Reduced NGF in Gastric Endothelial Cells Is One of the Main Causes of Impaired Angiogenesis in Aging Gastric Mucosa.

BACKGROUND & AIMS: Aging gastric mucosa has increased susceptibility to injury and delayed healing owing to impaired angiogenesis, but the mechanisms are not fully known. We examined whether impairment of angiogenesis in aging gastric mucosa is caused by deficiency of nerve growth factor (NGF) in gastric endothelial cells (ECs), and whether NGF therapy could reverse this impairment. METHODS: In gastric mucosal ECs (GECs) isolated from young and aging rats we examined the following: (1) in vitro angiogenesis, (2) NGF expression, and (3) the effect of NGF treatment on angiogenesis, GEC proliferation and migration, and dependence on serum response factor. In in vivo studies in young and aging rats, we examined NGF expression in gastric mucosa and the effect of NGF treatment on angiogenesis and gastric ulcer healing. To determine human relevance, we examined NGF expression in gastric mucosal biopsy specimens of aging (≥70 y) and young (≤40 y) individuals. RESULTS: In cultured aging GECs, NGF expression and angiogenesis were reduced significantly by 3.0-fold and 4.1-fold vs young GECs. NGF therapy reversed impairment of angiogenesis in aging GECs, and serum response factor silencing completely abolished this response. In gastric mucosa of aging rats, NGF expression in GECs was reduced significantly vs young rats. In aging rats, local NGF treatment significantly increased angiogenesis and accelerated gastric ulcer healing. In aging human subjects, NGF expression in ECs of gastric mucosal vessels was 5.5-fold reduced vs young individuals. CONCLUSIONS: NGF deficiency in ECs is a key mechanism underlying impaired angiogenesis and delayed ulcer healing in aging gastric mucosa. Local NGF therapy can reverse these impairments.

Inhibition of Intestinal Thiamin Transport in Rat Model of Sepsis.

OBJECTIVES: Thiamin deficiency is highly prevalent in patients with sepsis, but the mechanism by which sepsis induces thiamin deficiency is unknown. This study aimed to determine the influence of various severity of sepsis on carrier-mediated intestinal thiamin uptake, level of expressions of thiamin transporters (thiamin transporter-1 and thiamin transporter-2), and mitochondrial thiamin pyrophosphate transporter. DESIGN: Randomized controlled study. SETTING: Research laboratory at a Veterans Affairs Medical Center. SUBJECTS: Twenty-four Sprague-Dawley rats were randomized into controls, mild, moderate, and severe sepsis with equal number of animals in each group. INTERVENTIONS: Sepsis was induced by cecal ligation and puncture with the cecum ligated below the cecal valve at 25%, 50%, and 75% of cecal length, defined as severe, moderate, and mild sepsis, respectively. Control animals underwent laparotomy only. MEASUREMENTS AND MAIN RESULTS: After 2 days of induced sepsis, carrier-mediated intestinal thiamin uptake was measured using [H]thiamin. Expressions of thiamin transporter-1, thiamin transporter-2, and mitochondrial thiamin pyrophosphate transporter proteins and messenger RNA were measured. Proinflammatory cytokines (interleukin-1ß and interleukin-6) and adenosine triphosphate were also measured. Sepsis inhibited [H]thiamin uptake, and the inhibition was a function of sepsis severity. Both cell membrane thiamin transporters and mitochondrial thiamin pyrophosphate transporter expression levels were suppressed; also levels of adenosine triphosphate in the intestine of animals with moderate and severe sepsis were significantly lower than that of sham-operated controls. CONCLUSIONS: For the first time, we demonstrated that sepsis inhibited carrier-mediated intestinal thiamin uptake as a function of sepsis severity, suppressed thiamin transporters and mitochondrial thiamin pyrophosphate transporter, leading to adenosine triphosphate depletion.

Positive end-expiratory airway pressure does not aggravate ventilator-induced diaphragmatic dysfunction in rabbits.

INTRODUCTION: Immobilization of hindlimb muscles in a shortened position results in an accelerated rate of inactivity-induced muscle atrophy and contractile dysfunction. Similarly, prolonged controlled mechanical ventilation (CMV) results in diaphragm inactivity and induces diaphragm muscle atrophy and contractile dysfunction. Further, the application of positive end-expiratory airway pressure (PEEP) during mechanical ventilation would result in shortened diaphragm muscle fibers throughout the respiratory cycle. Therefore, we tested the hypothesis that, compared to CMV without PEEP, the combination of PEEP and CMV would accelerate CMV-induced diaphragm muscle atrophy and contractile dysfunction. To test this hypothesis, we combined PEEP with CMV or with assist-control mechanical ventilation (AMV) and determined the effects on diaphragm muscle atrophy and contractile properties. METHODS: The PEEP level (8 cmH2O) that did not induce lung overdistension or compromise circulation was determined. In vivo segmental length changes of diaphragm muscle fiber were then measured using sonomicrometry. Sedated rabbits were randomized into seven groups: surgical controls and those receiving CMV, AMV or continuous positive airway pressure (CPAP) with or without PEEP for 2 days. We measured in vitro diaphragmatic force, diaphragm muscle morphometry, myosin heavy-chain (MyHC) protein isoforms, caspase 3, insulin-like growth factor 1 (IGF-1), muscle atrophy F-box (MAFbx) and muscle ring finger protein 1 (MuRF1) mRNA. RESULTS: PEEP shortened end-expiratory diaphragm muscle length by 15%, 14% and 12% with CMV, AMV and CPAP, respectively. Combined PEEP and CMV reduced tidal excursion of segmental diaphragm muscle length; consequently, tidal volume (VT) decreased. VT was maintained with combined PEEP and AMV. CMV alone decreased maximum tetanic force (Po) production by 35% versus control (P < 0.01). Combined PEEP and CMV did not decrease Po further. Po was preserved with AMV, with or without PEEP. Diaphragm muscle atrophy did not occur in any fiber types. Diaphragm MyHC shifted to the fast isoform in the combined PEEP and CMV group. In both the CMV and combined PEEP and CMV groups compared to controls, IGF-1 mRNAs were suppressed, whereas Caspase-3, MAFbx and MuRF1 mRNA expression were elevated. CONCLUSIONS: Two days of diaphragm muscle fiber shortening with PEEP did not exacerbate CMV-induced diaphragm muscle dysfunction.

Loss of parietal cell superoxide dismutase leads to gastric oxidative stress and increased injury susceptibility in mice.

Mitochondrial superoxide dismutase (SOD2) prevents accumulation of the superoxide that arises as a consequence of oxidative phosphorylation. However, SOD2 is a target of oxidative/nitrosative inactivation, and reduced SOD2 activity has been demonstrated to contribute to portal hypertensive gastropathy. We investigated the consequences of gastric parietal cell-specific SOD2 deficiency on mitochondrial function and gastric injury susceptibility. Mice expressing Cre recombinase under control of the parietal cell Atpase4b gene promoter were crossed with mice harboring loxP sequences flanking the sod2 gene (SOD2 floxed mice). Cre-positive mice and Cre-negative littermates (controls) were used in studies of SOD2 expression, parietal cell function (ATP synthesis, acid secretion, and mitochondrial enzymatic activity), increased oxidative/nitrosative stress, and gastric susceptibility to acute injury. Parietal cell SOD2 deficiency was accompanied by a 20% (P < 0.05) reduction in total gastric SOD activity and a 93% (P < 0.001) reduction in gastric SOD2 activity. In SOD2-deficient mice, mitochondrial aconitase and ATP synthase activities were impaired by 36% (P < 0.0001) and 44% (P < 0.005), respectively. Gastric tissue ATP content was reduced by 34% (P < 0.002). Basal acid secretion and peak secretagogue (histamine)-induced acid secretion were reduced by 43% (P < 0.0001) and 40% (P < 0.0005), respectively. There was a fourfold (P < 0.02) increase in gastric mucosal apoptosis and 41% (P < 0.001) greater alcohol-induced gastric damage in the parietal cell SOD2-deficient mice. Our findings indicate that loss of parietal cell SOD2 leads to mitochondrial dysfunction, resulting in perturbed energy metabolism, impaired parietal cell function, and increased gastric mucosal oxidative stress. These alterations render the gastric mucosa significantly more susceptible to acute injury.

Interactive effects of corticosteroid and mechanical ventilation on diaphragm muscle function.

Information on the interactive effects of methylprednisolone, controlled mechanical ventilation (CMV), and assisted mechanical ventilation (AMV) on diaphragm function is sparse. Sedated rabbits received 2 days of CMV, AMV, and spontaneous breathing (SB), with either methylprednisolone (MP; 60 mg/kg/day intravenously) or saline. There was also a control group. In vitro diaphragm force, myofibril ultrastructure, αII-spectrin proteins, insulin-like growth factor-1 (IGF-1), and muscle atrophy F-box (MAF-box) mRNA were measured. Maximal tetanic tension (P(o)) decreased significantly with CMV. Combined MP plus CMV did not decrease P(o) further. With AMV, P(o) was similar to SB and controls. Combined MP plus AMV or MP plus SB decreased P(o) substantially. Combined MP plus CMV, MP plus AMV, or MP plus SB induced myofibrillar disruption that correlated with the reduced P(o). αII-spectrin increased, IGF-1 decreased, and MAF-box mRNA increased in both the CMV group and MP plus CMV group. Short-term, high-dose MP had no additive effects on CMV-induced diaphragm dysfunction. Combined MP plus AMV impaired diaphragm function, but AMV alone did not. We found that acute, high-dose MP produces diaphragm dysfunction depending on the mode of mechanical ventilation.

[Functional consequences of eccentric contractions of the diaphragm]. / Consecuencias de las contracciones excéntricas del diafragma sobre su función.

INTRODUCTION AND OBJECTIVES: Eccentric contractions are those that occur after a muscle has been stretched, and they can predispose the muscle to damage. Most previous studies have been performed on limb muscles, and the potential consequences of eccentric contractions on the respiratory muscles are therefore unknown. The aim of this study was to evaluate the effects of repeated eccentric contractions on diaphragmatic function. METHODS: In 6 dogs, the diaphragm was stretched by applying pressure on the abdominal wall, and consecutive series of eccentric contractions were induced by bilateral supramaximal stimulation. The effect of these contractions on the diaphragm was then evaluated by applying bilateral twitch and tetanic stimulation of the phrenic nerves and measuring the changes in abdominal pressure and the shortening of the right and left hemidiaphragms (by sonomicrometry). Structural study of the muscle was also performed in 4 animals. RESULTS: Eccentric contractions were successfully achieved in all cases. Stimulation-induced diaphragmatic pressures became lower immediately after these contractions: twitch pressure fell by 53% and tetanic pressure by 67% after the first 10 eccentric contractions (P<.001 in both cases). Tetanic stimulation also demonstrated an early deterioration in contractility, which fell by 29% in the right hemidiaphragm (P<.05) and by 14% in the left hemidiaphragm (P<.001). Functional impairment was persistent, lasting at least 12 hours, and was associated with sarcomeric and sarcolemmal damage. CONCLUSIONS: This experimental model, which enabled the effects of eccentric contractions to be studied in the diaphragm, revealed a deterioration of muscle function that persisted for hours and that appeared to be partly due to structural damage. In the clinical setting, physiologic or therapeutic maneuvers that increase the resting length of the diaphragm should be used with caution.

[Modifications of diaphragmatic activity induced by midline laparotomy and changes in abdominal wall compliance]. / Modificaciones en la actividad del diafragma inducidas por laparotomía media y cambios en la rigidez de la pared abdominal.

INTRODUCTION AND OBJECTIVE: Diaphragmatic activity varies with the initial length of the muscle. Our objective was to evaluate the influence of surgery and changes in abdominal wall compliance on diaphragmatic activity. METHODS: Both phrenic nerves in 7 mongrel dogs were stimulated electrically with single supramaximal pulses (twitch). The gastric (Pga) and transdiaphragmatic (Pdi) pressures generated and muscle shortening (sonomicrometry) were used to evaluate diaphragmatic activity, which was determined at baseline, after midline laparotomy, with an elastic abdominal bandage, and with a rigid circular cast. Abdominal pressure was then gradually increased in order to induce progressive lengthening of the diaphragm. RESULTS: After laparotomy, the pressures were somewhat lower (by 12%) than at baseline. The elastic bandage produced a slight increase in the pressure generated by the diaphragm (mean [SE] values: Pga, from 4.2 [0.3]cm H(2)O to 6.3 [0.9]cm H(2)O, P<.01; Pdi(tw), from 12.1 [2.0]cm H(2)O to 15.4 [1.8]cm H(2)O, P<.05]), and these values increased even further with the rigid cast (Pga, to 12.6 [1.5]cm H(2)O; Pdi, to 20.2 [2.3]cm H(2)O; P<.01 for both comparisons); this occurred despite smaller degrees of muscle shortening: by 57% [5%] of the initial length at functional residual capacity at baseline, by 49% [5%] with the bandage (P<.05), and by 39% [6%] with the cast (P<.01). With progressive lengthening of the muscle, its contractile efficacy increased up to a certain point (105% of the length at functional residual capacity), after which it began to decline. CONCLUSIONS: Abdominal wall compliance plays an important role in the diaphragmatic response to stimulation. This appears to be due mainly to changes in its length at rest.

Consecuencias de las contracciones excéntricas del diafragma sobre su función / Functional Consequences of Eccentric Contractions of the Diaphragm

Introducción y objetivos las contracciones excéntricas (CC.EE.) se caracterizan por producirse previa elongación muscular, lo que facilita la lesión. La mayoría de los estudios precedentes se han desarrollado en músculos de las extremidades, por lo que se desconoce la relevancia potencial de las CC.EE. en los músculos respiratorios. El objetivo del presente trabajo ha sido evaluar los efectos funcionales de series repetidas de CC.EE. sobre el diafragma. Métodose provocó la elongación del diafragma mediante presión externa abdominal en 6 perros y se indujeron CC.EE. mediante series consecutivas de pulsos supramáximos bilaterales. El efecto se valoró mediante la posterior respuesta del músculo ante estimulación frénica bilateral tanto de pulso único como tetánica, en términos de presión y acortamiento (sonomicrometría) de los hemidiafragmas derecho e izquierdo. En 4 casos se realizó estudio estructural. Resultadosse consiguió inducir CC.EE. en todos los casos. Las presiones diafragmáticas inducidas por estimulación disminuyeron inmediatamente después de la actividad excéntrica (pulso único: 53%; tetánica: 67%; p<0,001 en ambas, tras las primeras 10 CC.EE.), al igual que la propia contractilidad diafragmática (evidenciable con la estimulación tetánica; hemidiafragma derecho un HD 29%, p<0,05, e hemidiafragma izquierdo, un 14%, p<0,001). La disfunción fue persistente (duró al menos 12h) y se asoció a la presencia de daño sarcomérico y sarcolémico. Conclusióncon el modelo propuesto, que permite estudiar el efecto de las CC.EE. en el diafragma, se demuestra una pérdida funcional mantenida durante horas, que en parte parece debida a una lesión estructural. Clínicamente se debería ser cauto con las maniobras fisiológicas o terapéuticas que impliquen la elongación basal del diafragma(AU)

Introduction and Objectives Eccentric contractions are those that occur after a muscle has been stretched, and they can predispose the muscle to damage. Most previous studies have been performed on limb muscles, and the potential consequences of eccentric contractions on the respiratory muscles are therefore unknown. The aim of this study was to evaluate the effects of repeated eccentric contractions on diaphragmatic function. MethodsIn 6 dogs, the diaphragm was stretched by applying pressure on the abdominal wall, and consecutive series of eccentric contractions were induced by bilateral supramaximal stimulation. The effect of these contractions on the diaphragm was then evaluated by applying bilateral twitch and tetanic stimulation of the phrenic nerves and measuring the changes in abdominal pressure and the shortening of the right and left hemidiaphragms (by sonomicrometry). Structural study of the muscle was also performed in 4 animals. ResultsEccentric contractions were successfully achieved in all cases. Stimulation-induced diaphragmatic pressures became lower immediately after these contractions: twitch pressure fell by 53% and tetanic pressure by 67% after the first 10 eccentric contractions (P<.001 in both cases). Tetanic stimulation also demonstrated an early deterioration in contractility, which fell by 29% in the right hemidiaphragm (P<.05) and by 14% in the left hemidiaphragm (P<.001). Functional impairment was persistent, lasting at least 12 hours, and was associated with sarcomeric and sarcolemmal damage. ConclusionsThis experimental model, which enabled the effects of eccentric contractions to be studied in the diaphragm, revealed a deterioration of muscle function that persisted for hours and that appeared to be partly due to structural damage. In the clinical setting, physiologic or therapeutic maneuvers that increase the resting length of the diaphragm should be used with caution(AU)

Modificaciones en la actividad del diafragma inducidas por laparotomía media y cambios en la rigidez de la pared abdominal / Modifications of Diaphragmatic Activity Induced by Midline Laparotomy and Changes in Abdominal Wall Compliance

Introducción y objetivos la actividad del diafragma puede verse modificada por su longitud inicial. Nuestro objetivo ha sido evaluar la influencia de la cirugía y los cambios en la rigidez de la pared abdominal sobre la actividad del músculo.Métodoen 7 perros mestizos se estimularon eléctricamente ambos nervios frénicos con pulsos únicos supramáximos (twitch). Para evaluar la actividad del diafragma se determinaron las presiones generadas —gástrica (Pgatw) y transdiafragmática (Pditw)— y el acortamiento muscular (sonomicrometría). La respuesta diafragmática se obtuvo en situación basal, tras laparotomía media, con venda abdominal elástica y con prótesis rígida circular. A continuación se incrementó ligera y progresivamente la presión abdominal para conseguir el alargamiento sucesivo del diafragma.Resultadostras la laparotomía, las presiones fueron algo inferiores a las basales (12%). La banda elástica provocó un leve aumento de la presión generada por el diafragma (valores medios±error estándar. Pgatw: 4,2±0,3 a 6,3±0,9cmH2O, p<0,01; Pditw: 12,1±2,0 a 15,4±1,8cmH2O, p<0,05), que se incrementó aún más con la prótesis rígida (Pgatw: 12,6±1,5cmH2O; Pditw: 20,2±2,3cmH2O; p<0,01 para ambas), a pesar de valores de acortamiento inferiores —un 57±5% de la longitud inicial a capacidad funcional residual en situación basal, un 49±5% con banda (p<0,05) y un 39±6% con prótesis (p<0,01)—. Al alargar progresivamente el músculo, su efectividad contráctil aumentó hasta un punto (un 105% de la longitud a capacidad funcional residual) a partir del cual comenzó a declinar.Conclusiónla rigidez de la pared abdominal desempeña un papel importante en la respuesta del diafragma a la estimulación. Esto parece deberse fundamentalmente a cambios en su longitud de reposo(AU)

Introduction and Objective Diaphragmatic activity varies with the initial length of the muscle. Our objective was to evaluate the influence of surgery and changes in abdominal wall compliance on diaphragmatic activity.MethodsBoth phrenic nerves in 7 mongrel dogs were stimulated electrically with single supramaximal pulses (twitch). The gastric (Pga) and transdiaphragmatic (Pdi) pressures generated and muscle shortening (sonomicrometry) were used to evaluate diaphragmatic activity, which was determined at baseline, after midline laparotomy, with an elastic abdominal bandage, and with a rigid circular cast. Abdominal pressure was then gradually increased in order to induce progressive lengthening of the diaphragm.ResultsAfter laparotomy, the pressures were somewhat lower (by 12%) than at baseline. The elastic bandage produced a slight increase in the pressure generated by the diaphragm (mean [SE] values: Pga, from 4.2 [0.3]cm H2O to 6.3 [0.9]cm H2O, P<.01; Pditw, from 12.1 [2.0]cm H2O to 15.4 [1.8]cm H2O, P<.05]), and these values increased even further with the rigid cast (Pga, to 12.6 [1.5]cm H2O; Pdi, to 20.2 [2.3]cm H2O; P<.01 for both comparisons); this occurred despite smaller degrees of muscle shortening: by 57% [5%] of the initial length at functional residual capacity at baseline, by 49% [5%] with the bandage (P<.05), and by 39% [6%] with the cast (P<.01). With progressive lengthening of the muscle, its contractile efficacy increased up to a certain point (105% of the length at functional residual capacity), after which it began to decline.ConclusionsAbdominal wall compliance plays an important role in the diaphragmatic response to stimulation. This appears to be due mainly to changes in its length at rest(AU)

[Diaphragmatic response is influenced by previous muscle activity]. / Respuesta diafragmática en función de la actividad previa del músculo.

OBJECTIVE: Previous muscle activity can alter muscle contractility and lead to strength underestimation or overestimation in functional measurements. The objective of this study was to evaluate changes in the maximum pressure produced by the diaphragm after different series of spontaneous near-to-maximal isometric contractions. METHODS: Duplicate studies were performed on 6 dogs with a mean (SD) weight of 26 (7) kg. The supramaximal response of the diaphragm was achieved by simultaneous supramaximal stimulation of both phrenic nerves, both under basal conditions and after series of 5, 10, and 20 spontaneous inspiratory efforts against the occluded airway, performed before and after spinal anesthesia (which eliminates the ventilatory contribution of the intercostal muscles). The response was measured using the twitch gastric pressure (Pga) and twitch esophageal pressure (Pes) and by muscle shortening (sonomicrometry). RESULTS: The short series of 5 inspiratory efforts and, in particular, the medium series of 10 efforts produced potentiation of the contractile response, with a rise in the Pga from 3.2 (0.4) cm H(2)O to 3.7 (0.3) cm H(2)O, and from 3.5 (0.3) cm H(2)O to 3.9 (0.3) cm H(2)O, respectively (P=.05 in both cases). The potentiation was somewhat greater after subarachnoid anesthesia (an increase in the Pga of 21% after the medium series of 10 efforts with anesthesia vs 11% without anesthesia). However, the long series of 20 efforts produced a fall in the response, with a decrease in the Pga from 3.2 (0.4) cm H(2)O to 2.5 (0.3) cm H(2)O (P< .05), probably due to fatigue overcoming the effect of potentiation. CONCLUSIONS: Previous effort affects the contractile capacity of the diaphragm and it is difficult to predict the predominance of fatigue or potentiation in the response. This factor must be taken into account when determining the maximum respiratory pressures in daily clinical practice.

Respuesta diafragmática en función de la actividad previa del músculo / Diaphragmatic response is influenced by previous muscle activity

OBJETIVO: La actividad previa puede modificar la contractilidadmuscular, lo que puede conducir a la infra o supraestimaciónde la fuerza en las determinaciones funcionales.El presente trabajo se ha propuesto como objetivovalorar cambios en la presión máxima generada por el diafragmatras diferentes series de contracciones isométricasespontáneas y cuasi máximas.MÉTODOS: Se estudiaron por duplicado 6 perros con unpeso medio ± desviación estándar de 26 ± 7 kg. Se obtuvo larespuesta supramáxima del diafragma –presiones gástrica(Pgatw) y esofágica (Pestw) inducidas por estimulación frénicabilateral, y acortamiento muscular (sonomicrometría)— porestimulación simultánea supramáxima de ambos nervios frénicos,tanto en situación basal como tras series cortas(5), medianas (10) y largas (20) de esfuerzos inspiratorios espontáneoscontra la vía aérea ocluida, antes y después de administraranestesia subaracnoidea (elimina la contribuciónventilatoria de los músculos intercostales).RESULTADOS: La serie corta y, sobre todo, la serie medianaprovocaron la potenciación de la respuesta contráctil (Pgatwde 3,2 ± 0,4 a 3,7 ± 0,3, y de 3,5 ± 0,3 a 3,9 ± 0,3 cmH2O, respectivamente;p < 0,05 ambas). La potenciación fue algo superiorcon anestesia subaracnoidea (un 21 frente al 11% sinanestesia, para la Pgatw tras las series medianas). La serielarga provocó, sin embargo, una disminución de la respuesta(Pgatw: 3,2 ± 0,4 a 2,5 ± 0,3 cmH2O; p < 0,05), probablementepor predominio de la fatiga sobre la potenciación.CONCLUSIONES: Los esfuerzos previos determinan la capacidadcontráctil del diafragma y resulta difícil predecir elpredominio de fatiga o de potenciación en la respuesta. Estefactor debería tenerse en cuenta al determinar las presionesrespiratorias máximas en la clínica diaria

OBJECTIVE: Previous muscle activity can alter musclecontractility and lead to strength underestimation oroverestimation in functional measurements. The objectiveof this study was to evaluate changes in the maximumpressure produced by the diaphragm after different seriesof spontaneous near-to-maximal isometric contractions.METHODS: Duplicate studies were performed on 6 dogs witha mean (SD) weight of 26 (7) kg. The supramaximal responseof the diaphragm was achieved by simultaneous supramaximalstimulation of both phrenic nerves, both under basal conditionsand after series of 5, 10, and 20 spontaneous inspiratory effortsagainst the occluded airway, performed before and after spinalanesthesia (which eliminates the ventilatory contribution of theintercostal muscles). The response was measured using thetwitch gastric pressure (Pga) and twitch esophageal pressure(Pes) and by muscle shortening (sonomicrometry).RESULTS: The short series of 5 inspiratory efforts and, inparticular, the medium series of 10 efforts produced potentiationof the contractile response, with a rise in the Pga from 3.2 (0.4)cmH2O to 3.7 (0.3) cmH2O, and from 3.5 (0.3) cmH2O to 3.9 (0.3)cmH2O, respectively (P=.05 in both cases). The potentiation wassomewhat greater after subarachnoid anesthesia (an increase inthe Pga of 21% after the medium series of 10 efforts withanesthesia vs 11% without anesthesia). However, the long seriesof 20 efforts produced a fall in the response, with a decrease in thePga from 3.2 (0.4) cmH2O to 2.5 (0.3) cmH2O (P<.05), probablydue to fatigue overcoming the effect of potentiation.CONCLUSIONS: Previous effort affects the contractilecapacity of the diaphragm and it is difficult to predict thepredominance of fatigue or potentiation in the response. Thisfactor must be taken into account when determining themaximum respiratory pressures in daily clinical practice

Acute effects of high-dose methylprednisolone on diaphragm muscle function.

The time- and dose-dependent effects of acute high-dose corticosteroids on the diaphragm muscle are poorly defined. This study aimed to examine in rabbits the temporal relationships and dose-response effects of acute high-dose methylprednisolone succinate on diaphragmatic contractile and structural properties. Animals were assigned to groups receiving: (1) 80 mg/kg/day methylprednisolone (MP80) intramuscularly for 1, 2, and 3 days; (2) 10 mg/kg/day methylprednisolone (MP10, pulse-dose) for 3 days; or (3) saline (placebo) for 3 days; and (4) a control group. Diaphragmatic in vitro force-frequency and force-velocity relationships, myosin heavy chain (MyHC) isoform protein and mRNA, insulin-like growth factor-1 (IGF-1), muscle atrophy F-box (MAF-box) mRNA, and volume density of abnormal myofibrils were measured at each time-point. MP80 did not affect animal nutritional state or fiber cross-sectional area as assessed in separate pair-fed groups receiving methylprednisolone or saline for 3 days. Compared with control values, MP80 decreased diaphragmatic maximum tetanic tension (Po) by 19%, 24%, and 34% after 1, 2, and 3 days (P < 0.05), respectively, whereas MP10 decreased Po modestly (12%; P > 0.05). Vmax and MyHC protein proportions were unchanged in both the MP80 and MP10 groups. Maximum power output decreased after 2 and 3 days of MP80. Suppression of IGF-1 and overexpression of MAF-box mRNA occurred in both MP groups. Significant myofibrillar disarray was also observed in both MP groups. The decline in Po was significantly associated with the increased volume density of abnormal myofibrils. Thus, very high-dose methylprednisolone (MP80) can produce rapid reductions in diaphragmatic function, whereas pulse-dose methylprednisolone (MP10) produces only modest functional loss.

Rab-mediated endocytosis: linking neurodegeneration, neuroprotection, and synaptic plasticity?

Rab proteins are small GTPases involved in endocytosis and recycling of cell surface molecules. Recently they have been implicated in the etiopathogenesis of several neurodegenerative disorders including Alzheimer's and Lewy body disease. In experiments on organotypic hippocampal cultures, upregulation of Rab protein family member Rab5b after group I metabotropic glutamate receptor (mGluR) stimulation was associated with reduced neuronal vulnerability to excitotoxic injury. This mGluR-mediated neuroprotection was abolished by antisense-induced deficiency of Rab5b. Electrophysiological measurements of excitatory synaptic transmission in the Schaffer collateral-CA1 pathway revealed that mGluR activation that induces neuroprotection also induced long-term depression (LTD) of synaptic transmission. Similar to the neuroprotection, Rab5b deficiency abolished dihydroxyphenylglycine-induced LTD. Together, these findings support the idea that Rab proteins, and the Rab5b protein in particular, may provide a link between neurodegenerative disease, neuroprotection, and synaptic plasticity, as well as possibly being a useful target for pharmacological interventions.

Early effects of mechanical ventilation on isotonic contractile properties and MAF-box gene expression in the diaphragm.

This study aimed to determine the time-dependent effects of diaphragmatic inactivity on its maximum shortening velocity (V(max)) and the muscle atrophy F-box (MAF-box, atrogin-1) gene expression during controlled mechanical ventilation (CMV). Twenty-four New Zealand White rabbits were grouped into 1 day, 2 days, and 3 days of CMV and controls in equal numbers. The in vitro isotonic contractile properties of the diaphragm were determined. In addition, myosin heavy chain protein and mRNA, myosin light chain, MAF-box mRNA, and volume density of abnormal myofibrils were measured. Tetanic force decreased, and V(max) increased from control of 6.4 to 6.6, 7.7, and 8.1 muscle lengths per second after 1, 2, and 3 days of CMV, respectively (P < 0.02). The increased V(max) compensated for the decreased tetanic force; consequently, compared with the controls, maximum power output was unchanged after 3 days of CMV. V(max) correlated with the volume density of abnormal myofibrils [y = 0.1x + 5.7 (r = 0.87, P < 0.01)]. In the diaphragm, MAF-box was overexpressed (355% of control) after 1 day of CMV, before the evidence of structural myofibril disarray. In conclusion, CMV produced a time-dependent increase in V(max) that was associated with the degree of myofibrillar disarray and independent of changes in myosin isoform expression. Furthermore, CMV produced an increase in MAF-box mRNA levels that may be partially or completely responsible for the degree of myofibrillar disarray resulting from CMV.

Optimal arrangement of magnetic coils for functional magnetic stimulation of the inspiratory muscles in dogs.

In an attempt to maximize inspiratory pressure and volume, the optimal position of a single or of dual magnetic coils during functional magnetic stimulation (FMS) of the inspiratory muscles was evaluated in twenty-three dogs. Unilateral phrenic magnetic stimulation (UPMS) or bilateral phrenic magnetic stimulation (BPMS), posterior cervical magnetic stimulation (PCMS), anterior cervical magnetic stimulation (ACMS) as well as a combination of PCMS and ACMS were performed. Trans-diaphragmatic pressure (Pdi), flow, and lung volume changes with an open airway were measured. Transdiaphragmatic pressure was also measured with an occluded airway. Changes in inspiratory parameters during FMS were compared with 1) electrical stimulation of surgically exposed bilateral phrenic nerves (BPES) and 2) ventral root electrical stimulation at C5-C7 (VRES C5-C7). Relative to the Pdi generated by BPES of 36.3 +/- 4.5 cm H2O (Mean +/- SEM), occluded Pdi(s) produced by UPMS, BPMS, PCMS, ACMS, and a combined PCMS + ACMS were 51.7%, 61.5%, 22.4%, 100.3%, and 104.5% of the maximal Pdi, respectively. Pdi(s) produced by UPMS, BPMS, PCMS, ACMS, and combined ACMS + PCMS were 38.0%, 45.2%, 16.5%, 73.8%, and 76.8%, respectively, of the Pdi induced by VRES (C5-C7) (48.0 +/- 3.9 cm H2O). The maximal Pdi(s) generated during ACMS and combined PCMS + ACMS were higher than the maximal Pdi(s) generated during UPMS, BPMS, or PCMS (p < 0.05). ACMS alone induced 129.8% of the inspiratory flow (73.0 +/- 9.4 L/ min) and 77.5% of the volume (626 +/- 556 ml) induced by BPES. ACMS and combined PCMS + ACMS produce a greater inspiratory pressure than UPMS, BPMS or PCMS. ACMS can be used to generate sufficient inspiratory pressure, flow, and volume for activation of the inspiratory muscles.

Assist-control mechanical ventilation attenuates ventilator-induced diaphragmatic dysfunction.

Controlled mechanical ventilation induced a profound diaphragm muscle dysfunction and atrophy. The effects of diaphragmatic contractions with assisted mechanical ventilation on diaphragmatic isometric, isotonic contractile properties, or the expression of muscle atrophy factor-box (MAF-box), the gene responsible for muscle atrophy, are unknown. We hypothesize that assisted mechanical ventilation will preserve diaphragmatic force and prevent overexpression of MAF-box. Studying sedated rabbits randomized equally into control animals, those with 3 days of assisted ventilation, and those with controlled ventilation, we assessed in vitro diaphragmatic isometric and isotonic contractile function. The concentrations of contractile proteins, myosin heavy chain isoform, and MAF-box mRNA were measured. Tetanic force decreased by 14% with assisted ventilation and 48% with controlled ventilation. Maximum shortening velocity tended to increase with controlled compared with assisted ventilation and control. Peak power output decreased 20% with assisted ventilation and 41% with controlled ventilation. Contractile proteins were unchanged with either modes of ventilation; myosin heavy chain 2X mRNA tended to increase and that of 2A to decrease with controlled ventilation. MAF-box gene was overexpressed with controlled ventilation. We conclude that preserving diaphragmatic contractions during mechanical ventilation attenuates the force loss induced by complete inactivity and maintains MAF-box gene expression in control.