Mechanisms of inhibition of endothelium-dependent relaxation by halothane,isoflurane, and sevoflurane

Volatile anaesthetics inhibit endothelium-dependent relaxation, but the underlying mechanism(s) have not been clarified. In an attempt to elucidate the mechanism(s), we determined the effects of halothane, isoflurane and sevoflurane on relaxation induced by acetylcholine and sodium nitro-prusside (SNP) and the cGMP formation elicited by exogenous nitric oxide (NO) and SNP in rat aortas. Acetylcholine (10^?7?10^?5M) - induced relaxation was attenuated by halothane (2%), isoflurane (2%) and sevoflurane (4%). SNP (10^?8 M) - induced relaxation was reduced by halothane (2%), but not by isoflurane (2%) or sevoflurane (4%). The cGMP level of NO-stimulated aorta was reduced by halothane (2%) and sevoflurane (4%), but not by isoflurane (2%). The cGMP level of SNP (10^?7 M) - stimulated aorta was reduced by halothane (2%), but not by isoflurane (2%) and sevoflurane (4%). We conclude that the mechanisms responsible for the inhibition of endothelium-dependent relaxation differ among anaesthetics. Isoflurane inhibits the relaxation mainly by inhibiting the formation of NO in the endothelium. In contrast, the effect of halothane on endotheliumdependent relaxation may be largely due to the inhibition of action of NO in the vascular smooth muscle and the effect of sevoflurane may be to inactivate NO or to inhibit the action of NO.     

七氟醚和硝普钠控制性降压对患者一氧化氮、内皮素及氧自由基的影响

目的 探讨七氟醚和硝普钠(SNP)控制性降压对患者一氧化氮(NO)、内皮素(ET)和氧自由基的影响.方法 择期手术病人48例,年龄28～64岁,ASA Ⅰ或Ⅱ级,随机分为3组(n=16):七氟醚常压组(Ⅰ组)、七氟醚降压组(Ⅱ组)和SNP降压组(Ⅲ组).3组麻醉诱导后均吸入七氟醚1 MAC.手术开始后10 min,Ⅱ组吸入七氟醚浓度增加至3 MAC,Ⅲ组开始持续静脉输注0.01% SNP 2～5 μg·kg-1·min-1,使平均动脉压(MAP)快速降至基础值的60%-70%(55-73 mm Hg),再调整七氟醚呼气末浓度(1.87～2.54 MAC)和SNP输注速率(1.5～4 μg·ks-1·min-1)维持降压,降压40 min后,Ⅱ组七氟醚呼气末浓度降至0.8 MAC;Ⅲ组停止输注SNP,使血压很快升至降压前水平.分别于手术开始后10 min(降压前即刻,T0)、降压20 min(T1)、40 min(T2)和停止降压后20 min(T3)采集静脉血,测定血浆NO、ET、丙二醛(MDA)浓度及超氧化物歧化酶(SOD)活性.结果 与T0比较,Ⅰ组和Ⅱ组血浆NO浓度在T1～3时降低,Ⅲ组血浆NO浓度在T1,2时升高,Ⅲ组在T1,2时血浆ET浓度升高,3组在T1～3,时血浆MDA和SOD浓度均升高(P＜0.05或0.01);与Ⅰ组比较,Ⅱ组在T1,2时血浆NO浓度降低,Ⅲ组在T1～3时血浆NO浓度升高,Ⅲ组血浆ET浓度在T1～3时升高(P＜0.05),Ⅱ组各时点血浆NO浓度差异无统计学意义(P＞0.05);Ⅱ组在T1～3时血浆MDA和SOD水平升高(P＜0.05).结论 七氟醚控制性降压可降低患者血浆NO浓度,SNP控制性降压可升高血浆NO及ET浓度;七氟醚控制性降压及硝普钠控制性降压均可导致患者氧自由基生成增加,七氟醚控制性降压使氧自由基增加的程度更高.     

Is postburn dermal ischaemia enhanced by oxygen free radicals?

The accumulated data suggest that oxygen free radicals are actively involved in the pathophysiology of the wound healing process. Since OH. and O2- directly correlate with the release of arachidonic acid and catalyse some of the enzymes participating in its cascade, their involvement in the enhancement of dermal ischaemia in the stasis zone is postulated. Experimental data using topically applied scavengers of superoxide have shown their beneficial effects on the burn wound healing process.     

Surgical stress and the small intestine: role of oxygen free radicals.

BACKGROUND: Any surgical procedure can be associated with altered intestinal function. The mechanism involved in these changes at the cellular level during surgical stress has not been worked out. This study looked at the biochemical and functional alterations, along with ultrastructural changes, in the intestine during surgical stress in a simple rat model. METHODS: Surgical stress was induced by opening the abdominal wall and handling the intestine as during laparotomy. The effect of oxidative stress on the enterocyte and altered intestinal permeability as well as the ultrastructural changes to the mucosa were studied. RESULTS: Surgical stress results in oxidative stress on enterocytes, as evidenced by increased xanthine oxidase and decreased catalase activity along with altered thiol redox status. This was associated with increased intestinal permeability and widened intercellular spaces. These changes were prominent at 60 minutes after laparotomy and returned to normal by 24 hours. CONCLUSIONS: Mild intestinal handling is capable of inducing oxidative stress in enterocytes; this could be one of the mechanisms by which intestinal mucosal alterations occur during surgical stress.     

Halothane and isoflurane inhibit endothelium-dependent relaxation elicited by acetylcholine.

The purpose of this study was to determine whether volatile anesthetics modify the release of endothelium-derived relaxing factor. We examined the effects of halothane and isoflurane on endothelium-dependent relaxation and 3',5'-cyclic guanosine monophosphate formation elicited by acetylcholine and ionophore A23187 in isolated rat aorta. Halothane and isoflurane (1%-2%) significantly attenuated acetylcholine-induced relaxation of the phenylephrine-contracted aorta but had no significant effect on relaxation induced by A23187, nitroprusside, and nitroglycerin. Basal and A23187 (10(-7) M)-stimulated levels of 3',5'-cyclic guanosine monophosphate were slightly lowered by halothane and isoflurane (2%). In contrast, the increase of 3',5'-cyclic guanosine monophosphate elicited by acetylcholine (10(-5) M) was significantly attenuated by halothane (2%) and abolished by isoflurane (2%). These findings indicate that halothane and isoflurane strongly inhibit the release of endothelium-derived relaxing factor elicited by acetylcholine.     

Interleukin-2-induced lung injury is mediated by oxygen free radicals

Interleukin-2 therapy leads to respiratory dysfunction caused by increased vascular permeability. This study examines the role of oxygen-derived free radicals (OFR). Sheep (n = 6) with chronic lung lymph fistulae were given interleukin-2, 10(5) units/kg, as an intravenous bolus. The mean pulmonary artery pressure rose from 13 to 23 mm Hg (p less than 0.05) at 1 hour and remained elevated for 4 hours, although the pulmonary artery wedge pressure was unchanged at 4 mm Hg. Arterial oxygen tension fell from 88 to 77 mm Hg (p less than 0.05). Lung lymph flow rose from 2.2 to 6.4 ml/30 min (p less than 0.05) at 3 hours. This rise coincided with an increase in the lymph/plasma protein ratio from 0.67 to 0.77 (p less than 0.05) and lymph protein clearance from 1.5 to 4.4 ml/30 min (p less than 0.05), indicating increased lung microvascular permeability. Interleukin-2 led to transient increases in plasma thromboxane B2 from 168 to 388 pg/ml (p less than 0.05) and lung lymph thromboxane B2 from 235 to 694 pg/ml (p less than 0.05). The leukocyte count fell from 8156 to 4375/mm3 (p less than 0.05) primarily caused by a 78% drop in lymphocyte count. Platelet count declined from 292 to 184 X 10(3)/mm3 (p less than 0.05). Pretreatment with the hydroxyl radical scavenger dimethylthiourea, 1 gm/kg, intravenously, (n = 6) prevented the interleukin-2-induced increase in mean pulmonary artery pressure, lung lymph flow, lymph/plasma protein ration, lymph protein clearance, and thromboxane B2 levels in plasma and lung lymph. The arterial oxygen tension decreased from 85 to 80 mm Hg (p less than 0.05). The leukocyte count declined from 7854 to 6229/mm3 (p less than 0.05), but this was not as low nor as prolonged as the interleukin-2 group. Further, the decrease in platelet count was prevented (p less than 0.05). Interleukin-2 incubated with sheep or human leukocytes led to a dose-dependent increase in intracellular hydrogen peroxide production by neutrophils as measured by flow cytometry of dichlorofluorescein oxidation. These data indicate that interleukin-2 stimulates OFR generation and that OFR moderate the interleukin-2-induced increased lung permeability.     

The role of oxygen free radicals in craniocerebral injury

Serum LPO content was measured by means of TBA in 41 patients suffering from craniocerebral injury in present study. The relationships between OFR and progressing course of craniocerebral injury, level of LPO and patient condition of an injury and prognosis were analysed. Results showed that serum LPO increased obviously in 24 hours after injury. The more severe the condition of an injury was, the higher the serum LPO content was, the worse prognosis would be. Serum LPO content increased statistically in group of death in 24 to 72 hours after injury, while it didn't change significantly in group of survival. The author suggest that the reaction of OFR enhanced after craniocerebral injury, and which was an important factor giving rise to secondary brain injury. Measurement of serum LPO content plays an important role in estimating the patients condition of injury and their prognosis.     

A role for oxygen free radicals in aminonucleoside nephrosis

The cellular processes responsible for the proteinuria induced by the aminonucleoside of puromycin (PA) remain inadequately defined. Hypoxanthine is both a metabolic breakdown product of PA as well as a substrate for xanthine oxidase, which catalyzes its enzymatic conversion to xanthine and uric acid, yielding the superoxide anion in the process. We examined whether oxygen free radical production contributes to the development of proteinuria in this model. Seven groups of male Sprague-Dawley rats were studied. Proteinuria was quantitated and histology examined 7 days after rats were treated with PA intravenously over 5 min. PA-treated animals received either saline, dimethyl sulfoxide, superoxide dismutase, or catalase over 30 min prior to and 30 min following PA administration. Another group received allopurinol over 4 hr prior to PA. The superoxide dismutase and allopurinol treatment groups had a significant suppression of urinary protein excretion compared to the PA control group. There were also less severe glomerular morphologic changes in the superoxide dismutase group vs. the PA controls, which demonstrated a pathologic pattern that included epithelial cell blebbing, segmental mesangial cell proliferation and matrix expansion, loss of glomerular capillary lumina, and occasional adhesions between the glomerular tuft and Bowman's capsule. The allopurinol group exhibited normal glomerular morphology on light microscopy, with the exception of occasional epithelial cell blebs. All groups showed spreading of the epithelial cell cytoplasm along the glomerular basement membrane with loss of foot processes, focal areas of lifting of the epithelial cell from the glomerular basement membrane, cytoplasmic vacuolization, and protein reabsorption droplets; however, allopurinol-treated animals demonstrated these changes to a lesser extent.(ABSTRACT TRUNCATED AT 250 WORDS)     

Impact of oxygen free radicals in rat partial liver transplantation

Background

Due to the shortage of suitable organs, the demand for partial liver transplantation from living donors has increased worldwide. N-acetylcysteine (NAC) has shown protective effects as a free radical scavenger during hypothermic preservation and warm ischemia–reperfusion liver injury; however, no study has reported the effects in partial liver transplantation. The aim of this study was to analyze the impact of NAC on liver graft microcirculation and graft function after partial liver transplantation in rats.

Methods

Orthotopic partial liver transplantations were performed in 40 rats following cold storage in histidine-tryptophan-ketoglutarate solution for 3 h with 20 mM NAC (NAC group, n = 20) or without (control group, n = 20). We assessed portal circulation, graft microcirculation, and biochemical analyses of plasma at 1, 3, 24, and 168 h after portal reperfusion.

Results

(Control versus NAC, median and range): Portal venous pressure was significantly lower with NAC (P = 0.03). Microcirculation measured by laser Doppler was significantly improved with NAC throughout the time course (P = 0.003). Alanine aminotransferase levels were significantly lower in the NAC group (P < 0.05). Total antioxidative capacity was significantly higher in the NAC group at 1 h after reperfusion (Trolox equivalents: median, 3 μM; range, 2.9–6.7 versus median, 16.45 μM; range, 10.4–18.8). Lipid peroxidation was significantly abrogated in the NAC group (median, 177.6 nmol/mL; range, 75.9–398.1 versus median, 71.5 nmol/mL; range, 58.5–79 at 3 h).

Conclusions

This study showed that NAC treatment during cold storage resulted in improved microcirculation and preservation quality of partial liver graft likely because of enhanced antioxidant capacity and reduced lipid peroxidation.     

Postischemic renal dysfunction: the limited role of xanthine oxidase-generated oxygen free radicals

Oxygen free radicals (OFRs) generated during reperfusion are putative mediators of postischemic renal dysfunction. To address this issue, the renal response to ischemia and reperfusion was compared to the response to OFR generation without ischemia. Isolated rat kidneys were perfused at 37 degrees C and 90-100 mm Hg with an asanguinous modified Krebs' buffer. Kidneys were subjected to 30 min of ischemia followed by reperfusion or to OFRs generated by combining 25 mumole hypoxanthine with 1 unit xanthine oxidase. Both insults caused a 50% increase in vascular resistance. This was accompanied by a 30% reduction in perfusate flow rate and an 80% reduction in glomerular filtration and urine flow rates. The OFR scavengers, superoxide dismutase (SOD, 250 units/ml) and catalase (CAT, 500 units/ml), prevented these alterations after OFR generation but not after 30 min of ischemia and reperfusion. SOD and CAT also afforded no protection against the less severe dysfunction observed after 10 or 20 min of ischemia and reperfusion. OFRs do not appear to be prominent mediators of postischemic renal dysfunction; other factors, probably associated with ischemia must be primarily responsible.     

锌-金属硫蛋白对严重烫伤大鼠氧自由基损伤的保护作用

目的　研究严重烫伤大鼠延迟复苏后氧自由基损伤及锌-金属硫蛋白(MT)的保护作用。　方法　采用大鼠30%TBSAⅢ度烫伤模型,分成正常对照组、延迟复苏组、MT治疗组、维生素C(VitC)治疗组,应用电子自旋共振(ESR)技术和传统间接检测手段,观察伤后24、48h血浆及烧伤水肿液中超氧化物歧化酶(SOD)、丙二醛（MDA）的变化,同时对心、肝、肾、小肠的组织形态及血浆生化指标进行检测。　结果　延迟复苏组血SOD含量下降,血及水肿液MDA明显升高,各脏器组织形态及血生化指标发生明显变化。MT治疗组较延迟复苏组SOD增高（P<0.05）,MDA含量明显下降（P<0.05）,脏器组织形态及血生化指标改善,且优于VitC治疗组。　结论　严重烫伤大鼠延迟复苏后存在氧自由基损伤,应用锌-金属硫蛋白治疗有一定保护作用。     

Total antioxidant status and oxygen free radicals during hepatic regeneration

OBJECTIVES: The damage induced by oxygen free radicals (OFRs) is caused by an imbalance of the production of versus the antioxidant defenses against OFRs. METHODS: To understand hepatic damage induced by oxygen free radicals after hepatectomy in rats, total antioxidant status and total production of oxygen free radicals were serially measured in regeneration liver. At 1, 2, 3, 7, and 10 days after hepatectomy of Sprague-Dawley rats, blood was obtained into a capillary tube from a tail vein. Total antioxidant status and total production of oxygen free radicals were measured using the Randox kit, a colorimetric method, and the Free Radical Analytical System. We also measured the amount of malonyldialdehyde, which provides an indirect index of oxidative injury. RESULTS: The level of malonyldialdehyde after hepatectomy was higher compared with that before hepatectomy. The level of total oxygen free radicals after hepatectomy was higher compared with that before hepatectomy. Total antioxidant status after hepatectomy was lower compared with that before hepatectomy. CONCLUSIONS: The results suggested that the damage by OFRs to the regenerating liver was caused by increased production of OFRs and decreased antioxidant defense against OFRs.     

Pharmacologic approach to tissue injury mediated by free radicals and other reactive oxygen metabolites

Highly toxic metabolites of oxygen are generated normally by aerobic metabolism in most cells, and this generation is often greatly increased in pathologic conditions. When this oxidant flux exceeds the capability of the multiple endogenous antioxidant mechanisms, tissue injury ensues. The pharmacologic modification of this injury process, with agents that scavenge these reactive oxygen metabolites, block their generation, or enhance the endogenous antioxidant capability, has shown great promise in animal models of common clinical conditions, and has already been successfully applied in controlled clinical trials. This approach represents an interruption of tissue injury at its most basic level.     

七氟醚对罗库溴铵肌松效应的影响

目的 研究吸入不同浓度的七氟醚对不同剂量的罗库溴铵肌松效应的影响.方法 90例择期手术患者随机均分为六组.记录各组静注罗库溴铵后其起效时间、四个成串刺激(TOF)无反应时间、T1 25%恢复时间、T1 75%恢复时间及恢复指数(T1 25%恢复到75%的时间).结果 静注等效剂量的罗库溴铵Ⅲ组与Ⅰ组、Ⅳ组与Ⅱ组比较,起效时间差异无统计学意义.而静注等效剂量的Ⅴ组与Ⅰ组、Ⅵ组与Ⅱ组比较,起效时间明显缩短(P＜0.05);在无反应时间、T1 25%恢复时间、T1 75%恢复时间及恢复指数上,复合吸入七氟醚的Ⅲ到Ⅵ组较注入等效剂量的罗库溴铵Ⅰ组与Ⅱ组比较均有明显的延长(P＜0.05或P＜0.01);Ⅱ组与Ⅲ组之间以及Ⅳ组与Ⅴ组之间罗库溴铵的肌松维持时间差异无统计学意义.结论 七氟醚能明显延长罗库溴铵的作用时间,有时间依赖及剂量依赖趋势.