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Biomedical subjects

B F Becker

Publications and source records attributed to B F Becker.

At least 55 records · Page 3Linked to original sources
PubMed1998

Cyclooxygenase inhibition aggravates ischemia-reperfusion injury in the perfused guinea pig heart: involvement of isoprostanes.

OBJECTIVES: Postischemic contractile dysfunction in the heart may be due, in part, to isoprostanes, thought to accumulate during myocardial reperfusion. This study tested whether cyclooxygenase (COX) inhibitors increase the amount of isoprostanes and, consequently, lead to deterioration of postischemic heart function. BACKGROUND: Isoprostanes are bioactive prostaglandin-like compounds that are formed in vivo directly by free radical-catalyzed peroxidation of arachidonic acid. In particular, 8-isoprostaglandin (PG) F2alpha is a potent vasoconstrictor. METHODS: Isolated working guinea pig hearts underwent 30-min low flow ischemia followed by reperfusion, 15 min in a nonworking mode and 20 min performing pressure-volume work. Hearts were perfused with or without 100 micromol/liter acetylsalicylic acid (ASA), 3 or 10 micromol/liter indomethacin or 1 micromol/liter SQ 29548, a thromboxane-A2 (TxA2) receptor antagonist able to abolish the vasoconstrictive actions of 8-iso-PGF2alpha. External heart work (EHW) and coronary resistance were compared before and after ischemia. Coronary release and tissue content of 8-iso-PGF2alpha were also determined. RESULTS: During reperfusion, 8-iso-PGF2alpha release increased tenfold compared with the preischemic value in all groups. However, in ASA- and indomethacin-treated hearts, 8-iso-PGF2alpha levels were approximately 15-fold higher than in control hearts (5.4 vs. 0.35 pg/ml, respectively). Postischemic tissue levels of 8-iso-PGF2alpha were also markedly higher: 215 (indomethacin) and 301 (ASA) pg/ml g dry weight versus 43 pg/mg dry weight for control hearts (p < 0.05). Treatment of hearts with COX inhibitor led to a reduction in recovery of EHW (40% vs. 71%, p < 0.05) and seemed to be due to impaired myocardial oxygenation: Coronary venous oxygen was lower (67% of control values), whereas anaerobic metabolism (lactate release vs. pyruvate consumption) was enhanced. Coronary resistance was correspondingly elevated (164% of control values). SQ 29548 caused all variables to revert to control values. CONCLUSIONS: These data demonstrate that in the guinea pig heart, COX-inhibiting drugs exacerbate loss of cardiac function after ischemia. The enhanced production of isoprostanes favors coronary vasoconstriction and leads to myocardial oxygen deprivation.

Animals↗
PubMed1998

Adenosine endogenously released during early reperfusion mitigates postischemic myocardial dysfunction by inhibiting platelet adhesion.

The purpose of this study was to investigate platelet effects on postischemic heart function in conjunction with adenosine effects on intracoronary platelet adhesion. Homologous platelets were infused into the coronaries of isolated guinea pig hearts, either during low-flow ischemia or during reperfusion, and external heart work (EHW) and intracoronary platelet adhesion were determined. In most experiments, thrombin was added to the perfusate. The influence of endogenous adenosine was studied by use of the uptake blocker dipyridamole and the unspecific adenosine-receptor blocker theophylline, the A1-receptor blocker 8-cyclopentyl-1,3-dipropylxanthine (DPCPX), and the A2-receptor blocker 3,7-dimethyl-1-propargylxanthine (DMPX). The importance of nitric oxide and prostaglandin I2 (PGI2) was tested by using nitro-L-arginine (NOLAG) and indomethacin, respectively. When platelets were applied with thrombin during low-flow ischemia, EHW recovered to only 63 +/- 4% of the preischemic value, as compared with 89 +/- 3% without platelets (p < 0.05). Despite thrombin, platelets incurred no significant functional loss when applied in the first minute of reperfusion (but again in the fifth minute); however, when theophylline was also present, recovery of EHW amounted to only 42 +/- 12%. Intracoronary adhesion of platelets was negligible without thrombin, and highest during low-flow ischemia with thrombin (35 +/- 3% of the applied number). No adhesion occurred during the first minute of reperfusion, whereas in the fifth minute, adhesion was again 20.8 +/- 4%. Dipyridamole increased adenosine release and attenuated adhesion at this time. Theophylline increased adhesion in the first minute of reperfusion (33 +/- 6.4%), whereas NOLAG and indomethacin proved to be ineffective. DPCPX and DMPX each increased platelet retention during the first minute of reperfusion, their effects being additive. Intracoronary adhesion of platelets induced by thrombin in isolated hearts can reduce postischemic recovery of heart function. During reperfusion, but not during low-flow, endogenous adenosine can prevent platelet adhesion and loss of myocardial function, an action mediated both by A1- and A2-receptor-dependent mechanisms.

Adenosine↗
PubMed1998

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.

Anesthetics, Inhalation↗
PubMed1997

The function of neutrophils isolated by a magnetic antibody cell separation technique is not altered in comparison to a density gradient centrifugation method.

Most comparative studies on neutrophil (PMN) isolation techniques have shown either activation or functional impairment of the cells due to the different separation processes. We have established a preparation method for PMN from human whole blood employing iron tagged, magnetizable antibodies against the cell surface antigen CD15. The aim of our study was to test whether this magnetic separation (MACS) alters cellular functions of PMN in comparison to a conventional density gradient technique (Percoll). The purity, cell yield, and pre-activation of the cells were evaluated. The latter was assessed by quantifying the expression of the integrin CD11b using flow cytometry. Furthermore, as functional tests, cell morphology and the oxidative burst reaction were investigated. We have shown that the use of 'magnetic' antibodies leads to highly purified PMN (> 99% of isolated leukocytes), while there is still contamination by eosinophils (about 6%) after Percoll separation. Platelet contamination was about the same in both procedures (approx. one platelet per two PMN). The basal expression of CD11b and, hence, neutrophil activation, was significantly lower and the upregulation of CD11b in response to FMLP was more pronounced after magnetic separation, as compared to density gradient centrifugation. The MACS technique did not lead to polarisation of PMN, nor did it affect the oxidative burst. This study suggests that magnetic separation is a simple, time-saving technique, yielding highly purified and functionally intact PMN.

Centrifugation, Density Gradient↗
PubMed1997

Cardioprotection by cyclosporine A in experimental ischemia and reperfusion--evidence for a nitric oxide-dependent mechanism mediated by endothelin.

The acute effect of cyclosporine A (CSA) on myocardial function after ischemia and reperfusion and the mechanism of action was investigated in isolated working guinea-pig hearts. Myocardial function was experimentally infringed by imposing short-term global ischemia and reperfusion (15 min each). External heart work (EHW), determined before and after ischemia, served as the criterion for quantitation of recovery. Control hearts were perfused with modified Krebs-Henseleit buffer, other hearts received buffer supplemented with CsA +/- an endothelin receptor antagonist or exogenous endothelin +/- an inhibitor of nitric oxide (NO) synthesis. To assess the importance of endothelial production of mediators directly, NO release in coronary effluent (continuously measured with an amperometric sensor) and release of 6-keto-prostaglandin F1, (6-keto-PGFb), a stable metabolite of prostacyclin (PGI2), were determined in non-working. Langendorff hearts. Oxidative stress during reperfusion was assessed by measuring glutathione release in coronary venous effluent. Cyclosporine A (0.8 microM) improved post-ischemic function significantly (59% recovery of EHW nu 31% for controls). At 0.08 microM. CsA was without beneficial effect (30% recovery). The endothelin (ET)A- and ETB-receptor antagonist bosentan inhibited the protective action of 0.8 microM CsA (32% recovery). Exogenous ET-1 (80 pM) improved recovery to 53%, an effect which was blocked by the inhibitor of NO-synthase, NG-nitro-L-arginine (NOLAG. 1 microM. 31% recovery. In the control group, post-ischemic NO release in coronary effluent recovered from zero to about 100% of the pre-ischemic value by 10 min. but then decreased rapidly during the subsequent 15 min of reperfusion. In hearts treated with 0.8 microM CsA, NO release stayed at 100% of the pre-ischemic value throughout reperfusion, the difference between controls and CsA-treated hearts being significant after 20 min of reperfusion. On the other hand, coronary venous release of 6-keto-PGF1a was not different between the groups. Release of glutathione during early reperfusion first 5 min) was significantly lowered (P < 0.05) to about 50% in CsA (0.8 microMI- and ET-I-treated compared with controls (8.8 nmol/min). Cyclosporine A acts as a cardioprotective agent in our model of ischemia and reperfusion, presumably by elevating the level of endogenous nitric oxide and thereby reducing oxidative stress.

6-Ketoprostaglandin F1 alpha↗
PubMed1997

Nitric oxide attenuates reoxygenation-induced ICAM-1 expression in coronary microvascular endothelium: role of NFkappaB.

Enhanced leukocyte adhesion has been shown to occur in post-ischemic reperfused hearts due to the upregulation of specific cell-surface adhesion molecules. Therefore, we investigated the influence of 4 h of reoxygenation after 20 h of hypoxia on ICAM-1 induction in primary cultures of rat coronary microvascular endothelial cells (CMEC). ICAM-1 surface expression as well as oxygen free radical formation were measured by flow cytometry. Changes in ICAM-1 mRNA levels were assessed by Northern blot and activation of NFkappaB and AP-1 signalling were analysed by electrophoretic mobility shift assays (EMSA) in CMEC lysates. Although hypoxia alone did not affect cell-surface ICAM-1 expression, 4 h of reoxygenation induced a significant upregulation of ICAM-1. ICAM-1 mRNA could not be found after hypoxia alone, but could be detected as early as 1 h following reoxygenation. Unlike AP-1, the activation of which could be detected in CMEC lysates following hypoxia alone, NFkappaB binding activity was induced only following reoxygenation, concurrent with an increase in the formation of reactive oxygen species (ROS). A proteasome inhibitor, nor-Leu (25 microM) inhibited NFkappaB activation by reoxygenation and ICAM-1 expression. Blockade of endogenous nitric oxide (NO) synthesis in CMEC with L-nitroarginine (10 microM) accentuated post-reoxygenation ICAM-1 expression. Finally, an exogenous NO donor, S-nitrosoacetyl-penicillamine (SNAP, 100 microM), suppressed the generation of ROS upon reoxygenation, and blocked the activation of NFkappaB and the upregulation of ICAM-1. Thus, ICAM-1 upregulation in CMEC primary cultures is not induced by hypoxia alone, but appears shortly after reoxygenation in the absence of exogenous cytokines or inflammatory cells. Because upregulation of AP-1 through hypoxia alone did not affect ICAM-1 expression, we conclude that redox-sensitive NFkappaB activation triggers ICAM-1 upregulation. NO inhibits reoxygenation-specific ICAM-1 upregulation, most likely by diminishing oxidative stress that leads to NFkappaB activation.

Animals↗
PubMed1997

Effects of ACE-inhibition on redox status and expression of P-selectin of endothelial cells subjected to oxidative stress.

Redox stress during post-ischemic reperfusion may be the prime signal for processes leading to myocardial remodelling and hypertrophy. Nitric oxide (NO) is antioxidative, antiadhesive for neutrophils (PMN) and antiproliferative. Thus, enhancing endothelial production of NO, e.g. by inhibiting breakdown of endogenous bradykinin via angiotensin converting enzyme (ACE), could be beneficial. The effect of cilazaprilat (CILA, 10 micro M), an ACE inhibitor, on redox status, expression of the adhesion molecule P-selectin, and PMN adhesion under conditions of oxidative stress was investigated in cultured human umbilical vein endothelial cells (HUVECs). Incubation of the cells with H2O2 (0.1 and 1 mm) for 15 min served as oxidative stimulus. The intra- and extracellular concentrations of reduced and oxidized glutathione (GSH and GSSG) were measured by HPLC as indicators of endothelial redox status. Expression of P-selectin was measured by flow cytometry. Furthermore, firm leukocyte adhesion to HUVECs was assessed. In controls, the intracellular ratio GSH/GSSG averaged 47 and dropped to 30 after incubation with 0.1 mm H2O2. The ratio declined to 6.5 with 1 mm H2O2. CILA blocked the effects of 0.1 mm H2O2, but was ineffective against 1 mm peroxide. The extracellular ratio did not discriminate between 0.1 and 1 mm H2O2, falling from 18 to 1 in both situations. P-selectin expression rose from 100% (control) to 146% after 1 mm H2O2 without CILA, but only to 114% in the presence of CILA. PMN adhesion was enhanced from about 1600 PMN per microwell (control) to 4300/well by 1 mm H2O2. CILA had no significant effect on adhesion (3900 PMN/well). Exposure of HUVECs to 0.1 mm H2O2 affected neither P-selectin expression nor PMN adhesion. Consequently, ACE inhibition can mitigate mild (0.1 mm H2O2) but not more severe redox stress in HUVECs. Irrespectively, CILA reduced the upregulation of P-selectin at the higher H2O2 concentration, indicating that this process is regulated independently of the cellular redox status. The firm adhesion of PMN to HUVECs was independent of P-selectin expression.

Angiotensin-Converting Enzyme Inhibitors↗
PubMed1997

Retention of leucocytes in reperfused, isolated hearts does not cause haemodynamically relevant permanent capillary plugging.

Effects of microspheres (5 microns or 10 microns diameter) and polymorphonuclear leucocytes (PMN) on coronary resistance were compared in beating, non-working isolated guinea-pig hearts (Langendorff preparation). The hearts were buffer perfused (5 ml/min, constant flow) and particles or cells were infused into the coronary system as a bolus (1 ml, 1 min). Coronary perfusion pressure, coronary flow and formation of epicardial transudate were measured before and after bolus administration. Coronary resistance was estimated from these parameters. Retention of particles or cells was monitored by quantifying the numbers emerging in the coronary effluent in relation to the number administered. The effects of PMN were also studied after 15 min of global ischemia. Coronary resistance correlated with the number of 10-micron particles infused, which were almost quantitatively retained. In contrast, 5-micron beads had no such effect and were not retained in the coronary system. Though considerable numbers of PMN were retained in the hearts (about 21% under control conditions and 35% after ischaemia), coronary resistance was not increased in either case. Blockage of the CD18 adhesion complex by monoclonal antibodies lowered basal retention to 11% and completely prevented the elevation of retention by ischaemia. We conclude that, in this experimental model, PMN, permanently retained in the hearts under normal flow conditions and especially after brief ischaemia, do not cause acute, haemodynamically relevant capillary plugging, but adhere to postcapillary venules via CD18.

Animals↗
PubMed1997

ACE-inhibition prevents postischemic coronary leukocyte adhesion and leukocyte-dependent reperfusion injury.

OBJECTIVE: Polymorphonuclear leukocytes (PMN), retained in the microvascular bed, can contribute to postischemic myocardial reperfusion injury. Since a beneficial effect of ACE-inhibition on reperfusion injury has been reported, we investigated the impact of cilazaprilat on PMN dependent reperfusion injury in isolated guinea pig hearts. METHODS: Hearts (n = 5 per group) were subjected to 15 min of ischemia. Immediately thereafter, a bolus of PMN was injected into the coronary system. External heart work (EHW) and total cardiac nitric oxide release were measured. For microscopic evaluation, hearts received rhodamine 6G labelled PMN after ischemia, were arrested 5 min later and further perfused with FITC dextran (0.1%). Localization of retained PMN was assessed by fluorescence microscopy. Leukocyte activation was studied by FACS analysis of the adhesion molecule CD11b before and after coronary passage of the PMN. The ACE-inhibitor cilazaprilat (Cila, 2 microM) and the NO-synthase inhibitor nitro-L-arginine (NOLAG, 10 microM) were used to modulate nitric oxide formation of the heart. RESULTS: Postischemic EHW recovered to 67 +/- 5% (controls) and 64 +/- 6% (Cila) of the preischemic value. Addition of PMN severely depressed recovery of EHW (39 +/- 2%) and NO release (39 +/- 6% of the preischemic value). Simultaneously, ischemia led to a substantial increase in postcapillary PMN adhesion (from 21 +/- 5 to 172 +/- 27 PMN/mm2 surface) and CD11b-expression of the recovered PMN (3-fold). Cila attenuated postischemic PMN adhesion (83 +/- 52 PMN/mm2) and activation of PMN, whereas it improved recovery of work performance (64 +/- 4%) and NO release (65 +/- 4%) in the presence of PMN. Conversely, NOLAG increased PMN adhesion (284 +/- 40 PMN/mm2) and myocardial injury. We conclude that ACE-inhibition prevents leukocyte dependent reperfusion injury mainly by inhibition of postcapillary leukocyte adhesion. The effect may be mediated by NO, given the proadhesive effect of NOLAG.

Analysis of Variance↗
PubMed1997

Halothane, isoflurane, and sevoflurane reduce postischemic adhesion of neutrophils in the coronary system.

BACKGROUND: Polymorphonuclear neutrophils (PMNs) contribute to postischemic reperfusion damage in many organs and tissues, a prerequisite being adhesion of PMNs to vascular endothelial cells. Because adhesion processes involve orderly interactions of membrane proteins, it appeared possible that "membrane effects" of volatile anesthetics could interfere. We investigated the effects of halothane, isoflurane, and sevoflurane on postischemic adhesion of human PMNs in the intact coronary system of isolated perfused guinea pig hearts. METHODS: The hearts (n = 7-10 per group) were perfused in the "Langendorff" mode under conditions of constant flow (5 ml/min) using modified Krebs-Henseleit buffer equilibrated with 94.4% oxygen and 5.6% carbon dioxide. Global myocardial ischemia was induced by interrupting perfusion for 15 min. In the second minute of reperfusion (5 ml/min), a bolus dose of 6 x 10(5) PMNs was injected into the coronary system. The number of cells reemerging in the coronary effluent was expressed as a percentage of the total number of applied PMNs. Halothane, isoflurane, and sevoflurane, each at 1 and 2 minimal alveolar concentration (MAC), were vaporized in the gas mixture and applied from 14 min before ischemia until the end of the experiment. RESULTS: Under nonischemic conditions, 24.7 +/- 1.3% of the injected neutrophils did not reemerge from the perfused coronary system. Subjecting the hearts to global ischemia augmented retention (36.4 +/- 2.8%, P < .05). Application of halothane reduced adhesion of neutrophils to 22.6 +/- 2.1% and 24.2 +/- 1.8% at 1 and 2 MAC, respectively (P < .05). Exposure to 1 and 2 MAC isoflurane was similarly effective, whereas basal adhesion was not significantly influenced. Sevoflurane-treated hearts (1 and 2 MAC) also showed decreased adhesion of PMNs (23 +/- 2.3% and 24.8 +/- 1.8%, respectively; P < .05) and an identical reduction resulted when sevoflurane (1 MAC) was applied only with the onset of reperfusion. CONCLUSIONS: Although the mechanism of action of volatile anesthetics remains unclear in these preliminary studies, their inhibitory effect on ischemia-induced adhesion of PMNs may be beneficial for the heart during general anesthesia.

Anesthetics, Inhalation↗
PubMed1997

Hemodynamic effects of isoprostanes (8-iso-prostaglandin F2alpha and E2) in isolated guinea pig hearts.

Isoprostanes are a family of prostaglandin-related compounds formed from arachidonic acid in a cyclooxygenase-independent manner as products of free radical-initiated lipid peroxidation. To elucidate the biological activity of the F2-and E2-isoprostanes, 8-iso-prostaglandin F2alpha (8-iso-PGF2alpha) and 8-iso-prostaglandin E2 (8-iso-PGE2), we measured hemodynamic effects in isolated perfused guinea pig hearts after cumulative administration (3 x 10(-9)-10(-5) M) of these compounds into the coronary system. Coronary flow (CF), left ventricular pressure (LVP), maximal rate of pressure development (dP/dt(max)), and heart rate were determined continuously. Furthermore, net release of lactate into the coronary venous effluent and myocardial pyruvate consumption were measured. Comparative studies were performed with the known potent vasoconstrictor endothelin-1 (6 x 10(-12)-2 x 10(-9) M). Both 8-iso-PGF2alpha and 8-iso-PGE2 induced concentration-dependent decreases in CF, which declined maximally to approximately 50% of the baseline level. The potencies of the two compounds were almost identical. Alterations in CF were associated in both groups with parallel reductions of LVP and dP/dt(max); heart rate was not influenced. Furthermore, the diminished CF caused enhanced lactate release and a reduced pyruvate consumption. All isoprostane-induced hemodynamic changes were prevented by coapplication of the thromboxane A2-receptor antagonist SQ 29548 (1 microM). Endothelin-1 caused CF reductions associated with loss of myocardial contractility, just like the isoprostanes. We conclude that in isolated guinea pig hearts, 8-iso-PGF2alpha and 8-iso-PGE2 are potent vasoconstrictors. The action appears to be mediated by SQ 29548-responsive thromboxane receptors. The accompanying loss of contractility is a secondary phenomenon, elicited by infringed oxygen supply.

Animals↗
PubMed1996

Nitric oxide mitigates leukocyte adhesion and vascular leak after myocardial ischemia.

Tissue edema is a facet of ischemia/reperfusion injury in many organs, polymorphonuclear leukocytes (PMN) presumably playing a contributory role. We studied the intracoronary adhesion of PMN and its effect on vascular permeability during reperfusion in isolated guinea-pig hearts. After a global ischemia of 15 min duration. PMN (10(7)) were infused into the coronary system during the first minute of reperfusion. PMN adhesion was measured as difference of applied PMN and those recovered in the effluent perfusate. Coronary permeability was assessed by measuring the rate of transudate formation (TF) on the epicardial surface, before as well as 5, 15 and 30 min after ischemia. Experiments were also performed in the presence of the NO-synthase inhibitor nitro-L-arginine (10 microM) and the ACE-inhibitor ramiprilat (2 microM), the latter known to enhance endogenous nitric oxide formation. Furthermore, the radical scavenger uric acid (0.5 mM) was applied either before and during ischemia or starting after PMN application. Ischemia/reperfusion increased coronary PMN adherence from 23 +/- 1% (basal) to 33 +/- 2%. Whereas ischemia alone did not influence TF (about 100 microliters/min during reperfusion), postischemic PMN infusion led to progressive TF. With nitro-L-arginine, PMN adhesion rose to 45 +/- 3%; TF increased to 212 +/- 30 microliters/min. In contrast, ramiprilat caused post-ischemic adhesion and TF to decline to basal values. In the presence of uric acid (UA) PMN adhesion declined to 26 +/- 2%, however, the subsequent increase in TF after withdrawal of UA was not markedly attenuated. On the other hand, infusion of UA after application of PMN caused a significant decrease of TF. The extracellular antioxidants SOD/catalase were without effect. As shown using luminol enhanced chemiluminescence. No was able to scavenge oxygen free radicals released by activated PMN. These findings indicate that enhanced PMN adhesion in reperfusion leads to an increase in coronary permeability. Scavenging of oxygen free radicals with NO or UA appears to mitigate both, postischemic PMN adhesion and PMN-induced vascular injury, even after adhesion.

Angiotensin-Converting Enzyme Inhibitors↗
PubMed1996

[Interaction of adenosine with leukocytes and thrombocytes].

Platelets and polymorphonuclear granulocytes (PMN) contribute to post-ischemic myocardial reperfusion damage. However, to elicit any deleterious actions, they first need to become adherent to the vascular endothelium. Numerous studies have documented an A2-receptor mediated platelet-stabilizing action of adenosine and an A2-dependent antiinflammatory effect on PMN themselves. Intriguingly, an A1-receptor mediated chemotactic action of adenosine on isolated PMN has also been reported. A1-receptors are more sensitive towards adenosine than A2-receptors, and interactions between platelets and leukocytes could alter the net-adhesive potential. Furthermore, the endothelial cells also express adenosine A1- and A2-receptors. In the situation of ischemia and reperfusion both, the intracoronary concentration of adenosine and the shear forces, vary with time. We have, therefore, investigated the influence of adenosine on intracoronary adhesion of PMN and platelets, applied to isolated heart preparations (guinea pig), both separately and in combination, and determined the resultant effect on postischemic myocardial pump function. At submicromolar adenosine concentrations, as found after brief ischemia (15 min stopped-flow or 30 min low-flow), adenosine enhanced intracoronary PMN retention by preferentially stimulating endothelial A1-receptors. The effect required the intermediate formation of platelet activating factor (PAF) and occurred via CD11/CD18 adhesion molecules on the PMN. Higher, i.e., micromolar levels of adenosine, in contrast, inhibited PMN adhesion via an A2-receptor dependent mechanism. Thrombin-induced platelet adhesion was inhibited by adenosine at high shear rates by both A1- and A2-receptor dependent mechanisms. However, adenosine was not protective at low shear rates, or at high flow in the presence of PMN. Pertinently, adhesion of either PMN or platelets, alone or in combination, regularly caused deterioration of post-ischemic myocardial function. Thus, depending on its concentration and on the phase of ischemia/reperfusion, adenosine may elicit cardioprotective or detrimental effects in the reperfused myocardium, which makes general prognosis of its role in such situations difficult. However, in the course of every reperfusion, the adenosine levels will inevitably fall into the proadhesive range. Thus, prophylactic inhibition of A1-receptor effects may be beneficial.

Adenosine↗
PubMed1995

Taurine protects the heart from neutrophil-induced reperfusion injury.

Deficiency of the amino acid taurine is implicated in various pathologic states of the heart. Besides other effects, taurine has been proposed to be an antioxidant. However, its benefit under conditions associated with the generation of reactive oxygen species in the heart has not been clearly demonstrated. To assess the potential of taurine to influence neutrophil-dependent reperfusion injury, a model was developed based on the isolated working guinea pig heart. After an initial work phase, hearts were subjected to 15 min of global ischemia. Reperfusion, in a nonworking mode, was carried out in the absence or presence of homologous neutrophils (PMN) and/or taurine. After 15 min, work was resumed and percentage recovery of function was determined another 20 min later. During the reperfusion phase, coronary venous effluent was collected to quantify release of lactate and glutathione, markers of ischemic challenge and redox-stress, respectively. Furthermore, direct effects of taurine on radical formation were investigated in a chemiluminescence assay. Control hearts without application of PMN or taurine had a postischemic recovery of external heart work (EHW) of 76%, in the presence of taurine (15 mM) recovery was 72%. The application of PMN for merely the first minute of reperfusion led to a significant decrease in recovery to 30%, PMN having no effect without a foregoing ischemia. When taurine was additionally applied during reperfusion, EHW recovered to 60%. Release of lactate and of oxidized glutathione (GSSG) did not differ between the groups. In contrast, effluent concentrations of reduced glutathione (GSH) were considerably elevated by the presence of PMN in the sample and remained high even after PMN-washout. Taurine tended to attenuate this PMN effect. At the 5th and 10th min of reperfusion, GSH release of individual hearts correlated inversely with postischemic recovery of EHW. Surprisingly, taurine, by itself, did not significantly alter glutathione release. However, taurine (15 mM) markedly reduced luminol-dependent chemiluminescence elicited by activated guinea pig PMN as well as by chemically generated hypochlorous acid and hydroxyl radicals, but not superoxide radicals. Our results demonstrate that taurine protects the heart from PMN-induced reperfusion injury and oxidative stress. Because respiratory burst activity of PMN was also significantly reduced in the presence of taurine, the beneficial effect appears to be mediated by antioxidative properties of taurine.

Animals↗
PubMed1995

Nitric oxide accounts for postischemic cardioprotection resulting from angiotensin-converting enzyme inhibition: indirect evidence for a radical scavenger effect in isolated guinea pig heart.

The cardioprotective effect of angiotensin-converting enzyme (ACE) inhibitors in cardiac ischemia/reperfusion damage is assumed to result largely from inhibition of the enzymatic breakdown of endogenous bradykinin (BK). We assessed the role of nitric oxide (NO) in mediating the beneficial actions of BK and the possible mechanism of the effect of NO. We experimentally infringed myocardial function in a working guinea pig heart preparation by ischemia (15 min) and reperfusion. The parameter external heart work (EHW), determined before and after ischemia, served as criterion for quantitation of recovery. We assessed oxidative stress during reperfusion by measuring glutathione release in coronary venous effluent; lactate release was used as a measure of ischemic challenge. The principal ability of NO to scavenge oxygen radicals was separately investigated in a chemiluminescence (CL) assay with the NO-donor sodium nitroprusside (SNP) and lucigenin. The ACE inhibitor ramiprilat (RT 25 microM) improved postischemic function significantly (55% recovery of EHW vs. 29% for controls). BK 1 nM was even more cardioprotective (71% recovery). The NO-synthase inhibitor Ng-nitro-L-arginine (NOLAG 10 microM) inhibited the effects of RT and BK (18% recovery each). SNP (0.3 microM) improved recovery to 57%, the prostacyclin analogue iloprost (ILO, 0.1 and 3 nM) had no beneficial effect (21 and 20% recovery, respectively). With 8-bromo-cyclicGMP, a membrane-permeable cGMP analogue, function was not better than control (30% recovery). Release of glutathione during reperfusion was decreased by the three compounds known to increase NO concentration in the heart; lactate release was the same in all groups.(ABSTRACT TRUNCATED AT 250 WORDS)

Acridines↗
PubMed1995

Adenosine and PAF dependent mechanisms lead to myocardial reperfusion injury by neutrophils after brief ischaemia.

OBJECTIVE: The aim was to establish whether polymorphonuclear neutrophils can, by themselves, elicit depression of postischaemic heart function immediately after short periods of ischaemia, and to examine the involvement of endogenous adenosine and platelet activating factor (PAF) in the observed phenomena. METHODS: Isolated buffer perfused guinea pig hearts performing pressure-volume work under standardised conditions were subjected to 15 min of global ischaemia. Constant flow reperfusion (5 ml.min-1) was carried out in the presence or absence of homologous neutrophils (approximately 2000 cells.microliters-1 perfusate). After 15 min of reflow, work was resumed and functional recovery assessed another 20 min later. RESULTS: In hearts perfused only with Krebs-Henseleit buffer, postischaemic heart function recovered to 67(SEM 3)% (n = 13) of the preischaemic value. As early as the first minute of reperfusion, the application of neutrophils already led to a significant decrease in recovery to 39(3)% (n = 12; P < 0.05). Without ischaemia, neutrophils did not have any deleterious effect, recovery of external heart work amounting to 91(4)% (n = 6). Adenosine concentrations measured in the coronary effluent after ischaemia were substantially increased during reperfusion from preischaemic values of < 20 nM to about 800 nM. The adenosine A1 receptor antagonist dipropyl-8-cyclopentyl-xanthine prevented the neutrophil dependent loss of heart function, as did application of the PAF receptor antagonist WEB 2086, recoveries being 60(4)% (n = 6) and 58(8)% (n = 6), respectively. In contrast, the A2 antagonist 3,7-dimethyl-1-propargyl-xanthine tended to worsen the neutrophil induced dysfunction of the heart, recovery amounting to 18(2)% (n = 5). CONCLUSIONS: Even after brief ischaemia, neutrophils introduced into the coronary system can exacerbate reperfusion injury. Adenosine, through its A1 receptor, and PAF appear to play a significant role as mediators of this action.

Adenosine↗
PubMed1995

Preischaemic as well as postischaemic application of a calcium antagonist affords cardioprotection in the isolated guinea pig heart.

OBJECTIVE: The aim was to answer the following questions: (1) Does treatment with calcium antagonists have to be begun before ischaemia or is postischaemic application also protective? (2) When applied before ischaemia, do calcium antagonists have to depress preischaemic cardiac function in order to elicit protection? (3) Is cardioprotection a matter of improved reflow or do the agents influence the degree of oxidative injury during reperfusion? METHODS: Isolated working guinea pig hearts underwent ischaemia (15 min) and reperfusion (15 min). The calcium antagonist gallopamil was given either before (0.1 nM and 1 nM) or after ischaemia (0.1 nM) during early reperfusion (first 5 min). Recovery was defined as postischaemic compared to preischaemic external heart work, expressed in percent. Oxidative stress was assessed by the release of glutathione (GSH). Lactate release served as a measure of the ischaemic challenge. The ability of gallopamil to scavenge oxygen radicals directly was investigated in an in vitro chemiluminescence assay. RESULTS: Pump function of control hearts recovered to only 28% after reperfusion. Pretreatment with 0.1 and 1 nM gallopamil improved recovery to the same extent (48.7% and 43.4%, respectively); however, postischaemic application of 0.1 nM gallopamil afforded equal protection (45.4% recovery). Only the higher concentration of 1 nM gallopamil depressed preischaemic external heart work (by 11%). During earliest reperfusion (1-5 min), release of GSH only tended to be lower in treated hearts. During the subsequent minutes of reperfusion (5-15 min), release of GSH was significantly less in hearts postischaemically treated with 0.1 nM gallopamil (40 pmol.min-1 v 940 pmol.min-1 for controls). In contrast, ischaemia-induced lactate release did not differ between the groups. Gallopamil did not scavenge reactive oxygen species in vitro. CONCLUSIONS: Short term postischaemic application of the calcium antagonist gallopamil is almost as effective at restoring pump function as preischaemic application which, in turn, does not have to depress preischaemic cardiac function in order to elicit protection. A reduction of oxidative stress during reperfusion seems to contribute to the beneficial effects of postischaemic application of gallopamil, but a direct oxygen radical scavenging activity of gallopamil is not involved.

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