自噬在吉西他滨诱导胰腺癌细胞凋亡中的作用

目的:研究自噬在吉西他滨(gemcitabine,Gem)诱导胰腺癌细胞SW1990凋亡中的作用,并以氯喹特异性抑制自噬,以探讨其可能机制。方法:采用CCK8法检测Gem对胰腺癌细胞增殖的影响,并用实时定量PCR检测自噬相关基因LC3的表达,以p62免疫荧光染色检测细胞内自噬泡,通过Western印迹法检测自噬相关蛋白LC3、Beclin 1的表达,并用AnnexinⅤ/PI流式细胞方法检测Gem诱导后细胞凋亡的变化。进一步通过氯喹抑制自噬,检测自噬抑制前后细胞增殖、自噬及凋亡的变化。结果:Gem对胰腺癌细胞SW1990增殖具有部分抑制作用,Gem作用能迅速激活细胞自噬从而产生耐药。LC3的mRNA表达升高1.4~2.2倍(P<0.05),LC3-Ⅱ蛋白水平升高1.5~2.7倍(P<0.05)。Gem和氯喹联合用药组较Gem单药组细胞凋亡蛋白Caspase-3表达升高,细胞存活率从64.3%±3.1%降低为35.2%±3.4%(P<0.05)。结论:自噬在Gem诱导胰腺癌细胞凋亡的过程中可能起到保护作用,氯喹抑制自噬后可增强Gem的促凋亡作用。     

精索静脉曲张大鼠睾丸自噬对生精细胞的影响

目的:研究精索静脉曲张(VC)大鼠模型中睾丸不同水平自噬对生精细胞凋亡的影响。方法:雄性SD大鼠54只随机分为6组:空白对照组、雷帕霉素对照组、氯喹对照组各6只,VC组、VC+雷帕霉素组、VC+氯喹组各12只。采用HE染色观察睾丸、附睾组织形态学变化,并对睾丸及附睾中精子形成情况进行评分,TUNEL染色检测生精细胞凋亡指数(AI),Western印迹检测LC3、p62、Bax、Bcl-2的表达。结果:空白对照组、雷帕霉素对照组、氯喹对照组大鼠睾丸及附睾组织均未发生明显形态学变化,精子形成情况评分及AI亦无显著差异(P>0.05);VC组大鼠睾丸及附睾组织发生明显病理损伤,精子形成情况评分显著降低(P<0.01),AI显著升高(P<0.01),但VC+雷帕霉素组较VC组明显改善,而VC+氯喹组较VC组轻度加重。此外,与空白对照组比较,VC组自噬相关蛋白LC3(包括LC3-Ⅱ/LC3-Ⅰ的比值)和促凋亡蛋白Bax表达显著增加(P<0.01),抑凋亡蛋白Bcl-2表达则显著降低(P<0.01);且VC+雷帕霉素组LC3与Bcl-2表达显著高于VC组(P<0.01),p62和Bax表达则显著低于VC组(P<0.01);而VC+氯喹组LC3与Bcl-2表达显著低于VC组(P<0.01),p62和Bax的表达则显著高于VC组(P<0.01)。结论:VC可诱导大鼠睾丸自噬和生精细胞凋亡,上调自噬可抑制生精细胞凋亡,阻滞自噬则可促进生精细胞凋亡。     

去势对犬前列腺基质平滑肌细胞的影响及其临床意义

目的 探讨去势治疗对犬前列腺平滑肌细胞病变的影响。方法 采用光镜,电镜,原位凋亡检测和免疫组化技术,观察去势犬前列腺平滑肌细胞的病理改变,用ＲＴ－ＰＣＲ方法检测平滑肌肌球蛋白的转录水平。结果 去势后犬前列腺平滑肌细胞发生了凋亡和萎缩病变。ＲＴ－ＰＣＲ结果显示,去势后和前列腺组织内平滑肌肌球蛋白表达降低。     

细胞自噬在去势后前列腺萎缩中的作用及机理研究

细胞自噬足广泛存在于真核细胞内的一种分解细胞质等自身构成成分的生理现象.自噬的功能主要是在营养缺乏状态下维持着细胞代谢的平衡以及在环境压力下清除损伤的细胞器以利于细胞的存活.去势后前列腺萎缩是前列腺细胞凋亡、组织中蛋白质合成减少和降解速度增加等多重因素作用的结果.近年来发现细胞自噬在去势后前列腺萎缩过程中起重要作用,成...     

去势前后大鼠腹叶前列腺显微结构的动态变化

目的：探讨去势后大鼠前列腺显微结构变化规律及机制。方法：90只大鼠分为9组,于去势后不同时间光镜、电镜下观察前列腺改变,用图像分析系统计算腺体面积与间质面积比值（G）,管腔分泌物与管腔面积比值（S）,腺体高度（H）及腺体横截面细胞数（N）。采用TUNEL法检测凋亡。免疫组化检测PCNA,计算凋亡指数（AI）和增殖指数（PI）。结果：去势后G、S、H下降,N减少。出现脂肪变、凋亡及坏死,增殖下降。结论：去势后前列腺内细胞萎缩、分泌物减少、坏死、AI升高和PI降低共同导致前列腺缩小。     

蛋白激酶Cδ通过抑制自噬促进TRAIL诱导前列腺癌细胞凋亡

目的探讨蛋白激酶Cδ在去势抵抗性前列腺癌细胞中对自噬的影响,并研究其相关机制。方法使用去势抵抗性前列腺癌细胞C4-2和CWR22Rv1作为研究对象,将细胞进行分组,分别使用DMSO对照、BAF-A1、TRAIL、PKCδ激活剂PMA和PKCδ抑制剂rottlerin对细胞进行处理。用MTT检测各组药物处理后细胞存活状况;用Western blot检测各组药物处理后mTOR通路、自噬相关蛋白和凋亡相关蛋白的变化;用GFP-LC3荧光蛋白标记检测细胞内自噬作用的变化。结果 TRAIL诱导去势抵抗性前列腺癌细胞C4-2和CWR22Rv1自噬作用增强。PMA可以通过激活mTOR通路抑制自噬并提高细胞对TRAIL的凋亡敏感性。PKCδ在此过程中是抑制自噬作用的关键分子。结论本研究证实在去势抵抗性前列腺癌细胞C4-2和CWR22Rv1中,PKCδ/AKT/mTOR通路对细胞自噬的负向调节作用,激活该通路可以促进TRAIL诱导的细胞凋亡现象。     

雄激素剥夺条件下阻断自噬增加LNCaP细胞凋亡

目的 探讨雄激素剥夺条件下阻断自噬后LNCaP细胞凋亡变化与半胱天冬酶(caspase)激活的关系.方法 应用激光共聚焦显微镜、RT-PCR方法观察雄激素剥夺致细胞自噬增加后,利用DAPI染色观察细胞凋亡变化及药物抑制caspase后对凋亡的影响.结果 ①雄激素去除后LNCaP细胞自噬体增加,标准培养基(CM)培养下LNCaP细胞自噬体数量为1.90分;无血清培养基(SF)中细胞自噬体数量增高为2.64分;加入双氧睾酮(SFA组)后细胞自噬体下降至1.85分(P<0.01).CM中LNCaP细胞LC3 mRNA表达率为23%,血清饥饿12 h后,LC3表达量上调至100%,而SFA组LC3 mRNA表达量为86%;血清饥饿24 h后,SF组LC3 mRNA表达量为62%,SFA组为35%.②SF组和SFA组LNCaP细胞基础凋亡率分别为(3.19±1.09)0A和(3.01±0.33)%,加入3-甲基腺嘌呤(3-MA)阻断自噬24 h后,SF组凋亡率为(10.90±2.91)%,SFA组为(4.63±1.69)%.SF+3-MA组中加入Z-VAD-FMK后,细胞凋亡减至(1.16±0.52)%.组间差异有统计学意义(P<0.01).结论 剥夺雄激素后LNCaP细胞中自噬明显增加,阻断自噬后凋亡发生率增加.     

硫酸糖基化蛋白2在去势大鼠前列腺中的表达

目的 探讨硫酸糖基化蛋白2（SGP－2）在去势大腹叶前列腺表达的规律及其与前列腺凋亡的相关性。方法 将90只大鼠随机分为9组，每组10只，分别于去势后0、1、2、3、5、7、10、14、21d处死，取前列腺包埋切片后行免疫组织化学检测SGP－2和增殖细胞核抗原（PCNA),缺口末端标记术（TUNEL）和电镜检测前列腺细胞凋亡，计算阳性率，并作连续切片，行计算机图像重叠技术比较SGP－2表达与凋亡的相关性，及与PCNA表达的关系。结果 正常大鼠前列腺SGP－2表达较少，去势后则显著增加，与凋亡的变化及分布规律相似，其表达的阳性率与凋亡阳性率呈正相关（r＝0．8075，P＜0．01）。SGP－2的表达和PCNA呈负相关（r=－0．8061，P＜0．01）。结论 SGP－2在去势大鼠腹叶前列腺表达增高，与凋亡呈正相关，与PCNA呈负相关，提示可能有促凋亡和抑制增殖的作用。     

miR-21调节缺血缺氧诱导的大鼠肝卵圆细胞自噬的研究

目的探讨miR-21在缺血缺氧诱导的大鼠肝卵圆细胞自噬中的作用。方法体外培养肝卵圆细胞,慢病毒转染肝卵圆细胞构建稳定的细胞株,分别提取各组细胞RNA逆转录后行SYBR Green实时荧光定量PCR,检测各组miR-21的表达,以转染好的稳定的细胞建立缺血缺氧模型,共分为3组:miR-21空载体慢病毒转染HOC自噬组,miR-21增强慢病毒载体转染HOC自噬组,miR-21-inhibition慢病毒载体转染HOC自噬组。Hoechst 33258染色观察细胞凋亡;应用丹(磺)酰戊二胺(Monodansylcadaverine,MDC)染色荧光定位法、观察各组细胞的自噬;免疫印迹法(Western blotting)检测各组细胞LC3-Ⅱ/Ⅰ蛋白表达情况。结果与空载体组比,增强组miR-21基因水平表达增强,而MDC染色减弱(自噬减少),蛋白LC3-Ⅱ/LC3-Ⅰ的比值减少;而抑制组miR-21基因水平表达减少,MDC染色增强(自噬增强),蛋白LC3-Ⅱ/LC3-Ⅰ的比值增多。结论抑制miR-21过表达可以增强缺血缺氧引起的肝卵圆细胞的自噬,有利于肝卵圆细胞在缺血缺氧微环境中稳定细胞内环境,维持细胞的存活。     

高糖通过PI3K-AKT-mTOR信号通路增加足细胞自噬

目的 研究高糖引起足细胞自噬变化及其相关的信号机制.方法 培养的足细胞被分为6组,正常浓度葡萄糖(NG)组、高浓度葡萄糖(HG)组、NG+雷帕霉素(Rap)组、HG+Rap组、NG+LY294002组和HG+LY294002组.观察自噬增强剂Rap和PI3K抑制剂LY294002对高糖条件下培养的足细胞自噬和凋亡的影响.电镜和吖啶橙染色观察细胞内自噬体的形成;Western印迹检测自噬标志蛋白微管相关蛋白1轻链3(LC3)和自噬血管基因Beclin-1的表达;通过阻断自噬的信号通路观察磷脂酰肌醇3激酶-蛋白激酶B-哺乳动物雷帕霉素靶蛋白(PI3K-AKT-mTOR)相关蛋白AKT和mTOR的磷酸化水平的改变.结果 高糖可导致足细胞凋亡增加,促进足细胞内自噬体和自噬相关蛋白表达增加(均P＜ 0.05).与高糖组相比,HG+ Rap组LC3-Ⅱ和Beclin-1的表达增加(均P＜0.05);LY294002部分抑制高糖导致的LC3-Ⅱ和Beclin-1表达增加(均P＜0.05).与高糖组相比,HG+ LY294002组足细胞内AKT磷酸化的水平增加(P＜0.05),mTOR的磷酸化水平降低(P＜0.01);HG+ LY294002组足细胞的AKT和mTOR磷酸化水平较高糖组均降低(均P＜0.05).结论 高糖可促进足细胞的自噬和凋亡,推测高糖诱导的足细胞自噬作用部分通过PI3K-AKT-mTOR信号通路调节实现的.     

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 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.     

Influence of dopexamine hydrochloride on haemodynamics and regulators of circulation in patients undergoing major abdominal surgery

Background: Catecholaminergic support is often used to improve haemodynamics in patients undergoing major abdominal surgery. Dopexamine is a synthetic vasoactive catecholamine with beneficial microcirculatory properties. Methods: The influence of perioperative administration of dopexamine on cardiorespiratory data and important regulators of macro- and microcirculation were studied in 30 patients undergoing Whipple pancreaticduodenectomy. The patients received randomized and blinded either 2 μg · kg^?1 · min^?1 of dopexamine (n=15) or placebo (n=15, control group). The infusion was started after induction of anaesthesia and continued until the morning of the first postoperative day. Endothelin-1 (ET-1), vasopressin, atrial natriuretic peptide (ANP), and catecholamine plasma levels were measured from arterial blood samples. Measurements were carried out after induction of anaesthesia, 2 h after onset of surgery, at the end of surgery, 2 h after surgery, and on the morning of the first postoperative day. Results: Cardiac index (CI) increased significantly in the dopexamine group (from 2.61±0.41 to 4.57±0.78 1 · min^?1 · m^?2) and remained elevated until the morning of the first postoperative day. Oxygen delivery index (DO₂I) and oxygen consumption index (VO₂I) were also significantly increased in the dopexamine group (DO₂I: from 416±91 to 717±110 ml/m² · m²; VO₂I: from 98±25 to 157±22 ml/m² · m²), being significantly higher than in the control group. pHi remained stable only in the dopexamine patients, indicating adequate splanchnic perfusion. Vasopressive regulators of circulation increased significantly only in the untreated control patients (vasopressin: from 4.37±1.1 to 35.9±12.1 pg/ml; ET-1: from 2.88±0.91 to 6.91±1.20 pg/ml). Conclusion: Patients undergoing major abdominal surgery may profit from prophylactic perioperative administration of dopexamine hydrochloride in the form of improved haemodynamics and oxygenation as well as beneficial influence on important regulators of organ blood flow.     

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.