Role of A2A receptor in the modulation of myocardial reperfusion damage

Adenosine protects myocardium from ischemia and reperfusion damage; however, the mechanism of action is still under discussion. We investigated whether (a) adenosine protects isolated crystalloid-perfused rabbit heart from ischemia/ reperfusion injury; (b) this action is receptor mediated and what receptor subtypes are involved, and (c) this action is dependent on an enhanced nitric oxide production. Our results showed a cardioprotective effect of adenosine (10(-4) M), of nonselective adenosine-receptor agonist 5'-N-ethyl-carboxamidoadenosine (NECA; 5 x 10(-6) M), and of A2A agonists CGS 21680 (10(-8) and 10(-6) M), 2-hexynylNECA (10(-7) M). On the contrary, A1 agonist CCPA (10(-8) and 10(-6) M) does not provide any protection. The effect has been achieved in terms of significant reduction in contracture development during reperfusion [diastolic pressure was 46.8 +/- 7.1 mm Hg (p < 0.01); 46.1 +/- 7.8 mm Hg (p < 0.01); 46.9 +/- 5.5 mm Hg (p < 0.01); and 59.3 +/- 6.7 mm Hg (p < 0.05) with 10(-4) M adenosine, 5 x 10(-6) M NECA, 10(-6) M CGS 21680, and 10(-7) M 2-hexynylNECA, respectively, versus 77.6 +/- 5.0 mm Hg in control]; reduced creatine phosphokinase release (13.5 +/- 1.6, 22.2 +/- 7.9, 14.2 +/- 3.3, and 14.1 +/- 4.5 U/gww in treated hearts vs. 34.6 +/- 7.2 U/gww in controls; p < 0.05); improved energy metabolism [adenosine triphosphate (ATP) content is 9.9 +/- 0.5, 10.4 +/- 0.6, 9.8 +/- 0.5, and 10.5 +/- 0.5 micromol/gdw in treated hearts vs. 7.6 +/- 0.2 micromol/gdw; p < 0.05]. Moreover, our data indirectly show a functional presence of A2A receptors on cardiomyocytes as the protection is A2A mediated and exerted only during reperfusion, although in the absence of blood and coronary flow changes. These activities appear independent of nitric oxide pathways, as adenosine and 2-hexynylNECA effects are not affected by the presence of a nitric oxide-synthase inhibitor (10(-4) M L-NNA).

Changes in oxidative stress and cellular redox potential during myocardial storage for transplantation: experimental studies

BACKGROUND

Cardioplegic solutions assure only a sub-optimal myocardial protection during prolonged storage for transplantation. The ultimate cause of myocardial damage during storage is unknown, but oxygen free radicals might be involved. We evaluated the occurrence of oxidative stress and changes in cellular redox potential after different periods of hypothermic storage.

METHODS

Langendorff-perfused rabbit hearts were subjected to a protocol mimicking each stage of a cardiac transplantation procedure: explantation, storage and reperfusion. Three periods of storage were considered: Group A = 5 hours, Group B = 15 hours, and Group C = 24 hours. Oxidative stress was determined in terms of myocardial content and release of reduced (GSH) and oxidized (GSSG) glutathione, and cellular redox potential as oxidized and reduced pyridine nucleotides ratio (NAD/NADH). Data on mechanical function, cellular integrity and myocardial energetic status were collected.

RESULTS

At the end of reperfusion, despite the different timings of storage, recovery of left ventricular developed pressure (46.1+/-7.0, 54.7+/-6.7, and 45.7+/-7.4% of the baseline pre-ischaemic value), energy charge (0.81+/-0.02, 0.81+/-0.02, and 0.77+/-0.01) and NAD/NADH ratio (8.87+/-1.08, 9.39+/-1.72, and 10.26+/-1.98) were similar in all groups (A, B and C). On the contrary, the rise in left ventricular resting pressure (LVRP) and GSH/GSSG ratio were significantly different between Group C, and Groups A and B (p<0.0001, analyzed by Generalized Estimating Equations model for repeated measures, and p<0.05, respectively).

CONCLUSIONS

The pathophysiology of myocardial damage during hypothermic storage cannot be considered as a normothermic ischaemic injury and parameters other than energetic metabolism, such as thiolic redox state, are more predictive of functional recovery upon reperfusion.

Recognized molecular mechanisms of heart failure: approaches to treatment

Abnormalities of cytosolic calcium handling and myocyte energetics appear to play an important role in mediating contractile dysfunction in heart failure. Systolic and diastolic dysfunction in the failing heart are related to abnormalities of the excitation-contraction mechanism as well as myofilament calcium sensitivity. These abnormalities can be viewed as a compensatory mechanism as the myocytes by down regulating its function and metabolic activity preserve energy consumption and allow better maintenance of basal cellular homeostasis. The end point of myocyte dysfunction, however, is a reduced contraction, which, in turn, might cause a reduced cardiac output and a threatening of arterial pressure. This causes a second level of adaptation, which implies a neuroendocrine response of the whole organism. Consequently, the syndrome of congestive heart failure is characterized not only by impaired ventricular function, but also by an increase in some endogenous substances leading to vasoconstriction and water and salt retention. Although activation of the systems that release these substances is presumed to be compensatory, the sympathetic nervous system and renin-angiotensin-aldosterone system as well as the endothelins may contribute to the pathogenesis of the syndrome. Opposite to the effects of these systems are those evoked by the release of atrial natriuretic peptides. The peptides exert a potent direct vasodilatation and natriuresis. In addition, atrial natriuretic peptides inhibit the release of norepinephrine from nerve terminals and suppress the formation of renin. However, the natriuretic and vasodilator effects of these peptides in patients with congestive heart failure are outweighed by the sodium retention and vasoconstriction caused by sympathetic stimulation and activation of the renin-angiotensin-aldosterone system. The reasons for this are not entirely known. The atrial stretch receptors that are responsible for the release of the atrial peptides become impaired, and it has been suggested that patient with heart failure may adapt to the physiologic effects of atrial natriuretic peptides. The possibility that congestive heart failure is in part a humoral disease is reviewed here and consequently pharmacologic treatment aimed at reducing the effects of the neuroendocrine response as to be advantageous for patients with heart failure.

Effects of chronic noradrenaline on the nitric oxide pathway in human endothelial cells

Altered endothelium-dependent vasodilation has been observed in congestive heart failure (CHF), a disease characterized by a sustained adrenergic activation. The purpose of our study was to test the hypothesis that chronically elevated catecholamines influence the nitric oxide (NO) pathway in the human endothelium. Human umbilical vein endothelial cells (HUVEC) were exposed for 7 days to a concentration of noradrenaline (NA, 1 ng/mL) similar to that found in the blood of patients with CHF. Kinetics of endothelial constitutive NO synthase (ecNOS) and inducible NO synthase (iNOS) activity, measured by [3H]L-arginine to [3H]L-citrulline conversion, and protein expression of ecNOS and iNOS, assessed by Western blot analysis, were unaffected by chronic NA treatment. Furthermore, no changes in subcellular fraction-associated ecNOS were found; this indirectly shows that chronic NA did not cause phosphorylation of the enzyme. Moreover, [3H]L-arginine transport through the plasma membrane was conserved in chronically NA-treated cells. The data demonstrate that prolonged in vitro exposure to pathologic CHF-like NA does not affect the L-arginine: NO pathway in human endothelial cells.

Oxidative stress during myocardial ischaemia and heart failure

Oxidative stress is a condition in which oxidant metabolites exert toxic effects because of their increased production or an altered cellular mechanism of protection. The heart needs oxygen but it is also susceptible to oxidative stress, which occurs during post-ischaemic reperfusion, for example. Ischaemia causes alterations in the defence mechanisms against oxygen free radicals. At the same time, production of oxygen free radicals increases. In man, there is evidence of oxidative stress during surgical reperfusion of the whole heart, or after thrombolysis, and it is related to transient left ventricular dysfunction or stunning. At present, there are few data on oxidative stress in the failing heart. It is not clear whether the defence mechanisms of the myocyte are altered or whether the production of oxygen free radicals is increased, or both. Recent data have shown a close link between oxidative stress and apoptosis. Importantly, tumour necrosis factor causes a rapid rise in intracellular reactive oxygen intermediates and apoptosis. This series of events is not confined to the myocytes, but also occurs at the level of endothelium, where tumour necrosis factor causes expression of inducible nitric oxide synthase, production of the reactive radical nitric oxide, oxidative stress and apoptosis. The immunological response to heart failure may result in endothelial and myocyte dysfunction through oxidative stress-mediated apoptosis. A better understanding of these mechanisms may lead to novel therapeutic strategies.

Heat shock protein changes in hibernation: a similarity with heart failure?

Myocardial hibernation is an adaptive phenomenon occurring during ischaemia. Patients with hibernating myocardium often have a history of an acute ischaemic insult, followed by prolonged hypoperfusion and symptoms of congestive heart failure (CHF), which is a complex syndrome involving several adaptational mechanisms. We tested the hypothesis that these two conditions evoke the myocardial expression of heat shock protein 72 (hsp72) as an adaptive response at the molecular level. Short-term acute hibernation was induced in isolated and perfused rat hearts subjected to 8 min total ischaemia followed by 292 min low-flow ischaemia (coronary flow: 1.0 ml/min), followed by 60 min of reperfusion. Total ischaemia caused quiescience. Subsequent low-flow resulted in a temporal early increase of lactate release, no re-establishment of developed pressure, no increase in diastolic pressure. Reperfusion resulted in 85.7 +/- 7.2% recovery of developed pressure, a small washout of lactate and CPK, no contracture, confirming that viability was maintained despite prolonged hypoperfusion. This sequence of events was linked to an increase in hsp72 content in the right (from 18.1 +/- 3.8% to 34.6 +/- 2.3%. P < 0.01) and left (from 19.7 +/- 2.6% to 37.6 +/- 3.3%, P < 0.01) ventricles. Three-hundred min of low-flow perfusion of the rat heart in absence of the short period of total ischaemia caused irreversible damage and failed to induced hsp72. CHF was induced in rats by intraperitoneal administration of monocrotaline. As a result, right ventricular weight increased from 171.3 +/- 7.2 to 412.3 +/- 18.7 mg. P < 0.001, peripheral and pleural effusion were evident and measurable, plasma arterial natriuretic peptide increased from 15.2 +/- 1.9 to 123.5 +/- 5.4 pg/ml, P < 0.001, confirming the occurrence of the syndrome of CHF. This was concomitant with significant expression of hsp72, more evident in the right (from 5.0 +/- 0.9% to 39.4 +/- 1.6%, P < 0.001) than in the left (from 3.5 +/- 0.6% to 13.0 +/- 1.2%, P < 0.001) ventricle. These data suggest that an adaptational process occurs at myocardial level during either hibernation or CHF. The expression of hsp72 could be viewed as a stereotyped adaptational reaction of the cardiac cell to stress conditions.

Is stunning an important component of preconditioning?

We tested the hypothesis that stunning following a brief period of ischaemia is a component of cardioprotection afforded by preconditioning in an in vitro model of global normothermic ischaemia. Isolated Langendorff-perfused rat hearts, after 120-150 min of aerobic perfusion, were divided into four groups. Groups 1 and 2 constituted the aerobic and ischaemic controls. The other hearts were preconditioned by two 2-min ischaemia/reperfusion cycles. Two ischaemic preconditioning protocols were used, the only difference being prolongation of the reperfusion cycle from 5 (group 3) to 20 min (group 4) before the onset of severe ischaemic insult. Mechanical function, energetic metabolism and the rate of enzyme release were followed throughout. In group 3, myocardial function remained significantly downregulated before the onset of severe ischaemia. This resulted in cardiac protection as evidenced by enhanced recovery of systolic pressure (37.7 +/- 3.6 v 61.9 +/- 5.7 mmHg for groups 2 and 3, respectively; P < 0.02), reduced rise in diastolic pressure (55.8 +/- 5.9 v 34.3 +/- 5.2 mmHg; P < 0.02), reduced creatine kinase (CK) release (957.3 +/- 175.7 v 541.5 +/- 85.9 mU/min/gww; P < 0.05) and higher contents of high-energy phosphate at the end of ischaemia [3.6 +/- 0.3 v 25.3 +/- 2.9 mumol/gdw for creatine phosphate (CP), P < 0.001] as well as after reperfusion (16.8 +/- 2.4 v 31.4 +/- 1.8 for CP, P < 0.01, and 3.9 +/- 0.5 v 6.2 +/- 0.8 mumol/gdw for ATP, P < 0.05). When severe ischaemia was started only after complete recovery of mechanical function (group 4), no protection was observed. Our data suggest that a decrease in mechanical function or stunning occurring after the short period of ischaemia causes ATP sparing and constitutes an additional mechanism of preconditioning cardioprotection in vitro.

Metabolic adaptation during a sequence of no-flow and low-flow ischemia. A possible trigger for hibernation

BACKGROUND

Myocardial hibernation is an adaptive phenomenon occurring in patients with a history of acute ischemia followed by prolonged hypoperfusion.

METHODS AND RESULTS

We investigated, in isolated rabbit heart, whether a brief episode of global ischemia followed by hypoperfusion maintains viability. Four groups were studied; group 1,300 minutes of aerobia; group 2,240 minutes of total ischemia and 60 minutes of reperfusion; group 3, 10 minutes of total ischemia, 230 minutes of hypoperfusion (90% coronary flow reduction), and 60 minutes of reperfusion; and group 4, 240 minutes of hypoperfusion followed by reperfusion. In group 3, viability was maintained. Ten minutes of ischemia caused quiescence, a fall in interstitial pH (from 7.2 +/- 0.01 to 6.1 +/- 0.8), creatine phosphate (CP), and ATP (from 54.5 +/- 5.0 and 25.0 +/- 1.9 to 5.0 +/- 1.1 and 15.3 +/- 2.5 mumol/g dry wt, P < .01). Subsequent hypoperfusion failed to restore contraction and pH but improved CP (from 5.0 +/- 1.1 to 20.1 +/- 3.4, P < .01). Reperfusion restored pH, developed pressure (to 92.3%), and NAD/NADH and caused a washout of lactate and creatine phosphokinase with no alterations of mitochondrial function or oxidative stress. In group 4, hypoperfusion resulted in progressive damage. pH fell to 6.2 +/- 0.7, diastolic pressure increased to 34 +/- 5.6 mm Hg, CP and ATP became depressed, and oxidative stress occurred. Reperfusion partially restored cardiac metabolism and function (47%).

CONCLUSIONS

A brief episode of total ischemia without intermittent reperfusion maintains viability despite prolonged hypoperfusion. This could be mediated by metabolic adaptation, preconditioning, or both.

Effects of felodipine on the ischemic heart: insight into the mechanism of cytoprotection

To assess whether the administration of felodipine protects the myocardium in a dose-dependent manner against ischemia and reperfusion, isolated rabbit hearts were infused with three different concentrations of felodipine: 10(-10), 10(-9), and 10(-8) M. Diastolic and developed pressures were monitored; coronary effluent was collected and assayed for CPK activity and for noradrenaline concentration; mitochondria were harvested and assayed for respiratory activity; and ATP production and calcium content and tissue concentration of ATP, creatine phosphate (CP), and calcium were determined. The occurrence of oxidative stress during ischemia and reperfusion was also monitored in terms of tissue content and release of reduced (GSH) and oxidized (GSSG) glutathione. Treatment with felodipine at 10(-10) and 10(-9) M had no effect on the hearts when perfused under aerobic conditions, whilst the higher dose reduced developed pressure from 57.7 +/- 2.6 to 30.0 +/- 2.6 mmHg (p < 0.01). On reperfusion treated hearts recovered better than the untreated hearts with respect to left ventricular performance, replenishment of ATP and CP stores, and mitochondrial function. Recovery of developed pressure was 100% at 10(-8) M, 55% at 10(-9) M, and 46% at 10(-10) M. The reperfusion-induced tissue and mitochondrial calcium overload, release of CPK and noradrenaline, and oxidative stress were also significantly reduced. The effects of felodipine were dose dependent. Felodipine inhibited the initial rate of ATP-driven calcium uptake but failed to affect the initial rate of mitochondrial calcium transport. It is concluded that felodipine infusion provides dose-dependent protection of the heart against ischemia and reperfusion. Because this protection also occurred at 10(-9) M and 10(-10) M in the absence of a negative inotropic effect during normoxia and of a coronary dilatory effect during ischaemia, it cannot be attributed to an energy-sparing effect or to improvement in oxygen delivery. From our data we can envisage two other major mechanisms-(1) membrane protection and (2) reduction in oxygen toxicity. The ATP-sparing effect occurring at 10(-8) M is likely to be responsible for the further protection.

Relation between energy metabolism, glycolysis, noradrenaline release and duration of ischemia

We studied the effect of 12-36 min of global ischemia followed by 36 min of reperfusion in Langendorff perfused rabbit hearts (n = 26). Metabolism was determined in terms of peak and total release of purines (adenosine, inosine, hypoxanthine), lactate and noradrenaline during reperfusion; and myocardial content of nucleotides (ATP, ADP, AMP), glycogen and noradrenaline at the end of reperfusion. An inverse relationship (r = -0.79) existed between duration of ischemia and developed pressure post-ischemia. Early during reperfusion, after 12 min of ischemia, the purine concentration (peak release) increased 100x (p < 0.01), that of lactate and noradrenaline 10x (p < 0.05). Total purine release rose with progression of the ischemic period (30x after 36 min of ischemia; p < 0.01), concomitant with a reduction in nucleotide content. Lactate release was independent from the duration of ischemia, although glycogen had declined by 30% (p < 0.01) after 36 min of ischemia. The acid insoluble glycogen fraction, which presumably contains proglycogen, increased substantially during short-term ischemia. Peak noradrenaline increased 100x, and 200x, (p < 0.05) after 24 and 36 min of ischemia, respectively. Total noradrenaline release due to various periods of ischemia mirrored its peak release. Function recovery was inversely related to total purine and noradrenaline efflux (both r = -0.81); it correlated with tissue nucleotide content (r = 0.84). In conclusion, larger amounts of noradrenaline are released only after a substantial drop in myocardial ATP. During severe ischemia ATP consumption more than limited ATP production by anaerobic glycolysis, is a key factor affecting recovery on subsequent reperfusion. In contrast to lactate efflux, purine and noradrenaline release are useful markers of ischemic and reperfusion damage.

Dichotomy in the post-ischemic metabolic and functional recovery profiles of isolated blood-versus buffer-perfused heart

There is evidence that buffer- and blood-perfused hearts differ in their postischemic functional recoveries. The present study was designed to: (i) compare ischemia-induced contracture and post-ischemic functional recovery, and (ii) investigate whether the recovery profiles were related to either the release of purines and norepinephrine or high-energy phosphate content. Rat hearts (n = 8/group) were perfused at 37 degrees C with buffer (60 mmHg) or blood (60 mmHg from a support rat), made globally ischemic (15 min) and reperfused (15 min). The onset and severity of ischemic contracture were identical in both models [left ventricular end-diastolic pressure (LVEDP) at the end of 15 min ischemia was 30 +/- 5 and 27 +/- 4 mmHg respectively; P = N.S.]. However, the rate and extent of post-ischemic left ventricular developed pressure (LVDP) differed considerably. Blood-perfused hearts exhibited an initial rapid and complete recovery of LVDP followed by a steady decline to approximately 60% of pre-ischemic values. Buffer-perfused hearts recovered to only 80% after 5 min reperfusion and remained at this level for the duration of reperfusion LVEDP was higher in buffer-perfused than in blood-perfused hearts during the first 5 min of reperfusion; thereafter, LVEDP fell in buffer-perfused hearts to a level than was not significantly different from the observed in blood-perfused hearts. In buffer-perfused hearts, coronary flow recovered to 90% within 5 min and then remained constant; in blood-perfused hearts flow recovered to 100% by 1 min and continued to rise to a maximum by 7 min (201 +/- 15%). This increase appeared to mirror the secondary decline in LVDP. During the first 4 min of reperfusion, in both preparations, venous norepinephrine increased to six- to nine-fold of pre-ischemic values and then fell rapidly to near control levels by 6-9 min. Total purine release was high in early reperfusion in both groups. At the end of 15 min reperfusion, the tissue adenylate pool was similar in both groups. This study demonstrates that the nature of the perfusate used for an isolated rat heart preparation: (i) does not appear to influence the severity of ischemic injury as assessed by ischemic contracture, but (ii) does influence the qualitative and quantitative characteristics of the temporal profile that describes the recovery of systolic and diastolic function during the first 15 min of reperfusion: and (iii) it has no effect upon the changes seen in a number of metabolic indices that are often used for the assessment of injury and protection.

In vitro administration of ergothioneine failed to protect isolated ischaemic and reperfused rabbit heart

Ergothioneine, a natural thiol-containing molecule, has recently been proposed to protect the heart against damage caused by ischaemia and reperfusion. We investigated the possibility that ergothioneine can have a role in maintaining the myocardial thiol/disulfide balance and consequently also a protective effect against ischaemic and reperfusion injury. We used isolated Langendorff-perfused rabbit hearts subjected to 45 min global and total ischaemia followed by 30 min reperfusion at baseline coronary flow (22 ml/min). Ergothioneine was delivered at 10(-5) M and 10(-4) M 60 min before ischaemia and during reperfusion. Myocardial damage was determined in terms of mechanical function, creatine kinase (CK) and lactate release, energy phosphate stores and the occurrence of oxidative stress. In our experimental conditions the treatment was unable to prevent myocardial damage. Ergothioneine, independently from the dosage used, failed to: (i) increase recovery of developed pressure upon reperfusion (14.4 +/- 2.3 mmHg in control hearts vs. 10.3 +/- 2.9 and 12.5 +/- 2.3 mmHg in 10(-5) M and 10(-4) M ergothioneine treated hearts, respectively); (ii) decrease the rise in diastolic pressure (44.3 +/- 4.4 mmHg in control hearts vs. 49.8 +/- 5.8 and 48.0 +/- 7.7 mmHg in treated hearts); (iii) decrease the release of CK and lactate; (iv) increase the levels of adenosine triphosphate (ATP) and creatine phosphate (CP) in tissue upon reperfusion; (v) maintain ratio between oxidized and reduced forms of adenine nucleotide coenzyme, as index of aerobic metabolism; (vi) prevent the decline of reduced glutathione (GSH), or the accumulation of oxidized glutathione (GSSG) as an index of oxidative stress.

Intermittent v continuous ischemia decelerates adenylate breakdown and prevents norepinephrine release in reperfused rabbit heart

Myocardium tolerates intermittent ischemia followed by short reperfusions better than continuous ischemia of the same duration. We attempted to delineate the differential mechanism(s) involved in intermittent v continuous ischemia. Isolated, paced rabbit hearts were perfused at 22 ml/min. Coronary flow was stopped intermittently 12 x for 2 or 4 min, with 3-min reperfusions (total reperfusion period: 36 min). In two other groups, flow was stopped continuously for 24 or 36 min followed by a flat 36-min reperfusion. Following the first intermittent 2-min ischemia, adenosine efflux increased ninefold; in all subsequent ischemia/reperfusion cycles, adenosine and total purine releases were substantially less despite identical heart rates, coronary flows and ischemic periods. The rate-pressure product prior to the intermittent ischemias exhibited exponential correlations with total purine efflux during the 3 min of reperfusion. When intermittent ischemia was extended to 4 min, the initial attenuation of ATP breakdown during the prior 2-min occlusions was overcome, but during subsequent 4-min ischemia/reperfusion cycles, ATP breakdown was again attenuated relative to the first 4-min ischemia. After the prolonged continuous ischemias, purine efflux was up to 6 x higher than with intermittent ischemias of the same total time of zero flow. Lactate release and hence cellular H+ export after intermittent ischemias remained consistently elevated, but following the continuous ischemia of 36 min, release of lactate, and thus H+, was subsequentially decreased. Glycogen mobilization occurred regardless of the ischemia's nature, but it was markedly enhanced during continuous ischemias, where no fall in proglycogen levels occurred. Similarly, myocardial norepinephrine release increased substantially only during the prolonged continuous ischemias. Thus short intermittent ischemia attenuates cardiac adenylate degradation and glycogen mobilization; such ischemic insult also provides for better lactate and H+ washouts immediately upon reperfusion. Another beneficial effect of intermittent ischemia was the near-complete absence of free interstitial norepinephrine, which exacerbates myocardial ischemic insults. In addition, the exponential correlations between preischemic rate-pressure product and postischemic purine release suggest that preischemic energy demand may determine ATP breakdown in ischemic rabbit myocardium.

Extraction and assay of creatine phosphate, purine, and pyridine nucleotides in cardiac tissue by reversed-phase high-performance liquid chromatography

The levels of creatine phosphate, purine, and pyridine nucleotides in tissues provide important information on energetic and oxidative cellular states. Nevertheless, technical, theoretical, and methodological difficulties in extraction and quantification procedures have so far limited our understanding of the exact role that these substances play in metabolic processes which take place in cells. The objective of our study was to find an easy and rapid method for extracting, separating, and quantifying creatine phosphate, purine, and pyridine nucleotides in solid tissues. We adapted the classic acid-extraction procedure with HClO4 for purine and oxidized pyridine nucleotides and then developed a new alkaline extraction with phenol in a phosphate buffer solution (pH 7.8) for reduced pyridine nucleotides. Biopsies of myocardial tissue were frozen and ground at -180 degrees C using the appropriate extraction procedure. The separation and quantification of the metabolites were performed using a reversed-phase 3-microns Supelchem C18 column, with the addition of tetrabutylammonium as an ion-pair agent to the buffer solution, by ultraviolet detection. The recovery of the external and internal standards always exceeded 90%. The autooxidation or interconversion processes were almost insignificant for each reduced form. This technique allowed us to avoid complex enzymatic procedures and difficulties in the selective assay of pyridine nucleotides with chemiluminescence and surface spectroscopy.

Effect of angiotensin converting enzyme inhibition with quinaprilat on the ischaemic and reperfused myocardium

We assessed whether the local inhibition of myocardial converting enzyme by quinaprilat and captopril reduces the functional and metabolic damage caused by ischaemia and reperfusion. Quinaprilat and captopril were either subcutaneously injected (0.3 mg/kg once daily for 5-6 days) in the rabbit before isolation of the heart or delivered to the isolated hearts in the perfusate (10(-6) M) 60 min before ischaemia. Cardiac protection was evaluated in terms of left ventricular pressure recovery during reperfusion, creatine phosphokinase (CPK) release, mitochondrial function, ATP and CP tissue contents, calcium homeostasis and the occurrence of oxidative stress, established by measuring content and release of reduced and oxidized glutathione. Both drugs exerted cardioprotection. Optimal myocardial preservation is achieved when quinaprilat is prophylactically administered to the rabbit. Recovery of developed pressure on reperfusion improved from 11.3 +/- 2.7 (S.E.) to 25.4 +/- 5.4 mmHg, P < 0.01 and the release of CPK was reduced from 665.8 +/- 101.4 to 231.8 +/- 81.4 mU/min/g wet wt, P < 0.01. Peak of noradrenaline release was also attenuated, from 5.253 ng/min/g wet wt to 1.764 ng/min/g wet wt. The accumulation of tissue and mitochondrial calcium was reduced from 52.3 +/- 7.5 and 44.1 +/- 5.6 to 20.5 +/- 3.2 and 27.3 +/- 4.6 nmol/kg dry wt, respectively, P < 0.01. This resulted in significant (P < 0.01) improvement of left ventricular diastolic dysfunction during ischaemia and reperfusion and in a preservation of all indices of mitochondrial function, allowing a higher recovery of ATP and CP after reperfusion (from 4.1 +/- 0.5 and 5.2 +/- 0.5 to 11.1 +/- 1.1 and 24.8 +/- 1.0 mumol/g dry wt, respectively, P < 0.01). Reperfusion-induced myocardial accumulation and release of oxidized glutathione were reduced from 0.301 +/- 0.056 and 0.318 +/- 0.083 to 0.138 +/- 0.025 nmol/mg protein and 0.076 +/- 0.012 nmol/min/g wet wt, respectively, P < 0.01. Similar results were obtained when quinaprilat was administered to the isolated heart. These data suggest that the cardioprotective effect of quinaprilat is independent from haemodynamic changes or direct reduction of toxicity due to oxygen free-radicals but it is likely to be related to a reduction in the release of noradrenaline, maintenance of high energy phosphates and membrane integrity.

Cardioprotection by nisoldipine: role of timing of administration

Nisoldipine was administered at 10(-9) M, a dose lacking negative inotropism, to isolated and perfused rabbit hearts submitted to 60 min ischaemia (1 ml.min-1) followed by 30 min reperfusion. The drug was delivered either 30 min before ischaemia, at the onset and after 30 min of ischaemia and during reperfusion only. Cardiac protection was evaluated in terms of recovery of left ventricular pressure during reperfusion, release of creatine phosphokinase (CPK), mitochondrial function, tissue content of adenosine triphosphate (ATP) and creatine phosphate (CP), calcium homeostasis and the occurrence of oxidative stress, established measuring content and release of reduced and oxidized glutathione. The cytoprotective action of nisoldipine occurs in the absence of negative inotropism and is closely related to the time of administration. Optimal myocardial preservation is achieved when nisoldipine is given before or at the onset of ischaemia. Prophylactic administration of nisoldipine improved the recovery of the developed pressure from 15.9 +/- 1.0 (SE) mmHg to 47.8 +/- 1.9 mmHg, P < 0.01 and reduced the release of CPK from 830 +/- 29 to 229 +/- 27 mU.min-1 g-1 wet wt, P < 0.01. The accumulation of tissue and mitochondrial calcium was reduced from 58 +/- 11 and 49 +/- 9 to 14 +/- 6 and 10 +/- 4 mmol.kg-1 dry wt respectively, P < 0.01. This resulted in a significant (P < 0.01) preservation of all indices of mitochondrial function, allowing a higher recovery of ATP and CP after reperfusion (from 4.1 +/- 0.7 and 10.0 +/- 0.6 to 16.1 +/- 1.0 and 29.9 +/- 0.2 mumol.g-1 dry wt respectively, P < 0.001). Reperfusion-induced myocardial accumulation and release of oxidized glutathione were reduced from 0.493 +/- 0.07 nmol.mg-1 protein and 0.768 +/- 0.063 nmol.min-1 g-1 wet wt to 0.225 +/- 0.07 and 0.157 +/- 0.038 respectively, P < 0.01. Similar data were obtained when nisoldipine was given at the time of ischaemia, while administration 30 min after the onset of ischaemia showed only a trend towards protection. Nisoldipine lost its protective effect when given on reperfusion. A multifactorial analysis of the data suggest that the cardioprotective effect of nisoldipine is related to the maintenance of membrane integrity, possibly since nisoldipine is highly lipophilic.

Effect of lacidipine on ischaemic and reperfused isolated rabbit hearts

Lacidipine is a new developed dihydropyridine calcium-antagonist, showing a slow onset and long lasting-selective activity. To assess whether the administration of lacidipine protects the myocardium in a dose-dependent manner against ischaemia and reperfusion, isolated rabbit heart were infused with three different concentrations of lacidipine: 10(-10); 10(-9); 10(-8) M. Diastolic and developed pressures were monitored; coronary effluent was collected and assayed for CPK activity and for noradrenaline concentration; mitochondria were harvested and assayed for respiratory activity, ATP production and calcium content and tissue concentration of ATP, creatine phosphate (CP) and calcium were determined. Occurrence of oxidative stress during ischaemia and reperfusion was also monitored in terms of tissue content and release of reduced (GSH) and oxidized (GSSG) glutathione. Treatment with lacidipine at 10(-10) and 10(-9) M had no effects on the hearts when perfused under aerobic condition, whilst the higher dose reduced developed pressure of 36%. The ischaemic-induced deterioration of mitochondrial function was attenuated. On reperfusion treated hearts recovered better than the untreated hearts with respect to left ventricular performance, replenishment of ATP and CP stores and mitochondrial function. The reperfusion-induced tissue and mitochondrial calcium overload, release of CPK and of noradrenaline and oxidative stress were also significantly reduced. The effects of lacidipine were dose-dependent. The lower concentration (10(-10) M) failed to modify ischaemic and reperfusion damage. The dose of 10(-9) M was cardioprotective, but the best effect was found at 10(-8) M. It is concluded that lacidipine infusion provides a dose dependent protection of the heart against ischaemia and reperfusion. Because this protection occurred also at 10(-9) M, in the absence of negative inotropic effect during normoxia and of a coronary dilatory effect during ischaemia, it cannot be attributed to an energy sparing effect or to improvement of oxygen delivery. From our data we can envisage two other major mechanism: -1) membrane protection -2) reduction of oxygen toxicity. The ATP sparing effect occurring at 10(-8) M is likely to be responsable for the further protection.

PEG-SOD improves postischemic functional recovery and antioxidant status in blood-perfused rabbit hearts

The isolated blood-perfused rabbit heart, subjected to 60 min of cardioplegic arrest and 60 min of reperfusion, was used to assess the effects of polyethylene glycol-conjugated superoxide dismutase (PEG-SOD) on postischemic recovery of left ventricular developed pressure (LVDP), the tissue activity of SOD, and tissue redox state. The five groups studied were the following: PEG-SOD-free control (group A), PEG-SOD as a pretreatment and as an additive during cardioplegia and reperfusion (group B), PEG-SOD as a pretreatment and a cardioplegic additive (group C), PEG-SOD in cardioplegia alone (group D), and PEG-SOD in reperfusion alone (group E). The results show that pretreatment with PEG-SOD improves postischemic recovery of LVDP (72 +/- 2% and 66 +/- 7 vs. 47 +/- 4% in groups B, C, and A, respectively). This protection was associated with an improved tissue redox state. Thus the ischemia-induced rise in oxidized glutathione was reduced from 313 +/- 26% (group A) to 162 +/- 15 and 138 +/- 14% (groups B and C, respectively), and the fall in reduced glutathione was attenuated from 51 +/- 5% to 35 +/- 6 and 13 +/- 5%, respectively. Tissue Mn-SOD activity was also conserved from 36 +/- 4% (group A) to 71 +/- 6 and 94 +/- 4% (groups B and C, respectively). No significant effect was seen when PEG-SOD was applied in cardioplegia or during reperfusion alone.

PEG-SOD and myocardial antioxidant status during ischaemia and reperfusion: dose-response studies in the isolated blood perfused rabbit heart

We have previously shown that the polyethylene glycol conjugated superoxide dismutase (SOD), which has a plasma half-life of more than 24 h, protects the blood perfused rabbit heart against injury during ischaemia and reperfusion. However, the profile for the dose-dependency of protection was bell-shaped with loss of efficacy below 6000 and above 30,000 U/kg. In the present study, isolated rabbit hearts, perfused with blood from support rabbits, were subjected to a 2 min infusion with St Thomas' Hospital cardioplegic solution followed by 60 min of global ischaemia (37 degrees C) and 60 min of reperfusion. PEG-SOD was administered 1 h or 12-24 h before ischaemia. We assessed the effect of PEG-SOD on ischaemia- and reperfusion-induced changes in: (i) the tissue content of reduced glutathione (GSH), oxidized glutathione (GSSG) and malondialdehyde (MDA) and (ii) the activity of CuZn-SOD, Mn-SOD and glutathione peroxidase and reductase (GPD and GRD). Ischaemia and reperfusion reduced tissue GSH content by 70% and increased GSSG content by 400% (from their fresh aerobic values of 13.1.9 and 0.09 +/- 0.01 nmol/mg protein, respectively). PEG-SOD, given intravenously at various doses to donor and support rabbits 1 h or 12-24 h before ischaemia, protected against these changes with a bell-shaped dose-response relationship. Thus, with 0, 3000, 6000, 12,000, 30,000 and 60,000 U/kg, GSH content was 4.1 +/- 0.4, 4.8 +/- 0.4, 8.5 +/- 0.5, 12.3 +/- 1.6, 12.3 +/- 1.6 and 5.0 +/- 0.5 nmol/mg protein in the 1 h pretreatment group and 4.1 +/- 0.4, 4.2 +/- 0.5, 10.4 +/- 1.5, 11.2 +/- 1.1, 11.4 +/- 0.7 and 4.7 +/- 0.6 nmol/mg protein in the 12-24 h pretreatment group (means +/- S.E.M.). For GSSG the corresponding values were 0.36 +/- 0.04, 0.34 +/- 0.03, 0.12 +/- 0.01, 0.12 +/- 0.01, 0.11 +/- 0.01 and 0.41 +/- 0.03 nmol/mg protein for the 1 h group and 0.36 +/- 0.04, 0.35 +/- 0.02, 0.15 +/- 0.01, 0.12 +/- 0.01, 0.11 +/- 0.01 and 0.34 +/- 0.02 nmol/mg protein for the 12-24 h group. Ischaemia and reperfusion had no effect on tissue MDA content or CuZn-SOD, GDP and GRD activity, and in general, PEG-SOD also lacked significant effect on any of these variables at any dose studied. However, Mn-SOD activity was severely reduced by ischaemia and reperfusion (from 42 +/- 7 U/mg protein in fresh aerobic controls to 6 +/- 1 U/mg protein at the end of reperfusion).(ABSTRACT TRUNCATED AT 400 WORDS)