The nitric oxide synthase inhibitor N(G)-nitro-L-arginine decreases defibrillation-induced free radical generation

OBJECTIVES

to demonstrate that nitric oxide (NO) contributes to free radical generation after epicardial shocks and to determinethe effect of a nitric oxide synthase (NOS) inhibitor, N(G)-nitro-L-arginine (L-NNA), on free radical generation.

BACKGROUND

Free radicals are generated by direct current shocks for defibrillation. NO reacts with the superoxide (O2*-) radical to for peroxynitrite (O = NOO-), which is toxic and initiates additional free radical generation. The contribution of NO to free radical generation after defibrillation is not fully defined.

METHODS AND RESULTS

Fourteen open chest dogs were studied. In the initial eight dogs, 40 J damped sinusoidal monophasic epicardial shocks was administered. Using electron paramagnetic resonance, we monitored the coronary sinus concentration of ascorbate free radical (Asc*-), a measure of free radical generation (total oxidative flux). Epicardial shocks were repeated after L-NNA, 5 mg/kg IV. In six additional dogs, immunohistochemical staining was done to identify nitrotyrosine, a marker of reactive nitrogen species-mediated injury, in post-shock myocardial tissue. Three of these dogs received L-NNA pre-shock. After the initial 40 J shock, Asc*- rose 39 +/- 2.5% from baseline. After L-NNA infusion, a similar 40 J shock caused Asc*- to increase only 2 +/- 3% form baseline (P < 0.05, post-L-NNA shock versus initial shock). Nitrotyrosine staining was more prominent in control animals than dogs receiving L-NNA, suggesting prevention of O = NOO- formation.

CONCLUSION

NO contributes to free radical generation and nitrosative injury after epicardial shocks; NOS inhibitors decrease radical generation by inhibiting the production of O = NOO-.

Stretch activation of GTP-binding proteins in C2C12 myoblasts

Mechanical stimulation has been proposed as a fundamental determinant of muscle physiology. The mechanotransduction of strain and strain rate in C2C12 myoblasts were investigated utilizing a radiolabeled GTP analogue to detect stretch-induced GTP-binding protein activation. Cyclic uniaxial strains of 10% and 20% at a strain rate of 20% s(-1) rapidly (within 1 min) activated a 25-kDa GTPase (183 +/- 17% and 186 +/- 19%, respectively), while 2% strain failed to elicit a response (109 +/- 11%) relative to controls. One, five, and sixty cycles of 10% strain elicited 187 +/- 20%, 183 +/- 17%, and 276 +/- 38% increases in activation. A single 10% stretch at 20% s(-1), but not 0.3% s(-1), resulted in activation. Insulin activated the same 25-kDa band in a dose-dependent manner. Western blot analysis revealed a panel of GTP-binding proteins in C2C12 myoblasts, and tentatively identified the 25-kDa GTPase as rab5. In separate experiments, a 40-kDa protein tentatively identified as Galpha(i) was activated (240 +/- 16%) by 10% strain at 1 Hz for 15 min. These results demonstrate the rapid activation of GTP-binding proteins by mechanical strain in myoblasts in both a strain magnitude- and strain rate-dependent manner.

Coronary vascular dysfunction associated with direct current shock injury

OBJECTIVE

To determine if cardiac injury following DC shocks includes impairment of coronary vascular reactivity.

METHODS

36 dogs (18-32 kg) were anesthetized and a thoracotomy was performed. Either antioxidant enzymes, superoxide dismutase (SOD, 15,000 U/kg) plus catalase (55,000 U/kg) or the NO synthase inhibitor N(G)-nitro-L-arginine (L-NNA, 5 mg/kg) was administered IV prior to sham (no shocks) or DC shock treatment, and the results were compared to dogs which did not receive SOD/catalase or L-NNA. In sham dogs, electrodes cradled the heart, but no shocks were delivered. In shock dogs, three 20 Joule DC shocks were delivered to the epicardium using hand-held paddles. Other dogs were allowed a 3-hour recovery period after the shocks. Epicardial microvessels and conduit rings were studied in vitro. Antagonists were not added to the bath of the study vessel. Internal diameter was measured in microvessels after constriction with endothelin. Tension of conduit arteries was measured after constriction with PGF(2alpha). Responses to acetylcholine (Ach, 10(-10)-10(-4) M), bradykinin (10(-14)-10(-6) M), the calcium ionophore A23187 (A23187, 10(-12)-10(-4) M) or nitroprusside (SNP, 10(-10)-10(-4) M) were measured.

RESULTS

Bradykinin, A23187 and SNP dependent dilation was not different between vessels from sham and shocked animals. Dilation to Ach was attenuated in vessels from shocked dogs. Superoxide production probably contributed to the impaired dilation to Ach since treatment with SOD/catalase improved dilation. Treatment with L-NNA also improved vascular function after DC shock.

CONCLUSION

DC shocks cause endothelial dysfunction, as demonstrated by impaired dilation to acetylcholine, in both canine coronary microvascular and conduit arteries. Since pretreatment with either SOD/catalase or L-NNA protects against this damage, a free radical mechanism, possibly involving eNOS, may contribute to endothelial dysfunction.DC shocks for cardioversion and defibrillation cause myocardial injury that may be free radical mediated.

The nitric oxide synthase inhibitor N(G)-nitro-L-arginine decreases defibrillation-induced free radical generation

OBJECTIVES

To demonstrate that nitric oxide (NO) contributes to free radical generation after epicardial shocks and to determine the effect of a nitric oxide synthase (NOS) inhibitor, N(G)-nitro-L-arginine (L-NNA), on free radical generation.

BACKGROUND

Free radicals are generated by direct current shocks for defibrillation. NO reacts with the superoxide (O(2).(-)) radical to form peroxynitrite (O=NOO(-)), which is toxic and initiates additional free radical generation. The contribution of NO to free radical generation after defibrillation is not fully defined.

METHODS AND RESULTS

Fourteen open chest dogs were studied. In the initial eight dogs, 40 J damped sinusoidal monophasic epicardial shocks was administered. Using electron paramagnetic resonance, we monitored the coronary sinus concentration of ascorbate free radical (Ascz.(-)), a measure of free radical generation (total oxidative flux). Epicardial shocks were repeated after L-NNA, 5 mg/kg IV. In six additional dogs, immunohistochemical staining was done to identify nitrotyrosine, a marker of reactive nitrogen species-mediated injury, in post-shock myocardial tissue. Three of these dogs received L-NNA pre-shock. After the initial 40 J shock, Ascz.(-) rose 39+/-2.5% from baseline. After L-NNA infusion, a similar 40 J shock caused Ascz.(-) to increase only 2+/-3% from baseline (P<0.05, post-L-NNA shock versus initial shock). Nitrotyrosine staining was more prominent in control animals than dogs receiving L-NNA, suggesting prevention of O=NOO(-) formation.

CONCLUSIONS

NO contributes to free radical generation and nitrosative injury after epicardial shocks; NOS inhibitors decrease radical generation by inhibiting the production of O=NOO(-).

Strain and strain rate activation of G proteins in human endothelial cells

The endothelium is known to sense and respond to its physical environment, but the underlying mechanisms and early events of endothelial cell mechanotransduction are not well understood. The present study measured G protein activation by mechanical strain in human umbilical vein endothelial cells (HUVEC) directly by photoincorporation of a hydrolysis resistant, radiolabeled GTP analog. Ten percent uniaxial strain at a strain rate of 20% s(-1) over 1min activated a 38kDa Galpha subunit 167+/-17% relative to controls, while 2% cyclic strain failed to significantly activate the protein (117+/-19%). A single cycle of 10% strain at 20% s(-1) strain rate activated the Galpha subunit 152+/-25%, while activation at the same strain but lower strain rate (0.3% s(-1)) was not significantly different from controls (116+/-12%). Western blot analysis identified the 38kDa protein as Galpha(q/11). These results demonstrate the rapid activation of G proteins in HUVEC by cyclic uniaxial strain in a strain- and strain rate-dependent manner.

Body weight is a predictor of biphasic shock success for low energy transthoracic defibrillation

BACKGROUND

Transthoracic impedance and current flow are determinants of defibrillation success with monophasic shocks. Whether transthoracic impedance, either independently or via its association with body weight, is a determinant of biphasic waveform shock success has not been determined.

METHODS AND RESULTS

We studied 22 swine, weighing 18-41 kg. After 15 s of ventricular fibrillation, each pig received transthoracic truncated exponential biphasic shocks (5/5 ms), 70-360 J. Shock success was strongly associated individually with body weight, leading-edge transthoracic impedance and current at low energy levels (70 and 100 J, all P<0.001). Multiple logistic regression analysis showed a significant association of body weight with shock success after adjusting for the effect of leading-edge impedance (odds ratio of success for 1 kg decrease in weight at 70 J was 1.29, 95% CI: 1.05-1.59, P=0.02; and at 100 J was 1.30, 95% CI: 1.14-1.49, P<0.0001). The same result was observed after adjusting for the effect of leading-edge current. At 150 J or higher energy levels, no significant association was observed.

CONCLUSIONS

Body weight is a determinant of shock success with biphasic waveforms at low energy levels in this swine model.

Transthoracic biphasic waveform defibrillation at very high and very low energies: a comparison with monophasic waveforms in an animal model of ventricular fibrillation

The purpose of this study was to compare truncated exponential biphasic waveform versus truncated exponential monophasic waveform shocks for transthoracic defibrillation over a wide range of energies. Biphasic waveforms are more effective than monophasic shocks for defibrillation at energies of 150-200 Joules (J) but there are few data available comparing efficacy and safety of biphasic versus monophasic defibrillation at energies of <150 J or >200 J. Thirteen adult swine (weighing 18-26 kg, mean 20 kg) were deeply anesthetized and intubated. After 15 s of electrically-induced ventricular fibrillation (VF), each pig received truncated exponential monophasic shocks (10 ms) and truncated exponential biphasic shocks (5/5 ms) in random order. Energy doses ranged from 70 to 360 J. Success was defined as termination of VF at 5 s post-shock. For both biphasic and monophasic waveforms success rate rose as energy was increased. Biphasic waveform shocks (5/5 ms) were superior to 10 ms monophasic waveform shocks at the very low energy levels (at 70 J, biphasic: 80+/-9%, monophasic; 32+/-11% and at 100 J, biphasic; 96+/-3% and monophasic 39+/-11%, both P < 0.01). No significant differences in shock success were seen between biphasic and monophasic waveform shocks at 200 J or higher energy levels. Shock success of > 75% was achieved with 200 J (10 J/kg) for both waveforms. Pulseless electrical activity (PEA) or ventricular asystole occurred in 4 animals receiving monophasic shocks and 1 animal receiving biphasic shocks. Biphasic waveform shocks (5/5 ms) for transthoracic defibrillation were superior to monophasic shocks (10 ms) at low energy levels. Percent success increased with increasing energies. PEA occurred infrequently with either waveform.

Pediatric transthoracic defibrillation: biphasic versus monophasic waveforms in an experimental model

OBJECTIVES

The purpose of this study was to determine and compare the efficacy of biphasic and monophasic waveforms in a porcine model of pediatric defibrillation.

BACKGROUND

The efficacy and safety of biphasic waveforms in children has not been established.

METHODS

We initially studied 27 piglets: 12 weighed 3-6 kg ('infants'), and 15 weighed 7-12 kg ('children'). Ventricular fibrillation (VF) was induced by rapid right ventricular pacing and maintained for 15 s. Transthoracic shocks of 7-100 J energy were given using monophasic (5 ms truncated exponential) and biphasic (5 ms positive, 5 ms negative pulse, truncated exponential) waveforms. A second study of four 'infant' and four 'child' piglets utilized the same protocol but with a 10 ms instead of 5 ms monophasic truncated exponential shock waveform compared with the 10 ms biphasic waveform.

RESULTS

For both biphasic and monophasic waveforms, shock success rate (termination of VF) rose steadily as energy was increased. In the first study in the 'infant' 3-6 kg group, the 10 ms biphasic waveforms were superior to 5 ms monophasic waveforms at 10, 20, and 30 J energies, and in the 'child' 7-12 kg group at 20 and 30 J energies (P<0.05). High success rates (>80%) were achieved by 20 J (4 J/kg) biphasic waveform shocks in the 'infant' piglets and 30 J (3 J/kg) biphasic waveform shocks in the 'child' piglets. In the second study using a 10 ms monophasic waveform, we found similar results. Pulseless electrical activity occurred in two animals following biphasic shocks and in two animals following monophasic shocks.

CONCLUSIONS

Biphasic waveforms proved superior to monophasic waveforms in both infant and child models. High success rates were achieved with low-energy biphasic shocks. Biphasic waveform defibrillation is a promising advance in pediatric resuscitation.

Intracardiac echocardiography identifies pericardial fluid and can monitor the success of pericardiocentesis: experimental studies

Pericardial tamponade is a complication of cardiac catheterization. Our purpose was to evaluate the ability of intracardiac echocardiography (ICE) to identify pericardial fluid and the success of pericardiocentesis in an experimental model. Seven dogs were studied with the use of a 10F, 10-MHz ICE catheter in the left ventricle. Normal saline was injected into the pericardial space while heart rate and arterial pressure were continuously monitored. The ability of ICE to identify the presence of pericardial fluid and the maximum pericardial separation and to monitor fluid accumulation and withdrawal was evaluated. Thirteen sequences of saline injection/withdrawal were studied. ICE correctly identified the presence or absence of pericardial fluid in all 13 injection/withdrawal sequences. The average sonolucent space separating epicardium from pericardium was 12 +/- 7 mm, generated from 148 +/- 65 mL of saline and producing a 35 +/- 23 mm Hg decrease in systolic blood pressure. ICE readily identified the accumulation and removal of pericardial fluid in this experimental model and should be an excellent tool to monitor pericardiocentesis in the catheterization laboratory.

Temporal gradient in shear-induced signaling pathway: involvement of MAP kinase, c-fos, and connexin43

The effect of a temporal gradient in shear and steady shear on the activity of extracellular signal-regulated protein kinases 1 and 2 (ERK1/ERK2), c-fos, and connexin43 (Cx43) in human endothelial cells was investigated. Three laminar flow profiles (16 dyn/cm(2)), including impulse flow (shear stress abruptly applied for 3 s), ramp flow (shear stress smoothly transitioned at flow onset), and step flow (shear stress abruptly applied at flow onset) were utilized. Relative to static controls, impulse flow stimulated the phosphorylation of ERK1/ERK2 8.5- to 7.5-fold, respectively at 10 min, as well as the mRNA expression of c-fos 51-fold at 30 min, and Cx43 8-fold at 90 min. These high levels of mRNA expression were sustained for at least 4 h. In contrast, ramp flow was unable to significantly induce gene expression and even inhibited the activation of ERK1/ERK2. Step flow, which contains both a sharp temporal gradient in shear stress and a steady shear component, elicited only moderate and transient responses, indicating the distinct role of these fluid shear stimuli in endothelial signal transduction. The specific inhibitor of mitogen-activated protein kinase kinase PD-98059 inhibited impulse flow-induced c-fos and Cx43 mRNA expression. Thus these findings implicate the involvement of ERK1/ERK2, c-fos, and Cx43 in the signaling pathway induced by the temporal gradient in shear.

Equibiaxial strain and strain rate stimulate early activation of G proteins in cardiac fibroblasts

Cardiac fibroblasts are responsible for the production of the extracellular matrix of the heart, with alterations of fibroblast function implicated in myocardial infarction and cardiac hypertrophy. Here the role of heterotrimeric GTP-binding proteins (G proteins) in the mechanotransduction of strain in rat cardiac fibroblasts was investigated. Cells in an equibiaxial stretch device were incubated with the photoreactive GTP analog azidoanalido [alpha-32P]GTP (AAGTP) and were subjected to various regimens of strain. Autoradiographic analysis showed a 42-kDa protein labeled for cells exposed to 12 cycles of 3% strain or 6 cycles of 6% strain over 60 s (strain rate of 1.2%/s), whereas 6 cycles of 3% strain (0.6%/s) elicited no measurable response. To further investigate the role of strain rate, a single 6% cycle over 10 or 60 s (1.2% and 0.2%/s, respectively) was applied, with the more rapid cycle stimulating AAGTP binding, whereas the lower strain rate showed no response. In cells subjected to a single 6% cycle/10 s, immunoprecipitation identified the AAGTP-labeled 42-kDa band as the G protein subunits G alpha q and G alpha i1. These results demonstrate that G protein activation represents one of the early mechanotransduction events in cardiac fibroblasts subjected to mechanical strain, with the rate at which the strain is applied modulating this response.

Fluid flow rapidly activates G proteins in human endothelial cells. Involvement of G proteins in mechanochemical signal transduction

Fluid shear stimulates endothelial cells, with the external hemodynamic forces transduced across the plasma membrane to modulate intracellular events. We report the first direct evidence that identifies specific GTP binding proteins (G proteins) activated within 1 second of flow onset, representing one of the earliest mechanochemical signal transduction events reported to date in shear-stimulated endothelium. A nonhydrolyzable GTP photoreactive analogue, azidoanilido [alpha-32P]GTP (AAGTP), allowed irreversible labeling of flow-stimulated G proteins, with two protein bands (42 kD and 31 kD) identified in human umbilical vein endothelial cells (HUVECs) subjected to laminar flow (10 dyne/cm2) in a parallel-plate flow chamber. Immunoprecipitation of labeled whole-cell lysates identified the specific G-protein subunits G q zero/alpha 11 and G alpha i3/alpha 0) as being activated by flow. Endothelial cell membrane vesicles were sheared in a cone-and-plate viscometer, with the 42-kD protein band labeled by AAGTP, but the 31-kD protein absent, indicating that the 42-kD G protein is membrane associated and activated independently of intact cytoskeletal or cytosolic components. Our results describe one of the earliest flow-induced signaling events reported in HUVECs, providing insight into the primary mechanosensing and signal transduction mechanisms.

Steady shear and step changes in shear stimulate endothelium via independent mechanisms--superposition of transient and sustained nitric oxide production

We propose that fluid shear presents two distinct stimuli to endothelium-the rate of change of flow and flow itself, to which cells sense and respond via independent mechanochemical transduction pathways. We demonstrate that nitric oxide production occurs by two independent mechanisms; a G protein-dependent transient burst stimulated by rapid changes in flow, and a G protein-independent sustained production under steady or smoothly transitioned flow. The novel use of step, ramp, and impulse flow in this study to stimulate nitric oxide production allows the isolation of these individual production events. Impulse flow activates only the G protein-dependent transient burst, which ramp flow fails to stimulate yielding only the sustained response. Step flow, which contains both a rapid increase and a steady flow component, stimulates both pathways, with the response of the superposition of the transient burst and sustained production.

Cubital tunnel syndrome

The symptoms of cubital tunnel syndrome in 118 patients were mainly those of muscular atrophy, but they also included sensory disturbances in the ring and little fingers and pain in the ulnar side of the forearm. The syndrome occurs equally in men and women, with no particular age preference in adults. Seven tests are useful in diagnosing the condition. Treatment consists of excising the band, which constricts the ulnar nerve at the elbow. Sensory recovery is usually complete, but muscular atrophy may not recover in older patients. In my series of 561 nerve decompressions, ulnar nerve decompression was carried out eight times more often at the elbow than at the wrist.

Size and shape analysis of schistomsome egg-counts in Egyptian autopsy data

We study egg-counts from a series of Egyptian autopsy cases with active schistosomiasis at death (Kamel, Cheever, Elwi, Mosimann and Danner 1977). The data are unique, and enable us to study the proportional distribution of eggs among various organs in relation to infection intensity for two species of schistosome worms. We develop a model for the distribution of eggs in three organs of the mesenteric circulation. Under a lognormal distribution assumption, several exact statistical procedures are presented and used to examine model consistency as well as isometry with respect to geometric means. Mesenteric egg counts for both Schistosoma mansoni and S. haematobium behave consistently with the model, and show little or no departure from isometry in cases without Symmers' fibrosis of the liver. We show that cases with Symmers' fibrosis have relatively more S. mansoni eggs in the small, as opposed to large, intestine. In the genito-urinary organs we show that the proportion of S. haematobium eggs in the bladder is high for low-intensity infections. This is consistent with the conclusion of Smith, Elwi, Kamel and Lichtenberg (1975), based on egg/gram data, that such infections may be initiated in the bladder. The correspondingly high proportion of eggs in the ureters with high-intensity infections indicates that increased intensity may have a disproportionately large pathologic effect on the infected individual.