Tumor necrosis factor-alpha contributes to ischemia- and reperfusion-induced endothelial activation in isolated hearts

-During myocardial reperfusion, polymorphonuclear neutrophil (PMN) adhesion involving the intercellular adhesion molecule-1 (ICAM-1) may lead to aggravation and prolongation of reperfusion injury. We studied the role of early tumor necrosis factor-alpha (TNF-alpha) cleavage and nuclear factor-kappaB (NF-kappaB) activation on ICAM-1 expression and venular adhesion of PMN in isolated hearts after ischemia (15 minutes) and reperfusion (30 to 480 minutes). NF-kappaB activation (electromobility shift assay) was found after 30 minutes of reperfusion and up to 240 minutes. ICAM-1 mRNA, assessed by Northern blot, increased during the same interval. Functional effect of newly synthesized adhesion molecules was found by quantification (in situ fluorescence microscopy) of PMN, given as bolus after ischemia, which became adherent to small coronary venules (10 to 50 microm in diameter). After 480 minutes of reperfusion, ICAM-1-dependent PMN adhesion increased 2.5-fold compared with PMN adhesion obtained during acute reperfusion. To study the influence of NF-kappaB on PMN adhesion, we inhibited NF-kappaB activation by transfection of NF-kappaB decoy oligonucleotides into isolated hearts using HJV-liposomes. Decoy NF-kappaB but not control oligonucleotides blocked ICAM-1 upregulation and inhibited the subacute increase in PMN adhesion. Similar effects were obtained using BB 1101 (10 microg), an inhibitor of TNF-alpha cleavage enzyme. These data suggest that ischemia and reperfusion in isolated hearts cause liberation of TNF-alpha, activation of NF-kappaB, and upregulation of ICAM-1, an adhesion molecule involved in inflammatory response after ischemia and reperfusion.

Acute cardiac inflammatory responses to postischemic reperfusion during cardiopulmonary bypass

OBJECTIVES

The investigation centers on whether there is a reperfusion-induced specific cardiac inflammatory reaction after bypass surgery.

BACKGROUND

Cardiopulmonary bypass (CPB) leads to systemic inflammation. Additionally, cardiac inflammation due to reperfusion could occur. Knowledge about nature and time course of this reaction might help to develop cardioprotective interventions.

METHODS

In 12 patients receiving coronary bypass grafts, arterial and coronary venous blood was obtained before onset of CPB, and 1, 5, 10, 25, 35 and 75 min after cardiac reperfusion. Plasma levels of IL6 and IL8 were measured by immunoassay. CD11b, CD41, and CD62 on blood cells were quantified by flow cytometry. Measurement of CD41, a platelet marker, on neutrophils and monocytes allowed detection of leukocyte-platelet microaggregates.

RESULTS

Transcardiac veno-arterial difference of IL6 rose in the 10th and 25th min of reperfusion (from 0 to 7 pg/ml; p < 0.05), and after 75 min (15 pg/ml). IL8 did not change. CD11b on neutrophils (PMN) decreased transcardially to 95, 88 and 82% of the initial level in the 5th, 10th, and 75th min, respectively, suggesting sequestration of activated neutrophils. CD62 on platelets rose about 30% in the 75th min. Initially, leukocyte-platelet microaggregates were formed during coronary passage (+31% of the arterial level for PMN, +23% for monocytes). During reperfusion, coaggregates were retained (PMN: -1% and -7% in the 5th and 10th min, monocytes: -22%, -13% and -12% in the 1st, 5th and 10th min.

CONCLUSIONS

During early reperfusion after aortic declamping, the coronary bed is already a source of proinflammatory stimuli and target for activated leukocytes, partly in conjunction with platelets. Mitigation of these phenomena might help to improve cardiac function after CPB especially in patients at risk.

Influence of intact left atrial appendage on hemodynamic parameters of isolated guinea pig heart

BACKGROUND

In isolated working guinea pig heart preparations using the conventional technique of cannulating the left atrium via the atrial appendage, the resulting cardiac output is often insufficiently low (15-20 ml/min). This is a problem in ischemia reperfusion studies where small absolute differences can be responsible for large relative changes comparing pre- and postischemic values. In an attempt to increase cardiac output, the left atrium was left intact in isolated working guinea pig hearts. The two techniques were compared for hemodynamic parameters and their similarity to the physiological condition.

METHODS

The left atrium was cannulated either via the orifices of the pulmonary veins or via an incision in the atrial appendage with its subsequent ligation around the cannula (n = 45-46/group). After 20 min of pressure-volume work cardiac output, heart rate and oxygen partial pressures were measured and myocardial oxygen consumption and cardiac efficiency were calculated.

RESULTS

Cardiac output was higher in hearts with intact atrial appendage (64 +/- 2 ml/min) than in hearts with ligated atrial appendage (33 +/- 1 ml/min). Myocardial oxygen consumption (6.1 +/- 0.2 and 8.4 +/- 0.3 micromol/min, resp.) and cardiac efficiency (12.8 +/- 0.6% and 19.9 +/- 0.8%, resp.) were significantly higher in hearts with intact left atrial appendage.

CONCLUSIONS

Isolated working guinea pig hearts with an intact left auricle exhibit higher values for important hemodynamic parameters compared to a preparation technique involving ligation of the left auricle.

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.

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.

Disparate effects of adhesion and degranulation of platelets on myocardial and coronary function in postischaemic hearts

OBJECTIVE

Beside the major effect of acute thrombus formation, little is known about the interaction of platelets with the coronary endothelium in an ischaemia-reperfusion situation. The present study was designed to investigate, separately, the consequences of platelet adhesion and degranulation during myocardial reperfusion.

METHODS

Isolated guinea pig hearts perfused with Krebs-Henseleit buffer and performing pressure-volume work were used. We infringed myocardial function by imposing ischaemia (20 min of low-flow perfusion with 1 ml/min and 10 min of global ischaemia) and reperfusion (15 min with 5 ml/min). During low-flow perfusion, the coronary endothelium was stimulated by thrombin before and during infusion of a bolus: 10(8) washed human platelets +/- the Arg-Gly-Asp (RGD) analogon lamifiban, the supernatant of 10(8) thrombin-stimulated platelets, fibrinogen (2 microM), lamifiban (2 microM) or Tyrode's solution (control group). The parameter external heart work (EHW), determined pre- and postischaemically, served as criterion for recovery of myocardial function. Additionally, the formation of capillary transudate was measured during the reperfusion phase to assess coronary permeability. Coronary perfusion pressure was monitored continuously and myocardial production of lactate and consumption of pyruvate were measured. Electron microscopy of hearts was performed after platelet application to verify platelet adhesion in the coronary system.

RESULTS

Recovery of EHW by hearts without platelet application was 64 +/- 3% and was significantly reduced to 49 +/- 5% by platelet infusion (n = 8 each). Infusion of supernatant of thrombin-stimulated platelets did not impair recovery of heart work. In the reperfusion phase (6th-10th min), hearts that either had received platelets or supernatant of platelets exhibited a significantly reduced production of capillary transudate (70 microliters/min vs. 180 microliters/min for the controls). Intracoronary bolus application of fibrinogen or lamifiban also reduced coronary leak. Coronary perfusion pressure and metabolic parameters were not statistically different between the groups at any time.

CONCLUSIONS

Platelet adhesion to the coronary endothelium in a situation of myocardial ischaemia impairs cardiac recovery, whereas constituents released by platelets may have beneficial effects on the integrity of the coronary endothelium. In particular, fibrinogen seems to contribute to the permeability reducing effect, possibly by interaction with endothelial receptors recognising the RGD sequence.

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.

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.

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.

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.

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.

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.

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.

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.

[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.

Stimulation of endothelial adenosine A1 receptors enhances adhesion of neutrophils in the intact guinea pig coronary system

OBJECTIVE

The primary aim was to determine the action of pathophysiologically relevant adenosine concentrations (0.1-1 microM) on adhesion of neutrophils to coronary endothelium. Further aims were to evaluate the nature and localisation of the adenosine receptor involved, and to assess the effect of endogenous adenosine.

METHODS

Adhesion was studied in isolated perfused guinea pig hearts by determining the number of cells emerging in the coronary effluent after intracoronary bolus injections of 600,000 neutrophils prepared from guinea pig or human blood. The system was characterised by the use of the proadhesive stimulus thrombin.

RESULTS

A 5 min infusion of adenosine (0.1-0.3 microM) or the A1 receptor agonist N6-cyclopentyladenosine (CPA, 0.01 microM) significantly increased adhesion from about 20% (control) to 30%. This effect was prevented by the A1 receptor antagonist dipropyl-8-cyclopentylxanthine (DPCPX, 0.1 microM). It was not diminished by cessation of adenosine infusion 90 s prior to neutrophil injection. At a higher concentration of adenosine (1 microM), adhesion did not seem to be enhanced. However, coinfusion of the A2 receptor antagonist 3,7-dimethyl-1-propargylxanthine (DMPX, 0.1 microM) with 1 microM adenosine unmasked the A1 action, adhesion rising to 39%. Adenosine had a quantitatively identical effect on adhesion of human neutrophils. Total ischaemia of 15 min duration raised adhesion of subsequently applied neutrophils to 35%. This effect was completely blocked by DPCPX, as well as by ischaemic preconditioning (3 x 3 min). Preconditioning raised initial postischaemic coronary effluent adenosine from about 0.8 microM to 1.5 microM.

CONCLUSIONS

The findings suggest a bimodal participation of adenosine in the development of postischaemic dysfunction by an endothelium dependent modulation of neutrophil adhesion. Stimulation occurs via endothelial A1 receptors at submicromolar adenosine levels, whereas cardioprotection by adenosine may in part relate to the use of pharmacologically high concentrations of adenosine or enhanced endogenous production after preconditioning.

Postischemic dysfunction of the heart induced by small numbers of neutrophils via formation of hypochlorous acid

The role of polymorphonuclear neutrophils (PMN) in the injury of the heart following ischemia and reperfusion is still controversial. The aim of this study was to investigate whether small numbers of PMN may cause myocardial dysfunction in an isolated system, how the resulting loss of function can be characterized and whether the formation of hypochlorous acid (HOCl) can be responsible for the PMN-mediated effect. Isolated working guinea pig hearts were subjected to a 90% reduction of coronary flow for 30 min, with or without intracoronary infusion of homologous PMN (approximately 1-2 x 10(5) cells/min, i.e. about 5-10% of normal blood count). This ischemia was followed by a 15 min reflow period in a non-working ("Langendorff") mode before work was resumed. In hearts perfused only with buffer, post-hypoxic heart function recovered to 75-80% of the initial value. Inclusion of unstimulated PMN did not further attenuate cardiac function. However, cardiac output was decreased to 42% of the initial value, provided thrombin (0.3 U/ml) and H2O2 (10(-5) M) were also present, and the retained PMN (about 10% of those infused) were additionally stimulated during reflow by application of FMLP (10(-6) M for 1 min). In these instances, coronary flow at any time of the experiment and release of lactate or purines during ischemia and reflow did not differ significantly between hearts perfused with or without PMN. There was no substantial release of myoglobin in controls and in PMN-treated hearts. Inotropic stimulation of the hearts with noradrenaline or exogenous Ca2+ caused a sustained increase in contractile force. However, the response was significantly reduced in PMN-perfused hearts in comparison to control hearts. The myocardial contents of high-energy phosphates with and without inotropic stimulation proved to be identical irrespective of whether experiments had been performed in the absence or presence of PMN. A similar loss of myocardial function as mediated by PMN could be produced by infusing chemically generated hypochlorous acid (HOCl, 5 x 10(-7) M for 10 min). Strikingly, that portion of the infused HOCl which actually reacted with cardiac tissue was comparable to the amount shown to be generated by stimulating 10(6) PMN retained in the coronary system (about 7 nmoles). Supplementing the perfusate with the scavengers L-methionine (10(-4) M) or uric acid (5 x 10(-4) M) prevented the attenuation of heart function provoked by PMN. The results indicate that small numbers of PMN, sufficiently activated, can depress cardiac function after 30 min of ischemia.(ABSTRACT TRUNCATED AT 400 WORDS)

Histological investigations on the thyroid glands of marine mammals (Phoca vitulina, Phocoena phocoena) and the possible implications of marine pollution

In 1988 and 1989, thousands of harbor seals (Phoca vitulina) died in the North Sea from phocine distemper infection. The morphology of thyroid glands from 40 harbor seals found dead on the North Sea coastlines of Schleswig-Holstein, Federal Republic of Germany, during an epizootic of phocine distemper, was compared with the morphology of thyroid glands from five healthy harbor seals collected in Iceland. Thyroid glands from seven harbor porpoises (Phocoena phocoena) found dead in 1990 on the North Sea coastlines also were evaluated. Colloid depletion and fibrosis were found in the thyroid glands of harbor seals which died during the epizootic, but not in animals from Iceland. Thyroid glands of the porpoises showed similar lesions, but to a lesser degree, than those observed in the North Sea seals.

Glutamine synthetase subunit mixing and regulation in Bacillus subtilis partial diploids

A specialized transducing phage, SP beta c2 dglnA2, of Bacillus subtilis was used to construct partial diploids with various glutamine auxotrophs. The overproduction of manganese-stimulated glutamine synthetase no longer occurred in the diploids. The kinetics of heat inactivation of the enzyme extracted from two diploids suggests that there was subunit mixing.