COX-2-derived prostacyclin protects against bleomycin-induced pulmonary fibrosis

Prostacyclin is one of a number of lipid mediators elaborated from the metabolism of arachidonic acid by the cyclooxygenase (COX) enzymes. This prostanoid is a potent inhibitor of platelet aggregation, and its production by endothelial cells and protective role in the vasculature are well established. In contrast, much less is known regarding the function of this prostanoid in other disease processes. We show here that COX-2-dependent production of prostacyclin plays an important role in the development of fibrotic lung disease, limiting both the development of fibrosis and the consequential alterations in lung mechanics. In stark contrast, loss of prostaglandin E(2) synthesis and signaling through the G(s)-coupled EP2 and EP4 receptors had no effect on the development of disease. These findings suggest that prostacyclin analogs will protect against bleomycin-induced pulmonary fibrosis in COX-2(-/-) mice. If such protection is observed, investigation of these agents as a novel therapeutic approach to pulmonary fibrosis in humans may be warranted.     

COX-2 and iNOS in opioid-induced delayed cardioprotection in the intact rat

Cyclooxygenase-2 (COX-2) and inducible nitric oxide synthase (iNOS) have been previously implicated in the late phase of cardioprotection associated with opioid-induced and ischemic preconditioning (IPC) in conscious rabbits and COX-2 in isolated rat hearts pretreated with an exogenous delta opioid agonist. However, it is not know if both iNOS and COX-2 mediate the late phase of cardioprotection induced by opioids in the intact blood-perfused rat. Therefore, we investigated the role of COX-2 and iNOS in the delayed phase of protection mediated by delta opioid receptor activation. Rats were pretreated 24 hours prior to an occlusion/reperfusion protocol with the selective non-peptide delta opioid agonists, BW373U86 (BW) and SNC-121 (SNC). NS-398, a selective COX-2 inhibitor was administered after the 24-hour recovery period just prior to index ischemia. The selective iNOS inhibitors, S-methylthiourea (SMT) and aminoguanidine (AG), were administered in conjunction with opioid pretreatment or were also given 24 hours after opioid administration just prior to index ischemia. COX-2 inhibition by NS-398 given 24 hours after opioid administration attenuated the protective effects of both BW and SNC (46 +/- 6 vs. 13 +/- 3 and 51 +/- 5 vs. 29 +/- 2, p < 0.001, respectively). Similarly, inhibition of iNOS following 24 hours of treatment with opioids also attenuated the protective effects of BW and SNC. However, the delayed protective effects of the opioids were not attenuated by pretreatment with the iNOS inhibitors 24 hours prior to the infarct protocol. These results suggest that both COX-2 and iNOS are mediators of delayed protection induced by non-peptide delta opioid agonists. It appears that the trigger effect is not dependent on the activity of iNOS or COX-2 but the late phase of cardioprotection is dependent on the upregulation of these enzymes.     

Effect of estrogen replacement treatment on ischemic preconditioning in isolated rat hearts

In the present study, we tested the effects of long-term estrogen replacement treatment on myocardial ischemia-reperfusion injury and on the cardioprotection of ischemic preconditioning in isolated hearts from ovariectomized rats. Ovariectomized rats were treated with 17beta-estradiol (30 micro g/kg/d, s.c.) for 12 weeks. Isolated rat hearts were perfused in the Langendorff mode. Heart rate, coronary flow, left ventricular pressure and its first derivative (+/-LVdp/dtmax) were recorded. Fifteen-min global ischemia and 30-min reperfusion caused a significant decrease of cardiac mechanical function, which were not affected by ovariectomy or estrogen replacement treatment. The isolated hearts in all groups could be preconditioned, and the cardioprotection afforded by preconditioning in the sham-operated rats was greater compared with ovariectomized rats with or without estrogen treatment. These results suggest that long-term estrogen replacement treatment exerts no effect on the inhibition of mechanical function after ischemia-reperfusion, and this study also suggests that estrogen does not affect ischemic preconditioning in isolated hearts of ovariectomized rats.     

Translocation of HSP27 to sarcomere induced by ischemic preconditioning in isolated rat hearts

We investigated the role of the 27-kDa heat shock protein (HSP27) in cardiac protection using Langendorff-perfused rat hearts. After preconditioning (a single episode of 5 min global ischemia followed by 5 min of reperfusion), HSP27 redistributed from the cytosol to the sarcomere and recovery of the contractile function, after 40 min of global ischemia and 50 min of reperfusion, was significantly enhanced. Both SB203580, a p38 MAP kinase inhibitor, and bisindolylmaleimide I, a protein kinase C inhibitor, prevented the effects of preconditioning. Both 2-chloro-N(6)-cyclopentyladenosine (adenosine A1 agonist) and anisomycin (activator of p38 MAP kinase and c-jun N-terminal kinase) mimicked preconditioning. These results suggest that activation of protein kinase C followed by activation of p38 MAP kinase elicits translocation of HSP27 to the sarcomere, a process which may be involved in the cardioprotective mechanism afforded by ischemic preconditioning in rat heart.     

The cardioprotection of the late phase of ischemic preconditioning is enhanced by postconditioning via a COX-2-mediated mechanism in conscious rats

The present study sought to determine whether the combination of late preconditioning (PC) with postconditioning enhances the reduction in infarct size. Chronically instrumented rats were assigned to a 45-min (subset 1) or 60-min (subset 2) coronary occlusion followed by 24 h of reperfusion. In each subset, rats received no further intervention (control) or were preconditioned 24 h before occlusion (PC), postconditioned at the onset of reperfusion following occlusion, or preconditioned and postconditioned without (PC + postconditioning) or with the COX-2 inhibitor celecoxib (3 mg/kg ip; PC + postconditioning + celecoxib) 10 min before postconditioning. Myocardial cyclooxygenase-2 (COX-2) protein expression and COX-2 activity (assessed as myocardial levels of PGE(2)) were measured 6 min after reperfusion in an additional five groups (control, PC, postconditioning, PC + postconditioning, and PC + postconditioning + celecoxib) subjected to a 45-min occlusion. PC alone reduced infarct size after a 45-min occlusion but not after a 60-min occlusion. Postconditioning alone did not reduce infarct size in either setting. However, the combination of late PC and postconditioning resulted in a robust infarct-sparing effect in both settings, suggesting additive cardioprotection. Celecoxib completely abrogated the infarct-sparing effect of the combined interventions in both settings. Late PC increased COX-2 protein expression and PGE(2) content. PGE(2) content (but not COX-2 protein) was further increased by the combination of both interventions, suggesting that postconditioning increases the activity of COX-2 induced by late PC. In conclusion, the combination of late PC and postconditioning produces additive protection, likely due to a postconditioning-induced enhancement of COX-2 activity.     

Influence of extracellular potassium on the antiarrhythmic effect of global preconditioning in isolated perfused rat hearts

The objective of this study was to investigate if a variation in extracellular-K+ concentrations alters the effects of global preconditioning on ischemia-induced arrhythmias. Rat hearts were Langendorff-perfused with Krebs-Henseleit solution and randomised in 8 groups (n = 12/group): four control groups (K⁺: 2, 4, 6, or 8 mmol/L) which underwent 30-min coronary artery occlusion and four preconditioned groups (K⁺: 2, 4, 6, or 8 mmol/L) in which the 30-min regional ischemia was preceded by 2 cycles of 3 min global ischemia. In the presence of low K⁺ (2 mmol/L), there were no differences between control and preconditioning groups in the number of ventricular premature beats (VPBs): 194 ± 64 vs. 217 ± 81, the incidence of ventricular tachycardia (VT): 100% vs. 100% and of ventricular fibrillation (VF): 100% vs. 100%. In the presence of normal K⁺ concentration (4 mmol/L), ischemic preconditioning reduced the number of VPBs from 88 ± 26 to 25 ± 10, (p < 0.05), the incidence of VT from 100 to 50% (p < 0.05), and of VF from 67 to 16% (p < 0.05). In the condition of higher K⁺ concentration (6 mmol/L), VPBs (34 ± 8 vs. 11 ± 4), the incidence of VT (100% vs. 25%; p < 0.05 ) and VF (25% vs. 8%) were further reduced in preconditioned hearts. In the condition of K⁺ concentration (8 mmol/L), there were no differences in VPBs (11 ± 3 vs. 7 ± 2), the incidence of VT (8% vs. 0%) and VF (8% vs. 0%) between control and preconditioned hearts. Our data show that ischemic preconditioning affords protection against arrhythmias during coronary artery occlusion in the isolated rat heart and that hypokalemia abolishes the antiarrhythmic effects of global preconditioning.     

Simulated ischemia-induced preconditioning of isolated ventricular myocytes from young adult and aged Fischer-344 rat hearts

The impact of ischemic preconditioning (IPC) on contraction, Ca(2+) homeostasis, and cell survival was compared in isolated ventricular myocytes from young adult ( approximately 3 mo) and aged ( approximately 24 mo) male Fischer-344 rats. Myocytes were field stimulated at 4 Hz (37 degrees C). Contraction (edge detector) and intracellular Ca(2+) (fura-2) were measured simultaneously. Viability was assessed with trypan blue. All cells were exposed to 30 min of simulated ischemia followed by reperfusion. Some cells were preconditioned by exposure to 5 min of simulated ischemia before prolonged ischemia. Pretreatment with IPC abolished postischemic contractile depression, inhibited diastolic contracture, and increased Ca(2+) transient amplitudes in reperfusion in young adult and aged cells. IPC did not affect the modest rise in diastolic Ca(2+) in ischemia in young adult myocytes. However, IPC abolished the marked rise in diastolic Ca(2+) observed in ischemia and early reperfusion in aged myocytes. IPC also suppressed mechanical alternans in ischemia in aged cells, but younger myocytes showed little evidence of mechanical alternans whether or not cells were preconditioned. IPC markedly improved cell viability in reperfusion in young adult but not aged cells. These results suggest that IPC augments the recovery of contractile function in reperfusion by increasing Ca(2+) transient amplitudes in ventricular myocytes from young adult and aged rats. IPC reduced diastolic Ca(2+) accumulation in ischemia in aged myocytes, which may diminish the severity of mechanical alternans in aged cells. Nonetheless, the efficacy of IPC is compromised in aging, as IPC did not improve survival of aged myocytes exposed to ischemia and reperfusion.     

Role of reactive oxygen species in cardiac preconditioning: study with photoactivated Rose Bengal in isolated rat hearts

Oxygen radical scavengers have been shown to prevent the development of ischemic preconditioning, suggesting that reactive oxygen species (ROS) might be involved in this phenomenon. In the present study, we have investigated whether direct exposure to ROS produced by photoactivated Rose Bengal (RB) could mimic the protective effects of ischemic preconditioning.

Methods In vitro generation of ROS from photoactivated RB in a physiological buffer was first characterised by ESR spectroscopy in the presence of 2,2,6,6-tetramethyl-1-piperidone (oxoTEMP) or 5,5-dimethyl-1-pyrroline-N-oxide (DMPO). In a second part of the study, isolated rat hearts were exposed for 2.5 min to photoactivated RB. After 5 min washout, hearts underwent 30 min no-flow normothermic ischemia followed by 30 min of reperfusion.

Results and Conclusions The production of singlet oxygen (¹O₂) by photoactivated RB in the perfusion medium was evidenced by the ESR detection of the nitroxyl radical oxoTEMPO. Histidine completely inhibited oxoTEMPO formation. In addition, the use of DMPO has indicated that (i) superoxide anions (O^·-₂) are produced directly and (ii) hydroxyl radicals (HO^·) are formed indirectly from the successive O^·-₂ dismutation and the Fenton reaction. In the perfusion experiments, myocardial post-ischemic recovery was dramatically impaired in hearts previously exposed to the ROS produced by RB photoactivation (¹O₂, O^·-₂, H₂O₂ and HO^·) as well as when ¹O₂ was removed by histidine (50 mM) addition. However, functional recovery was significantly improved when hearts were exposed to photoactivated RB in presence of superoxide dismutase (10⁵ IU/L) and catalase (10⁶ IU/L).

Further studies are now required to determine whether the cardioprotective effects of Rose Bengal in presence of O^·-₂ and H₂O₂ scavengers are due to singlet oxygen or to other species produced by Rose Bengal degradation.     

Role of reactive oxygen species in cardiac preconditioning: Study with photoactivated rose bengal in isolated rat hearts

Oxygen radical scavengers have been shown to prevent the development of ischemic preconditioning, suggesting that reactive oxygen species (ROS) might be involved in this phenomenon. In the present study, we have investigated whether direct exposure to ROS produced by photoactivated Rose Bengal (RB) could mimic the protective effects of ischemic preconditioning.

Methods In vitro generation of ROS from photoactivated RB in a physiological buffer was first characterised by ESR spectroscopy in the presence of 2,2,6,6-tetramethyl-1-piperidone (oxoTEMP) or 5,5-dimethyl-1-pyrroline-N-oxide (DMPO). In a second part of the study, isolated rat hearts were exposed for 2.5 min to photoactivated RB. After 5 min washout, hearts underwent 30 min no-flow normothermic ischemia followed by 30 min of reperfusion.

Results and Conclusions The production of singlet oxygen (¹O₂) by photoactivated RB in the perfusion medium was evidenced by the ESR detection of the nitroxyl radical oxoTEMPO. Histidine completely inhibited oxoTEMPO formation. In addition, the use of DMPO has indicated that (i) superoxide anions (O^·-₂) are produced directly and (ii) hydroxyl radicals (HO^·) are formed indirectly from the successive O^·-₂ dismutation and the Fenton reaction. In the perfusion experiments, myocardial post-ischemic recovery was dramatically impaired in hearts previously exposed to the ROS produced by RB photoactivation (¹O₂, O^·-₂, H₂O₂ and HO^·) as well as when ¹O₂ was removed by histidine (50 mM) addition. However, functional recovery was significantly improved when hearts were exposed to photoactivated RB in presence of superoxide dismutase (10⁵ IU/L) and catalase (10⁶ IU/L).

Further studies are now required to determine whether the cardioprotective effects of Rose Bengal in presence of O^·-₂ and H₂O₂ scavengers are due to singlet oxygen or to other species produced by Rose Bengal degradation.     

Role of endogenous nitric oxide in classic preconditioning in rat hearts

Ischemic preconditioning (IPC) protects the heart against subsequent sustained ischemia reperfusion (RP). Despite many triggers and signaling pathways, which seem to be involved in IPC, the IPC-mechanisms remain a controversial issue. One of them is endogenous production of nitric oxide (NO). To assess the role of NO in IPC and its relation with glycogen and glycolysis, the effects of inhibiting NO synthase with L-NAME (50 microM) were examined in IPC rat hearts perfused with medium containing 10 mM glucose. Left ventricular developed pressure-rate product (RPP) and end diastolic pressure (EDP), lactate and glycogen contents, and cell viability were measured. Global ischemia (25 min) was followed by 30 min RP. IPC consisted in one cycle of 3 min ischemia-5 min RP. IPC reduced EDP and improved RP recovery of RPP. L-NAME had no effects on the non-IPC group but abolished these effects of IPC. IPC reduced ischemic decrease of glycogen and the acceleration of glycolysis, and improved cell viability. L-NAME did not affect these effects of IPC. The results suggest that NO is ineffective on the noxious effects of ischemia-RP in non-IPC hearts and on the effects of IPC on cell viability, glycogenolysis and glycolysis whereas it is only involved in functional protection.     

Inducible COX-2 dominates over COX-1 in prostacyclin biosynthesis: mechanisms of COX-2 inhibitor risk to heart disease

AimOur aim is to understand the molecular mechanisms of the selective nonsteroidal anti-inflammatory drugs (NSAID), cyclooxygenase-2 (COX-2) inhibitors', higher “priority” to reduce synthesis of the vascular protector, prostacyclin (PGI2), compared to that of nonselective NSAIDs.Main methodsCOX-1 or COX-2 was co-expressed with PGI2 synthase (PGIS) in COS-7 cells. The Km and initial velocity (½t Vmax) of the coupling reaction between COX-1 and COX-2 to PGIS were established. The experiment was further confirmed by a kinetics study using hybrid enzymes linking COX-1 or COX-2 to PGIS. Finally, COX-1 or COX-2 and PGIS were respectively fused to red (RFP) and cyanic (CFP) fluorescence proteins, and co-expressed in cells. The distances between COXs and PGIS were compared by FRET.Key findingsThe Km for converting arachidonic acid (AA) to PGI2 by COX-2 coupled to PGIS is ~ 2.0 μM; however, it was 3-fold more (~ 6.0 μM) for COX-1 coupled to PGIS. The Km and ½t Vmax for COX-2 linked to PGIS were ~ 2.0 μM and 20 s, respectively, which were 2–5 folds faster than that of COX-1 linked to PGIS. The FRET study found that the distance between COX-2-RFP and PGIS–CFP is shorter than that between COX-1-RFP and PGIS–CFP.SignificanceThe study provided strong evidence suggesting that the low Km, faster ½t Vmax, and closer distance are the basis for COX-2 dominance over COX-1 (coupled to PGIS) in PGI2 synthesis, and further demonstrated the mechanisms of selective COX-2 inhibitors with higher potential to reduce synthesis of the vascular protector, PGI2.     

Cyclooxygenase-2-derived endogenous prostacyclin reduces apoptosis and enhances embryo viability in mouse

The role of prostaglandins (PGs) in apoptosis in preimplantation mice embryo development is reported in this study. It is known that apoptosis plays a very important role in normal mice embryo development. Very few reports are available on this subject. Embryos (6-8 cells) were cultured in the presence of a selective cyclooxygenase (COX)1 inhibitor (SC560), a selective COX2 inhibitor (NS398) and a selective prostacyclin synthase (PGIS) inhibitor (U51605) in a 48-h culture. In another experiment, culture media were supplemented with prostaglandin E2 (PGE2) and prostaglandin I2 (PGI2 or prostacyclin) analogues. The apoptosis was evaluated by detection of active caspase-3. It was strongly detected in the presence of selective COX-2 and PGIS inhibitors, which can be decreased by a PGI2 analogue. In our embryo transfer experiment, the implantation rate decreased with exposure to either the COX2 or the PGIS inhibitor which is increased further after PGI2 supplementation. The level of PGI2 is also higher at the 8-16-cell stage, compaction and blastocyst stage than PGE2. All these results indicate that COX2-derived PGI2 plays an important role in preimplantation embryo development and acts as an antiapopetic factor in in vitro culture.     

The effects of exogenous histamine in isolated rat hearts

The role of histamine in cardiac physiology and pathophysiology is not clarified, but is dependent on species. The effects of exogenous histamine in Langendorff-perfused rat hearts were investigated. 1 mM, 100, 10, 1 and 0.1 M of histamine (n=7 each) as 15 min infusions were employed in a dose-response study, and compared to control perfused hearts (n=7). In another experimental series, 100 M histamine (n=15) was added during reperfusion after 25 min global ischemia, and compared to control ischemia-reperfusion (n=15). The maximal response to histamine in the dose-response study (100 M) was an increase of left ventricular developed pressure to 126±8% of initial value (mean±SEM, p<0.04), and increase of coronary flow to 152+6% (p<0.02) after 5 min infusion. 100 M histamine did not significantly influence heart rate or rhythm. The lowest concentration (0.1 M) did not have effects cardiac performance. Reperfusion with histamine for 2 min after ischemia reduced left ventricular developed pressure to 68±10% of initial value versus 116+17% in ischemic controls (p<0.05), and increased left ventricular end-diastolic pressure to 24±8 mmHg compared to 6±2 mmHg in controls (p<0.04). Left ventricular pressures were similar in hearts reperfused with histamine and in ischemic controls for the rest of the observation. Coronary flow increased during reperfusion in hearts given histamine. Histamine had a dose-dependent positive inotropic and vasodilatory effect in isolated rat hearts. Exogenous histamine had only minor effects on post-ischemic cardiac function.     

Anesthetic preconditioning: triggering role of reactive oxygen and nitrogen species in isolated hearts

We postulated that anesthetic preconditioning (APC) is triggered by reactive oxygen/nitrogen species (ROS/RNS). We used the isolated guinea pig heart perfused with L-tyrosine, which reacts with ROS and RNS to form strong oxidants, principally peroxynitrite (ONOO(-)), and then forms fluorescent dityrosine. ROS scavengers superoxide dismutase, catalase, and glutathione (SCG) and NO. synthesis inhibitor N(G)-nitro-L-arginine methyl ester (L-NAME) were given 5 min before and after sevoflurane preconditioning stimuli. Drugs were washed out before 30 min of ischemia and 120 min of reperfusion. Groups were control (nontreated ischemia control), APC (two, 2-min periods of perfusion with 0.32 +/- 0.02 mM of sevoflurane; separated by a 6-min period of perfusion without sevoflurane), SCG, APC + SCG, L-NAME, and APC + L-NAME. Effluent dityrosine at 1 min reperfusion was 56 +/- 6 (SE), 15 +/- 5, 40 +/- 5(++), 39 +/- 4(++), 35 +/- 4(++) , and 33 +/- 5(++) units ((++)P< 0.05 vs. APC), respectively; left ventricular pressure (%baseline) at 60 min of reperfusion was 30 +/- 5(++), 60 +/- 4, 35 +/- 5(++), 37 +/- 5(++), 44 +/- 4, and 47 +/- 4; and infarct size (%total heart weight) was 50 +/- 5(++), 19 +/- 2, 48 +/- 3(++), 46 +/- 4(++), 42 +/- 4(++), and 45 +/- 2(++). Thus APC is initiated by ROS as shown by improved function, reduced infarct size, and reduced dityrosine on reperfusion; protective and ROS/RNS-reducing effect of APC were attenuated when bracketed by ROS scavengers or NO* inhibition.     

Cytosolic Ca2+ concentration during Ca2+ depletion of isolated rat hearts

Reperfusion of isolated mammalian hearts with a Ca²⁺-containing solution after a short Ca²⁺-free period at 37°:C results in massive influx of Ca²⁺ into the cells and irreversible cell damage: the Ca²⁺paradox. Information about the free intracellular, cytosolic [Ca²⁺] ([Ca²⁺]_i) during Ca²⁺ depletion is essential to assess the possibility of Ca²⁺ influx through reversed Na⁺/Ca²⁺ exchange upon Ca²⁺ repletion. Furthermore, the increase in end-diastolic pressure often seen during Ca²⁺-free perfusion of intact hearts may be similar to that seen during ischemia and caused by liberation of Ca²⁺ from intracellular stores. Therefore, in this study, we measured [Ca²⁺]i during Ca²⁺- free perfusion of isolated rat hearts. To this end, the fluorescent indicator Indo-1 was loaded into isolated Langendorff-perfused hearts and Ca²⁺-transients were recorded. Ca²⁺-transients disappeared within 1 min of Ca²⁺ depletion. Systolic [Ca²⁺]i during control perfusion was 268±54 nM. Diastolic [Ca²⁺]i during control perfusion was 114±34 nM and decreased to 53±19 nM after 10 min of Ca²⁺ depletion. Left ventricular end-diastolic pressure (LVEDP) significantly increased from 13±4 mmHg during control perfusion after Indo-1 AM loading to 31±5 mmHg after 10 min Ca²⁺ depletion. Left ventricular developed pressure did not recover during Ca²⁺ repletion, indicating a full Ca²⁺ paradox. These results show that LVEDP increased during Ca²⁺ depletion despite a decrease in [Ca²⁺]i, and is therefore not comparable to the contracture seen during ischemia. Furthermore, calculation of the driving force for the Na⁺/Ca²⁺ exchanger showed that reversed Na⁺/Ca²⁺ exchange during Ca²⁺ repletion is not able to increase [Ca²⁺]i to cytotoxic levels.     

Effect of prostacyclin on perfusion pressure, electrical activity, rate and force of contraction in isolated rat and rabbit hearts.

Prostacyclin when added to medium perfusing rat and rabbit hearts caused an increase in perfusion pressure at concentrations from 1 pg/ml ? 1 ng/ml (2.8 × 10^?12 ? 2.8 × 10^?9M) and a decrease at higher concentrations. Rhythm disturbances were observed with low prostacyclin concentrations in 6 of 10 rat hearts and 2 of 5 rabbit hearts studied. Increased heart rates were seen in the isolated rat hearts but not in the rabbit hearts. Force of contraction of isolated rat hearts was increased with increasing prostacyclin concentrations up to 100 pg/ml. Higher concentrations decreased contractile force. No inotropic effects were seen with rabbit hearts.     

丙泊酚预处理对大鼠离体心肌浅低温缺血／再灌注损伤后线粒体细胞色素C释放的影响

目的：探讨丙泊酚预处理对大鼠离体心肌浅低温缺血／再灌注（I／R）损伤后心肌细胞凋亡及线粒体细胞色素C释放的影响。方法：应用Langendorff离体心脏灌注模型,取50只SD大鼠随机分为5组：对照组（C组）,二甲基亚砜（DMSO）预处理组（D组）,25、50、100μmol·L^-1丙泊酚预处理纽（P1、P2、P3组）。各组均浅低温缺血55min,再常温灌注60min。D组、P1、P2、P3组在缺血前分别以含DMSO、相应浓度丙泊酚的K-H液灌注10min,再冲洗5min,重复2次。记录平衡灌注末、缺血前即刻、再灌注30、60min时的心功能指标。再灌注60min时测定凋亡细胞,提取心肌线粒体,测定线粒体和胞浆的细胞色素C水平。结果：与C组相比,P3组再灌注30min、60min时左室舒张末压（LVEDP）降低、左室发展压（LVDP）升高（P〈0．05或P〈0．01）;P2、P3组再灌注末心肌细胞凋亡率降低（P〈0．05或P〈0．01）,线粒体细胞色素c释放减少,胞浆细胞色素C的量明显降低（P〈0．05或P〈0．01）。结论：丙泊酚预处理能够通过抑制心肌线粒体细胞色素C释放到胞浆,降低浅低温I／R损伤心肌细胞凋亡率,减轻心肌桶伤．     

Mechanical factors affecting protein turnover in isolated rat hearts

Induction of cardiac work increased protein synthesis in hearts supplied glucose or a mixture simulating normal plasma levels of glucose, insulin, glucagon, lactate, and beta-hydroxybutyrate. During 2 h of perfusion, cardiac work did not accelerate protein synthesis in hearts supplied a mixture of glucose, lactate, and higher concentrations of insulin. Protein degradation was decreased by work in hearts supplied glucose. Nitrogen balance was negative in Langendorff-perfused hearts provided glucose, but was less so in working preparations. Nitrogen balance was zero or positive in working hearts provided the mixture simulating plasma or the mixture of glucose, lactate, and insulin. In Langendorff preparations, increased aortic pressure accelerated protein synthesis during the second hour of perfusion in hearts supplied glucose, glucose plus insulin, or pyruvate. When ventricular pressure development was prevented by ventricular draining or when drained hearts were arrested with tetrodotoxin, protein synthesis still increased as perfusion pressure was raised from 60 to 120 mm Hg. Oxygen consumption increased as aortic pressure was increased in drained, beating hearts, but was unaffected in arrested, drained hearts. These studies indicated that increased aortic pressure and its attendant stretch of the ventricular wall were the mechanical parameter most closely associated with faster rates of protein synthesis.