重组腺相关病毒介导的MDA-7基因对人肝癌细胞的选择性凋亡诱导效应

目的 探讨PEG启动子调控腺相关病人毒介导的黑色素瘤分化相关基因MDA-7对肝癌细胞的选择性凋亡诱导效应.方法 以重组腺相关病人毒rAAV-PEG-MDA-7表达系统感染人肝癌细胞株HepG2细胞和正常人肝细胞株LO2细胞,Westerm Blot检测转染细胞内MDA-7蛋白,MTT法检测细胞增殖抑制率,流式细胞术分析细胞周期、Annexin-Ⅴ、线粒体跨膜电位(△Ψm),RT-PCR检测bcl-2基因mRNA.结果 重组腺相关病毒rAAV-PEG-MDA7可特异性转染HepG2细胞,MDA7蛋白在HepG2细胞中高效表达,并呈时间依赖性;重组腺相关病毒rAAV-PEC-MDA-7可抑制HepG2细胞增殖并诱导其凋亡,细胞周期分析处于G0/G1期细胞百分比明显增多,处于G2/M期的细胞减少,并且可见到较明显的凋亡峰的形成,从24 h开始Annexin-Ⅴ阳性细胞比例增多,△Ψm降低,抗凋亡基因bcl-2 mRNA表达降低.而重组腺相关病毒rAAV-PEG-MDA-7对LO2细胞无类似效应.结论 构建出的重组腺相关病毒rAAV-PEG-MDA-7表达系统可选择性抑制肝癌细胞增殖和诱导其凋亡,其诱导凋亡机制受到bcl-2家族经线粒体途径的调节.     

慢病毒介导的RNA干扰沉默Wip1基因对人脑胶质母细胞瘤细胞生长的影响

目的 构建人Wip1基因的RNA干扰(RNAi)慢病毒载体,有效沉默人胶质瘤U251细胞的Wip1基因并观察其对细胞生长的影响.方法 设计并合成3条Wip1基因特异性RNAi靶序列,构建到慢病毒pFU-GW-iRNA载体中.慢病毒包装转染HEK293T细胞,获得病毒上清并测定其滴度;感染U251细胞,实时定量聚合酶链反应(PCR)及Western blot鉴定RNA干扰效率;筛选出基因沉默效率最高的慢病毒感染U251细胞,CCK-8法检测细胞的增殖,Western blot检测RNA干扰后的bcl-2蛋白表达.结果 PCR扩增和测序表明成功构建Wip1慢病毒干扰载体,病毒载体包装获得的病毒上清滴度在3×10~8～8×10~8 TU/ml.可以有效地沉默U251细胞中Wip1基因的表达,构建的RNAi慢病毒载体感染U251细胞后Wip1基因的mRNA表达量同对照组比较分别为36.3%、32.9%、23.8%.稳定Wip1 RNA干扰后的U251细胞4 d后细胞增殖能力下降35.1%.结论 慢病毒介导的RNA干扰可以高效稳定地沉默基因表达,Wip1基因促进了U251细胞的增殖.     

尾型同源盒转录因子2 shRNA慢病毒表达载体的构建及其转染对结肠癌细胞生长的影响

目的:构建尾型同源盒转录因子2(CDX2)shRNA慢病毒表达载体,并观察下调CDX2基因其对结肠癌细胞生长的影响。方法:根据CDX2 m RNA序列设计shRNA,并合成shRNA的互补序列,通过连接酶链接到GV248载体上,用测序方法鉴定阳性克隆后,将构建好的慢病毒表达载体与慢病毒包装载体用Lpofectamine 2000共转染293T细胞,产生慢病毒颗粒并用稀释法进行滴度测定。将CDX2 shRNA慢病毒表达载体转染人结肠癌细胞SW480、HT29后,分别用q RT-PCR和Western blot检测CDX2 m RNA及蛋白水平,CCK8实验及克隆形成实验检测细胞增殖能力。结果:DNA测序鉴定证实,CDX2 shRNA表达片段正确插入GV248载体中,包装后的病毒滴度为1×109TU/m L;SW480、HT29细胞转染CDX2-shRNA慢病毒表达载体后,CDX2 mRNA及蛋白表达水平均明显降低(均P0.05),但细胞的增殖与克隆形成能力无明显改变(均P0.05)。结论:成功构建shRNA慢病毒表达载体,其转染结肠癌细胞后能有效地抑制CDX2基因的表达;下调CDX2基因对人结肠癌细胞的增殖无明显影响。     

血管内皮生长因子-C shRNA对肝癌HepG2细胞增殖及侵袭能力的影响

目的 检测靶向血管内皮生长因子-C(vasenlar endothelial growth factor-C,VEGF-C)shRNA质粒载体对肝癌HepG2细胞增殖及侵袭能力的影响.方法 构建VEGF-C shRNA质粒载体,脂质体转染方法转入肝癌HepG2细胞.通过倒置荧光显微镜及流式细胞仪检测细胞的转染率;RT-PCR及Western blot检测转染细胞内VEGF-C mRNA及蛋白的表达变化;MTT法检测细胞增殖抑制率;人工基底膜体外侵袭实验检测细胞侵袭能力.结果 VEGF-C shRNA稳定转染后,肝癌HepG2细胞内VEGF-C mRNA及蛋白表达水平显著下降;VEGF-C shRNA对肝癌HepG2细胞具有明显的增殖抑制作用,其抑制增殖效应呈时间依赖性;VEGF-C shRNA可有效抑制肝癌HepG2细胞的人工基底膜体外侵袭能力,抑制率为51.54%.结论 VEGF-C在肝癌增殖、侵袭转移中发挥重要作用;通过RNA干扰技术实现VEGF-C沉默,在肝癌的基因治疗中具有较好的应用前景.     

人前脑啡肽基因修饰人胚胎肾细胞的构建

目的 构建人前脑啡肽基因(hPPE)修饰的人胚胎肾细胞(HEK293细胞).方法 重组质粒pcDNA3.1(+)/hPPE经限制性内切酶HindⅢ和Not Ⅰ进行双酶切获得hPPE基因,运用基因重组技术将hPPE基因与表达载体同源重组,转染293T细胞进行慢病毒包装、扩增、纯化,测定病毒滴度,再将重组的慢病毒载体转染HEK293细胞.用Western blot法检测hPPE基因在HEK293细胞中的表达.结果 重组慢病毒载体阳性克隆测序结果和基因库的hPPE基因序列完全一致.含有hPPE基因的慢病毒载体,滴度为2.07×108TU/ml.转染慢病毒载体后的HEK293细胞,在荧光显微镜下未见到GFP荧光.转染Ubc-GFP-L.V.空病毒载体的HEK293细胞,可见到较强的荧光.Western blot法检测到经慢病毒载体转染后的HEK293细胞中hPPE基因表达呈阳性.结论 成功构建了hPPE基因修饰的HEK293细胞,使hPPE基因可在HEK293细胞中稳定表达.     

shRNA慢病毒表达载体对人结肠癌细胞CXCR7表达的影响

目的 探讨CXCR7的shRNA慢病毒表达载体对人结肠癌细胞HT-29 CXCR7表达的影响.方法 设计CXCR7的3条siRNA的靶点序列,合成含干扰序列的双链DNA发卡结构shRNA,分别与双酶切后的plVTHM载体连接,构建3种重组穿梭质粒plVTHM shRNA1,plVTHM shRNA2和plVTHM shR-NA3,并转化于DH5α感受态细胞,Amp筛选阳性克隆,抽取质粒行酶切鉴定并测序.分别将3种重组质粒与慢病毒包装质粒共转染293T细胞,生产慢病毒颗粒,并检测病毒滴度.将3种重组慢病毒及阴性对照病毒分别感染人结肠癌细胞HT-29,实时定量PCR和Western blot分别检测CXCR7 mRNA和蛋白的沉默效果.结果 酶切鉴定及测序结果 证实3种慢病毒载体均包装成功,滴度分别为6×107 TU/mL,4×107 TU/mL和5×107 TU/mL.感染HT-29后,CXCR7 mRNA及蛋白的表达量均较阴性对照组和未感染组明显降低(P＜0.05);其中以LV-CXCR7 shRNA-2和LV-CXCR7 shRNA-3作用显著,mRNA表达分别下调72%和67%,蛋白表达下调68%和55%(P＜0.05);而阴性感染对照组和未感染组相比差异无统计学意义(P＞0.05)结论 成功构建了3种CXCR7 shRNA慢病毒表达,可有效下调HT-29细胞CXCR7mRNA和蛋白的表达,其为进一步研究以CXCR7为靶点的结肠癌基因治疗提供稳定转染细胞的载体奠定基础.     

构建携带hTERT基因的慢病毒重组载体及其包装和表达

目的构建含hTERT基因的慢病毒重组载体,进行病毒包装并检测hTERT在293T细胞中的表达。方法PCR扩增hTERT．插入慢病毒载体,并与包装质粒转染293T细胞,进行病毒包装,并测定其滴度。Western—Blot检测慢病毒液感染293T细胞后hTERT的表达。结果成功构建了含hTERT的慢病毒重组载体,滴度为2．79×10^7Tu／mL,Western-B10t检测显示慢病毒液感染的293T细胞中hTERT基因高表达。结论含hTERT的慢病毒重组载体成功构建并包装后能够顺利感染293T细胞．并阳性表达目的基因。     

转染RECK基因对肝癌细胞生物学行为的影响

目的 探讨RECK基因对HepG2肝癌细胞生物学活性的影响。方法 构建真核表达载体pcDNA3-RECK，采用脂质体介导将重组质粒导人体外培养的HepG2细胞，Westernblot法检测转染前、后HepG2细胞中RECK蛋白的表达。明胶酶谱试验检测转染前、后MMP-9的表达。观察稳定转染RECK基因对HepG2细胞生物学行为的影响。结果 成功构建了RECK基因真核表达载体并建立了稳定表达的细胞株。转染后RECK基因稳定高表达，具有生物活性的MMP-9的表达显著降低。转染前、后HepG2细胞的增殖能力无明显改变，但其侵袭能力明显下降。结论 外源性的RECK基因能通过脂质体有效转染肝癌细胞，抑制MMP-9的活性，降低肝癌细胞HepG2的体外侵袭能力。     

Let-7a对人乳腺癌细胞生长的抑制作用及机制

目的探讨let-7a对人乳腺癌MCF-7细胞株的抑制作用及机制。方法分别用lipofectami-neTM2000介导的let-7a转染MCF-7细胞株(实验组)和siRNA转染细胞株(阴性对照组),并设空白对照组(脂质体转染组)。使用荧光显微镜观察细胞转染效率;CCK-8法检测细胞增殖抑制率;半定量RT-PCR法检测IMP-1 mRNA的表达;Western blot法测定转染48 h后IMP-1蛋白的表达水平。结果实验组和阴性对照组的细胞转染效率无明显差别;let-7a组细胞增殖抑制率明显高于阴性对照组及空白对照组(均为P0.05),且具有时间和浓度依赖性;let-7a组的IMP-1 mRNA表达水平明显低于空白对照组和阴性对照组(F=220.384,P=0.000);在MCF-7细胞中存在IMP-1蛋白表达,let-7a转染组特异性条带明显弱于两个对照组。结论 let-7a对人乳腺癌MCF-7细胞增殖有抑制作用,其机制可能与抑制IMP-1的基因表达有关。     

人VEGF基因慢病毒介导RNA干扰有效靶点的设计及筛选

目的:设计并筛选人血管内皮生长因子(VEGF)有效RNA干扰片段,构建VEGF慢病毒表达载体。方法:对人VEGF基因编码区分析,筛选序列3条,阴性对照序列l条,通过连接线性化的plenti6.3-MIR载体,构建miRNA慢病毒载体质粒,并转化至感受态细胞DH5α,进行测序验证。在脂质体介导下转染293T细胞,包装生产慢病毒,测定其滴度。慢病毒载体转染人肝癌细胞MHCC97L,用Real-time PCR检测干扰效果。结果:测序证实3个VEGF基因RNAi慢病毒载体质粒构建成功。慢病毒载体经293T细胞包装成功,测定病毒的滴度分别为3.23×109、3.30×109、3.73×109TU/mL。3个慢病毒载体转染人肝癌细胞MHCC97L后,VEGF基因在mRNA水平受到抑制,其中miR-200序列效果最佳,对VEGF基因表达的干扰效率可达72%。结论:成功构建并筛选了人VEGF基因RNAi慢病毒载体及有效靶点,为进一步深入研究VEGF基因与抗肿瘤药物药效关系提供实验基础。     

Vasopressor hormone response following mesenteric traction during major abdominal surgery

Background : We investigated the vasopressor hormone response following mesenteric traction (MT) with hypotension due to prostacyclin (PGI₂) release in patients undergoing abdominal surgery with a combined general and epidural anesthesia. Methods : In a prospective, randomized, placebo-controlled study we administered 400 mg ibuprofen (i.v.) in 42 patients scheduled for abdominal surgery. General anesthesia was combined with epidural anesthesia (T4-L1). Before as well as 5, 15, 30, 45, and 90 min after MT we recorded plasma osmolality, hemodynamics and measured 6-keto-PGFlα (stabile metabolite of PGI₂), TXB₂ (stabile metabolite of thromboxane A₂) active renin, and arginine vasopressin (AVP) plasma concentrations by radioimmunoassay. Catecholamine levels were assessed by high-pressure liquid chromatography (HPLC) with electrochemical detection. Results : Following MT, arterial hypotension occurred along with a substantial PGI₂ release. This was completely abolished by ibuprofen administration. Although plasma levels of 6-keto-PGF_1α (1133 (708) vs. 60 (3) ng/L, median (median absolute deviation), P=0.0001, placebo vs. ibuprofen) remained significantly elevated, blood pressure was restored within 30 min after MT in the placebo group. At the same point in time plasma concentrations of TXB² (164 (87) vs. 58 (1) ng/L, P=0.0001), epinephrine (46 (33) vs. 14 (6) ng/L, P=0.001), AVP (41 ± (18) vs. 12 (7) ng/L, P=0.0004), and active renin (27 (12) vs. 12 (4) ng/L, P = 0.001) were significantly higher in placebo-treated patients. Conclusion : Under combined general and epidural anesthesia arterial hypotension following MT due to endogenous PGI₂ release is associated with enhanced release of AVP, active renin, epinephrine and thromboxane A₂, presumably contributing to hemodynamic stability within 30 min after MT.     

A comparison of the inhibitory effects of four volatile anaesthetics on the metabolism of chlorzoxazone, a substrate for CYP2E1, in rabbits

Background: Halothane inhibits in vitro and in vivo activity of cytochrome P-450 (CYP) 2E1. There are several fluorinated volatile anaesthetics besides halothane, and most of them are defluorinated by CYP2E1. It is unclear whether other fluorinated anaesthetics inhibit the in vivo activity of CYP2E1.
Methods: We compared the inhibitory effects of therapeutic concentrations of four inhalational anaesthetics, halothane, enflurane, isoflurane, and sevoflurane, on chlorzoxazone metabolism in rabbits receiving artificial ventilation.
Results: All four inhalational anaesthetics decreased arterial blood pressure and increased plasma chlorzoxazone concentration. However, no significant differences in the plasma chlorzoxazone concentration were found between the four anaesthetics. The estimated chlorzoxazone clearance increased after beginning inhalation with all four agents, but no significant difference in clearance was noted between agents.
Conclusions: At therapeutic concentrations, the in vivo inhibitory effect on chlorzoxazone metabolism was similar for all four inhalational anaesthetics examined, even though their chemical characteristics and extent of hepatic metabolism differ considerably.     

A Teaspoon Pump for Pumping Blood with High Hydraulic Efficiency and Low Hemolysis Potential

Abstract: Virtually all blood pumps contain some kind of rubbing, sliding, closely moving machinery surfaces that are exposed to the blood being pumped. These valves, internal bearings, magnetic bearing position sensors, and shaft seals cause most of the problems with blood pumps. The original teaspoon pump design prevented the rubbing, sliding machinery surfaces from contacting the blood. However, the hydraulic efficiency was low because the blood was able to "slip around" the rotating impeller so that the blood itself never rotated fast enough to develop adequate pressure. An improved teaspoon blood pump has been designed and tested and has shown acceptable hydraulic performance and low hemolysis potential. The new pump uses a nonrotating "swinging" hose as the pump impeller. The fluid enters the pump through the center of the swinging hose; therefore, there can be no fluid slip between the revolving blood and the revolving impeller. The new pump uses an impeller that is comparable to a flexible garden hose. If the free end of the hose were swung around in a circle like half of a jump rope, the fluid inside the hose would rotate and develop pressure even though the hose impeller itself did not "rotate"; therefore, no rotating shaft seal or internal bearings are required.     

Microspheres Based Detoxification System: A New Method in Convective Blood Purification

Abstract: A variety of protein-bound or hydrophobic substances, accumulating as a result of pathologic conditions such as exogenous or endogenous intoxications, are removed poorly by conventional detoxification methods because of low accessibility (hemodialysis), insufficient adsorption capabilities (hemosorption), low efficiency (peritoneal dialysis), or economic limitations (high-volume plasmapheresis). Combining advantages of existing methods with microspheric technology, a module-based system was designed. Major operating parameters of the latter can be modified to allow for adjustment to individual clinical situations. An extracorporeal blood circuit including a plasmafilter is combined with a secondary high-velocity plasma circuit driven by a centrifugal pump. Different microspheric adsorbers can be combined in one circuit or applied in sequence. Thus, a prolonged treatment can be tailored using specially designed selective adsorber materials. Comparing this system with existing methods (high-flux hemodialysis, molecular adsorbent recycling system), results from our in vitro studies and animal experiments demonstrate the superior efficiency of substance removal.     

Tissue perfusion in relation to cardiac output during continuous positive-pressure ventilation and administration of propranolol or verapamil

Background : Our objective was to determine whether administration of propranolol or verapamil modifies the hemodynamic adaptation to continuous positive-pressure ventilation (CPPV), in particular the regional distribution of cardiac output (CO).
Methods : General hemodynamics and regional blood flows assessed by microsphere technique (15 (μm) were recorded in 16 anesthetized pigs during spontaneous breathing (SB) and CPPV with 8 cm H₂O end-expiratory pressure (CPPV8) before and after intravenous administration of propranolol (0.3 mg · kg⁻¹ followed by 0.15 mg · kg⁻¹ · h⁻¹, n=8) or verapamil (0.1 mg · kg⁻¹ followed by 0.3 mg · kg⁻¹ · h⁻¹, n=8).
Results : CPPV8 depressed CO by 25% without shifts in its relative distribution with the exception of a noteworthy increase in adrenal perfusion. Propranolol increased arterial blood pressure, and due to a fall in heart rate, CO dropped by 25%. The kidneys and, to a lesser extent, the splanchic region and central nervous system received increased fractions of the remaining CO at the expense of skeletal muscle flow. Similar patterns were seen during SB and CPPV8 such that the combination of propranolol and CPPV8 depressed CO by 50%. The circulatory effects of verapamil were less evident but myocardial perfusion tended to increase.
Conclusions : The combination of propranolol or verapamil with CPPV does not result in any specific hemodynamic interaction in anesthetized pigs, except that the combined effect of propranolol and CPPV may severely reduce CO.     

Volatile anaesthetics reduce adhesion of blood platelets under low-flow conditions in the coronary system of isolated guinea pig hearts

Background : Inhibitory effects of volatile anaesthetics on platelet aggregation have been demonstrated in several studies. However, the influence of volatile anaesthetics on intracoronary platelet adhesion has not been elucidated so far.
Methods : Isolated hearts of guinea pigs were perfused with buffer in the absence or presence of volatile anaesthetics (0.5 and 1 MAC) at constant coronary flow rates of 5 ml/min for 25 min, then 1 ml/min for 30 min and again 5 ml/min for 10 min. Before, during and after low-flow perfusion, a bolus of human platelets was applied into the coronary system. To simulate thrombogenic conditions, 0.3 U/ml human thrombin was infused during low-flow perfusion and reperfusion. The number of platelets sequestered to the endothelium was calculated from the difference between coronary in- and output of platelets. The myocardial production of lactate and consumption of pyruvate and coronary perfusion pressure were also determined.
Results : At a flow rate of 5 ml/min only about 3% of the applied platelets did not emerge from the coronary system, in any group. In contrast, 13.1±1.2% (mean±SEM) of infused platelets became adherent in low-flow perfusion in the control group without anaesthetic. The adherence was reduced with each 1 MAC isoflurane (to 6.2±1.2%), sevoflurane (to 4.4±0.9%) or halothane (to 3.2±1.5%) (each P <0.05 vs. control). Volatile anaesthetic, 0.5 MAC, did not inhibit platelet adhesion to a statistically significant extent in any case. Perfusion pressure and metabolic parameters were not statistically different between the control and the hearts exposed to anaesthetics.
Conclusion : Volatile anaesthetics in a concentration of 1 MAC can reduce the adhesion of platelets in the coronary system under reduced flow conditions. This action does not arise from vasodilation or inhibition of ischaemic stress.     

Bariatric Surgery in Some "Central and East-European (former Eastern bloc)"Countries - Current Status and Prediction for the Next Millennium

Background: Obesity is increasing globallly, including in the formerly "Eastern Bloc" countries. Methods: A survey was made of obesity and bariatric surgery. Results: In the 8 East and Central European countries studied, with total population 300 million, roughly 43% of the population was overweight (BMI 25-30), 23% obese (BMI > 30), with about 15 million people morbidly obese (BMI > 40). From 0-10 morbidly obese individuals/100,000/year undergo bariatric surgery. Conclusion: Most countries were found to provide inadequate treatment for obesity.The majority of the morbidly obese are not treated effectively. However, health-care awareness of obesity and bariatric surgeons are slowly increasing.     

Is the recovery profile of mivacurium independent of the rate of decay of its plasma concentration in patients with normal plasma cholinesterase activity?

Background: The duration of action of muscle relaxants is poorly correlated to the rate of decay of their plasma concentration. The plasma concentration of mivacurium may rapidly decrease below its active concentration because of the extensive hydrolysis of mivacurium. By inflating a tourniquet on one upper limb for 3 min after the administration of atracurium, mivacurium or vecuronium, we studied the influence of the initial decline of their plasma concentration on their effect. Methods: In 50 patients anaesthetised with thiopental, isoflurane and fentanyl, the effect of bolus doses of 0.15 or 0.25 mg . kg^?1 mivacurium (MIV 15, MIV 25), 0.3 or 0.5 mg . kg^?1 atracurium (ATR 30, ATR 50) and 0.06 or 0.1 mg . kg^?1 vecuronium (VEC 06, VEC 10) were measured on both arms (evoked response of the adductor pollicis to train-of-four stimulation every 12 s), a tourniquet being applied on one arm just before and during 3 min after the muscle relaxant bolus. Results: Tourniquet inflation of 3 min almost abolished the neuromuscular effect of mivacurium. In the vecuronium groups and in the ATR 50 group, tourniquet inflation did not modify the maximum degree of depression of the twitch response. Also, the duration of action of vecuronium was unaffected by the tourniquet. In the ATR 30 group, times to return of the twitch response to 25% (duration 25%) and 75% (duration 75%) of control response were significantly shorter in the cuffed arm, 23 min vs 27 min, and 41 min vs 45 min, respectively. In the ATR 50 group, only duration 25% was significantly shorter in the cuffed arm (41 min vs 45 min). Conclusion: The results suggest that the rate of decline of the plasma concentration of mivacurium is so rapid, that a very low and almost clinically ineffective concentration is present as soon as 3 min after its administration. The results also indicate that the recovery from a mivacurium-induced neuromuscular blockade is not influenced by the rate of decay of its plasma concentration in patients with genotypically normal plasma cholinesterase.     

Membranes in Artificial Organs

Abstract: Membrane processes play a pivotal and enabling role in modern replacement therapy for acute and chronic organ failure and in the management of immunologic diseases. In fact, virtually all contemporary extracorporeal blood purification methods employ membrane devices, and the next generation of artificial organs and tissue engineering therapies are almost certain to be similarly grounded in membrane technology. In this short essay, we comment on the similarities and differences among synthetic membranes and their natural counterparts and also provide a critical overview of the demographics and technology of hemodialysis, hemofiltration, apheresis, oxygenation, and emerging membrane technologies and applications.     

Synergistic interaction between the effects of propofol and midazolam with fentanyl on phrenic nerve activity in rabbits

Background: It has been shown that the depressive effects of both propofol and midazolam on consciousness are synergistic with opioids, but the nature of their interactions on other physiological systems, e. g. respiration, has not been fully investigated. The present study examined the effect of propofol and midazolam alone and in combination with fentanyl on phrenic nerve activity (PNA) and whether such interactions are additive or synergistic. Methods: PNA was recorded in 27 anaesthetised and artificially ventilated rabbits. In three groups, propofol, fentanyl and midazolam were administered intravenously in incremental doses to construct dose-response curves for the depressant effects of each one on PNA. In another two groups, the effect of pretreatment with either fentanyl 1 μg · kg^?1 i. v. or midazolam 0.05 mg · kg^?1 i. v. on the effects of propofol and fentanyl respectively on PNA were studied. Results: Propofol and fentanyl caused a dose-dependent depression of PNA with complete abolition at the highest total doses of 16 mg · kg^?1 i. v. and 32 μg · kg^?1 i. v., respectively. In contrast, midazolam in incremental doses to a total of 0.8 mg · kg^?1 reduced mean PNA by 63%, but approximately 12% of PNA remained at a total dose as high as 6.4 mg · kg^?1. The mean ED₅₀s, calculated from dose-response curves, were 5.4 mg · kg^?1, 3.9 μg · kg^?1 and 0.4 mg · kg^?1 for propofol, fentanyl and midazolam, respectively. Initial doses of either fentanyl 1 μg · kg^?1 i. v. or midazolam 0.05 mg · kg^?1 i. v. acted synergistically with subsequent doses of either propofol or fentanyl to abolish PNA at total doses of 8 mg · kg^?1 and 8 μg · kg^?1, respectively. Conclusion: Fentanyl has a synergistic interaction with both propofol and midazolam on PNA and hence potentially on respiration.