The effects of adenine nucleotide perfusion on interstitial adenosine production in rat skeletal muscle.

The purpose of the present study was to utilize the microdialysis technique in rat skeletal muscle to perfuse varying concentrations of AMP, ADP, and ATP into the interstitium to examine the effects that these adenine nucleotides have on the production of adenosine in the interstitial space. Interstitial adenosine production appears to be related to the type (ATP, ADP, or AMP) and concentration (2-60 µmol/L) of the adenine nucleotide perfused. Interstitial adenosine levels increased (P < 0.05) from baseline (0.18 ± 0.02 and 0.22 ± 0.02 µmol/L) to 0.23 ± 0.02 and 0.41 ± 0.05 µmol/L following 5 and 30 µmol/L AMP perfusion, respectively. Similarly, perfusion with 30 µmol/L ADP and 30, 40, and 60 µmol/L ATP resulted in an increase (P < 0.05) in interstitial adenosine concentration from baseline (0.25 ± 0.02, 0.26 ± 0.02, 0.19 ± 0.03, and 0.14 ± 0.02 µmol/L) to 0.30 ± 0.02, 0.32 ± 0.02, 0.36 ± 0.04, and 0.33 ± 0.04 µmol/L, respectively. Interestingly, the most prominent increase in interstitial adenosine production occurred during the perfusion of 60 µmol/L ATP (126% increase from baseline). These data strongly suggest that interstitial ATP may play a more potent role in stimulating interstitial adenosine production as compared with ADP or AMP. In addition, interstitial adenosine production can occur independent of muscle contraction (voluntary or involuntary) or hypoxia when adequate concentrations of adenine nucleotides are available.

Doxorubicin chemotherapy affects intracellular and interstitial nitric oxide concentrations in skeletal muscle : Effect of doxorubicin on intracellular and interstitial NO in skeletal muscle.

The role of nitric oxide (NO) in doxorubicin (DOX; cancer chemotherapeutic)-induced cardiotoxicity is well established. In skeletal muscle (SM), NO regulation plays a critical role in health, biogenesis, and function. Despite the increasing evidence that indicates the negative impact of DOX on SM function, the effect of DOX on NO production in SM has yet to be examined. The purpose of the current study was to simultaneously examine intracellular and interstitial NO concentrations in the SM following the administration of DOX. A single dose of 1.5 or 4.5 mg/kg was administered intraperitoneally to male Sprague Dawley rats, and interstitial (IS) and intracellular (IC) NO was quantified every 24 up to 192 h post-injection. There was no significant difference in IC NO following the injection of 1.5 mg/kg DOX when compared to the control; however, the administration of 4.5 mg/kg DOX resulted in lower (P < 0.05) concentrations of NO in the IC. Interestingly, a consistently higher (P < 0.05) concentration of NO in the IS was established following the administration of 1.5 mg/kg compared to the control while no significant changes in IS NO resulted from the administration of the 4.5 mg/kg dose. The fluctuation of IS and IC NO was not a result of substrate availability as arginine concentrations remained stable throughout the experiment. By utilizing the microdialysis technique, we have simultaneously quantified for the first time the IS and IC concentrations of NO in SM following DOX administration. These data provide important insight in the possible mechanisms leading to DOX-related SM dysfunction.

Historical pesticide applications for the treatment of eastern spruce budworm infestations in New Brunswick.

Pesticides have been used in Canada since 1945 as part of large-scale aerial spray applications to control insect pests on forested lands. Some of the pesticides used historically were efficacious, nonselective, persistent, and have led to serious impacts on the environment. A well known, and extensively documented example is the large-scale aerial spray programs in New Brunswick, Canada. From 1952 to 1993, 97% of the 6.2 million ha of the forested lands of New Brunswick were treated with at least one application of one insecticide, the majority of which were applied to control outbreaks of eastern spruce budworm (Choristoneura fumiferana). The most well known insecticide was dichlorodiphenyltrichloroethane (DDT), applied from 1952 to 1968, which still persists in treated soils and adjacent water bodies, and caused the individual and cumulative ecosystem effects that can still be measured today. The insecticides that replaced DDT were nonpersistent and unlikely to be found today. However, during the years of application some of the insecticides were likely to have impacted local ecosystems to some degree. To aid future studies on the efficacy and environmental impact of these insecticides we created a digital spatial data set of known pesticide application in New Brunswick forestry from 1952 to 1993. The data set includes active ingredient, formulation, application rate, tank mix, aircraft type, and other ancillary information. The current version of the data is available on the New Brunswick Department of Natural Resources and Energy Development, GIS Open Data Page and in the supplemental material. Use of the data set for academic and educational purposes is encouraged, provided that both this data paper and the data source are properly cited; the Government of New Brunswick should be acknowledged as the data source (Open Government License http://www.snb.ca/e/2000/data-E.html).

Role of aldo-keto reductases and other doxorubicin pharmacokinetic genes in doxorubicin resistance, DNA binding, and subcellular localization.

BACKGROUND: Since proteins involved in chemotherapy drug pharmacokinetics and pharmacodynamics have a strong impact on the uptake, metabolism, and efflux of such drugs, they likely play critical roles in resistance to chemotherapy drugs in cancer patients. METHODS: To investigate this hypothesis, we conducted a whole genome microarray study to identify difference in the expression of genes between isogenic doxorubicin-sensitive and doxorubicin-resistant MCF-7 breast tumour cells. We then assessed the degree of over-representation of doxorubicin pharmacokinetic and pharmacodynamic genes in the dataset of doxorubicin resistance genes. RESULTS: Of 27,958 Entrez genes on the array, 7.4 per cent or 2,063 genes were differentially expressed by ≥ 2-fold between wildtype and doxorubicin-resistant cells. The false discovery rate was set at 0.01 and the minimum p value for significance for any gene within the "hit list" was 0.01. Seventeen and 43 per cent of doxorubicin pharmacokinetic genes were over-represented in the hit list, depending upon whether the gene name was identical or within the same gene family, respectively. The most over-represented genes were within the 1C and 1B families of aldo-keto reductases (AKRs), which convert doxorubicin to doxorubicinol. Other genes convert doxorubicin to other metabolites or affect the influx, efflux, or cytotoxicity of the drug. In further support of the role of AKRs in doxorubicin resistance, we observed that, in comparison to doxorubicin, doxorubincol exhibited dramatically reduced cytotoxicity, reduced DNA-binding activity, and strong localization to extra nuclear lysosomes. Pharmacologic inhibition of the above AKRs in doxorubicin-resistant cells increased cellular doxorubicin levels, restored doxorubicin cytotoxicity and re-established doxorubicin localization to the nucleus. The properties of doxorubicinol were unaffected. CONCLUSIONS: These findings demonstrate the utility of using curated pharmacokinetic and pharmacodynamic knowledge bases to identify highly relevant genes associated with doxorubicin resistance. The induction of one or more of these genes was found to be correlated with changes in the drug's properties, while inhibiting one specific class of these genes (the AKRs) increased cellular doxorubicin content and restored drug DNA binding, cytotoxicity, and subcellular localization.

Benefit-cost analysis of spruce budworm (Choristoneura fumiferana Clem.) control: incorporating market and non-market values.

This study employs a benefit-cost analysis framework to estimate market and non-market benefits and costs of controlling future spruce budworm (Choristoneura fumiferana) outbreaks on Crown forest lands in New Brunswick, Canada. We used: (i) an advanced timber supply model to project potential timber volume saved, timber value benefits, and costs of pest control efforts; and (ii) a recent contingent valuation method analysis that evaluated non-market benefits (i.e., changes in recreation opportunities and existence values) of controlling future spruce budworm outbreaks in the Province. A total of six alternative scenarios were evaluated, including two uncontrolled future budworm outbreak severities (moderate vs. severe) and, for each severity, three control program levels (protecting 10%, 20%, or 40% of the susceptible Crown land forest area). The economic criteria used to evaluate each scenario included benefit-cost ratios and net present values. Under severe outbreak conditions, results indicated that the highest benefit-cost ratio (4.04) occurred when protecting 10% (284,000 ha) of the susceptible area, and the highest net present value ($111 M) occurred when protecting 20% (568,000 ha) of the susceptible area. Under moderate outbreak conditions, the highest benefit-cost ratio (3.24) and net present value ($58.7 M) occurred when protecting 10% (284,000 ha) of the susceptible area. Inclusion of non-market values generally increased the benefit-cost ratios and net present values of the control programs, and in some cases, led to higher levels of control being supported. Results of this study highlight the importance of including non-market values into the decision making process of forest pest management.

Doxorubicin chemotherapy affects the intracellular and interstitial free amino acid pools in skeletal muscle.

Skeletal muscle (SM) health and integrity is dependent on the dynamic balance between protein synthesis and degradation, and central to this process is the availability of amino acids (AA) in the amino pool. While Doxorubicin (DOX) remains one of the most widely used chemotherapeutic agents for the treatment of solid and hematological malignancies, little is known of the effect of the drug on SM, particularly its effect on the availability of amino acids in the tissue. The purpose of this study was to examine the effect of DOX administration on vascular, interstitial and intracellular concentrations of AA in SM of the rat up to 8 days after the administration of a 1.5 or 4.5 mg/kg i.p. dose of DOX. In the plasma, total amino acids (TAA) were significantly increased compared to control where greater (P<0.05) concentrations were observed following the 1.5 mg/kg dose compared to the 4.5 mg/kg dose. Compared to control, the 1.5 mg/kg dose resulted in an increase (P<0.05) in interstitial TAA whereas the 4.5 mg/kg resulted in a sustained decrease (P<0.05). Intracellular TAA, essential amino acids (EAA) and branched-chain amino acids (BCAA) where significantly increased in each muscle group analyzed, following the 1.5 and 4.5 mg/kg doses compared to control. This study provides important insight into the amino acid response following DOX chemotherapy and presents a substantial foundation for future studies focused on reducing SM damage and recovery by targeting amino acid metabolism.

Cross-scale effects of spruce budworm outbreaks on boreal warblers in eastern Canada.

Insect outbreaks are major natural disturbance events that affect communities of forest birds, either directly by affecting the food supply or indirectly by changing the vegetation composition of forest canopies. An examination of correlations between measures of bird and insect abundance across different spatial scales and over varying time lag effects may provide insight into underlying mechanisms. We developed a hierarchical Bayesian model to assess correlations between counts of eight warbler species from the Breeding Bird Survey in eastern Canada, 1966 to 2009, with the presence of spruce budworm (Choristoneura fumiferana Clem.) at immediate local scales and time-lagged regional scales, as measured by extent of defoliation on host tree species. Budworm-associated species Cape May warbler (Setophaga tigrina), bay-breasted warbler (Setophaga castanea), and Tennessee warbler (Oreothlypis peregrina) responded strongly and positively to both local and regional effects. In contrast, non-budworm-associated species, Blackburnian warbler (Setophaga fusca), magnolia warbler (Setophaga magnolia), Canada warbler (Cardellina canadensis), black-throated blue warbler (Setophaga caerulescens), and black-throated green warbler (Setophaga virens), only responded to regional effects in a manner that varied across eastern Canada. The complex responses by forest birds to insect outbreaks involve both increased numerical responses to food supply and to longer term responses to changes in forest structure and composition. These effects can vary across spatial scales and be captured in hierarchical population models, which can serve to disentangle common trends from data when examining drivers of population dynamics like forest management or climate change.

Statins and dietary and serum cholesterol are associated with increased lean mass following resistance training.

BACKGROUND: Age-related muscle loss (sarcopenia) is a prevalent condition associated with disability and mortality. Exercise and optimal nutrition are interventions to prevent and treat sarcopenia, yet little is known, outside of protein, of the effect of common nutrition recommendations and medication use on exercise-related muscle gain. METHODS: Forty-nine community-dwelling, 60- to 69-year-old men and women completed 2 weeks of nutrition education (American Dietetic Association recommendations) followed by 12 weeks of high intensity resistance exercise training (RET) with postexercise protein supplementation and 3x/wk dietary logs. RESULTS: We observed a dose-response relationship between dietary cholesterol (from food logs) and gains in lean mass that was not affected by variability in protein intake. Serum cholesterol and the serum cholesterol lowering agent statin were also independently associated with greater increases in lean mass. Dietary cholesterol was not associated with serum cholesterol or the significant reduction in blood pressure observed, but trends were observed for altered plasma C-reactive protein. CONCLUSION: These data suggest that dietary and serum cholesterol contribute to the skeletal muscles' response to RET in this generally healthy older population and that some statins may improve this response.

Mast cell degranulation and de novo histamine formation contribute to sustained postexercise vasodilation in humans.

In humans, acute aerobic exercise elicits a sustained postexercise vasodilation within previously active skeletal muscle. This response is dependent on activation of histamine H1 and H2 receptors, but the source of intramuscular histamine remains unclear. We tested the hypothesis that interstitial histamine in skeletal muscle would be increased with exercise and would be dependent on de novo formation via the inducible enzyme histidine decarboxylase and/or mast cell degranulation. Subjects performed 1 h of unilateral dynamic knee-extension exercise or sham (seated rest). We measured the interstitial histamine concentration and local blood flow (ethanol washout) via skeletal muscle microdialysis of the vastus lateralis. In some probes, we infused either α-fluoromethylhistidine hydrochloride (α-FMH), a potent inhibitor of histidine decarboxylase, or histamine H1/H2-receptor blockers. We also measured interstitial tryptase concentrations, a biomarker of mast cell degranulation. Compared with preexercise, histamine was increased after exercise by a change (Δ) of 4.2 ± 1.8 ng/ml (P < 0.05), but not when α-FMH was administered (Δ-0.3 ± 1.3 ng/ml, P = 0.9). Likewise, local blood flow after exercise was reduced to preexercise levels by both α-FMH and H1/H2 blockade. In addition, tryptase was elevated during exercise by Δ6.8 ± 1.1 ng/ml (P < 0.05). Taken together, these data suggest that interstitial histamine in skeletal muscle increases with exercise and results from both de novo formation and mast cell degranulation. This suggests that exercise produces an anaphylactoid signal, which affects recovery, and may influence skeletal muscle blood flow during exercise.NEW & NOTEWORTHY Blood flow to previously active skeletal muscle remains elevated following an acute bout of aerobic exercise and is dependent on activation of histamine H1 and H2 receptors. The intramuscular source of histamine that drives this response to exercise has not been identified. Using intramuscular microdialysis in exercising humans, we show both mast cell degranulation and formation of histamine by histidine decarboxylase contributes to the histamine-mediated vasodilation that occurs following a bout of aerobic exercise.

Muscle interstitial calcium during head-up tilt in humans.

BACKGROUND: During head-up tilt (HUT), peripheral vasoconstriction occurs. This response requires appropriate communication between the sympathetic nerve terminal and vascular smooth muscle cell in the neurovascular space. Both of these cell types require extracellular calcium ([Ca2+]o) for proper activation and function. We hypothesize that [Ca2+]o rises with tilt and in the process contributes to vasoconstriction. METHODS AND RESULTS: We used microdialysis techniques in the lower-limb skeletal muscle to measure [Ca2+]o changes in this space with HUT. [Ca2+]o was measured in 10 healthy subjects during HUT. We found a 62% increase in the dialysate [Ca2+] (0.223+/-0.018 to 0.353+/-0.028 mmol/L) with HUT. CONCLUSIONS: This result implies a significant increase in [Ca2+]o in the neurovascular space during HUT. This represents the first report of such in situ [Ca2+]o measurements in humans. This rise in [Ca2+]o may provide a mechanism for proper cell-cell interaction, helping to promote peripheral vasoconstriction during HUT. How this [Ca2+]o transient affects the nerve terminal, vascular smooth muscle cells, or both remains to be determined.

Orally administered leucine enhances protein synthesis in skeletal muscle of diabetic rats in the absence of increases in 4E-BP1 or S6K1 phosphorylation.

In this study, food-deprived (18 h) control rats and rats with alloxan-induced diabetes were orally administered saline or the amino acid leucine to assess whether it regulates protein synthesis independently of a change in serum insulin concentrations. Immediately after leucine administration, diabetic rats were infused with insulin (0.0, 4.0, or 20 pmol small middle dot min(-1) small middle dot kg(-1)) for 1 h to examine the role of the hormone in the protein synthetic response to leucine. In control rats, leucine stimulated protein synthesis by 58% and increased phosphorylation of the translational repressor, eukaryotic initiation factor (eIF) 4E-binding protein (BP)-1, 4E-BP1, fivefold. Consequently, association of the mRNA cap-binding protein eukaryotic initiation factor (eIF)4E with 4E-BP1 was reduced to 50% of control values, and eIF4G*eIF4E complex assembly was increased 80%. Furthermore, leucine increased the phosphorylation of the 70-kDa ribosomal protein S6 (rp S6) and the ribosomal protein S6 kinase (S6K1). Diabetes attenuated protein synthesis compared with control rats. Nonetheless, in diabetic rats, leucine increased protein synthesis by 53% without concomitant changes in the phosphorylation of 4E-BP1 or S6K1. Skeletal muscle protein synthesis was stimulated in diabetic rats infused with insulin, but rates of synthesis remained less than values in nondiabetic controls that were administered leucine. Phosphorylation of 4E-BP1 and S6K1 was increased in diabetic rats infused with insulin in a dose-dependent manner, and the response was enhanced by leucine. The results suggest that leucine enhances protein synthesis in skeletal muscle through both insulin-dependent and -independent mechanisms. The insulin-dependent mechanism is associated with increased phosphorylation of 4E-BP1 and S6K1. In contrast, the insulin-independent effect on protein synthesis is mediated by an unknown mechanism.

Skeletal Muscle an Active Compartment in the Sequestering and Metabolism of Doxorubicin Chemotherapy.

Doxorubicin remains one of the most widely used chemotherapeutic agents however its effect on healthy tissue, such as skeletal muscle, remains poorly understood. The purpose of the current study was to examine the accumulation of doxorubicin (DOX) and its metabolite doxorubicinol (DOXol) in skeletal muscle of the rat up to 8 days after the administration of a 1.5 or 4.5 mg kg-1 i.p. dose. Subsequent to either dose, DOX and DOXol were observed in skeletal muscle throughout the length of the experiment. Interestingly an efflux of DOX was examined after 96 hours, followed by an apparent re-uptake of the drug which coincided with a spike and rapid decrease of plasma DOX concentrations. The interstitial space within the muscle did not appear to play a significant rate limiting compartment for the uptake or release of DOX or DOXol from the tissue to the circulation. Furthermore, there was no evidence that DOX preferentially accumulated in a specific muscle group with either dose. It appears that the sequestering of drug in skeletal muscle plays an acute and important role in the systemic availability and metabolism of DOX which may have a greater impact on the clinical outcome than previously considered.

A Novel Modelling Approach for Predicting Forest Growth and Yield under Climate Change.

Global climate is changing due to increasing anthropogenic emissions of greenhouse gases. Forest managers need growth and yield models that can be used to predict future forest dynamics during the transition period of present-day forests under a changing climatic regime. In this study, we developed a forest growth and yield model that can be used to predict individual-tree growth under current and projected future climatic conditions. The model was constructed by integrating historical tree growth records with predictions from an ecological process-based model using neural networks. The new model predicts basal area (BA) and volume growth for individual trees in pure or mixed species forests. For model development, tree-growth data under current climatic conditions were obtained using over 3000 permanent sample plots from the Province of Nova Scotia, Canada. Data to reflect tree growth under a changing climatic regime were projected with JABOWA-3 (an ecological process-based model). Model validation with designated data produced model efficiencies of 0.82 and 0.89 in predicting individual-tree BA and volume growth. Model efficiency is a relative index of model performance, where 1 indicates an ideal fit, while values lower than zero means the predictions are no better than the average of the observations. Overall mean prediction error (BIAS) of basal area and volume growth predictions was nominal (i.e., for BA: -0.0177 cm(2) 5-year(-1) and volume: 0.0008 m(3) 5-year(-1)). Model variability described by root mean squared error (RMSE) in basal area prediction was 40.53 cm(2) 5-year(-1) and 0.0393 m(3) 5-year(-1) in volume prediction. The new modelling approach has potential to reduce uncertainties in growth and yield predictions under different climate change scenarios. This novel approach provides an avenue for forest managers to generate required information for the management of forests in transitional periods of climate change. Artificial intelligence technology has substantial potential in forest modelling.

Leg blood flow during submaximal cycle ergometry is not reduced in healthy older normally active men.

The purpose of the present study was to test the hypothesis that leg blood flow responses during submaximal cycle ergometry are reduced with age in healthy normally active men. Eleven younger (20-25 yr) and eight older (62-73 yr) normotensive, nonendurance-trained men performed both graded and constant-load bouts of leg cycling at the same absolute and relative [% of peak O(2) consumption (Vo(2 peak))] exercise intensities while leg blood flow (femoral vein thermodilution), mean arterial pressure (MAP; radial artery), cardiac output (acetylene rebreathing), blood O(2) content, and plasma catecholamines were measured. Leg blood flow responses at the same absolute submaximal power outputs (20-100 W) and at a fixed systemic O(2) demand (1.1 l/min) did not differ between groups (P = 0.14-0.19), despite lower absolute levels of cardiac output in the older men (P < 0.05). MAP at the same absolute power outputs was 8-12 mmHg higher (P < 0.05) in the older men, but calculated leg vascular conductance responses (leg blood flow/MAP) were identical in the two groups (P > 0.9). At the same relative intensity (60% Vo(2 peak)), leg norepinephrine spillover rates were approximately twofold higher in the older men (P = 0.38). Exercise-induced increases in leg arterial-venous O(2) difference were identical between groups (P > 0.9) because both arterial and venous O(2) contents were lower in the older vs. younger men. These results suggest that the ability to augment active limb blood flow and O(2) extraction during submaximal large muscle mass exercise is not impaired but is well preserved with age in healthy men who are normally active.

Local histamine H(1-) and H(2)-receptor blockade reduces postexercise skeletal muscle interstitial glucose concentrations in humans.

Elevated blood flow can potentially influence skeletal muscle glucose uptake, but the impact of postexercise hyperemia on glucose availability to skeletal muscle remains unknown. Because postexercise hyperemia is mediated by histamine H(1)- and H(2)-receptors, we tested the hypothesis that postexercise interstitial glucose concentrations would be lower in the presence of combined H1- and H2-receptor blockade. To this end, 4 microdialysis probes were inserted into the vastus lateralis muscle of 14 healthy subjects (21-27 years old) immediately after 60 min of either upright cycling at 60% peak oxygen uptake (exercise, n = 7) or quiet rest (sham, n = 7). Microdialysis probes were perfused with a modified Ringer's solution containing 3 mmol L(-1) glucose, 5 mmol L(-1) ethanol, and [6-3H] glucose (200 disintegrations·min-1 microL(-1)). Two sites (blockade) received both H1- and H2-receptor antagonists (1 mmol L(-1) pyrilamine and 3 mmol L-1 cimetidine) and 2 sites (control) did not receive antagonists. Ethanol outflow/inflow ratios (an inverse surrogate of local blood flow) were higher in blockade sites than in control sites following exercise (p < 0.05), whereas blockade had no effect on ethanol outflow/inflow ratios following sham (p = 0.80). Consistent with our hypothesis, during 3 of the 5 dialysate collection periods, interstitial glucose concentrations were lower in blockade sites vs. control sites following exercise (p < 0.05), whereas blockade had no effect on interstitial glucose concentrations following sham (p = 0.79). These findings indicate that local H1- and H2-receptor activation modulates skeletal muscle interstitial glucose levels during recovery from exercise in humans and suggest that the availability of glucose to skeletal muscle is enhanced by postexercise hyperemia.

Induction of 1C aldoketoreductases and other drug dose-dependent genes upon acquisition of anthracycline resistance.

OBJECTIVES: Recent studies suggest that tumor cells overexpressing aldoketoreductases (AKRs) exhibit increased resistance to DNA damaging agents such as anthracyclines. AKRs may induce resistance to the anthracycline doxorubicin by catalyzing its conversion to the less toxic 13-hydroxy metabolite doxorubicinol. However, it has not been established whether during selection for anthracycline resistance, AKR overexpression in tumor cells can be correlated with the onset or magnitude of drug resistance and with appreciable conversion of anthracyclines to 13-hydroxy metabolites. METHODS AND FINDINGS: Through microarray and quantitative polymerase chain reaction studies involving rigid selection criteria and both correlative discriminate statistics and time-course models, we have identified several genes whose expression can be correlated with the onset and/or magnitude of anthracycline resistance, including AKR1C2 and AKR1C3. Also associated with the onset or magnitude of anthracycline resistance were genes involved in drug transport (ABCB1, ABCC1), cell signaling and transcription (RDC1, CXCR4), cell proliferation or apoptosis (BMP7, CAV1), protection from reactive oxygen species (AKR1C2, AKR1C3, FTL, FTH, TXNRD1, MT2A), and structural or immune system proteins (IFI30, STMN1). As expected, doxorubicin-resistant and epirubicin-resistant cells exhibited higher levels of doxorubicinol than wild-type cells, although at insufficient levels to account for significant drug resistance. Nevertheless, an inhibitor of Akr1c2 (5beta-cholanic acid) almost completely restored sensitivity to doxorubicin in ABCB1-deficient doxorubicin-resistant cells, while having no effect on ABCB1-expressing epirubicin-resistant cells. CONCLUSION: Taken together, we show for the first time that a variety of genes (particularly redox genes such as AKR1C2 and AKR1C3) can be temporally and causally correlated with the acquisition of anthracycline resistance in breast tumor cells.

Venous but not skeletal muscle interstitial nitric oxide is increased during hypobaric hypoxia.

Systemic hypoxia leads to peripheral vasodilation that serves to counteract the decrease in peripheral oxygen (O(2)) delivery. Skeletal muscle vasodilation associated with hypoxia is due to release of vasodilator substances such as adenosine and/or nitric oxide (NO). We hypothesized that skeletal muscle may act as a source of NO during exposure to hypoxia. Therefore, we measured NO in forearm venous plasma and in skeletal muscle interstitial dialysate in seven healthy young men during exposure to simulated altitude of 2,438 and 4,877 m (20 min at each level) in a hypobaric chamber. O(2) saturation (mean +/- SEM) fell from 98.0 +/- 0.2% at ambient conditions to 91.0 +/- 0.4% at 2,438 m and to 73.2 +/- 4.4% at 4,877 m (P < 0.05). While blood pressure remained unchanged, heart rate increased in a graded fashion (P < 0.05). Plasma NO (chemiluminescence method) rose from 11.6 +/- 1.3 to 16.9 +/- 2.9 microM at 2,438 m (P < 0.05) but remained similar at 16.4 +/- 2.3 microM at 4,877 m (NS). In contrast, skeletal muscle microdialysate NO levels were lower than plasma NO (P < 0.01) and did not change during simulated altitude. Thus, hypoxia produced by simulated high altitude exposure leads to an increase in plasma but not skeletal muscle interstitial NO. These data support an important role of NO in the peripheral vascular responses to hypoxia. The differential responses of plasma vs. interstitial NO during hypoxia suggest an endothelial or intravascular source of NO.

Protein intake for skeletal muscle hypertrophy with resistance training in seniors.

Variability in protein consumption may influence muscle mass changes induced by resistance exercise training (RET). We sought to administer a post-exercise protein supplement and determine if daily protein intake variability affected variability in muscle mass gains. Men (N=22) and women (N=30) ranging in age from 60 to 69 y participated in a 12-wk RET program. At each RET session, participants consumed a post-exercise drink (0.4 g/kg lean mass protein). RET resulted in significant increases in lean mass (1.1 +/- 1.5 kg), similar between sexes (P > 0.05). Variability in mean daily protein intake was not associated with change in lean mass (r < 0.10, P > 0.05). The group with the highest protein intake (1.35 g x kg(-1) x d(-1), n=8) had similar (P > 0.05) changes in lean mass as the group with the lowest daily protein intake (0.72 g x kg(-1) x d(-1), n=9). These data suggest that variability in total daily protein intake does not affect variability in lean mass gains with RET in the context of post-exercise protein supplementation.

Effects of graded LBNP on MSNA and interstitial norepinephrine.

Exposure to lower body negative pressure (LBNP) leads to an increased activation of the sympathetic nervous system (SNS) and an increase in muscle sympathetic nerve activity (MSNA). In this study, we examined the relationship between MSNA and interstitial norepinephrine (NE(i)) concentrations during LBNP. Twelve healthy volunteers were studied (26 +/- 6 yr). Simultaneous MSNA and microdialysis data were collected in six of these subjects. Measurements of MSNA (microneurography) and NE(i) (microdialysis, vastus lateralis) were performed at rest and then during an incremental LBNP paradigm (-10, -30, and -50 mmHg). MSNA rose as a function of LBNP (P < 0.001, n = 12). The plasma norepinephrine (NE(p)) concentration was 0.9 +/- 0.1 nmol/l at rest (n = 12). NE(i) measured in six subjects rose from 5.2 +/- 0.8 nmol/l at rest to 17.0 +/- 1.7 nmol/l at -50 mmHg (P < 0.001). Of note, the rise in NE(p) with LBNP was considerably less compared with the changes in NE(i) (Delta21 +/- 6% vs. Delta197 +/- 52%, n = 6, P < 0.015). MSNA and NE(i) showed a significant linear relationship (r = 0.721, P < 0.004). Activation of the SNS increased MSNA and NE(i) levels. The magnitude of the NE(i) increase was far greater than that seen for NE(p) suggesting that NE movement into the circulation decreases with baroreceptor unloading.

In vivo muscle amino acid transport involves two distinct processes.

We have tested the hypothesis that transit through the interstitial fluid, rather than across cell membranes, is rate limiting for amino acid uptake from blood into muscle in human subjects. To quantify muscle transmembrane transport of naturally occurring amino acids, we developed a novel 4-pool model that distinguishes between the interstitial and intracellular fluid compartments. Transport kinetics of phenylalanine, leucine, lysine, and alanine were quantified using tracers labeled with stable isotopes. The results indicate that interstitial fluid is a functional compartment insofar as amino acid kinetics are concerned. In the case of leucine and alanine, transit between blood and interstitial fluid was potentially rate limiting for muscle amino acid uptake and release in the postabsorptive state. For example, in the case of leucine, the rate of transport between blood and interstitial fluid compared with the corresponding rate between interstitial fluid and muscle was 247 +/- 36 vs. 610 +/- 95 nmol.min(-1).100 ml leg(-1), respectively (P < 0.05). Our results are consistent with the process of diffusion governing transit from blood to interstitial fluid without selectivity, and of specific amino acid transport systems with varying degrees of efficiency governing transit from interstitial fluid to muscle. These results imply that changes in factors that affect the transit of amino acids from blood through interstitial fluid, such as muscle blood flow or edema, could play a major role in controlling the rate of muscle amino acid uptake.