Hyperbaric oxygen pretreatment reduces the incidence of decompression sickness in rats

We have previously hypothesised that the number of bubbles evolving during decompression from a dive, and therefore the incidence of decompression sickness (DCS), might be reduced by pretreatment with hyperbaric oxygen (HBO). The inert gas in the gas micronuclei would be replaced by oxygen, which would subsequently be consumed by the mitochondria. This has been demonstrated in the transparent prawn. To investigate whether our hypothesis holds for mammals, we pretreated rats with HBO at 304, 405, or 507 kPa for 20 min, after which they were exposed to air at 1,013 kPa for 33 min and decompressed at 202 kPa/min. Twenty control rats were exposed to air at 1,013 kPa for 32 min, without HBO pretreatment. On reaching the surface, the rat was immediately placed in a rotating cage for 30 min. The animal’s behaviour enabled us to make an early diagnosis of DCS according to accepted symptoms. Rats were examined again after 2 and 24 h. After 2 h, 65% of the control rats had suffered DCS (45% were dead), whereas 35% had no DCS. HBO pretreatment at 304, 405 and 507 kPa significantly reduced the incidence of DCS at 2 h to 40, 40 and 35%, respectively. Compared with the 45% mortality rate in the control group after 24 h, in all of the pretreated groups this was 15%. HBO pretreatment is equally effective at 304, 405 or 507 kPa, bringing about a significant reduction in the incidence of DCS in rats decompressed from 1,013 kPa.     

Perfluorochemicals as a treatment of decompression sickness in rats

Perfluorodecalin and perfluorotripropylamine which have N₂ solubility coefficients of 28.4 and 35.7 ml/dl, respectively, were used for treatment of decompression sickness in this study. Rats with chronically implanted venous catheters were held for 30 min at 800 kPa (7 bar, 8 ATA) by introducing compressed air into a chamber in which they were kept; a relatively short period of decompression followed (200 kPa/min). Immediately thereafter injections of the perfluorochemicals (PFCs) in a dose of 10 g/kg were given, controls received saline in the same volume or remained without treatment. An observation period of 2 h followed; after this time the incidence of death amongst the experimental animals (as compared with controls tested by theX ²-test) showed that PFC treatment increased the likelihood of survival. Probit-log time relationship for the incidence of death also revealed a significant decrease in lethality in treated rats 30 min after the end of decompression. The mean lethal timesLt ₅₀ differed significantly, too.A still greater effect might be expected if the PFC emulsion were deprived of its normal nitrogen content by oxygenation before administration. Under the conditions of the present experiments PFCs produced an improvement in N₂ exhalation at least in terms of the survival rate after compression followed by a very short decompression time.Supported by the Deutsche Forschungsgemeinschaft (Lu 162/7)     

Lithium protection against oxygen toxicity in rats: ammonia and amino acid metabolism.

1. The use of Li pre-treatment in rats before high pressure oxygen exposure has been reported effective in controlling convulsions. This is an effect which is better demonstrated if exposure to oxygen follows shortly after Li injection than exposure following several hours later. 2. This study has investigated the hypothesis that the protective action of Li may be exerted, in the short term, by its removing ammonia from the blood and alleviating the latter's known toxic action. 3. A normal Li distribution time profile in unstressed rat brain and blood following intraperitoneal injection has been established. Brain and blood ammonia, amino acids and Li concentrations were also measured in Li-treated animals exposed and convulsed by oxygen. These measurements were made both shortly (15 min) and also several hours after (24 hr) Li treatment. Ammonia and amino acid values in Li-protected groups were compared to normal unstressed animal values and also to values in animals convulsed by oxygen unprotected by Li pre-treatment. 4. In rat brain abd blood significant (P less than 0-001) elevation of ammonia and glutamine and depression of gamma-amino butyric acid (brain only) and glutamate was noted following oxygen treatment in unprotected animals. Prior injection of Li 15 min before high pressure oxygen exposure delayed convulsions twice as long. Additionally if these animals were only exposed to oxygen for a period of time equal to that which would normally produce convulsions in unprotected animals, brain and blood ammonia and amino acids were maintained near to unstressed animal levels. Concomitantly, blood Li concentrations were considerably depressed below the values one would expect from the previously determined Li distribution time profile. 5. In rats exposed to high pressure oxygen 24 hr after Li treatment there was no protective action against high pressure oxygen convulsion, rather a potentiating effect for convulsion was seen. 6. These data present compelling evidence for the controlling effect of Li in rats, on rising blood ammonia concentration which occurs in high pressure oxygen exposure. The effect might well be due to the known chelating properties of Li with ammonia.     

Poly(rac-lactide) nanocapsules containing diclofenac: protection against muscular damage in rats

The aim of this work was to determine whether encapsulation of a non steroidal antiinflammatory agent within nanocapsules could reduce local toxicity after intramuscular injection. Diclofenac-loaded nanocapsules were prepared by deposition of poly(rac-lactic acid) polymer, and administered intramuscularly to male Wistar rats. Plasma creatine phosphokinase (CPK) activity and histological examination were used to assess local tissue damage. Following a single intramuscular injection of diclofenac (0.8 mg), CPK activity was shown to depend on both the type of dosage form and, in the case of nanocapsules, on the chemical nature of the central oily core. Lower CPK activity was observed with nanocapsules prepared from Miglyol 810, a caprylic/capric triglyceride, while nanocapsules prepared from benzyl benzoate, either empty or containing diclofenac, exhibited the same CPK activity as the drug solution. Histopathological examination performed three days after administration of free diclofenac or nanocapsules containing diclofenac prepared from Miglyol 810 revealed that a much more intense inflammation was obtained with the solution than with nanocapsules. In conclusion, when appropriately formulated, nanocapsules can considerably reduce the muscular damage caused by diclofenac.     

Poly(rac-lactide) nanocapsules containing diclofenac: protection against muscular damage in rats

The aim of this work was to determine whether encapsulation of a non steroidal antiinflammatory agent within nanocapsules could reduce local toxicity after intramuscular injection. Diclofenac-loaded nanocapsules were prepared by deposition of poly( rac -lactic acid) polymer, and administered intramuscularly to male Wistar rats. Plasma creatine phosphokinase (CPK) activity and histological examination were used to assess local tissue damage. Following a single intramuscular injection of diclofenac (0.8 mg), CPK activity was shown to depend on both the type of dosage form and, in the case of nanocapsules, on the chemical nature of the central oily core. Lower CPK activity was observed with nanocapsules prepared from Miglyol 810^fi, a caprylic/capric triglyceride, while nanocapsules prepared from benzyl benzoate, either empty or containing diclofenac, exhibited the same CPK activity as the drug solution. Histopathological examination performed three days after administration of free diclofenac or nanocapsules containing diclofenac prepared from Miglyol 810^fi revealed that a much more intense inflammation was obtained with the solution than with nanocapsules. In conclusion, when appropriately formulated, nanocapsules can considerably reduce the muscular damage caused by diclofenac.     

The right ventricle under pressure: Anatomy and imaging in sickness and health

The right ventricle (RV) is an important structure which serves a multitude of vital physiological functions in health. For many years, the left ventricle has dominated the focus of understanding in both biology and pathophysiology and the RV was felt to be more of a passive structure which rarely had an effect on disease states. However, it is increasingly recognised that the RV is essential to the homoeostasis of normal physiology and disturbances in RV structure and function have a substantial effect on patient outcomes. Indeed, the prognosis of diseases of lung diseases affecting the pulmonary vasculature and left heart disease is intimately linked to the function of the right ventricle. This review sets out to describe the developmental and anatomical complexities of the right ventricle while exploring the modern techniques employed to image and understand its function from a clinical perspective.     

Experimental Salmonella typhimurium infections in rats. II. Active and passive immunization as protection against a lethal bacterial dose

Immunization against a lethal dose of Salmonella typhimurium was studied in athymic and thymus-bearing LEW rats. Active immunization was performed with formalin-killed whole cell vaccine or sublethal infection prior to the lethal infection. After vaccination with killed bacteria the euthymic animals produced antibodies against S.typhimurium, but neither the euthymic nor the athymic animals survived the infection. After non-lethal infection euthymic and thymus-grafted nude rats were not affected by the second and otherwise lethal bacterial dose, and had high antibody titres. All the athymic nude rats died after the second and lethal bacterial challenge. Passive immunization with plasma from immunized euthymic animals did not protect any of the animals against the lethal bacterial dose. However, all animals survived when treated with large doses of spleen cells from immunized euthymic rats. Both athymic and thymus-bearing animals treated with primed spleen cells had high antibody titres. The percentages of splenic and lymph node T lymphocytes in primed spleen cell-treated athymic rats were comparable to those found in euthymic and thymus-grafted animals. Treatment with primed spleen cells from immunized thymus grafted animals provided only limited protective effect, and treatment with cells from athymic animals had no effect. The study shows that although isogeneic thymus-grafted nude rats become resistent to reinfection with S. typhimurium, only large doses of spleen cells from immunized euthymic animals can be used for passive transfer of immunity.     

Oxygen breathing or recompression during decompression from nitrox dives with a rebreather: effects on intravascular bubble burden and ramifications for decompression profiles

Preventive measures to reduce the risk of decompression sickness can involve several procedures such as oxygen breathing during in-water decompression. Theoretical predictions also suggest that brief periods of recompression during the course of decompression could be a method for controlling bubble formation. The aim of this study was to get clearer information about the effects of different experimental ascent profiles (EAPs) on bubble reduction, using pure oxygen or recompression during decompression for nitrox diving. Four EAPs were evaluated using bubble monitoring in a group of six military divers using Nitrox 40% O(2) breathing with a rebreather. For EAP 1 and 2, 100% O(2) was used for the end stage of decompression, with a 30% reduction of decompression time in EAP 1 and 50% in EAP 2, compared to the French navy standard schedule. For EAP 3 and 4, nitrox 40% O(2) was maintained throughout the decompression stage. EAP 3 is based on an air standard decompression schedule, whereas EAP 4 involved a brief period of recompression at the end of the stop. We found that EAP 1 significantly reduced bubble formation, whereas high bubble grades occurred with other EAPs. No statistical differences were observed in bubbles scores between EAP 3 and 4. One diver developed mild neurological symptoms after EAP 3. These results tend to demonstrate that the "oxygen window" plays a key role in the reduction of bubble production and that breathing pure oxygen during decompression stops is an optimal strategy to prevent decompression sickness for nitrox diving.     

Single-dose tumor necrosis factor protection against endotoxin-induced shock and tissue injury in rats.

Tumor necrosis factor (TNF), a macrophage product released in response to endotoxin and other stimuli, has been shown to be a central mediator of endotoxin or septic shock. However, its highly conserved and wide-ranging physiological effects suggest that it may also be an essential cytokine in the host defense against acute bacterial infection or sepsis. A single nontoxic dose of human recombinant TNF administered intravenously 24 h prior to a lethal infusion of Escherichia coli lipopolysaccharide (LPS) completely prevented acute LPS-induced hypotension, ameliorated tissue injury in the lungs and liver, and improved survival in male Fisher 344 rats. The protective effects of TNF were dose dependent and required a 24-h pretreatment interval. After the infusion of LPS, animals in both groups (TNF-treated animals and saline-pretreated controls) initially appeared acutely ill and had a similar severe metabolic acidosis, indicating that TNF did not inactivate or prevent the toxic effects of LPS. Twelve hours after the administration of TNF, the gene for manganous superoxide dismutase, a mitochondrial enzyme which scavenges toxic reactive oxygen species and is induced during conditions which generate a free radical stress, was expressed in liver tissue, suggesting that the induction of manganous superoxide dismutase may be an important in vivo protective mechanism against cellular injury during lethal endotoxemia.     

鼻黏膜诱导免疫耐受预防实验性自身免疫性脑脊髓炎机制的研究

目的：探讨鼻黏膜免疫耐受对实验性自身免疫性脑脊髓炎（EAE）的预防机制以及与耐受原相关的剂量依赖性。方法：建立Lewis大鼠EAE模型，用不同种属和剂量髓鞘碱性蛋白（MBP）诱导免疫耐受，评估EAE临床发病情况；检测特异性淋巴细胞增殖反应ELISPOT检测特异性单个核细胞IFN-γ表达及原位杂交方法检测相关细胞因子的变化。结果：经鼻黏膜给予低剂量（30μg／rat）和高剂量（600μg／rat）特异性抗原可诱导免疫耐受，抑制EAE的发生。淋巴细胞增殖实验显示，高、低剂量耐受组与对照组相比均可抑制特异性淋巴细胞增殖反应（P〈0．001；P〈0．01）。ELISPOT结果表明，与对照组相比高、低剂量耐受组单个核细胞IFN-γ表达数量明显降低（P〈0．01；P〈0．001）。原位杂交结果显示，与对照组相比，低剂量组IL-4mRNA的表达水平明显增高（P〈0．001），高剂量组未见明显增高（P〉0．05）。结论：经鼻黏膜可诱导机体产生免疫耐受，预防EAE的发生。给予低剂量抗原可引起Th1／Th2分泌的细胞因子发生偏离，产生免疫耐受。     

Brief femoral artery ischaemia provides protection against myocardial ischaemia-reperfusion injury in rats: the possible mechanisms.

The present study was conducted to examine the role of nitric oxide (NO), mitochondrial ATP-sensitive K(+) channels (mito K(+)(ATP) channels) and reactive oxygen species (ROS) and their interdependence in brief femoral artery ischaemia-induced myocardial preconditioning. To assess myocardial injury, myocardial infarction was induced by occlusion followed by reperfusion of the left anterior descending (LAD) coronary artery in anaesthetized rats and was assessed by triphenyl tetrazolium chloride (TTC) staining. Left ventricular function was assessed by left ventricular end-diastolic pressure (LVEDP) and the maximal rate of rise of left ventricular pressure [LV(dP/dt)(max)]. Serum creatine kinase-MB (CK-MB) and lactate dehydrogenase (LDH) were determined by colorimetric kits. Remote preconditioning (RPC) was induced by 15 min occlusion of femoral arteries followed by 10 min of reperfusion just before LAD coronary artery occlusion. Brief femoral artery ischaemia led to a 61% reduction in myocardial infarct size, 57% reduction in elevated serum LDH and 72% reduction in elevated CK-MB activities, and a significant improvement in LVEDP and LV(dP/dt)(max) compared with control animals. Pretreatment with 5-hydroxydecanoate (5-HD) or l-NAME or N-acetylcystein (NAC) blocked this protective effect of femoral artery ischaemia. Moreover, infusion of l-arginine or diazoxide before coronary artery occlusion markedly reduced the myocardial infarction and improved the left ventricular function. This effect of l-arginine was found to be abolished by the blockade of mito K(+)(ATP) channels with 5-HD and, similarly, the effect of diazoxide was blocked in the presence of a ROS scavenger, NAC. The results suggest that brief femoral artery ischaemia-induced RPC is mediated by a combination of increased NO synthesis, opening of mito K(+)(ATP) channels and increased ROS production. Moreover, it appears that NO is working upstream and acts via activation of mito K(+)(ATP) channels, which subsequently increases the production of ROS.     

Limb remote-preconditioning protects against focal ischemia in rats and contradicts the dogma of therapeutic time windows for preconditioning

Remote ischemic preconditioning is an emerging concept for stroke treatment, but its protection against focal stroke has not been established. We tested whether remote preconditioning, performed in the ipsilateral hind limb, protects against focal stroke and explored its protective parameters. Stroke was generated by a permanent occlusion of the left distal middle cerebral artery (MCA) combined with a 30 min occlusion of the bilateral common carotid arteries (CCA) in male rats. Limb preconditioning was generated by 5 or 15 min occlusion followed with the same period of reperfusion of the left hind femoral artery, and repeated for two or three cycles. Infarct was measured 2 days later. The results showed that rapid preconditioning with three cycles of 15 min performed immediately before stroke reduced infarct size from 47.7+/-7.6% of control ischemia to 9.8+/-8.6%; at two cycles of 15 min, infarct was reduced to 24.7+/-7.3%; at two cycles of 5 min, infarct was not reduced. Delayed preconditioning with three cycles of 15 min conducted 2 days before stroke also reduced infarct to 23.0+/-10.9%, but with two cycles of 15 min it offered no protection. The protective effects at these two therapeutic time windows of remote preconditioning are consistent with those of conventional preconditioning, in which the preconditioning ischemia is induced in the brain itself. Unexpectedly, intermediate preconditioning with three cycles of 15 min performed 12 h before stroke also reduced infarct to 24.7+/-4.7%, which contradicts the current dogma for therapeutic time windows for the conventional preconditioning that has no protection at this time point. In conclusion, remote preconditioning performed in one limb protected against ischemic damage after focal cerebral ischemia.     

Mechanisms of complete Freund's adjuvant protection against diabetes in BB rats: induction of non-specific suppressor cells.

We have previously reported that a single injection of complete Freund's adjuvant (CFA) can prevent diabetes appearance in diabetes-prone (DP) BB rats. In this study, we investigated further the mechanism of CFA-induced protection from diabetes. We found that adoptive transfer of splenic cells from CFA-treated DP rats into young DP rats protected the latter from diabetes development. This suggested that CFA-induced protection from diabetes resulted from activation of regulatory (suppressor) cells. Cell mixing experiments in vitro indicated that CFA activated splenic cells with antigen-nonspecific suppressor activity (suppression of lymphoproliferative responses to lipopolysaccharide and to allogeneic splenic cells). Fractionation of splenic cells on Percoll revealed that the suppressor activity resided in low density cells relatively depleted of T-cells, B-cells, macrophages and NK cells. These results suggest that non-specific (natural) suppressor cells in CFA-treated BB rats may be responsible for suppressing autoimmune responses and preventing insulitis and diabetes development.     

Dose-dependent mechanisms relate to nasal tolerance induction and protection against experimental autoimmune encephalomyelitis in Lewis rats.

Nasal administration of soluble antigens is an exciting means of specifically down-regulating pathogenic T-cell reactivities in autoimmune diseases. The mechanisms by which nasal administration of soluble antigens suppresses autoimmunity are poorly understood. To define further the principles of nasal tolerance induction, we studied the effects of nasal administration of myelin basic protein (MBP) on experimental autoimmune encephalomyelitis (EAE) in the Lewis rat. EAE is a CD4+ T-cell-mediated animal model for human multiple sclerosis. Nasal administration of guinea-pig (gp)-MBP at a dose as low as 30 micrograms/rat can completely prevent gp-MBP-induced EAE, whereas nasal administration of bovine (b)-MBP is not effective even at a much higher dosage. Cellular immune responses, as reflected by T-cell proliferation and interferon-gamma (IFN-gamma)-ELISPOT, were suppressed in rats receiving the two different doses (30 and 600 micrograms/rat) of gp-MBP, but not after administration of b-MBP. Rats tolerized with both doses of gp-MBP had also abrogated MBP-induced IFN-gamma mRNA expression in popliteal and inguinal lymph node mononuclear cells compared with rats receiving phosphate-buffered saline nasally. However, adoptive transfer revealed that only spleen mononuclear cells from rats pretreated with a low dose, but not from those pretreated with a high dose, of gp-MBP transferred protection to actively induced EAE. Low-dose (30 micrograms/rat) gp-MBP-tolerized rats also had high numbers of interleukin-4 (IL-4) mRNA-expressing lymph node cells, while high-dose (600 micrograms/rat) gp-MBP-tolerized rats had low numbers of IL-4 mRNA-expressing lymph node cells. Our data suggest an exquisite specificity of nasal tolerance. Dose-dependent mechanisms also relate to nasal tolerance induction and protection against EAE in the Lewis rat.     

Morphologic aspects of the protection by endotoxin against acute and chronic oxygen-induced lung injury in adult rats

Small doses of endotoxin are reported to protect against O2-induced lung injury in rats. To better understand the cellular basis of this effect, we morphometrically analyzed the extent to which endotoxin modified the changes in lung ultrastructure occurring in adult rats exposed acutely to 100% O2 for 60 hours or chronically to 85% O2 for 7 days. In rats exposed to 100% O2, endotoxin resulted in 34% less volume of noncellular interstitium (i.e., less interstitial edema) and 42% less volume of cellular interstitium; however, interstitial edema and cellularity were still more than in air-exposed controls. Endotoxin did not significantly prevent decreases in endothelial cell number and capillary surface area or increases in intracapillary neutrophil volume caused by 100% O2. There was also no change in the number of type I and type II epithelial cells and alveolar macrophages. In rats exposed chronically to a sublethal tolerance-inducing level (85%) of O2, endotoxin resulted in 36% more endothelial cells (i.e., less of a decrease from control values) and 30% less interstitial cells (i.e., less of an increase from control values). The increase in number of type II epithelial cells and the degree of endothelial cell hypertrophy caused by 85% O2 were not altered. We conclude that endotoxin resulted in significant protection against O2-induced changes in ultrastructure; this occurred mainly in the capillary endothelium and interstitium. The primary effect may be a reduction in damage to, and death of, endothelial cells leading secondarily to less of an increase in capillary permeability, less interstitial (and alveolar) edema, and less proliferation and recruitment of interstitial cells. There was no evidence of a mitogenic effect on type II epithelial cells or change in number of either alveolar macrophages or intravascular neutrophils.     

A blueberry-enriched diet provides cellular protection against oxidative stress and reduces a kainate-induced learning impairment in rats

Young male Fischer-344 rats were fed a diet containing 2% blueberry (BB) extract or control diet for at least 8 weeks and then received bilateral hippocampal injections of kainic acid (KA 200 ng/0.5 microl) or phosphate buffered saline (PBS). One week later rats were trained in one-way active footshock avoidance in a straight runway followed the next day by training in a footshock motivated 14-unit T-maze with documented sensitivity to hippocampal glutamatergic manipulations. Based on analyses of several performance variables, KA-treated rats exhibited clearly impaired learning performance; however, the BB diet significantly reduced this impairment. Supporting the behavioral findings, stereological assessment of CA1 pyramidal neurons documented greater neuronal loss in KA-treated controls compared to KA-treated rats on the BB diet. In an in vitro experiment, FaO cells grown in medium supplemented with serum from BB-fed rats had enhanced viability after exposure to hydrogen peroxide. These findings suggest that BB supplementation may protect against neurodegeneration and cognitive impairment mediated by excitotoxicity and oxidative stress.