and control (C) groups that were sacrificed at 0, 1, 2, 4, 10, 24, and 48 h (n=6) following an acute bout of treadmill exercise (25 m/min, 5% grade) to exhaustion (running time approximately equals 1 h). Nuclear factor-kappaB (NF-kappaB) in DVL and SVL showed maximal binding at 2 and 10 h respectively, and remained elevated. Activator protein-1 (AP-1) showed maximal binding at 1 h post-exercise, and returned to resting levels at 10 h in both muscles. Mn SOD mRNA abundance in the DVL was increased at 0 (P<0.01), 1, and 2 h (P<0.05) post-exercise, whereas Mn SOD protein was unchanged. In SVL, Mn SOD mRNA abundance was not altered by exercise, whereas Mn SOD protein content was increased at 10 (P<0.05) and 24 h (P<0.075) post-exercise. CuZn SOD mRNA was unchanged with exercise in DVL and SVL, but CuZn SOD protein was elevated 48 h after exercise in both DVL and SVL (P<0.01). Activities of Mn SOD, CuZn SOD and total SOD showed no change with exercise in either muscle examined. These findings indicate that an acute bout of exercise can increase binding of NF-kappaB and AP-1 in both SVL and DVL, which may stimulate Mn SOD mRNA transcription in the more oxidative type DVL muscle. The increased CuZn SOD protein contents seen post-exercise, without increases in mRNA abundance in both DVL and SVL, suggest a translational mechanism in this SOD isoform.

Superoxide dismutase gene expression in skeletal muscle: fiber-specific effect of age

The influence of ageing on the expression of two superoxide dismutase (SOD) isozymes was examined in three different skeletal muscle fiber types of young (Y, 8 mo) and old (O, 25 mo) rats. Total SOD activity was increased with age in the gastrocnemius (Gas, type II mix) and superficial vastus lateralis (SVL, type IIb) but unchanged in the soleus (Sol, type I). The increased SOD activity in SVL was due to increased cytosolic SOD (CuZn SOD), whereas both mitochondrial (Mn SOD) and CuZn SOD activities were increased in Gas. In Sol, Mn SOD activity was significantly increased in aged rats. Mn SOD mRNA level was significantly decreased with age in all three muscles examined, while Mn SOD protein content was not altered. Ageing did not affect CuZn SOD mRNA abundance in any of the muscles, but significantly increased CuZn SOD protein content in aged Gas and Sol. Binding of two redox-sensitive transcription factors, nuclear factor-κB (NFκB) and activator protein-1 (AP-1) was significantly decreased with age in all three muscle types. These results indicate that increased SOD activity in aged skeletal muscle is not associated with higher levels of gene transcription. Increases in Mn SOD activity seen in aged Gas and Sol are the result of post-translational modification of the enzyme, whereas increases in CuZn SOD activity during ageing may be due to both translational and post-translational control.

Superoxide dismutase gene expression in skeletal muscle: fiber-specific adaptation to endurance training.

The effects of endurance training on the enzyme activity, protein content, and mRNA abundance of Mn and CuZn superoxide dismutase (SOD) were studied in various phenotypes of rat skeletal muscle. Female Sprague-Dawley rats were randomly divided into trained (T, n = 8) and untrained (U, n = 8) groups. Training, consisting of treadmill running at 27 m/min and 12% grade for 2 h/day, 5 days/wk for 10 wk, significantly increased citrate synthase activity (P < 0. 01) in the type I (soleus), type IIa (deep vastus lateralis, DVL), and mixed type II (plantaris) muscles but not in type IIb (superficial vastus lateralis, SVL) muscle. Mitochondrial (Mn) SOD activity was elevated by 80% (P < 0.05) with training in DVL. SVL and plantaris muscle in T rats showed 54 and 42% higher pooled immunoreactive Mn SOD protein content, respectively, than those in U rats. However, no change in Mn SOD mRNA level was found in any of the muscles. CuZn SOD activity, protein content, and mRNA level in general were not affected by training, except for a 160% increase in pooled CuZn SOD protein in SVL. Training also significantly increased glutathione peroxidase and catalase activities (P < 0.05), but only in DVL muscle. These data indicate that training adaptations of Mn SOD and other antioxidant enzymes occur primarily in type IIa fibers, probably as a result of enhanced free radical generation and modest antioxidant capacity. Differential training responses of mRNA, enzyme protein, and activity suggest that separate cellular signals may control pre- and posttranslational regulation of SOD.

EFFECTS OF TRAINING AND DIETARY GLUTATHIONE ON LIVER AND MUSCLE GLUTATHIONE STATUS IN RATS

71 The purpose of the present study was to investigate the effects of endurance training (T) in conjunction with glutathione (GSH) supplementation (S) on liver and muscle GSH status in rats. Forty female Sprague-Dawley rats (age 4 mo.) were randomly divided into either untrained (U) or T (treadmill running at 25 m/min, 15% grade for 75 min/day, 5 d/wk for 10 wk). Half of U and T group of rats was fed a GSH-S diet (5g GSH/kg) during the final 17 days of training, whereas the other half received control (C) diet. Liver and muscle tissues were removed immediately after an open-heart sham surgery lasting 90 min performed 52 h after the last training session. GSH and glutathione disulfide (GSSG) contents were measured in liver, soleus (SOL), and deep (DVL) and superficial (SVL) vastus lateralis muscles using HPLC method. T increased citrate synthase activity in SOL by 50 and 47% (P<0.01) in C and GSH-S, respectively. Liver GSH content was increased by 9% with T (P<0.05), by 9% with GSH-S (P<0.05), and by 17% with T plus GSH-S (P<0.05). GSSG content was increased by 15 and 8% with T (P<0.05) in C and GSH-S, respectively. Thus, in U rats the GSH:GSSG ratio was elevated by 24% in GSH-S vs. C (P<0.05). GSH content in SOL decreased by 32 and 30% with T (P<0.05) in C and GSH-S, respectively, whereas GSSG level was unaltered. These changes resulted in a 26 and 23% lower GSH:GSSG ratio with T in C and GSH-S rats, respectively. Neither T nor GSH-S affected GSH and GSSG content in DVL and SVL. In conclusion, endurance training in conjunction with GSH-S improved post-surgical GSH content and redox status in the liver. GSH-S in the current regimen did not increase muscle GSH status or prevent the exercise-induced decrease in GSH content in the soleus. (Supported by AHA-WI grant-in-aid and CNPq-Brazil)

Training decreases muscle glycogen turnover during exercise.

The present study was undertaken to determine the effects of endurance training on glycogen kinetics during exercise. A new model describing glycogen kinetics was applied to quantitate the rates of synthesis and degradation of glycogen. Trained and untrained rats were infused with a 25% glucose solution with 6-3H-glucose and U-14C-lactate at 1.5 and 0.5 microCi x min(-1) (where 1 Ci=3.7 x 10(10) Bq), respectively, during rest (30 min) and exercise (60 min). Blood samples were taken at 10-min intervals starting just prior to isotopic infusion, until the cessation of exercise. Tissues harvested after the cessation of exercise were muscle (soleus, deep, and superficial vastus lateralis, gastrocnemius), liver, and heart. Tissue glycogen was quantitated and analyzed for incorporation of 3H and 14C via liquid scintillation counting. There were no net decreases in muscle glycogen concentration from trained rats, whereas muscle glycogen concentration decreased to as much as 64% (P < 0.05) in soleus in muscles from untrained rats after exercise. Liver glycogen decreased in both trained (30%) and untrained (40%) rats. Glycogen specific activity increased in all tissues after exercise indicating isotope incorporation and, thus, glycogen synthesis during exercise. There were no differences in muscle glycogen synthesis rates between trained and untrained rats after exercise. However, training decreased muscle glycogen degradation rates in total muscle (i.e., the sum of the degradation rates of all of the muscles sampled) tenfold (P < 0.05). We have applied a model to describe glycogen kinetics in relation to glucose and lactate metabolism during exercise in trained and untrained rats. Training significantly decreases muscle glycogen degradation rates during exercise.

Effect of vitamin E deprivation and exercise training on induction of HSP70.

To investigate the effect of dietary vitamin E deprivation and chronic exercise on the relative content of selected isoforms of the heat-shock protein 70 (HSP70) family in rat hindlimb muscle, vitamin E was withheld for 16 wk from female rats that underwent treadmill run training during the final 8 wk. As indicated by increased (P < 0.05) content of the stress-inducible isoform (HSP72), training did stress the exercising muscles. However, vitamin E deficiency did not alter HSP72 content in nontrained rats and was associated with a lesser induction (P < 0.01) in some muscles of trained animals. The constitutive isoform, which exhibited similar levels in muscles of varying fiber types, was demonstrated to be largely refractory to exercise, with an equivocal response to vitamin E deprivation. HSP72 content was correlated to type I myosin heavy chain (MHC-I) content but only in muscles of sedentary normal-diet rats. After training, HSP72 content in a muscle essentially devoid of MHC-I (superficial vastus lateralis) reached levels comparable to those in a muscle high in MHC-I (soleus).