REGULATION OF WHOLE-BODY ENERGY HOMEOSTASIS WITH GROWTH HORMONE REPLACEMENT THERAPY AND ENDURANCE EXERCISE

We hypothesized that network analysis is useful to expose coordination between whole body and myocellular levels of energy metabolism and can identify entities that underlie skeletal muscle's contribution to growth hormone-stimulated lipid handling and metabolic fitness. We assessed 112 metabolic parameters characterizing metabolic rate and substrate handling in tibialis anterior muscle and vascular compartment at rest, after a meal and exercise with growth hormone replacement therapy (GH-RT) of hypopituitary patients (n = 11). The topology of linear relationships (| r | ≥ 0.7, P ≤ 0.01) and mutual dependencies exposed the organization of metabolic relationships in three entities reflecting basal and exercise-induced metabolic rate, triglyceride handling, and substrate utilization in the pre- and postprandial state, respectively. GH-RT improved aerobic performance (+5%), lean-to-fat mass (+19%), and muscle area of tibialis anterior (+2%) but did not alter its mitochondrial and capillary content. Concomitantly, connectivity was established between myocellular parameters of mitochondrial lipid metabolism and meal-induced triglyceride handling in serum. This was mediated via the recruitment of transcripts of muscle lipid mobilization (LIPE, FABP3, and FABP4) and fatty acid-sensitive transcription factors (PPARA, PPARG) to the metabolic network. The interdependence of gene regulatory elements of muscle lipid metabolism reflected the norm in healthy subjects (n = 12) and distinguished the regulation of the mitochondrial respiration factor COX1 by GH and endurance exercise. Our observations validate the use of network analysis for systems medicine and highlight the notion that an improved stochiometry between muscle and whole body lipid metabolism, rather than alterations of single bottlenecks, contributes to GH-driven elevations in metabolic fitness.

Effect of two beta-alanine dosing protocols on muscle carnosine synthesis and washout

Carnosine (β-alanyl-L-histidine) is found in high concentrations in skeletal muscle and chronic β-alanine (BA) supplementation can increase carnosine content. This placebo-controlled, double-blind study compared two different 8-week BA dosing regimens on the time course of muscle carnosine loading and 8-week washout, leading to a BA dose-response study with serial muscle carnosine assessments throughout. Thirty-one young males were randomized into three BA dosing groups: (1) high-low: 3.2 g BA/day for 4 weeks, followed by 1.6 g BA/day for 4 weeks; (2) low-low: 1.6 g BA/day for 8 weeks; and (3) placebo. Muscle carnosine in tibialis-anterior (TA) and gastrocnemius (GA) muscles was measured by 1H-MRS at weeks 0, 2, 4, 8, 12 and 16. Flushing symptoms and blood clinical chemistry were trivial in all three groups and there were no muscle carnosine changes in the placebo group. During the first 4 weeks, the increase for high-low (TA 2.04 mmol/kgww, GA 1.75 mmol/kgww) was ~twofold greater than low-low (TA 1.12 mmol/kgww, GA 0.80 mmol/kgww). 1.6 g BA/day significantly increased muscle carnosine within 2 weeks and induced continual rises in already augmented muscle carnosine stores (week 4-8, high-low regime). The dose-response showed a carnosine increase of 2.01 mmol/kgww per 100 g of consumed BA, which was only dependent upon the total accumulated BA consumed (within a daily intake range of 1.6-3.2 g BA/day). Washout rates were gradual (0.18 mmol/kgww and 0.43 mmol/kgww/week; ~2%/week). In summary, the absolute increase in muscle carnosine is only dependent upon the total BA consumed and is not dependent upon baseline muscle carnosine, the muscle type, or the daily amount of supplemented BA.

Muscle velocity recovery cycles: effects of repetitive stimulation on two muscles

We sought to characterize the excitability properties of tibialis anterior (TA) and brachioradialis (BR) muscles at rest and during electrically induced muscle activation in normal subjects.

Magnetization exchange observed in human skeletal muscle by non-water-suppressed proton magnetic resonance spectroscopy

Many metabolites in the proton magnetic resonance spectrum undergo magnetization exchange with water, such as those in the downfield region (6.0-8.5 ppm) and the upfield peaks of creatine, which can be measured to reveal additional information about the molecular environment. In addition, these resonances are attenuated by conventional water suppression techniques complicating detection and quantification. To characterize these metabolites in human skeletal muscle in vivo at 3 T, metabolite cycled non-water-suppressed spectroscopy was used to conduct a water inversion transfer experiment in both the soleus and tibialis anterior muscles. Resulting median exchange-independent T(1) times for the creatine methylene resonances were 1.26 and 1.15 s, and for the methyl resonances were 1.57 and 1.74 s, for soleus and tibialis anterior muscles, respectively. Magnetization transfer rates from water to the creatine methylene resonances were 0.56 and 0.28 s(-1) , and for the methyl resonances were 0.39 and 0.30 s(-1) , with the soleus exhibiting faster transfer rates for both resonances, allowing speculation about possible influences of either muscle fibre orientation or muscle composition on the magnetization transfer process. These water magnetization transfer rates observed without water suppression are in good agreement with earlier reports that used either postexcitation water suppression in rats, or short CHESS sequences in human brain and skeletal muscle.

Spinal Cord Diffusion-Tensor Imaging and Motor-evoked Potentials in Multiple Sclerosis Patients: Microstructural and Functional Asymmetry

Purpose: To assess possible association between intrinsic structural damage and clinical disability by correlating spinal cord diffusion-tensor (DT) imaging data with electrophysiological parameters in patients with a diagnosis of multiple sclerosis (MS). Materials and Methods: This study was approved by the local ethical committee according to the declaration of Helsinki and written informed consent was obtained. DT images and T1- and T2-weighted images of the spinal cord were acquired in 28 healthy volunteers and 41 MS patients. Fractional anisotropy (FA) and apparent diffusion coefficients were evaluated in normal-appearing white matter (NAWM) at the cervical level and were correlated with motor-evoked potentials (n = 34). Asymmetry index was calculated for FA values with corresponding left and right regions of interest as percentage of the absolute difference between these values relative to the sum of the respective FA values. Statistical analysis included Spearman rank correlations, Mann-Whitney test, and reliability analysis. Results: Healthy volunteers had low asymmetry index (1.5%-2.2%). In MS patients, structural abnormalities were reflected by asymmetric decrease of FA (asymmetry index: 3.6%; P = .15). Frequently asymmetrically affected among MS patients was left and right central motor conduction time (CMCT) to abductor digiti minimi muscle (ADMM) (asymmetry index, 15%-16%) and tibialis anterior muscle (TAM) (asymmetry index, 9.5%-14.1%). Statistically significant correlations of functional (ie, electrophysiological) and structural (ie, DT imaging) asymmetries were found (P = .005 for CMCT to ADMM; P = .007 for CMCT to TAM) for the cervical lateral funiculi, which comprise the crossed pyramidal tract. Interobserver reliability for DT imaging measurements was excellent (78%-87%). Conclusion: DT imaging revealed asymmetric anatomic changes in spinal cord NAWM, which corresponded to asymmetric electrophysiological deficits for both arms and legs, and reflected a specific structure-function relationship in the human spinal cord. © RSNA, 2013.

Prolonged amelioration of acute lung allograft rejection by overexpression of human interleukin-10 under control of a long acting ubiquitin C promoter in rats

BACKGROUND: The prolonged effect of electroporation-mediated human interleukin-10 (hIL-10) overexpression in skeletal muscle under the control of the constitutional polyubiquitin C promoter (pUb hIL-10) on rat lung allograft rejection was evaluated. METHODS: Left lung allotransplantation was performed from Brown-Norway to Fischer-F344 rats. Either 2.5 mug pCIK hIL-10 (hIL-10/cytomegalovirus early promoter enhancer) alone (Group I/sacrifice Day 5 and II/sacrifice Day 10) or in combination with 2.5 mug pUb hIL-10 (hIL-10/UbC promoter; Group III/sacrifice Day 10) were injected into the tibialis anterior muscle of the recipient, followed by electroporation 24 hours before transplantation. Animals in Control Groups IV and V without gene transfer were euthanized on Day 5 and 10, respectively. All animals received a daily non-therapeutic dose of cyclosporine A (2.5 mg/kg). RESULTS: In Control Group IV, complete rejection (median A3B3) was noted on Day 5 with a Pao(2) of 43 +/- 9 mm Hg. In recipients of Control Group V, measurement of gas exchange on Day 10 and rejection grading was impossible because of complete destruction of the allograft. Group I animals on Day 5 (233 +/- 123 mm Hg; p = 0.02 vs Group IV) and Group II animals on Day 10 (150 +/- 139 mm Hg; p = 0.15 vs Group IV) demonstrated improved graft function. Graft function in Group III was further improved on Day 10 (299 +/- 123 mm Hg; p = 0.002 vs Group IV; p = 0.05 vs Group II; p = 0.36 vs Group I). Rejection was significantly reduced in Group III (median, A2B2) compared with Group II (median, A4B3; p < 0.05). CONCLUSIONS: Interleukin-10 overexpression under control of the constitutive ubiquitin C promoter ameliorates acute rejection and preserves lung graft function for a prolonged time.

Electroporation-mediated interleukin-10 overexpression in skeletal muscle reduces acute rejection in rat cardiac allografts

OBJECTIVES: Human interleukin 10 (hIL-10) may reduce acute rejection after organ transplantation. Our previous data shows that electroporation-mediated transfer of plasmid DNA to peripheral muscle enhances gene transduction dramatically. This study was designed to investigate the effect of electroporation-mediated overexpression of hIL-10 on acute rejection of cardiac allografts in the rat. METHODS: The study was designed to evaluate the effect of hIL-10 gene transfer on (a) early rejection pattern and (b) graft survival. Gene transfer was achieved by intramuscular (i.m.) injection into the tibialis anterior muscle of Fischer (F344) male recipients followed by electroporation 24 h prior to transplantation. Heterotopic cardiac transplantation was performed from male Brown Norway rat to F344. Four groups were studied (n = 6). Treated animals in groups B1 and B2 received 2.5 microg of pCIK hIL-10 and control animals in groups A1 and A2 distilled water. Graft function was assessed by daily palpation. Animals from group A1 were sacrificed at the cessation of the heart beat of the graft and those in group B1 were sacrificed at day 7; blood was taken for ELISA measurement of hIL-10 and tissue for myeloperoxidase (MPO) measurement and histological assessment. To evaluate graft survival, groups A2 and B2 were sacrificed at cessation of the heart beat of the graft. RESULTS: Histological examination revealed severe rejection (IIIB-IV) in group A1 in contrast to low to moderate rejection (IA-IIIA) in group B1 (p = 0.02). MPO activity was significantly lower in group B1 compared to group A1 (18 +/- 7 vs. 32 +/- 14 mU/mg protein, p = 0.05). Serum hIL-10 levels were 46 +/- 13 pg/ml in group B1 vs. 0 pg/ml in group A1. At day 7 all heart allografts in the treated groups B1 and B2 were beating, whereas they stopped beating at 5 +/- 2 days in groups A1 and A2 vs. 14 +/- 2 days in group B2 (p = 0.0012). CONCLUSIONS: Electroporation-mediated intramuscular overexpression of hIL-10 reduces acute rejection and improves survival of heterotopic heart allografts in rats. This study demonstrates that peripheral overexpression of specific genes in skeletal muscle may reduce acute rejection after whole organ transplantation.

Postexercise fat intake repletes intramyocellular lipids but no faster in trained than in sedentary subjects

The hypotheses that postexercise replenishment of intramyocellular lipids (IMCL) is enhanced by endurance training and that it depends on fat intake were tested. Trained and untrained subjects exercised on a treadmill for 2 h at 50% peak oxygen consumption, reducing IMCL by 26-22%. During recovery, they were fed 55% (high fat) or 15% (low fat) lipid energy diets. Muscle substrate stores were estimated by (1)H (IMCL)- and (13)C (glycogen)-magnetic resonance spectroscopy in tibialis anterior muscle before and after exercise. Resting IMCL content was 71% higher in trained than untrained subjects and correlated significantly with glycogen content. Both correlated positively with indexes of insulin sensitivity. After 30 h on the high-fat diet, IMCL concentration was 30-45% higher than preexercise, whereas it remained 5-17% lower on the low-fat diet. Training status had no significant influence on IMCL replenishment. Glycogen was restored within a day with both diets. We conclude that fat intake postexercise strongly promotes IMCL repletion independently of training status. Furthermore, replenishment of IMCL can be completed within a day when fat intake is sufficient.

Managing chronic whiplash associated pain with a combination of low-dose opioid (remifentanil) and NMDA-antagonist (ketamine)

The aim was to investigate the efficacy of a combination of low-dose remifentanil (REMI) and ketamine (KET) compared to the single drugs and placebo (P) on whiplash associated pain (WAD) in a double-blind, randomized, placebo-controlled, cross-over study. Twenty patients with chronic (>1 year) WAD were included. Four different drug combinations were tested in four sessions: placebo/placebo (P/P), placebo/remifentanil (P/REMI), ketamine/placebo (KET/P) and ketamine/remifentanil (KET/REMI). Target concentrations were 1 and 2ng/ml (stepwise) for remifentanil and 100ng/ml for ketamine. Habitual pain intensity was assessed on a visual analogue scale (VAS). Experimental pain was assessed with electrical stimulation (single and repeated) of tibialis anterior (TA) muscle, pressure pain algometry applied over infraspinatus (IS) and TA muscles and VAS scores after intramuscular hypertonic saline infusion in TA. KET/REMI significantly reduced habitual pain. KET/REMI infused at low REMI target concentration (1ng/ml) significantly elevated electrical intramuscular pain thresholds (single and repeated). Pain thresholds to electrical stimulation were similarly increased by both P/REMI and KET/REMI at 2ng/ml target concentration. Pressure pain thresholds were increased by both KET/REMI and P/REMI. VAS-scores after intramuscular saline were also similarly decreased by both REMI combinations. Seven out of 20 subjects were non-responders (<50% pain relief). No correlation was found between effects on spontaneous pain and experimental pain. KET/REMI showed an analgesic effect on habitual pain. Experimental pain was attenuated by both combinations containing the opioid, however, KET seemed to enhance the effect of REMI on electrical pain thresholds when a low REMI target concentration was used.

New method for quantification and statistical analysis of nociceptive reflex receptive fields in humans

A method for quantifying nociceptive withdrawal reflex receptive fields in human volunteers and patients is described. The reflex receptive field (RRF) for a specific muscle denotes the cutaneous area from which a muscle contraction can be evoked by a nociceptive stimulus. The method is based on random stimulations presented in a blinded sequence to 10 stimulation sites. The sensitivity map is derived by interpolating the reflex responses evoked from the 10 sites. A set of features describing the size and location of the RRF is presented based on statistical analysis of the sensitivity map within every subject. The features include RRF area, volume, peak location and center of gravity. The method was applied to 30 healthy volunteers. Electrical stimuli were applied to the sole of the foot evoking reflexes in the ankle flexor tibialis anterior. The RRF area covered a fraction of 0.57+/-0.06 (S.E.M.) of the foot and was located on the medial, distal part of the sole of the foot. An intramuscular injection into flexor digitorum brevis of capsaicin was performed in one spinal cord injured subject to attempt modulation of the reflex receptive field. The RRF area, RRF volume and location of the peak reflex response appear to be the most sensitive measures for detecting modulation of spinal nociceptive processing. This new method has important potential applications for exploring aspects of central plasticity in volunteers and patients. It may be utilized as a new diagnostic tool for central hypersensitivity and quantification of therapeutic interventions.

Distribution of intramyocellular lipids in human calf muscles as determined by MR spectroscopic imaging

In this study the distribution of intramyocellular lipids (IMCL) in human calf muscles was determined by 1H-MR spectroscopic imaging (MRSI) measurements. An obstacle for MRSI measurements in the calf, including different muscles, is the inevitable inclusion of regions with high concentrations of extramyocellular lipids (EMCL). This can lead to signal bleeding and consequently to unpredictable overlaps of IMCL resonances with EMCL in voxels of interest. The results of this study show that signal bleeding from EMCL can be substantially reduced in voxels from calf muscles by the application of a lipid extrapolation (LE) procedure (Haupt et al., Magn Reson Med 1996;35:678). The spectra of all voxels located within muscle tissue were fitted, and the metabolite values were assigned to one of 10 different muscles based on image segmentation. Significant IMCL differences between some muscles were obtained, with high values in m. soleus and two to three times lower values in the tibialis anterior, tibialis posterior, and gastrocnemius muscles. In addition to gross differences between muscles, significant intersubject differences were observed in both IMCL content and distribution over different muscles. A significant correlation between fiber orientation (obtained from orientation-dependent dipolar coupling of creatine and taurine resonances) and IMCL content was found, indicating that IMCL content is directly correlated to biomechanical properties.

Mechanisms of protein regulation in rat skeletal muscle during resistance exercise and training

The cellular mechanisms through which adult rat skeletal muscle protein is regulated during resistance exercise and training was investigated. A model of non-voluntary resistance exercise was described which involves the electrically-stimulated contraction of the lower leg muscles of anesthetized rats against a weighted pulley-bar. Muscle protein synthesis rates were measured by in vivo constant infusion of $\sp3$H-leucine following a single bout of resistance exercise. Specific messenger RNA levels were determined by dot-blot hybridization analysis using $\sp{32}$P-labelled DNA probes after a single bout and multiple bouts of phasic training. The effects of phasic training on increasing skeletal muscle mass was assessed. Between 12 and 36 hours following a single resistance exercise bout (24-192 contractions), total mixed and myofibril protein synthesis rates were significantly increase (32%-65%) after concentric (gastrocnemius m.) and eccentric (tibialis anterior m.) contractions. Eccentric contractions had greater effects on myofibril synthesis with more prolonged increases in synthesis rates. Lower numbers of eccentric than concentric contractions were required to increase synthesis. Cellular RNA was increased after exercise but the relative levels of skeletal $\alpha$-actin and cytochrome c mRNAs were unchanged. Since increases in synthesis rates exceeded increases in RNA, post-transcriptional mechanisms may be primarily responsible for increased protein synthesis after a resistance exercise bout. After 10-22 weeks of phasic eccentric resistance training, muscle enlargement (16%-30%) was produced in the tibialis anterior m. after all training paradigms examined. In contrast, gastrocnemius m. enlargement after phasic concentric training occurred after moderate (24/bout) but not after high (192/bout) repetition training. The absence of muscle growth in the gastrocnemius m. after high repetition training despite increased synthesis rates after the initial bout and RNA and possibly mRNA accumulation during training suggests a role for post-translational mechanisms (protein degradation) in the control of muscle growth in the gastrocnemius m. It is concluded that muscle protein during resistance exercise and training is regulated at several cellular levels. The particular response may be influenced by the exercise intensity and duration, the training frequency and the type of contractile work (eccentric vs. concentric) performed. ^

Neuromuscular disuse and atrophy: {\it In vivo\/} magnetic resonance studies of intramuscular lipid metabolism and fluid shift changes

We postulated that neuromuscular disuse results in deleteriously affected tissue-vascular fluid exchange processes and subsequently damages the important oxidative bioenergetic process of intramuscular lipid metabolism. The in-depth research reported in the literature is somewhat limited by the ex vivo nature and sporadic time-course characterization of disuse atrophy and recovery. Thus, an in vivo controlled, localized animal model of disuse atrophy was developed in one of the hindlimbs of laboratory rabbits (employing surgically implanted tetrodotoxin (TTX)-filled mini-osmotic pump-sciatic nerve superfusion system) and tested repeatedly with magnetic resonance (MR) throughout the 2-week period of temporarily induced disuse and during the recovery period (following explantation of the TTX-filled pump) for a period of 3 weeks. Controls consisted of saline/"sham"-implanted rabbit hindlimbs. The validity of this model was established with repeated electrophysiologic nerve conduction testing using a clinically appropriate protocol and percutaneously inserted small needle stimulating and recording electrodes. Evoked responses recorded from proximal (P) and distal (D) sites to the sciatic nerve cuff in the TTX-implanted group revealed significantly decreased (p $<$ 0.001) proximal-to-distal (P/D) amplitude ratios (as much as 50-70% below Baseline/pre-implanted and sham-implanted group values) and significantly increased (p $<$ 0.01) differential latency (PL-DL) values (as much as 1.5 times the pre- and sham-implanted groups). By Day 21 of recovery, observed P/D and PL-DL levels matched Baseline/sham-implemented levels. MRI-determined cross-sectional area (CSA) values of Baseline/pre-implanted, sham- or TTX-implanted, and recovering/explanted and the corresponding contralateral hindlimb tibialis anterior (TA) muscles normalized to tibial bone (TB) CSA (in TA/TB ratios) revealed that there was a significant decline (indicative of atrophic response) from pre- and sham-implanted controls by as much as 20% (p $<$ 0.01) at Day 7 and 50-55% (p $<$ 0.001) at Day 13 of TTX-implantation. In the non-implanted contralaterals, a significant increase (indicative of hypertrophic response) by as much as 10% (p $<$ 0.025) at Day 7 and 27% (p $<$ 0.001) at Day 13 + TTX was found. The induced atrophic/hypertrophic TA muscles were observed to be fully recovered by Day 21 post-explantation as evidenced by image TA/TB ratios. End-point biopsy results from a small group of rabbits revealed comprehensive atrophy of both Type I and Type II fibers, although the heterogeneity of the response supports the use of image-guided, volume-localized proton magnetic resonance spectroscopy (MRS) to noninvasively assess tissue-level metabolic changes. MRS-determined results of a 0.25cc volume of tissue within implanted limb TA muscles under resting/pre-ischemic, ischemic-stressed, and post-ischemic conditions at timepoints during and following disuse atrophy/recovery revealed significantly increased intramuscular spectral lipid levels, as much as 2-3 times (p $<$ 0.01) the Baseline/pre-implanted values at Day 7 and 6-7 times (p $<$ 0.001) at Day 13 + TTX, which approached normal levels (compared to pre- and sham-implanted groups) by Day 21 of post-explanation recovery. (Abstract shortened by UMI.) ^

THE EFFECTS OF STREPTOZOTOCIN DIABETES AND DIETARY IRON INTAKE ON CATALASE, GLUTATHIONE PEROXIDASE, SUPEROXIDE DISMUTASE AND LIPID PEROXIDATION IN CARDIAC AND SKELETAL MUSCLES OF RATS

Catalase, glutathione peroxidase (GSH-Px) and superoxide dismutase (SOD) prevent oxygen free radical mediated tissue damage. Diabetes increases and a low dietary intake of iron decreases catalase activity in muscle. Therefore, the combined effects of diabetes and iron deficiency on the free radical scavenging enzyme system and lipid peroxidation were studied. Male, weanling rats were injected with streptozotocin (65 mg/kg, IV) and fed diets containing either 35 ppm iron (Db + Fe) or 8 ppm iron (Db $-$ Fe). Sham injected animals served as iron adequate (C + Fe) or iron deficient (C $-$ Fe) controls. Heart, gastrocnemius (GT), soleus and tibialis anterior (TA) muscles were dissected, weighted and analyzed for catalase, GSH-Px and SOD activities after 3, 6 or 9 weeks on the respective diets. The TBA assay was used to assess lipid peroxidation in the GT muscle. Diabetes elevated catalase activity in all muscles while it had a slight lowering effect on SOD and GSH-Px activities in the GT and TA muscles. In the C $-$ Fe rats, catalase activity declined and remained depressed in all muscles except the heart. There was an elevation in GSH-Px and SOD in the GT muscles of these animals after 6 weeks but not after 9 weeks of consuming the low iron diet. The Db $-$ Fe animals were unable to respond to the diabetic state with catalase activity as high as observed in the Db + Fe rats. Treatment with insulin or iron returned catalase to control levels. The C $-$ Fe animals had significantly lower levels of lipid peroxidation than the other groups at 6 and 9 weeks. Refeeding an iron adequate diet resulted in an increase in lipid peroxidation levels. These studies indicate that skeletal muscle free radical scavenging enzymes are sensitive to metabolic states and that dietary iron influences lipid peroxidation in this tissue. ^

Protective Effect of Focal Adhesion Kinase against Skeletal Muscle Reperfusion Injury after Acute Limb Ischemia.

OBJECTIVES In cardiac muscle, ischemia reperfusion (IR) injury is attenuated by mitochondrial function, which may be upregulated by focal adhesion kinase (FAK). The aim of this study was to determine whether increased FAK levels reduced rhabdomyolysis in skeletal muscle too. MATERIAL AND METHODS In a translational in vivo experiment, rat lower limbs were subjected to 4 hours of ischemia followed by 24 or 72 hours of reperfusion. FAK expression was stimulated 7 days before (via somatic transfection with pCMV-driven FAK expression plasmid) and outcomes were measured against non-transfected and empty transfected controls. Slow oxidative (i.e., mitochondria-rich) and fast glycolytic (i.e., mitochondria-poor) type muscles were analyzed separately regarding rhabdomyolysis, apoptosis, and inflammation. Severity of IR injury was assessed using paired non-ischemic controls. RESULTS After 24 hours of reperfusion, marked rhabdomyolysis was found in non-transfected and empty plasmid-transfected fast-type glycolytic muscle, tibialis anterior. Prior transfection enhanced FAK concentration significantly (p = 0.01). Concomitantly, levels of BAX, promoting mitochondrial transition pores, were reduced sixfold (p = 0.02) together with a blunted inflammation (p = 0.01) and reduced rhabdomyolysis (p = 0.003). Slow oxidative muscle, m. soleus, reacted differently: although apoptosis was detectable after IR, rhabdomyolysis did not appear before 72 hours of reperfusion; and FAK levels were not enhanced in ischemic muscle despite transfection (p = 0.66). CONCLUSIONS IR-induced skeletal muscle rhabdomyolysis is a fiber type-specific phenomenon that appears to be modulated by mitochondria reserves. Stimulation of FAK may exploit these reserves constituting a potential therapeutic approach to reduce tissue loss following acute limb IR in fast-type muscle.