bluuebunny/crossref_metadata_2025 huggingface dataset:
Epidermal growth factor decreases PEPT2 transport capacity and expression in the rat kidney proximal tubule cell line SKPT0193 cl.2
Authors: Bravo Silvina A. , Nielsen Carsten Uhd , Amstrup Jan , Frokjaer Sven , Brodin Birger
Published: January 2004

The renal peptide transporter PEPT2 plays an important role in absorption of di- and tripetides in the proximal tubule; however, knowledge of regulation of PEPT2 by growth factors and hormones is limited. In the present study, we examined the effects of epidermal growth factor (EGF) on PEPT2 transport capacity and expression in the rat proximal tubule cell line SKPT0193 cl.2 (SKPT), which expresses rat PEPT2 (rPEPT2) in the apical membrane. Treatment of SKPT cells with EGF during cell culture growth caused a dose-dependent decrease in rPEPT2 transport capacity and expression, as determined by studies of apical uptake of [14C]glycylsarcosine, rPepT2 mRNA levels, and immunostaining of SKPT cells with a rPEPT2-specific antibody. On the contrary, apical uptake of glucose and lysine was increased in EGF-treated cells, indicating that EGF was not acting generally to decrease apical nutrient uptake mechanisms in the proximal tubule cells. Our findings indicate that EGF decreases rPEPT2 expression by lowering transcription of the rat PepT2 gene or by decreasing rat PepT2 mRNA stability. Previous investigators routinely used SKPT cell culture media with a high (10 ng/ml) EGF concentration. Our study suggests that this might be disadvantageous when studying PEPT2-mediated transport phenomena. These findings demonstrate for the first time EGF-mediated regulation of PEPT2 expression in a kidney cell line. The relevance for kidney regulation of peptide transport activity in physiological and/or pathophysiological situations, where EGF and EGF receptor levels change drastically, remains to be established.
Tuberous sclerosis-2 tumor suppressor modulates ERK and B-Raf activity in transformed renal epithelial cells
Authors: Yoon Hae-Seong , Ramachandiran Sampath , Chacko Mary Anne S. , Monks Terrence J. , Lau Serrine S.
Published: January 2004

The tuberous sclerosis-2 ( Tsc-2) gene is a suppressor of renal tumorigenesis and an early target of reactive oxygen species-induced renal cancer. Tuberin, the protein product of the Tsc-2 gene, participates in the regulation of cell proliferation, although the mechanism by which it suppresses proliferation is unknown. Quinol-thioether-transformed rat renal epithelial (QT-RRE) cell lines, derived from quinol-thioether-transformed primary renal epithelial cells from Eker rats, lack tuberin expression due to loss of heterozygosity of the Tsc-2 gene. These cell lines were used to examine the mechanism by which tuberin exerts its antiproliferative action. Loss of tuberin function correlates with high ERK activity ( 39 ), which could contribute to the formation of renal tumors. In this study, we sought to identify possible downstream effectors regulated by tuberin, using QT-RRE cells transfected with Tsc-2 cDNA to restore tuberin expression. Constitutively high ERK, B-Raf, and Raf-1 activities were observed in QT-RRE cells. However, restoration of tuberin expression in QT-RRE cells by transient transfection with Tsc-2 cDNA substantially decreased both ERK and B-Raf activity, with only modest changes in Raf-1 activity, suggesting tuberin functions as an upstream negative regulator of the ERK pathway. High ERK activity was not mediated through EGF receptor activation, but treatment with genistein demonstrated that protein kinases are involved in ERK cascade activation. The data indicate that loss of tuberin results in the upregulation of the ERK signaling pathway with subsequent increases in new DNA synthesis, and ultimately, tumor formation.
T-type calcium channels in the regulation of afferent and efferent arterioles in rats
Authors: Feng Ming-Guo , Li Ming , Navar L. Gabriel
Published: January 2004

L-type Ca2+ channels predominantly influence preglomerular arterioles, but there is less information regarding the role of T-type Ca2+ channels in regulating the renal microvasculature. We compared the effects of T- and L-type channel blockade on afferent and efferent arterioles using the in vitro blood-perfused juxtamedullary nephron preparation. Single afferent or efferent arterioles of Sprague-Dawley rats were visualized and superfused with solutions containing Ca2+ channel blockers. We confirmed that L-type channel blockade with diltiazem dilates afferent arterioles but has no significant effects on efferent arterioles. In contrast, T-type channel blockade with pimozide (10 μmol/l) or mibefradil (1 μmol/l) dilated both afferent (26.8 ± 3.4 and 24.6 ± 1.9%) and efferent (19.2 ± 2.9 and 19.1 ± 4.8%) arterioles. Adding diltiazem did not significantly augment the dilation of afferent arterioles elicited by pimozide and mibefradil, and adding pimozide after diltiazem likewise did not elicit further vasodilation. Diltiazem blocked the depolarization-induced afferent arteriolar constriction elicited by 55 mM KCl; however, the constrictor response to KCl remained intact during treatment with 10 μM pimozide. Pimozide also prevented the afferent arterioles from exhibiting autoregulatory-mediated constrictor responses to increases in perfusion pressure. We conclude that T-type channel blockers dilate efferent arterioles as well as afferent arterioles and diminish afferent arteriolar autoregulatory responses to changes in perfusion pressure. To the extent that these agents exert their effects primarily on T-type Ca2+ channels in our experimental setting, these results indicate that T-type channels are functionally expressed in juxtamedullary afferent and efferent arterioles and may act cooperatively with L-type channels to regulate afferent arteriolar resistance. Because L-type channels are not functionally expressed in efferent arterioles, T-type channels may be particularly significant in the regulation of efferent arteriolar function.
Extracellular matrix regulates glomerular epithelial cell survival and proliferation
Authors: Bijian Krikor , Takano Tomoko , Papillon Joan , Khadir Abdelkrim , Cybulsky Andrey V.
Published: January 2004

Glomerular epithelial cell (GEC) injury and apoptosis may contribute to sclerosis in glomerulonephritis. The present study addresses signals that regulate survival of GEC in culture and in the acute puromycin aminonucleoside nephrosis (PAN) model of GEC injury in vivo. Compared with GEC on plastic substratum, adhesion to collagen increased activation of focal adhesion kinase (FAK), c-Src, and ERK and facilitated survival (prevented apoptosis). GEC on plastic exhibited increased caspase-8 and -9 activities, increased expression of the proapoptotic protein, Bax, and decreased the antiapoptotic protein, Bcl-XL, compared with collagen. Stable expression of constitutively active mutants of FAK (CD2-FAK) or MEK (R4F-MEK) activated the ERK pathway and supplanted the requirement of collagen for survival. In contrast, expression of a Ras mutant that activates phosphatidylinositol 3-kinase but blocks ERK activation or pharmacological inhibition of the ERK pathway decreased survival on collagen. Glomeruli isolated from rats with PAN revealed increased β1-integrin expression, along with increased activation of FAK, c-Src, and ERK, compared with controls. EGF receptor activation was undetectable in PAN. Therefore, adhesion to collagen, resulting in activation of FAK and the Ras-ERK pathway, supports GEC survival. Analogous signals for GEC survival are activated in PAN.
Two-photon in vivo microscopy of sulfonefluorescein secretion in normal and cystic rat kidneys
Authors: Tanner George A. , Sandoval Ruben M. , Dunn Kenneth W.
Published: January 2004

Sulfonefluorescein (SF) is a fluorescent organic anion secreted by kidney proximal tubules. The purposes of this study were 1) to quantify accumulation of SF in normal and cystic rat kidneys in vivo and 2) to test whether SF accumulation could be used as a marker for cysts derived from proximal tubules. Male Munich-Wistar rats, normal Han:SPRD rats, and heterozygous Han:SPRD rats with autosomal-dominant polycystic kidney disease were anesthetized with Inactin and solutions containing SF were administered by constant intravenous infusion. In Munich-Wistar rats, SF fluorescence in the urinary space of Bowman's capsule averaged 0.15 ± 0.04 ( n = 17) times that of glomerular capillary plasma, consistent with extensive plasma protein binding of SF. In normal Han:SPRD rats, steady-state cell cytoplasm SF fluorescence in proximal tubule and distal tubule cells averaged, respectively, 2.7 ± 1.4 ( n = 99 tubules) and 0.2 ± 0.2 ( n = 17) times that of peritubular capillary plasma. No punctate SF fluorescence was seen in proximal tubule cell cytoplasm. Probenecid reduced proximal tubule cell SF fluorescence to 0.64 ± 0.40 ( n = 64) times that of plasma. Ureteral obstruction decreased the proximal tubule cell-to-lumen SF fluorescence gradient, suggesting that tubule fluid flow normally sweeps away secreted SF. In cystic kidneys, cysts derived from proximal tubules could be identified by their uptake of SF, but cell uptake was patchy. We conclude that in vivo two-photon microscopy is a powerful tool for quantifying glomerular and tubular handling of SF, and SF can be used to identify proximal tubule-derived cysts.
Protein kinase C-ϵ modulates mitochondrial function and active Na+transport after oxidant injury in renal cells
Authors: Nowak Grażyna , Bakajsova Diana , Clifton Ginger L.
Published: January 2004

The aim of this study was to determine whether protein kinase C-ϵ (PKC-ϵ) is involved in the repair of mitochondrial function and/or active Na+transport after oxidant injury in renal proximal tubular cells (RPTC). Sublethal injury was produced in primary cultures of RPTC using tert-butylhydroperoxide (TBHP), and the recovery of functions was examined. PKC-ϵ was activated three- to fivefold after injury. Active PKC-ϵ translocated to the mitochondria. Basal oxygen consumption (Qo2), uncoupled Qo2, and ATP production decreased 58, 60, and 41%, respectively, at 4 h and recovered by day 4 after injury. At 4 h, complex I-coupled respiration decreased 50% but complex II- and IV-coupled respirations were unchanged. Inhibition of PKC-ϵ translocation using a peptide selective inhibitor, PKC-ϵV1-2, reduced decreases in basal and uncoupled Qo2values and increased complex I-linked respiration in TBHP-injured RPTC at 4 h of recovery. Furthermore, PKC-ϵV1-2 prevented decreases in ATP production in injured RPTC. Na+-K+-ATPase activity and ouabain-sensitive86Rb+uptake were decreased by 60 and 53%, respectively, at 4 h of recovery. Inhibition of PKC-ϵ activation prevented a decline in Na+-K+-ATPase activity and reduced decreases in ouabain-sensitive86Rb+uptake. We conclude that during early repair after oxidant injury in RPTC 1) PKC-ϵ is activated and translocated to mitochondria; 2) PKC-ϵ activation decreases mitochondrial respiration, electron transport rate, and ATP production by reducing complex I-linked respiration; and 3) PKC-ϵ mediates decreases in active Na+transport and Na+-K+-ATPase activity. These data show that PKC-ϵ activation after oxidant injury in RPTC is involved in the decreases in mitochondrial function and active Na+transport and that inhibition of PKC-ϵ activation promotes the repair of these functions.
Three-dimensional functional reconstruction of inner medullary thin limbs of Henle's loop
Authors: Pannabecker Thomas L. , Abbott Diane E. , Dantzler William H.
Published: January 2004

Digital three-dimensional (3-D) functional reconstructions of inner medullary nephrons were performed. Antibodies against aquaporins (AQP)-1 and -2 and the chloride channel ClC-K1 identified descending thin limbs (DTLs), collecting ducts (CDs), and ascending thin limbs (ATLs), respectively, through indirect immunofluorescence. Tubules were labeled in transverse sections and assembled into 3-D arrays, permitting individual tubule or combined surface representations to depths of 3.3 mm to be viewed in an interactive digital model. Surface representations of 75 tubules positioned near the central region of the inner medulla were reconstructed. In most DTL segments that form loops below 1 mm from the inner medullary base, AQP1 expression begins at the base, becomes intermittent for variable lengths, and continues nearly midway to the loop. The terminal DTL segment exhibiting undetectable AQP1 represents nearly 60% of the distance from the medullary base to the tip of the loop. AQP1 expression was entirely undetectable in shorter long-looped DTLs. ClC-K1 is expressed continuously along the terminal portion of all DTLs reconstructed here, beginning with a prebend region ∼164 μm before the bend in all tubules and continuing through the entire ascent of the ATLs to the base of the inner medulla. CDs express AQP2 continuously and extensive branching patterns are illustrated. 3-D functional reconstruction of inner medullary nephrons is capable of showing axial distribution of membrane proteins in tubules of the inner medulla and can contribute to further development and refinement of models that attempt to elucidate the concentrating mechanism.
Water turnover in 458 American adults 40-79 yr of age
Authors: Raman Aarthi , Schoeller Dale A. , Subar Amy F. , Troiano Richard P. , Schatzkin Arthur , Harris Tamara , Bauer Douglas , Bingham Shiela A. , Everhart James E. , Newman Anne B. , Tylavsky Frances A.
Published: January 2004

Despite recent interest in water intake, few data are available on water metabolism in adults. To determine the average and range of usual water intake, urine output, and total body water, we administered 2H oxide to 458 noninstitutionalized 40- to 79-yr-old adults living in temperate climates. Urine was collected in a subset of individuals ( n = 280) to measure 24-h urine production using p-aminobenzoic acid to ensure complete collection. Preformed water intake was calculated from isotopic turnover and corrected for metabolic water and insensible water absorption from humidity. Preformed water intake, which is water from beverages and food moisture, averaged 3.0 l/day in men (range: 1.4-7.7 l/day) and 2.5 l/day in women (range: 1.2-4.6 l/day). Preformed water intake was lower in 70- to 79 (2.8 l/day)- than in 40- to 49-yr-old men and was lower in 70- to 79 (2.3 l/day)- than in 40- to 49- and 50- to 59-yr-old women. Urine production averaged 2.2 l/day in men (range: 0.6-4.9 l/day) and 2.2 l/day in women (0.9-6.0 l/day). There were no age-related differences in results in women, but 60- to 69-yr-old men had significantly higher urine output than 40- to 49- and 50- to 59-yr-old men. Only the 70- to 79-yr-old group included sufficient blacks for a racial analysis. Blacks in this age group showed significantly lower preformed water intake than did whites. Whites had significantly higher water turnover rates than blacks as well. Multivariate regression indicated that age, weight, height, and body mass index explained <12% of the gender-specific variance in water input or urine output, yet repeat measures indicated that within-individual coefficient of variation was 8% for preformed water intake ( n = 22) and 9% for 24-h urine production ( n = 222). These results demonstrate that water turnover is highly variable among individuals and that little of the variance is explained by anthropometric parameters.
Conditional gene expression in renal collecting duct epithelial cells: use of the inducible Cre-lox system
Authors: Ouvrard-Pascaud Antoine , Puttini Stefania , Sainte-Marie Yannis , Athman Rafika , Fontaine Virginie , Cluzeaud Françoise , Farman Nicolette , Rafestin-Oblin Marie-Edith , Blot-Chabaud Marcel , Jaisser Frederic
Published: January 2004

The renal collecting duct plays a key role in control of ion and fluid homeostasis. Genes encoding for ion transporters, hormone receptors, or regulatory proteins specifically expressed in the collecting duct are mutated in several genetic diseases with altered blood pressure. Suitable cellular models expressing genes in a conditional way should represent attractive systems for structure-function analyses and generation of appropriate physiopathological models of related diseases. However, generation of such systems remains laborious and quite inefficient. We adapted and improved a conditional Cre-lox-inducible system in the highly differentiated aldosterone-sensitive rat cortical collecting duct (RCCD2) cell line. The inducible MerCreMer recombinase allowed tight control and high levels of transgene expression, whereas flanking a selection marker with two loxP sites strongly improved the selection procedure. We have used this system to conditionally express an enhanced green fluorescent protein-tagged human mineralocorticoid receptor. In the future, this will allow structure-function analyses as well as mineralocorticoid receptor trafficking studies in these epithelial cells, which retain the features of the native collecting duct. Improvements in the conditional Cre-lox expression system have potentially wide applications in other epithelial or nonepithelial cell lines.
ERK and p38 mediate high-glucose-induced hypertrophy and TGF-β expression in renal tubular cells
Authors: Fujita Hisayo , Omori Sayu , Ishikura Kenji , Hida Mariko , Awazu Midori
Published: January 2004

We investigated the expression of ERK, p38 mitogen-activated protein kinase (p38), and JNK in renal tubules of diabetic rats following 3 wk after streptozotocin injection (DM). Although the expression of ERK was not different between controls and DM, phosphorylated ERK was expressed more intensely in DM. p38 And phosphorylated p38 were detected only in the diabetic kidney and were localized in all tubular segments. JNK and phosphorylated JNK were expressed similarly in controls and DM. Transforming growth factor (TGF)-β was expressed in all tubular segments of DM, coinciding with the localization of p38. In LLC-PK1cells, phosphorylation of ERK and p38 increased after 24- to 72-h exposure to high glucose (HG). Coincubation with a p38 inhibitor SB-203580 or a MEK inhibitor, PD-98059, suppressed the HG-induced increases in protein content, [3H]leucine incorporation, and the protein-to-DNA ratio. SB-203580 or PD-98059 also abolished the HG-stimulated expression of TGF-β protein. These results demonstrate that ERK and p38 are activated in renal tubular cells of DM and may mediate HG-induced cellular hypertrophy and TGF-β expression.
Aldosterone enhances renin gene expression in juxtaglomerular cells
Authors: Klar Jürgen , Vitzthum Helga , Kurtz Armin
Published: January 2004

The secretion and synthesis of renin as the key regulator of the renin-angiotensin-aldosterone system are directly controlled by ANG II in the sense of a negative feedback. Because we found that renal afferent arterioles including the juxtaglomerular portion express the mineralocorticoid receptor, we aimed to characterize a possible direct effect of aldosterone on renin synthesis and renin secretion at the level of renal juxtaglomerular cells. Aldosterone (100 nM) clearly enhanced renin mRNA levels in primary cultures of mouse juxtaglomerular cells prestimulated with isoproterenol (100 nM) but had no effect on the exocytosis of stored renin. Similarly, in the mouse juxtaglomerular cell line As4.1, aldosterone time and concentration dependently increased renin mRNA abundance and prorenin secretion up to 2.5-fold. Moreover, aldosterone potentiated cAMP-induced renin gene expression in As4.1 cells. The effect of aldosterone was inhibited by spironolactone and was mimicked by corticosteroid hormones but not by sex steroids. Aldosterone had no influence on basal renin promoter activity but increased the renin mRNA half-life about threefold. In summary, these data suggest that aldosterone exerts a direct positive effect on renin gene expression at the cellular level probably by stabilizing renin mRNA.
Pravastatin treatment attenuates interstitial inflammation and fibrosis in a rat model of chronic cyclosporine-induced nephropathy
Authors: Li Can , Yang Chul Woo , Park Joo Hyun , Lim Sun Woo , Sun Bo Kyung , Jung Ju Young , Kim Soon Bae , Kim Yong Soo , Kim Jin , Bang Byung Kee
Published: January 2004

We investigated the effects of pravastatin, a competitive inhibitor of 3-hydroxy-3-methylglutaryl-coenzyme A (HMG-CoA) reductase, on interstitial inflammation and fibrosis, using an animal model of chronic cyclosporine A (CsA)-induced nephropathy. Sprague-Dawley rats were maintained on a low-salt diet (0.05% sodium) and treated daily for 1 or 4 wk with vehicle (olive oil; 1 ml/kg sc), CsA (15 mg/kg sc), or both CsA and pravastatin (5 or 20 mg/kg in the drinking water). Anti-inflammatory and antifibrotic effects of pravastatin were studied by evaluating the concentrations of the inflammatory mediators osteopontin (OPN) and C-reactive protein (CRP), of fibrotic cytokine-transforming growth factor (TGF)-β1, and the presence of ED-1-positive cells (macrophages). In addition, renal function, serum lipid levels, histopathology (arteriolopathy and tubulointerstitial fibrosis), and the expression of the vasoactive factors endothelial nitric oxide synthase (eNOS) and renin protein were also compared for different treatment groups. Pravastatin induced dose-dependent decreases in the expression of OPN, intrarenal CRP, and TGF-β1, and in the numbers of ED-1-positive cells at 1 and 4 wk. These were accompanied by a significant attenuation of tubulointerstitial fibrosis at 4 wk. The downregulation of eNOS protein expression in CsA-treated rat kidney was markedly upregulated by pravastatin treatment, although intrarenal renin expression was unaffected. Renal dysfunction induced by CsA significantly improved with administration of pravastatin at a dose of 20 mg/kg. Neither CsA nor pravastatin influenced serum lipid or high-sensitivity CRP levels in the treatment groups. Thus in chronic CsA nephropathy, pravastatin effectively abrogates the progression of tubulointerstitial inflammation and fibrosis. This may support the clinical use of pravastatin.
Impact of muscle length during stretch-shortening contractions on real-time and temporal muscle performance measures in rats in vivo
Authors: Cutlip R. G. , Geronilla K. B. , Baker B. A. , Kashon M. L. , Miller G. R. , Schopper A. W.
Published: January 2004

The objective of the present study was to investigate the impact of muscle length during stretch-shortening cycles on static and dynamic muscle performance. Animals were randomly assigned to an isometric (control, Con, n = 12), a short-muscle-length (S-Inj, 1.22-2.09 rad, n = 12), or a long-muscle-length (L-Inj, 1.57-2.44 rad, n = 12) group. The dorsiflexor muscles were exposed in vivo to 7 sets of 10 stretch-shortening contractions (conducted at 8.72 rad/s) or 7 sets of isometric contractions of the same stimulation duration by using a custom-designed dynamometer. Performance was characterized by multipositional isometric exertions and positive, negative, and net work before exposure, 6 h after exposure, and 48 h after exposure to contractions. Real-time muscle performance during the stretch-shortening cycles was characterized by stretch-shortening parameters and negative, positive, and net work. The S-Inj group recovery (force difference) was similar to the Con group force difference at 48 h, whereas the L-Inj group force difference was statistically greater at 1.39, 1.57, and 1.74 rad than the Con group force difference ( P < 0.05). Negative work ( P < 0.05) and net work ( P < 0.05) were statistically lower in the S-Inj and L-Inj groups than in the Con group 48 h after exposure to contractions. Of the real-time parameters, there was a difference in cyclic force with treatment during the stretch-shortening cycles ( P < 0.0001), with the L-Inj group being the most affected. Thus longer ranges of motion result in a more profound isometric force decrement 48 h after exposure to contractions and in real-time changes in eccentric forces.
Interferon-γ increases monocyte HLA-DR expression without effects on glucose and fat metabolism in postoperative patients
Authors: de Metz Jesse , Romijn Johannes A. , Endert Erik , Ackermans Mariette T. , Weverling Gerrit Jan , Busch Olivier R. , de Wit Laurence Th. , Gouma Dirk J. , Berge Ineke J. M. ten , Sauerwein Hans P.
Published: January 2004

Tissue injury is associated with decreased cellular immunity and enhanced metabolism. Immunodepression is thought to be counteracted by interferon (IFN)-γ, which increases human leukocyte antigen (HLA)-DR expression. Hypermetabolism could be enhanced by IFN-γ because cytokines induce a hypermetabolic response to stress. In healthy humans, IFN-γ enhanced HLA-DR expression without effects on glucose and fat metabolism. In the present study, we evaluated whether IFN-γ lacks potential harmful side effects on metabolic and endocrine pathways while maintaining its beneficial effects on the immune system under conditions in which the inflammatory response system is activated. In 13 patients scheduled for major surgery, we studied HLA-DR expression on peripheral blood monocytes before surgery and postoperatively randomized the patients into an intervention and a placebo group. Subsequently, we evaluated the effects of a single dose of IFN-γ vs. saline on short-term monocyte activation, glucose and lipid metabolism, and glucose and lipid regulatory hormones. HLA-DR expression on monocytes was restored from postoperative levels of 54% (42-60%; median and interquartiles) to 92% (91-96%) 24 h after IFN-γ adminstration but stayed low in the placebo-treated patients. IFN-γ did not affect glucose metabolism (plasma glucose, rate of appearance and dissappearance of glucose) and lipid metabolism (plasma glycerol, plasma free fatty acids, and rates of appearance and disappearance of glycerol). IFN-γ had no effect on plasma cortisol, adrenocorticotropic hormone, growth hormone, insulin, C-peptide, glucagon, epinephrine, and norepinephrine concentrations. We conclude that IFN-γ exerts a favorable effect on cell-mediated immunity in patients after major surgery without effects on glucose and lipid metabolism.
Interval sprint training enhances endothelial function and eNOS content in some arteries that perfuse white gastrocnemius muscle
Authors: Laughlin M. H. , Woodman C. R. , Schrage W. G. , Gute D. , Price E. M.
Published: January 2004

The purpose of this study was to test the hypothesis that interval sprint training (IST) selectively increases endothelium-dependent dilation (EDD) and endothelial nitric oxide synthase and/or superoxide dismutase-1 protein content in arteries and/or arterioles that perfuse the white portion of rat gastrocnemius muscle (WG). Male Sprague-Dawley rats completed 10 wk of IST ( n = 62) or remained sedentary (Sed) ( n = 63). IST rats performed six 2.5-min exercise bouts, with 4.5 min of rest between bouts (60 m/min, 15% incline), 5 days/wk. EDD was assessed from acetylcholine (ACh)-induced increases in muscle blood flow measured in situ and by ACh-induced dilation of arteries and arterioles [first to third order (1A–3A)] that perfuse red gastrocnemius muscle (RG) and WG. Artery protein content was determined with immunoblot analysis. ACh-induced increases in blood flow were enhanced in WG of IST rats. eNOS content was increased in conduit arteries, gastrocnemius feed artery, and fourth-order arterioles from WG and fifth-order arterioles of RG but not in 2As from RG. EDD was examined in 2As and 3As from a subset of IST and Sed rats. Arterioles were canulated with micropipettes, and intraluminal pressure was set at 60 cmH2O. Results indicate that passive diameter (measured in 0 calcium PSS) of WG 2As was similar in IST and Sed, whereas diameter of WG 3As was greater in IST (96 ± 8 μm) than Sed (73 ± 4 μm). WG 2As and 3As of IST rats exhibited greater spontaneous tone, but sensitivity to stretch, phenylephrine, and sodium nitroprusside was similar to Sed arterioles. ACh-induced dilation was enhanced by IST in WG 2As but not in RG 2As or WG 3As. We conclude that IST induces vascular adaptations nonuniformly among arteries that perfuse WG muscle.
Assessment of skeletal muscle mass in men with spinal cord injury using dual-energy X-ray absorptiometry and magnetic resonance imaging
Authors: Modlesky Christopher M. , Bickel C. Scott , Slade Jill M. , Meyer Ronald A. , Cureton Kirk J. , Dudley Gary A.
Published: January 2004

The purpose of this study was to determine whether the proportion of skeletal muscle in the fat-free soft tissue mass (FFST) is the same in men with spinal cord injury (SCI) and able-bodied controls. Skeletal muscle mass and FFST of the midthigh were determined by using magnetic resonance imaging and dual-energy X-ray absorptiometry, respectively, in men with long-term (>2 yr) complete SCI ( n = 8) and able-bodied controls of similar age, height, and weight ( n = 8). Muscle mass (1.36 ± 0.77 vs. 2.44 ± 0.47 kg) and FFST (1.70 ± 0.94 vs. 2.73 ± 0.80 kg) were lower in the SCI group than in the controls ( P < 0.05), but the lower ratio of muscle to FFST in the SCI group (0.80 ± 0.09 vs. 0.91 ± 0.10, P < 0.05) suggested that they had a lower proportion of muscle in the FFST than in controls. This notion was supported by analysis of covariance, in that the mean muscle adjusted to the mean FFST of the groups combined was lower in the SCI group. Despite the lower proportion of muscle in the FFST of the SCI group, the relation between muscle and FFST was strong in the SCI group ( r = 0.99) and controls ( r = 0.96). The findings suggest a disproportionate loss of muscle in the paralyzed thighs after SCI relative to other nonfat constituents, which may be accurately estimated in men with long-term SCI by dual-energy X-ray absorptiometry if the lower proportion of muscle in the FFST (∼15%) is taken into account.
Tension-time index, fatigue, and energetics in isolated rat diaphragm: a new experimental model
Authors: Klawitter Paul F. , Clanton Thomas L.
Published: January 2004

The tension-time index (TTI) has been used to estimate mechanical load, energy utilization, blood flow, and susceptibility to fatigue in contracting muscle. The TTI can be defined, for a rhythmically contracting muscle, as the product of average force development divided by maximum tetanic force times duty cycle [contraction time ÷ (contraction + relaxation time)]. In this study, the TTI concept was applied to isolated diaphragm via a method that allowed TTI to be clamped at a predetermined value. The hypothesis tested was that, at constant TTI, muscle energetics and the extent of fatigue would vary with stimulation frequency. Isolated diaphragm strips were stimulated at 25, 50, 75, or 100 Hz for 4 min, one per second. Duty cycle was continuously adjusted to maintain TTI at 0.07, which was near the highest TTI tolerated for 4 min, at 20-Hz stimulation. At the end of the fatigue run, muscles were either immediately frozen for determination ATP, creatine, and creatine phosphate concentrations ( n = 6) or stimulated for evaluation of low- and high-frequency fatigue ( n = 5). Results demonstrated no difference in the extent of fatigue or in the final ATP and creatine phosphate concentrations between groups. Large within-run increases in duty cycle were required at low stimulation frequencies, but only small increases were required at the highest frequencies. The results demonstrate that, at a constant TTI, similar fatigue properties predominate at all stimulation frequencies with no clear distinction between high- and low-frequency fatigue. The method of clamping TTI during fatigue may be useful for evaluating energetics and contractile function between treatment groups in isolated muscle when treatment influences baseline contractile characteristics.
Effects of low and moderate exercise intensity on postprandial lipemia and postheparin plasma lipoprotein lipase activity in physically active men
Authors: Katsanos Christos S. , Grandjean Peter W. , Moffatt Robert J.
Published: January 2004

This study was designed to assess differences in the intensity of exercise to attenuate postprandial lipemia (PPL). Thirteen healthy men (age 23.8 ± 0.9 yr) participated in three random-ordered trials: in low-(25% peak oxygen consumption; Low) and moderate-intensity (65% peak oxygen consumption; Mod) exercise trials, which were completed 1 h before a high-fat meal (1.3 g fat/kg body mass), and a control (Con), fat meal only, trial. Venous blood samples were obtained before the fat meal, and at 2, 4, 6, 8, and 20 h after the fat meal. PPL in the Mod trial (267 ± 50 mg·dl-1·8 h) was lower compared with that in either Con (439 ± 81 mg·dl-1·8 h) or Low (403 ± 91 mg·dl-1·8 h) trials ( P < 0.05), whereas there was no difference in PPL between Con and Low trials ( P > 0.05). High-density lipoprotein cholesterol (HDL-C) and HDL subtype 2 cholesterol were not different between or within trials ( P > 0.05). Postprandial insulinemia was lower in the Mod trial (20.5 ± 5.7 μIU·ml-1·8 h; P < 0.05), but not in the Low trial (31.4 ± 4.7 μIU·ml-1·8 h), compared with that in the Con trial (34.9 ± 5.0 μIU·ml-1·8 h). Postheparin lipoprotein lipase activity at 8 h was higher in the Low trial compared with that in either Con or Mod trials, whereas there were no differences between trials at 20 h. These results suggest that, when exercise is performed 1 h before a fat meal, only exercise of moderate but not of low intensity attenuates PPL and that this effect is not associated with changes in postheparin lipoprotein lipase activity.
Dynamic mechanical consequences of deep inflation in mice depend on type and degree of lung injury
Authors: Allen Gilman , Bates Jason H. T.
Published: January 2004

In a previous study (Allen G, Lundblad LK, Parsons P, and Bates JH. J Appl Physiol 93: 1709-1715 , 2002), our laboratory used deep inflations (DI) in mice to show that recruitment of closed lung units can be a very transient phenomenon in lung injury. The purpose of this study was to investigate how this transience of lung recruitment depends on the nature and degree of acute lung injury. Mice were administered 50 μl of either saline ( n = 8), 0.01 M ( n = 9) or 0.025 M ( n = 8) hydrochloric acid, or 50 μg ( n = 10) or 150 μg ( n = 6) of LPS and were mechanically ventilated 24-48 h later. At various levels of positive end-expiratory pressure, two DIs were delivered, and forced oscillations were used to obtain a measure of lung stiffness ( H) periodically over 7 min. After LPS exposure, pressure-volume curve hysteresis and recovery in H after DI were no different from saline-exposed controls despite 500 times more neutrophils in bronchoalveolar lavage fluid. Pressure-volume hysteresis and recovery in H were increased in acid-exposed mice ( P < 0.001) and were correlated with bronchoalveolar lavage fluid protein content ( R = 0.81). Positive end-expiratory pressure reduced recovery in H in all groups ( P < 0.01) but reduced pressure-volume hysteresis in the acid-injured groups only ( P < 0.001). We conclude that the effects of DIs in acute lung injury depend on the degree of lung injury but only to the extent that this injury reflects a disruption of the air-liquid interface.
Thromboxane receptor analog, U-46619, redistributes pulmonary microvascular perfusion in isolated rat lungs
Authors: Conhaim Robert L. , Watson Kal E. , Heisey Dennis M. , Leverson Glen E. , Harms Bruce A.
Published: January 2004

Effects of vasoconstriction on the distribution of perfusion among alveoli are not well understood. To address this, we used a new method we developed to determine how microvascular perfusion distribution was affected by a potent vasoconstrictor, the thromboxane receptor analog U-46619. Our method was to infuse 4-μm-diameter fluorescent latex microspheres into the circulation of isolated rat lungs vasoconstricted with U-46619. We used a confocal microscope to image trapping patterns of the particles in dried sections of the lungs and then used dispersion index analysis to quantify the particle patterns in the images, which encompassed ∼2,000 alveoli. Dispersion indexes revealed significantly more particle clustering (inhomogeneous distribution) in vasoconstricted lungs than in normal flow controls or in controls in which flow was reduced by either lowering pulmonary arterial pressure or raising left atrial pressure. These results suggest that vasoconstriction occurred in the microvessels themselves, which are much smaller vessels than those previously thought to be capable of vasoconstriction.
A computed method for noninvasive MRI assessment of pulmonary arterial hypertension
Authors: Laffon Eric , Vallet Christophe , Bernard Virginie , Montaudon Michel , Ducassou Dominique , Laurent François , Marthan Roger
Published: January 2004

The present method enables the noninvasive assessment of mean pulmonary arterial pressure from magnetic resonance phase mapping by computing both physical and biophysical parameters. The physical parameters include the mean blood flow velocity over the cross-sectional area of the main pulmonary artery (MPA) at the systolic peak and the maximal systolic MPA cross-sectional area value, whereas the biophysical parameters are related to each patient, such as height, weight, and heart rate. These parameters have been measured in a series of 31 patients undergoing right-side heart catheterization, and the computed mean pulmonary arterial pressure value (PpaComp) has been compared with the mean pressure value obtained from catheterization (PpaCat) in each patient. A significant correlation was found that did not differ from the identity line PpaComp = PpaCat ( r = 0.92). The mean and maximal absolute differences between PpaComp and PpaCat were 5.4 and 11.9 mmHg, respectively. The method was also applied to compute the MPA systolic and diastolic pressures in the same patient series. We conclude that this computed method, which combines physical (whoever the patient) and biophysical parameters (related to each patient), improves the accuracy of MRI to noninvasively estimate pulmonary arterial pressures.
Does ACE inhibition enhance endurance performance and muscle energy metabolism in rats?
Authors: Bahi L. , Koulmann N. , Sanchez H. , Momken I. , Veksler V. , Bigard A. X. , Ventura-Clapier R.
Published: January 2004

The renin-angiotensin-aldosterone system plays an important role in the hydroelectrolytic balance, blood pressure regulation, and cell growth. In some studies, the insertion (I) allele of the angiotensin-converting enzyme (ACE) gene, associated with a lower ACE activity, has been found in excess frequency in elite endurance athletes, suggesting that decreased ACE activity could be involved in endurance performance (Myerson S, Hemingway H, Budget R, Martin J, Humphries S, and Montgomery H. J Appl Physiol 87: 1313-1316 , 1999). To test this hypothesis, we evaluated whether ACE inhibition could be associated with improved endurance performance and muscle oxidative capacity in rats. Eight male Wistar rats were treated for 10-12 wk with an ACE inhibitor, perindopril (2 mg·kg-1·day-1), and compared with eight control rats. Endurance time was measured on a treadmill, and oxidative capacity and regulation of mitochondrial respiration by substrates were evaluated in saponin-permeabilized fibers of slow soleus and fast gastrocnemius muscles. Endurance time did not differ between groups (57 ± 5 min for perindopril vs. 55 ± 6 min for control). Absolute and relative (to body weight) left ventricular weight was 20% ( P < 0.01) and 12% ( P < 0.01) lower, respectively, in the treated group. No difference in oxidative capacity, mitochondrial enzyme activities, or mitochondrial regulation by ADP was observed in soleus or gastrocnemius. Mitochondrial respiration with glycerol 3-phosphate was 17% higher in gastrocnemius ( P < 0.03) and with octanoylcarnitine 14% greater in soleus ( P < 0.01) of treated rats. These results demonstrate that ACE inhibition was not associated with improved endurance time and maximal oxidative capacity of skeletal muscles. This suggests that ACE activity has no implication in endurance capacity and only minor effects on mitochondrial function in sedentary animals.
Effects of exhaustive incremental treadmill exercise on diaphragm and quadriceps motor potentials evoked by transcranial magnetic stimulation
Authors: Verin Eric , Ross Ewen , Demoule Alexandre , Hopkinson Nicholas , Nickol Annabel , Fauroux Brigitte , Moxham John , Similowski Thomas , Polkey Michael I.
Published: January 2004

It is unknown whether changes in corticomotor excitability follow exercise in healthy humans. We hypothesized that a fall in the diaphragm and quadriceps motor-evoked potential (MEP) amplitude elicited by transcranial magnetic stimulation of the motor cortex would occur after an incremental exercise task. In 11 healthy subjects, we measured transdiaphragmatic pressure and isometric quadriceps tension in response to supramaximal peripheral magnetic nerve stimulation. MEPs were recorded from these muscles in response to transcranial magnetic stimulation. After baseline measurements, subjects performed a period of submaximal exercise (gentle walking). Measurements were repeated 5 and 20 min after this. The subjects then exercised on a treadmill with an incremental protocol to exhaustion. Transcranial magnetic stimulation was performed at baseline and at 5, 20, 40, and 60 min after exhaustive exercise, and force measurements were obtained at baseline, 20 min, and 60 min. Mean exercise duration was 18 ± 4 min, and mean maximum heart rate was 172 ± 10 beats/min. Twitch transdiaphragmatic pressure and twitch isometric quadriceps tension were not different from baseline after exercise, but a significant decrease was observed in diaphragm MEP amplitude 5 and 20 min after exercise (60 ± 38 and 45 ± 24%, respectively, of baseline, P = 0.0001). At the same times, the mean quadriceps MEPs were 59 ± 39 and 74 ± 32% of baseline ( P < 0.0001 and P < 0.01, respectively). Studies using paired stimuli confirmed a likely intracortical mechanism for this depression. Our data confirm significant depression of both diaphragm and quadriceps MEPs after incremental treadmill exercise.
Effect of carbohydrate intake on net muscle protein synthesis during recovery from resistance exercise
Authors: Børsheim Elisabet , Cree Melanie G. , Tipton Kevin D. , Elliott Tabatha A. , Aarsland Asle , Wolfe Robert R.
Published: January 2004

The purpose of this study was to determine the effect of ingestion of 100 g of carbohydrates on net muscle protein balance (protein synthesis minus protein breakdown) after resistance exercise. Two groups of eight subjects performed a resistance exercise bout (10 sets of 8 repetitions of leg presses at 80% of 1-repetition maximum) before they rested in bed for 4 h. One group (CHO) received a drink consisting of 100 g of carbohydrates 1 h postexercise. The other group (Pla) received a noncaloric placebo drink. Leg amino acid metabolism was determined by infusion of2H5- or13C6-labeled phenylalanine, sampling from femoral artery and vein, and muscle biopsies from vastus lateralis. Drink intake did not affect arterial insulin concentration in Pla, whereas insulin increased several times after the drink in CHO ( P < 0.05 vs. Pla). Arterial phenylalanine concentration fell slightly after the drink in CHO. Net muscle protein balance between synthesis and breakdown did not change in Pla, whereas it improved in CHO from -17 ± 3 nmol·ml-1·100 ml leg-1before drink to an average of -4 ± 4 and 0 ± 3 nmol·ml-1·100 ml leg-1during the second and third hour after the drink, respectively ( P < 0.05 vs. Pla during last hour). The improved net balance in CHO was due primarily to a progressive decrease in muscle protein breakdown. We conclude that ingestion of carbohydrates improved net leg protein balance after resistance exercise. However, the effect was minor and delayed compared with the previously reported effect of ingestion of amino acids.
Plasma C-reactive protein is not elevated in physically active postmenopausal women taking hormone replacement therapy
Authors: Stauffer Brian L. , Hoetzer Greta L. , Smith Derek T. , DeSouza Christopher A.
Published: January 2004

We tested the hypothesis that hormone replacement therapy (HRT)-related increases in C-reactive protein (CRP) would either be blunted or absent in postmenopausal women who regularly perform endurance exercise. Plasma CRP is an independent predictor of future cardiovascular events in healthy men and women. Oral HRT increases plasma CRP concentrations in postmenopausal women. Regular aerobic exercise reduces the risk of cardiovascular events and is associated with lower CRP concentrations in adults. To date, no study has evaluated the influence of habitual physical activity on the elevation of CRP associated with HRT. Plasma CRP concentrations were measured in 114 postmenopausal women: 39 physically active (endurance trained) and 75 sedentary postmenopausal subjects. Sixty-five women were users of HRT (22 physically active and 43 sedentary), and 49 were nonusers (17 physically active and 32 sedentary). CRP levels were ∼75% higher ( P < 0.01) in the sedentary users vs. nonusers of HRT (1.9 ± 1.8 vs. 1.1 ± 1.0 mg/l). In contrast, there was no difference in CRP levels between the physically active users and nonusers of HRT (0.6 ± 0.4 vs. 0.4 ± 0.2 mg/l; P = 0.61). Regardless of HRT status, CRP concentrations were ∼65% lower in the physically active compared with sedentary women. In conclusion, physically active postmenopausal women exhibit lower plasma CRP concentrations compared with sedentary controls. Importantly, the HRT-related elevation in plasma CRP levels observed in sedentary women is absent in women who engage in regular endurance exercise. These data suggest that habitual physical activity may prevent the elevation in CRP concentrations due to HRT.
Arm-cranking muscle power and arm isometric muscle strength are independent predictors of all-cause mortality in men
Authors: Metter E. Jeffrey , Talbot Laura A. , Schrager Matthew , Conwit Robin A.
Published: January 2004

Poor muscle strength is associated with mortality, presumably due to low muscle mass. Notably, muscle power declines more rapidly than muscle strength with increasing age, which may be related to more complex central nervous system movement control. We examined arm-cranking power against four workloads and isometric strength measured in the upper extremities of 993 men longitudinally tested over a 25-yr period. Muscle mass was estimated by using 24-h creatinine excretion; physical activity was assessed by self-reported questionnaire. Muscle power and strength were modeled by time by using mixed-effects models, which developed regression equations for each individual. The first derivative of these equations estimated rate of change in strength or power at each evaluation. Survival analyses, using the counting method, examined the impact of strength, power, and their rates of change on all-cause mortality while adjusting for age. Arm-cranking power [relative risk ( rr) = 0.984 per 100 kg·m·min-1, P < 0.001] was a stronger predictor of mortality than was arm strength ( rr = 0.986 per 10 kg, P = not significant), whereas rate of power change ( rr = 0.989 per 100 kg·min-1·yr-1) and rate of arm strength change ( rr = 0.888 per 10 kg/yr) were risks independent of the power or strength levels. The impacts of power and strength were partially independent of muscle mass and physical activity. The risk of mortality was similar across the four power workloads ( rr = 0.93-0.96 per 100 kg·m·min-1), whereas the lowest load generated less than one-half the power as the higher loads. Arm-cranking power is a risk factor for mortality, independent of muscle strength, physical activity, and muscle mass. The impact is found with loads that do not generate maximal power, suggesting an important role for motor coordination and speed of movement.