Lipopolysaccharide-induced diaphragmatic contractile dysfunction and sarcolemmal injury in mice lacking the neuronal nitric oxide synthase

Regional Distribution of Nitric Oxide Synthase in Human Anorectal Tissue: A Pilot Study on the Potential Role for Nitric Oxide in Haemorrhoids

OBJECTIVE

To study the distribution of nitric oxide synthase (NOS) isoforms and protein levels in human haemorrhoids and rectal tissue.

METHODS

Protein expression of NOS1, NOS2 and NOS3 was compared between haemorrhoids (n=14) and normal rectal submucosa (n=6) using Western blot analysis. The localisation of all NOS isoforms to specific structures was determined by immunohistochemistry.

RESULTS

Western blot analysis showed median (interquartile range) protein levels of all NOS isoforms were 1.5-2.4 times higher in haemorrhoids than rectal tissue; 121.4 (55.2-165.5) vs 50.0 (25.5-73.7) for NOS1 (p=0.020), 32.2 (23.8-140.6) vs 14.8 (9.6-34.0) for NOS2 (p=0.109), and 80.1 (62.0-139.5) vs 54.3 (48.7 -61.7) for NOS3 (p=0.015). Immunohistochemistry revealed a different distribution and location of all NOS isoforms in vascular and non-vascular structure of haemorrhoids and rectal tissues. The number of haemorrhoid specimens showing positive immunoreactivity of NOS in the vascular endothelium was significantly higher than that in rectal tissue for NOS1 (11/14 (79%) vs 1/6 (17%); p=0.018) and NOS3 (8/14 (57%) vs 0/6 (0%); p=0.042), but not for NOS2 (6/14 (43%) vs 4/6 (67%); p=0.63).

CONCLUSION

Haemorrhoids have significantly higher protein levels of NOS1 and NOS3 than rectal tissue. The vascular endothelium of haemorrhoids also has significantly higher positive immunoreactivity of NOS1 and NOS3 than rectal tissue suggesting that blood vessels in haemorrhoids are exposed to higher NO concentrations than those of rectal tissue. Since haemorrhoids exhibit marked vascular dilatation and present with bleeding or swelling, a reduction in NOS - by applying NOS inhibitors - may potentially improve the symptoms of haemorrhoids.

Cerium oxide nanoparticle treatment ameliorates peritonitis-induced diaphragm dysfunction

The severe inflammation observed during sepsis is thought to cause diaphragm dysfunction, which is associated with poor patient prognosis. Cerium oxide (CeO2) nanoparticles have been posited to exhibit anti-inflammatory and antioxidative activities suggesting that these particles may be of potential use for the treatment of inflammatory disorders. To investigate this possibility, Sprague Dawley rats were randomly assigned to the following groups: sham control, CeO2 nanoparticle treatment only (0.5 mg/kg iv), sepsis, and sepsis+CeO2 nanoparticles. Sepsis was induced by the introduction of cecal material (600 mg/kg) directly into the peritoneal cavity. Nanoparticle treatment decreased sepsis-associated impairments in diaphragmatic contractile (P(o)) function (sham: 25.6±1.6 N/cm(2) vs CeO2: 23.4±0.8 N/cm(2) vs Sep: 15.9±1.0 N/cm(2) vs Sep+CeO2: 20.0±1.0 N/cm(2), P<0.05). These improvements in diaphragm contractile function were accompanied by a normalization of protein translation signaling (Akt, FOXO-1, and 4EBP1), diminished proteolysis (caspase 8 and ubiquitin levels), and decreased inflammatory signaling (Stat3 and iNOS). Histological analysis suggested that nanoparticle treatment was associated with diminished sarcolemma damage and diminished inflammatory cell infiltration. These data indicate CeO2 nanoparticles may improve diaphragmatic function in the septic laboratory rat.

Chronic nitric oxide synthase inhibition does not impair upper airway muscle adaptation to chronic intermittent hypoxia in the rat

Nitric oxide (NO) is an important modulator of striated muscle function. Nitric oxide synthase (NOS) expression and activity is altered by hypoxia and NO is implicated in respiratory muscle remodeling following chronic sustained hypoxia. We sought to determine if NO is implicated in upper airway dilator muscle adaptation to chronic intermittent hypoxia (CIH). Thirty-two adult male Wistar rats (284±13, mean±SD) were exposed to alternating bouts of hypoxia (90 s; 5% O2 at the nadir) and normoxia (210 s; 21% O2) for 12 cycles per hour, 8h/day for 3 weeks. Sham animals were exposed to normoxia in parallel. Half of the animals in both groups received the nNOS inhibitor-L-NNA (2mM) in the drinking water throughout the study (N=8 for all groups). Sternohyoid (pharyngeal dilator) muscle contractile and endurance properties were determined ex vivo. Sternohyoid muscle myosin heavy chain (MHC) isoform composition and cross-sectional area was determined by fluorescence microscopy. Chronic nNOS blockade did not alter sternohyoid muscle peak force or force-frequency relationship in sham or CIH-treated animals. In contrast, chronic nNOS blockade significantly decreased sternohyoid muscle endurance with equivalent effects in sham and CIH-treated rats. Our results suggest that NO is an important modulator of sternohyoid muscle endurance. However, our data provide no evidence to suggest that NO is implicated in upper airway muscle adaptation to CIH.

[Inflammation and oxidative stress in respiratory and limb muscles of patients with severe sepsis]

BACKGROUND AND OBJECTIVE

Oxidative stress and inflammation contribute to the diaphragm contractile dysfunction observed in animal models of sepsis and endotoxemia. In septic patients, molecular events have never been explored in their respiratory muscles. Levels of oxidative stress and inflammation were evaluated in a respiratory muscle, the external intercostal, and a limb muscle, the vastus lateralis, of patients with sepsis.

PATIENTS AND METHODS

Levels of oxidized and nitrated proteins, protein adducts of malondialdehyde and hydroxinonenal, antioxidant enzymes catalase and Mn-superoxide dismutase, tumor necrosis factor (TNF)-α, TNF-α receptors i and ii, interleukin (IL)-1 and IL-6, the panleukocyte marker CD18, and fiber type composition were explored using immunoblotting, real time-polymerase chain reaction, and immunohistochemistry in the external intercostal and vastus lateralis of patients with severe sepsis and/or septic shock.

RESULTS

Compared to the controls, in septic patients, levels of oxidized and nitrated proteins were increased in the vastus lateralis, but not in the external intercostal, while those of the antioxidant enzymes did not differ, and the proportions and sizes of the muscle fibers were not significantly different in any muscle between patients and controls.

CONCLUSIONS

Differences in activity between the respiratory and limb muscles may account for the differential pattern of oxidative stress and inflammation observed among patients with severe sepsis. These findings may have relevant implications for the clinical and therapeutic management of these patients.

Critical diaphragm failure in sudden infant death syndrome

Sudden infant death syndrome (SIDS) is the leading cause of death in infants between the ages of 1 and 12 months in developed countries. SIDS is by definition a diagnosis of exclusion, and its mechanism of action is unknown. The SIDS-Critical Diaphragm Failure (CDF) hypothesis postulates that the cause of death in SIDS is respiratory failure caused by CDF. Four principal risk factors contribute to CDF in young infants: undeveloped respiratory muscles, non-lethal infections, prone resting position, and REM sleep. Even relatively minor infections can cause an acute and significant reduction in diaphragm force generation capacity that in conjunction with other risk factors can precipitate CDF. CDF-induced acute muscle weakness leaves few, if any pathological marks on the affected tissue.Understanding the underlying mechanism of SIDS may help in formulating new approaches to child care that can help to further reduce the incidence of SIDS.

Intensive care unit-acquired weakness (ICUAW) and muscle wasting in critically ill patients with severe sepsis and septic shock

Sepsis presents a major health care problem and remains one of the leading causes of death within the intensive care unit (ICU). Therapeutic approaches against severe sepsis and septic shock focus on early identification. Adequate source control, administration of antibiotics, preload optimization by fluid resuscitation and further hemodynamic stabilisation using vasopressors whenever appropriate are considered pivotal within the early-golden-hours of sepsis. However, organ dysfunction develops frequently in and represents a significant comorbidity of sepsis. A considerable amount of patients with sepsis will show signs of severe muscle wasting and/or ICU-acquired weakness (ICUAW), which describes a frequently observed complication in critically ill patients and refers to clinically weak ICU patients in whom there is no plausible aetiology other than critical illness. Some authors consider ICUAW as neuromuscular organ failure, caused by dysfunction of the motor unit, which consists of peripheral nerve, neuromuscular junction and skeletal muscle fibre. Electrophysiologic and/or biopsy studies facilitate further subclassification of ICUAW as critical illness myopathy, critical illness polyneuropathy or critical illness myoneuropathy, their combination. ICUAW may protract weaning from mechanical ventilation and impede rehabilitation measures, resulting in increased morbidity and mortality. This review provides an insight on the available literature on sepsis-mediated muscle wasting, ICUAW and their potential pathomechanisms.

Sepsis-induced myopathy

Sepsis is a major cause of morbidity and mortality in critically ill patients, and despite advances in management, mortality remains high. In survivors, sepsis increases the risk for the development of persistent acquired weakness syndromes affecting both the respiratory muscles and the limb muscles. This acquired weakness results in prolonged duration of mechanical ventilation, difficulty weaning, functional impairment, exercise limitation, and poor health-related quality of life. Abundant evidence indicates that sepsis induces a myopathy characterized by reductions in muscle force-generating capacity, atrophy (loss of muscle mass), and altered bioenergetics. Sepsis elicits derangements at multiple subcellular sites involved in excitation contraction coupling, such as decreasing membrane excitability, injuring sarcolemmal membranes, altering calcium homeostasis due to effects on the sarcoplasmic reticulum, and disrupting contractile protein interactions. Muscle wasting occurs later and results from increased proteolytic degradation as well as decreased protein synthesis. In addition, sepsis produces marked abnormalities in muscle mitochondrial functional capacity and when severe, these alterations correlate with increased death. The mechanisms leading to sepsis-induced changes in skeletal muscle are linked to excessive localized elaboration of proinflammatory cytokines, marked increases in free-radical generation, and activation of proteolytic pathways that are upstream of the proteasome including caspase and calpain. Emerging data suggest that targeted inhibition of these pathways may alter the evolution and progression of sepsis-induced myopathy and potentially reduce the occurrence of sepsis-mediated acquired weakness syndromes.

Glutamine preserves skeletal muscle force during an inflammatory insult

The purpose of this study was to test the hypothesis that acute glutamine (GLN) supplementation can counteract skeletal muscle contractile dysfunction occurring in response to inflammation by elevating muscle heat shock protein (Hsp) expression and reducing inflammatory cytokines. Mice received 5 mg/kg lipopolysaccharide (LPS) concurrently with 1 g/kg GLN or vehicle treatments. Plantarflexor isometric force production was measured at 2 hours post-injection. Blood and gastrocnemius muscles were collected, and serum and muscle tumor necrosis factor-alpha (TNF-alpha) and interleukin-6 (IL-6) and muscle Hsp70 and Hsp25 were quantified. Saline/LPS treatment was associated with a 33% reduction in maximal force and elevated serum TNF-alpha and IL-6. GLN completely prevented this force decrement with LPS. GLN was found to reduce muscle Hsp70 and IL-6, but only in the presence of LPS. GLN supplementation provides an effective, novel, clinically applicable means of preserving muscle force during acute inflammation. These data indicate that force preservation is not dependent on reductions in serum cytokines or muscle TNF-alpha, or elevated Hsp levels.

Nitric oxide synthase isoforms play distinct roles during acute peritonitis

Background. Acute peritonitis is the most frequent complication of peritoneal dialysis (PD). Increased nitric oxide (NO) release by NO synthase (NOS) isoforms has been implicated in acute peritonitis, but the role played by the NOS isoforms expressed in the peritoneum is unknown.

Methods. We investigated the structural and functional consequences of acute peritonitis induced by LPS in wild-type (WT) mice versus knockout mice (KO) for the endothelial NOS (eNOS), the inducible NOS (iNOS) or the neuronal NOS (nNOS).

Results. The level of NO metabolites (NOx) in the dialysate was maximal 18 h after LPS injection. LPS induced a significant increase in the transport of small solutes and decreased ultrafiltration in WT mice. These changes, which occurred without vascular proliferation, were paralleled by the upregulation of nNOS and eNOS, and the induction of iNOS. The transport modifications induced by LPS were significantly reversed in eNOS KO mice, but not modified in mice lacking iNOS or nNOS. In contrast, the increase of dialysate NOx was abolished in iNOS KO mice and significantly reduced in eNOS KO mice, but left unchanged in mice lacking nNOS. Mice lacking iNOS also showed more severe inflammatory changes, and a trend towards increased mortality following LPS.

Conclusion. These data demonstrate specific roles for NOS isoforms in the peritoneal membrane and suggest that selective eNOS inhibition may improve peritoneal transport during acute peritonitis.

Chemokine receptor and ligand upregulation in the diaphragm during endotoxemia and Pseudomonas lung infection

Sepsis-induced diaphragmatic inflammation has been associated with respiratory failure, but the role of chemokines in this process has not been evaluated. Here we sought to study the local expression and molecular regulation of the chemokines, regulated upon activation normal T cell expressed and secreted (RANTES) and macrophage inflammatory protein (MIP)-1α, in the murine diaphragm during sepsis. Constitutive expression levels of RANTES and MIP-1α, as well as their receptors, CCR1 and CCR5, were significantly higher in diaphragm than limb muscle. Sepsis was induced by acute lipopolysaccharide (LPS) delivery or subacutely by intratracheal administration of live Pseudomonas aeruginosa bacteria. Both sepsis models triggered a marked upregulation of RANTES and MIP-1α in the diaphragm. In vitro, stimulation of diaphragmatic muscle cells with LPS also led to RANTES upregulation. Inhibition of the NF-kB pathway using pharmacologic or dominant negative genetic approaches blocked the LPS-induced RANTES upregulation, while free radical scavengers had no effect. We conclude that sepsis leads to greatly increased expression of RANTES, MIP-1α and their cognate receptors in the diaphragm. Manipulation of the NF-kB pathway and other regulators of chemokine expression in the diaphragm could represent a novel method for mitigating the skeletal muscle inflammatory response associated with sepsis-induced diaphragmatic dysfunction.

Lipopolysaccharide-induced monocyte chemotactic protein-1 is enhanced by suppression of nitric oxide production, which depends on poor CD14 expression on the surface of skeletal muscle

It is known that lipopolysaccharide (LPS)-induced monocyte chemotactic protein (MCP)-1 secretion from tissues recruits monocytes from the circulation, but the mechanism of the LPS-induced MCP-1 production in skeletal muscle is largely unexplained. To clarify the effect of LPS on MCP-1 production in skeletal muscle cells, C2C12 cells from a mouse skeletal muscle cell line, and RAW 264.7 cells from a mouse macrophage cell line, were used to assess production of LPS-induced MCP-1, nitric oxide (NO) and interferon (IFN)-beta. In addition, we evaluated inducible NO synthases (iNOS) mRNA expression using RT-PCR, and cell surface expression of CD14 and toll-like receptor (TLR) 4 using flow cytometry. In C2C12 cells, LPS stimulation increased MCP-1 production (p < 0.01), but combined treatment with LPS and NO inducer, diethylammonium (Z)-1-(N,N-diethylamino) diazen-1-ium-1,2-diolate (NONOate), significantly inhibited its production (p < 0.01). LPS stimulation neither induced production of NO nor of IFN-beta, which is an NO inducer. Recombinant IFN-beta stimulation, on the other hand, enhanced LPS-induced NO production (p < 0.01). Interestingly, we found that surface expression of CD14, which regulates IFN-beta production, in C2C12 cells was much lower than that in RAW 264.7 cells, although TLR4 expression on C2C12 cells was similar to that on RAW 264.7 cells. These data suggest that the reduced NO production in response to LPS may depend on low expression of CD14 on the cell surface of skeletal muscle, and that it may enhance LPS-induced MCP-1 production. Together, these functions of skeletal muscle could decrease the risk of bacterial infection by recruitment of monocytes.

Fiber type-specific nitric oxide protects oxidative myofibers against cachectic stimuli

Oxidative skeletal muscles are more resistant than glycolytic muscles to cachexia caused by chronic heart failure and other chronic diseases. The molecular mechanism for the protection associated with oxidative phenotype remains elusive. We hypothesized that differences in reactive oxygen species (ROS) and nitric oxide (NO) determine the fiber type susceptibility. Here, we show that intraperitoneal injection of endotoxin (lipopolysaccharide, LPS) in mice resulted in higher level of ROS and greater expression of muscle-specific E3 ubiqitin ligases, muscle atrophy F-box (MAFbx)/atrogin-1 and muscle RING finger-1 (MuRF1), in glycolytic white vastus lateralis muscle than in oxidative soleus muscle. By contrast, NO production, inducible NO synthase (iNos) and antioxidant gene expression were greatly enhanced in oxidative, but not in glycolytic muscles, suggesting that NO mediates protection against muscle wasting. NO donors enhanced iNos and antioxidant gene expression and blocked cytokine/endotoxin-induced MAFbx/atrogin-1 expression in cultured myoblasts and in skeletal muscle in vivo. Our studies reveal a novel protective mechanism in oxidative myofibers mediated by enhanced iNos and antioxidant gene expression and suggest a significant value of enhanced NO signaling as a new therapeutic strategy for cachexia.

Endotoxin reduces availability of voltage-gated human skeletal muscle sodium channels at depolarized membrane potentials

OBJECTIVE

Critical illness myopathy is a common cause for difficulties in weaning from the respirator and prolonged rehabilitation of patients recovering from sepsis. Several studies have shown that the primary cause of acute generalized muscle weakness is loss of muscle membrane excitability. This study was designed to investigate a potential direct interaction of lipopolysaccharides from Escherichia coli with voltage-gated human skeletal muscle sodium channels (NaV1.4) in vitro.

DESIGN

In vitro laboratory investigation.

SETTING

University laboratory.

SUBJECTS

NaV1.4 sodium channel alpha-subunits stably expressed in human embryonic kidney (HEK293) cells.

INTERVENTIONS

We investigated the effect of lipopolysaccharide on voltage-dependent sodium channel gating by using two distinct modes of application: 1) acute perfusion (pharmacologic lipopolysaccharide concentrations between 5 ng/mL and 50 microg/mL) in order to establish a concentration-effect relationship; and 2) incubation with a clinically relevant concentration of lipopolysaccharide (300 pg/mL).

MEASUREMENTS AND MAIN RESULTS

Lipopolysaccharide did not alter the kinetics of sodium current activation or inactivation when depolarizations were started from hyperpolarized holding potentials. However, when either fast or slow inactivation was induced by membrane depolarization before the test pulse, lipopolysaccharide reversibly reduced channel availability during the test pulse at concentrations of > or = 50 ng/mL revealed by a maximum hyperpolarizing shift of -25 mV in the voltage dependence of fast and slow inactivation, respectively. Incubation with a lipopolysaccharide concentration of 300 pg/mL for 1 hr reproduced the effects on slow but not on fast inactivation. After 20 hrs of low-dose lipopolysaccharide, the peak sodium current was significantly reduced.

CONCLUSIONS

Our results show that lipopolysaccharide interacts with voltage-gated sodium channels, reducing channel availability at depolarized membrane potentials during acute application, independent of the membrane potential after chronic exposure. These effects may contribute to reduced muscle membrane excitability in sepsis.

Low-level laser therapy can reduce lipopolysaccharide-induced contractile force dysfunction and TNF-alpha levels in rat diaphragm muscle

Our objective was to investigate if low-level laser therapy (LLLT) could improve respiratory function and inhibit tumor necrosis factor (TNF-alpha) release into the diaphragm muscle of rats after an intravenous injection of lipopolysaccharide (LPS) (5 mg/kg). We randomly divided Wistar rats in a control group without LPS injection, and LPS groups receiving either (a) no therapy, (b) four sessions in 24 h with diode Ga-AsI-Al laser of 650 nm and a total dose of 5.2 J/cm2, or (c) an intravenous injection (1.25 mg/kg) of the TNF-alpha inhibitor chlorpromazine (CPZ). LPS injection reduced maximal force by electrical stimulation of diaphragm muscle from 24.15+/-0.87 N in controls, but the addition of LLLT partly inhibited this reduction (LPS only: 15.01+/-1.1 N vs LPS+LLLT: 18.84+/-0.73 N, P<0.05). In addition, this dose of LLLT and CPZ significantly (P<0.05 and P<0.01, respectively) reduced TNF-alpha concentrations in diaphragm muscle when compared to the untreated control group.

Endotoxin triggers nuclear factor-kappaB-dependent up-regulation of multiple proinflammatory genes in the diaphragm

BACKGROUND

Sepsis-induced diaphragmatic force loss and failure are associated with an increased exposure of the muscle to proinflammatory mediators.

OBJECTIVES

Our objectives were to test the hypothesis that force-inhibiting mediators may arise in large part from the diaphragm itself and to evaluate the roles of mechanical stress, free radicals, and the nuclear factor (NF)-kappaB transcription factor pathway in endotoxin (LPS)-induced proinflammatory responses of the diaphragm.

METHODS

Murine diaphragm and limb muscle cells were exposed to LPS in vitro and in vivo. Proinflammatory gene expression was measured using RNase protection assays (tumor necrosis factor [TNF]-alpha, TNF-alpha receptor p55, interleukin [IL]-1alpha, IL-1beta, IL-6, macrophage inflammatory peptide-2, intercellular adhesion molecule-1, Fas ligand, and inducible nitric oxide synthase) and ELISAs (TNF-alpha, IL-6, and macrophage inflammatory peptide-2). Cyclical muscle cell stretch and free-radical scavengers (N-acetylcysteine and catalase) were used to alter mechanical and oxidative stress levels, respectively. Pharmacologic (pyrrolidinedithiocarbamate) and dominant-negative transfection strategies were used to inhibit the NF-kappaB pathway.

RESULTS

In primary diaphragm muscle cell cultures, modulation of mechanical stress levels or free-radical exposure did not alter responses to LPS stimulation. However, pharmacologic blockade of the NF-kappaB pathway and dominant-negative molecular inhibition of IKB kinase-beta strongly suppressed LPS-induced proinflammatory gene expression. In vivo, acute endotoxemia induced significantly greater mRNA and protein levels for proinflammatory mediators in the diaphragm as compared with limb muscle. Basal expression levels of proinflammatory genes were significantly higher in the diaphragm.

CONCLUSIONS

Constitutive and LPS-induced proinflammatory gene expression are exaggerated in the diaphragm compared with limb muscles and are critically dependent on the NF-kappaB pathway. We suggest the diaphragm may be relatively predisposed to proinflammatory responses.

The role of nitric oxide on contractile impairment during endotoxemia in rat diaphragm muscle

We examined the contribution of nitric oxide (NO) on the contractile impairment in diaphragm muscles of endotoxemic rats. Force-frequency relationship was depressed 24 h after lipopolysaccharide administration. 7-Nitroindazole, aminoguanidine and 1H-[1,2,4]Oxadiazole (4,3-a)quinoxalin-1-one (ODQ) partially restored the contractile impairment, Nomega-Nitro-L-Arginine (L-NNA) was ineffective. K+ contractions were reduced by 50% in endotoxemic muscles, 7-nitroindazole partially recovered, while aminoguanidine and L-NNA were ineffective. Verapamil reduced contractility to a greater extent in endotoxemic muscles. Caffeine and ryanodine contractions were augmented during endotoxemia without NOS contribution. L-NNA, 7-nitroindazole, ODQ and hemoglobin did not affect, but aminoguanidine completely restored partially inhibited neurotransmission by d-tubocurarine. Endotoxemia did not change membrane potentials and neurotransmitter release but slightly increased excitability. At this stage of endotoxemia, (1) constitutive NOS appears to be the dominant isoform, (2) NO does not have a major role on contractile dysfunction and (3) impairment could be explained by altered sensitivity of the voltage sensor. (4) NO does not substantially modulate neuromuscular transmission in normal and endotoxemic rats.

Chemical sympathectomy by 6-OH dopamine during fetal life results in inguinal testis through altering cremasteric contractility in rats

BACKGROUND/PURPOSE

Androgens are proposed to influence testicular descent through modulating sympathetic tone. An experimental study was undertaken to evaluate the effects of prenatal chemical sympathectomy on testicular location associated with the alterations in contractile properties of cremaster muscles in rats.

METHODS

Time-mated pregnancies were started in 10 rats. Two groups, each receiving saline or 6-hydroxydopamine from day 15 to day 19 of intrauterine life were established. At 2 months of age, localization of testes were evaluated, cremaster muscles were removed, and contractile properties were studied. Twitch and tetanic contractions were recorded isometrically at 37 degrees C. Effects of verapamil, isoprenaline, and L-NNA were investigated. Results were compared through analysis of variance (ANOVA), and P values less than.05 were considered to be significant.

RESULTS

Both testes of all male offspring in the control group (n = 19) were in the scrotum. Six offspring among 17 subjected to 6-hydroxydopamine had undescended testes. Treatment with 6-hydroxydopamine had no effect on force-frequency relationship of cremaster muscle strips. Cremaster muscles of rats exposed to 6-hydroxydopamine had lower sensitivity to voltage-sensitive Ca++ channel blockade by verapamil (3 x 10(4) mol/L; P <.05). These muscles displayed greater contractile response to isoprenaline (10(-5) mol/L; P <.05) but not to nitric oxide synthase inhibition by N(omega)-nitro-L-arginine. Alterations in contractile properties of the muscles did not differ according to localization of testes among rats subjected to 6-hydroxydopamine.

CONCLUSIONS

Administration of 6-hydroxydopamine resulted in suprascrotally located testes. This localization has been associated with less exposure at sympathetic tonus. These findings support that sympathetic activity plays an important role in localization of testis.

Disorders of the respiratory muscles

The act of breathing depends on coordinated activity of the respiratory muscles to generate subatmospheric pressure. This action is compromised by disease states affecting anatomical sites ranging from the cerebral cortex to the alveolar sac. Weakness of the respiratory muscles can dominate the clinical manifestations in the later stages of several primary neurologic and neuromuscular disorders in a manner unique to each disease state. Structural abnormalities of the thoracic cage, such as scoliosis or flail chest, interfere with the action of the respiratory muscles-again in a manner unique to each disease state. The hyperinflation that accompanies diseases of the airways interferes with the ability of the respiratory muscles to generate subatmospheric pressure and it increases the load on the respiratory muscles. Impaired respiratory muscle function is the most severe consequence of several newly described syndromes affecting critically ill patients. Research on the respiratory muscles embraces techniques of molecular biology, integrative physiology, and controlled clinical trials. A detailed understanding of disease states affecting the respiratory muscles is necessary for every physician who practices pulmonary medicine or critical care medicine.

Severe muscle dysfunction precedes collagen tissue proliferation in mdx mouse diaphragm

After extensive necrosis, progressive diaphragm muscle weakness in the mdx mouse is thought to reflect progressive replacement of contractile tissue by fibrosis. However, little has been documented on diaphragm muscle performance at the stage at which necrosis and fibrosis are limited. Diaphragm morphometric characteristics, muscle performance, and cross-bridge (CB) properties were investigated in 6-wk-old control (C) and mdx mice. Compared with C, maximum tetanic tension and shortening velocity were 37 and 32% lower, respectively, in mdx mice (each P < 0.05). The total number of active CB per millimeter squared (13.0 +/- 1.2 vs. 18.4 +/- 1.7 x 10(9)/mm(2), P < 0.05) and the CB elementary force (8.0 +/- 0.2 vs. 9.0 +/- 0.1 pN, P < 0.01) were lower in mdx than in C. The time cycle duration was lower in mdx than in C (127 +/- 18 vs. 267 +/- 61 ms, P < 0.05). Percentages of fiber necrosis represented 2.8 +/- 0.6% of the total muscle fibers, and collagen surface area occupied 3.6 +/- 0.7% in mdx diaphragm. Our results pointed to severe muscular dysfunction in mdx mouse diaphragm, despite limited necrotic and fibrotic lesions.

Respiratory and limb muscle weakness induced by tumor necrosis factor-alpha: involvement of muscle myofilaments

The respiratory and limb skeletal muscles become weakened in sepsis, congestive heart failure, and other inflammatory diseases. A potential mediator of muscle weakness is tumor necrosis factor (TNF)-alpha, a cytokine that can stimulate muscle wasting and also can induce contractile dysfunction without overt catabolism. This study addressed the latter process. Murine diaphragm and limb muscle (flexor digitorum brevis [FDB]) preparations were used to determine the relative sensitivities of these muscles to TNF-alpha. Intact muscle fibers were isolated from FDB and microinjected with indo-1 to measure changes in sarcoplasmic calcium regulation. We found that TNF-alpha depressed tetanic force of the diaphragm and FDB to comparable degrees across a range of stimulus frequencies. In isolated muscle fibers, TNF-alpha decreased tetanic force without altering tetanic calcium transients or resting calcium levels. We conclude that (1) TNF-alpha compromises contractile function of diaphragm and limb muscle similarly, and (2) TNF-alpha decreases force by blunting the response of muscle myofilaments to calcium activation.