Is N-methylacetazolamide a possible new therapy against ischemia-reperfusion injury?

The increase of intracellular Ca2+ concentration, produced principally by its influx through the L-type Ca2+ channels, is one of the major contributors to the ischemia-reperfusion injury. The inhibition of those channels in different experimental models was effective to ameliorate the post-ischemic damage. However, at a clinical level, the results were contradictory. Recent results of our group obtained in an ¨ex vivo¨ heart model demonstrated that a chemical derived from acetazolamide, the N-methylacetazolamide (NMA) protected the heart against ischemia-reperfusion injury, diminishing the infarct size and improving the post-ischemic recovery of myocardial function and mitochondrial dynamic. A significant inhibitory action on L-type Ca2+ channels was also detected after NMA treatment, suggesting this action as responsible for the beneficial effects on myocardium exerted by this compound. Although these results were promising, the effectiveness of NMA in the treatment of ischemic heart disease in humans as well as the advantages or disadvantages in comparison to the classic calcium antagonists needs to be investigated.

Myocardial and mitochondrial effects of the anhydrase carbonic inhibitor ethoxzolamide in ischemia-reperfusion

We have previously demonstrated that inhibition of extracellularly oriented carbonic anhydrase (CA) isoforms protects the myocardium against ischemia-reperfusion injury. In this study, our aim was to assess the possible further contribution of CA intracellular isoforms examining the actions of the highly diffusible cell membrane permeant inhibitor of CA, ethoxzolamide (ETZ). Isolated rat hearts, after 20 min of stabilization, were assigned to the following groups: (1) Nonischemic control: 90 min of perfusion; (2) Ischemic control: 30 min of global ischemia and 60 min of reperfusion (R); and (3) ETZ: ETZ at a concentration of 100 μM was administered for 10 min before the onset of ischemia and then during the first 10 min of reperfusion. In additional groups, ETZ was administered in the presence of SB202190 (SB, a p38MAPK inhibitor) or chelerythrine (Chel, a protein kinase C [PKC] inhibitor). Infarct size, myocardial function, and the expression of phosphorylated forms of p38MAPK, PKCε, HSP27, and Drp1, and calcineurin Aβ content were assessed. In isolated mitochondria, the Ca2+ response, Ca2+ retention capacity, and membrane potential were measured. ETZ decreased infarct size by 60%, improved postischemic recovery of myocardial contractile and diastolic relaxation increased P-p38MAPK, P-PKCε, P-HSP27, and P-Drp1 expression, decreased calcineurin content, and normalized calcium and membrane potential parameters measured in isolated mitochondria. These effects were significantly attenuated when ETZ was administered in the presence of SB or Chel. These data show that ETZ protects the myocardium and mitochondria against ischemia-reperfusion injury through p38MAPK- and PKCε-dependent pathways and reinforces the role of CA as a possible target in the management of acute cardiac ischemic diseases.

Isoespintanol, a monoterpene isolated from oxandra cf xylopioides, ameliorates the myocardial ischemia-reperfusion injury by AKT/PKCε/eNOS-dependent pathways

PURPOSE

To determine the actions of isoespintanol (Isoesp) on post-ischemic myocardial and mitochondrial alterations.

METHODS

Hearts removed from Wistar rats were perfused by 20 min. After this period, the coronary flow was interrupted by half an hour and re-established during 1 h. In the treated group, Isoesp was administered at the beginning of reperfusion. To assess the participation of ε isoform of protein kinase C (PKCε), protein kinase B (PKB/Akt), and nitric oxide synthase (NOS), hearts were treated with Isoesp plus the respective inhibitors (chelerythrine, wortmannin, and N-nitro-L-arginine methyl ester). Cell death was determined by triphenyl tetrazolium chloride staining technique. Post-ischemic recovery of contractility, oxidative stress, and content of phosphorylated forms of PKCε, Akt, and eNOS were also examined. Mitochondrial state was assessed through the measurement of calcium-mediated response, calcium retention capacity, and mitochondrial potential.

RESULTS

Isoesp limited cell death, decreased post-ischemic dysfunction and oxidative stress, improved mitochondrial state, and increased the expression of PKCε, Akt, and eNOS phosphorylated. All these beneficial effects achieved by Isoesp were annulled by the inhibitors.

CONCLUSION

These findings suggest that activation of Akt/eNOS and PKCε signaling pathways are involved in the development of Isoesp-induced cardiac and mitochondria tolerance to ischemia-reperfusion.

Calcineurin/P38MAPK/HSP27-dependent pathways are involved in the attenuation of postischemic mitochondrial injury afforded by sodium bicarbonate co-transporter (NBCe1) inhibition

The electrogenic sodium bicarbonate co-transporter isoform 1 (NBCe1) plays an important role in ischemia-reperfusion injury. The cardioprotective action of an antibody directed to the extracellular loop 3 (a-L3) of NBCe1 was previously demonstrated by us. However, the role of a-L3 on mitochondrial post-ischemic alterations has not yet been determined. In this study, we aimed to elucidate the effects of a-L3 on post-ischemic mitochondrial state and dynamics analysing the involved mechanisms. Isolated rat hearts were assigned to the following groups: 1) Non-ischemic control (NIC): 110 min of perfusion; 2) Ischemic control (IC): 30 min of global ischemia and 60 min of reperfusion (R); 3) a-L3: a-L3 was administered during the initial 10 min of R; 4) SB + a-L3: SB202190 (p38MAPK inhibitor) plus a-L3. Infarct size (IS) was measured by TTC staining. Developed pressure (LVDP), maximal velocities of rise and decay of LVP (+dP/dt max, -dP/dt max) and end-diastolic pressure (LVEDP) of the left ventricle were used to assess systolic and diastolic function. Mitochondrial Ca²⁺ response (CaR), Ca²⁺ retention capacity (CRC), membrane potential (ΔΨm) and MnSOD levels were measured. The expression of P-p38MAPK, calcineurin, P-HSP27, P-Drp1, Drp1, and OPA1 were determined. a-L3 decreased IS, improved post-ischemic recovery of myocardial function, increased P-p38MAPK, P-HSP27, P-Drp1, cytosolic Drp1, and OPA1 expression and decreased calcineurin. These effects were abolished by p38MAPK inhibition with SB. These data show that NBCe1 inhibition by a-L3 limits the cell death, improves myocardial post-ischemic contractility and mitochondrial state and dynamic through calcium decrease/calcineurin inhibition-mediated p38MAPK activation and p38MAPK/HSP27-dependent pathways. Thus, we demonstrated that a-L3 is a potential therapeutic strategy in post-ischemic alterations.

Cardioprotection of benzolamide in a regional ischemia model: Role of eNOS/NO

BACKGROUND

Recent studies from our laboratory show the cardioprotective action of benzolamide (BZ, carbonic anhydrase inhibitor) against ischemia-reperfusion injury. However, the mechanisms involved have not been fully elucidated.

OBJECTIVE

To examine the participation of the endothelial nitric oxide synthase (eNOS)/nitric oxide (NO) in the effects of BZ in a model of regional ischemia.

METHODS

Isolated rat hearts perfused by Langendorff technique were submitted to 40 min of coronary artery occlusion followed by 60 min of reperfusion (IC). Other hearts received BZ during the first 10 min of reperfusion in absence or presence of L-NAME, NOS inhibitor. The infarct size (IS) and the post-ischemic recovery of myocardial function were measured. Oxidative/nitrosative damage were assessed by reduced glutathione (GSH) content, thiobarbituric acid reactive substances (TBARS) and 3-nitrotyrosine levels. The expression of phosphorylated forms of Akt, p38MAPK and eNOS, and the concentration of inducible nitric oxide synthase (iNOS) were also determined.

RESULTS

BZ significantly decreased IS (6.2 ± 0.5% vs. 34 ± 4%), improved post-ischemic contractility, preserved GSH levels and diminished TBARS and 3-nitrotyrosine. In IC hearts, P-Akt, P-p38MAPK and P-eNOS decreased and iNOS increased. After BZ addition the levels of P-kinases and P-eNOS increased and iNOS decreased. Except for P-Akt, P-p38MAPK and iNOS, the effects of BZ were abolished by L-NAME.

CONCLUSIONS

Our data demonstrate that the treatment with BZ at the onset of reperfusion was effective to reduce cell death, contractile dysfunction and oxidative/nitrosative damage produced by coronary artery occlusion. These BZ-mediated beneficial actions appear mediated by eNOS/NO-dependent pathways.

Cardioprotection and natural polyphenols: an update of clinical and experimental studies

Mechanisms involved in ischemia–reperfusion injury.

Survival kinase-dependent pathways contribute to gender difference in the response to myocardial ischemia-reperfusion and ischemic post-conditioning

The response to ischemia/reperfusion and the effects of ischemic post-conditioning (IPC) are sex-dependent, but the mechanisms have not been clarified. Male (M) and female (F) rat hearts isolated and perfused using the Langendorff technique were subject to 30 min of global ischemia (GI) and 60 min reperfusion (R). In IPC hearts, three cycles of 30-sec GI/30-sec R were applied at the beginning of R. Infarct size and myocardial function were assessed. Superoxide production, antioxidant systems, and expressions of phosphorylated forms of serine/threonine kinase (Akt), glycogen synthase kinase 3β (GSK-3β), protein kinase C ε (PKCε), endothelial nitric oxide synthase (eNOS), and apoptosis were measured. In the basal state, superoxide production and apoptosis were lower, and antioxidant systems and phospho-kinase expressions were higher in F rather than in M hearts. After ischemia-reperfusion, infarct size was less in F hearts, and post-ischemic recovery of myocardial function was higher in F rather than in M hearts. Superoxide production, phospho-kinase activity, phospho-eNOS, and apoptosis increased in both sexes while antioxidants decreased in both sexes. After IPC, infarct size, superoxide production, and apoptosis decreased and phospho-eNOS increased in F and M hearts but phospho-kinase expressions and post-ischemic recovery of myocardial function improved only in M hearts. These results show that Akt/GSK-3β/PKCε/eNOS-dependent pathways-mediated superoxide production and apoptosis appear as important factors involved in the observed gender differences.

Benzolamide perpetuates acidic conditions during reperfusion and reduces myocardial ischemia-reperfusion injury

During ischemia, increased anaerobic glycolysis results in intracellular acidosis. Activation of alkalinizing transport mechanisms associated with carbonic anhydrases (CAs) leads to myocardial intracellular Ca²⁺ increase. We characterize the effects of inhibition of CA with benzolamide (BZ) during cardiac ischemia-reperfusion (I/R). Langendorff-perfused isolated rat hearts were subjected to 30 min of global ischemia and 60 min of reperfusion. Other hearts were treated with BZ (5 μM) during the initial 10 min of reperfusion or perfused with acid solution (AR, pH 6.4) during the first 3 min of reperfusion. p38MAPK, a kinase linked to membrane transporters and involved in cardioprotection, was examined in hearts treated with BZ in presence of the p38MAPK inhibitor SB202190 (10 μM). Infarct size (IZ) and myocardial function were assessed, and phosphorylated forms of p38MAPK, Akt, and PKCε were evaluated by immunoblotting. We determined the rate of intracellular pH (pH_i) normalization after transient acid loading in the absence and presence of BZ or BZ + SB202190 in heart papillary muscles (HPMs). Mitochondrial membrane potential (ΔΨ_m), Ca²⁺ retention capacity and Ca²⁺-mediated swelling after I/R were also measured. BZ, similarly to AR, reduced IZ, improved postischemic recovery of myocardial contractility, increased phosphorylation of Akt, PKCε, and p38MAPK, and normalized ΔΨ_m and Ca²⁺ homeostasis, effects abolished after p38MAPK inhibition. In HPMs, BZ slowed pH_i recovery, an effect that was restored after p38MAPK inhibition. We conclude that prolongation of acidic conditions during reperfusion by BZ could be responsible for the cardioprotective benefits of reduced infarction and better myocontractile function, through p38MAPK-dependent pathways. NEW & NOTEWORTHY Carbonic anhydrase inhibition by benzolamide (BZ) maintains acidity, decreases infarct size, and improves postischemic myocardial dysfunction in ischemia-reperfusion (I/R) hearts. Protection afforded by BZ mimicked the beneficial effects elicited by an acidic solution (AR). Increased phosphorylation of p38MAPK occurs in I/R hearts reperfused with BZ or with AR. Mitochondria from I/R hearts possess abnormal Ca²⁺ handling and a more depolarized membrane potential compared with control hearts, and these changes were restored by treatment with BZ or AR.

Effect of an Ilex paraguariensis (yerba mate) extract on infarct size in isolated rat hearts: the mechanisms involved

Tea made from Ilex paraguariensis (IP) dried and minced leaves is a beverage widely consumed by large populations in South America as a source of caffeine (stimulant action) and for its medicinal properties. However, there is little information about the action of IP on the myocardium in the ischemia-reperfusion condition. Therefore, the objective of this study was to examine the effects of an aqueous extract of IP on infarct size in a model of regional ischemia. Isolated rat hearts were perfused by the Langendorff technique and subjected to 40 min of coronary artery occlusion followed by 60 min of reperfusion (ischemic control hearts). Other hearts received IP 30 μg mL(-1) during the first 10 min of reperfusion in the absence or presence of l(G)-nitro-l-arginine methyl ester [l-NAME, a nitric oxide synthase (NOS) inhibitor]. The infarct size was determined by triphenyltetrazolium chloride (TTC) staining. Post-ischemic myocardial function and coronary perfusion were also assessed. Cardiac oxidative damage was evaluated by using the thiobarbituric acid reactive substance (TBARS) concentration and the reduced glutathione (GSH) content. To analyze the mechanisms involved, the expressions of phosphorylated forms of eNOS and Akt were measured. In isolated mitochondria the Ca(2+)-induced mitochondrial permeability transition pore (mPTP) opening was determined. IP significantly decreased the infarct size and improved post-ischemic myocardial function and coronary perfusion. TBARS decreased, GSH was partially preserved, the levels of P-eNOS and P-Akt increased and mPTP opening diminished after IP addition. These changes were abolished by l-NAME. Therefore, our data demonstrate that acute treatment with IP only during reperfusion was effective in reducing myocardial post-ischemic alterations. These actions would be mediated by a decrease of mitochondrial permeability through IP-activated Akt/eNOS-dependent pathways.

Ex Vivo Treatment with a Polyphenol-Enriched Cocoa Extract Ameliorates Myocardial Infarct and Postischemic Mitochondrial Injury in Normotensive and Hypertensive Rats

Our objective was to determine the effects of a polyphenol-enriched cocoa extract (PCE) on myocardial postischemic alterations in normotensive (Wistar rats, W) and spontaneously hypertensive rats (SHR). Isolated hearts were submitted to 110 min of perfusion or 20 min stabilization, 30 min global ischemia, and 60 min reperfusion (R). Other hearts were treated with PCE at the onset of R. Infarct size, the reduced glutathione (GSH), and the expression of phospho-Akt, P-GSK-3β, and P-eNOS were assessed. In isolated mitochondria, the Ca(2+)-mediated response of mitochondrial permeability transition pore (mPTP), membrane potential (Δψm), and superoxide production were determined. PCE decreased infarct size, partly preserved GSH, increased the P-Akt, P-GSK-3β, and P-eNOS contents, improved mPTP response to Ca(2+), decreased the superoxide production, and restored Δψm. These data show that PCE decreases the cardiac postischemic damage in W rats and SHR and suggest that Akt/GSK-3β/eNOS dependent pathways are involved.

Data supporting the cardiac mitochondria calcium handling in female normotensive and spontaneously hypertensive rats

In association with the published article "Mitochondrial calcium handling in normotensive and spontaneously hypertensive rats: correlation with systolic blood pressure levels" [1], this data article contains information about calcium handling of cardiac mitochondria isolated from female of both rats strains (WKY and SHR). Dataset of mitochondrial permeability transition pore (mPTP) resistance to opening Ca(2+)-mediated, Ca(2+) retention capacity (CRC), time constants and mitochondrial membrane potential (ΔΨm) are showed.

Mitochondrial calcium handling in normotensive and spontaneously hypertensive rats: correlation with systolic blood pressure levels

The aim was to study the mitochondrial Ca(2+) handling of mitochondria isolated from normotensive Wistar Kyoto (WKY) and spontaneously hypertensive rats (SHR) hearts and to establish a possible correlation with systolic blood pressure (SBP). Mitochondrial swelling after Ca(2+) addition, Ca(2+)-retention capacity (CRC) by calcium green method, and membrane potential (ΔΨm) were assessed. SBP was 124±1 (WKY) and 235±6mmHg (SHR). CRC, Ca(2+) response and ΔΨm were lower in SHR than WKY mitochondria. The conclusion is: the more depolarized state of SHR than WKY mitochondria results in an abnormal Ca(2+) handling and this event is closely associated with the SBP.

The electrogenic cardiac sodium bicarbonate co-transporter (NBCe1) contributes to the reperfusion injury

BACKGROUND

Although the participation of the electrogenic sodium/bicarbonate cotransporter (NBCe1) in the recovery from an intracellular acid load is recognized, its role in ischemia-reperfusion is still unclear.

METHODS AND RESULTS

Our objective was to assess the role of NBCe1 in reperfusion injury. We use selective functional antibodies against extracellular loop 3 (a-L3) and loop 4 (a-L4) of NBCe1. a-L3 inhibits and a-L4 stimulates NBCe1 activity. Isolated rat hearts were submitted to 40 min of coronary occlusion and 1 h of reperfusion. a-L3, a-L4 or S0859--selective Na(+)-HCO3(-) co-transport inhibitor--were administered during the initial 10 min of reperfusion. The infarct size (IS) was measured by triphenyltetrazolium chloride staining technique. Postischemic systolic and diastolic functions were also assessed. a-L3 and S0859 treatments decreased significantly (P < .05) the IS (16 ± 3% for a-L3 vs. 32 ± 5% in hearts treated with control nonimmune serum and 19 ± 3% for S0859 vs. 39 ± 2% in untreated hearts). Myocardial function during reperfusion improved after a-L3 treatment, but it was not modified by S0859. The infusion of a-L4 did not modify neither the IS nor myocardial function.

CONCLUSIONS

The NBCe1 hyperactivity during reperfusion leads to Na(+) and Ca(2+) loading, conducing to Ca(2+) overload and myocardial damage. Consistently, we have shown herein that the selective NBCe1 blockade with a-L3 exerted cardioprotection. This beneficial action strongly suggests that NBCe1 could be a potential target for the treatment of coronary disease.

Protective effects of N-(2-mercaptopropionyl)-glycine against ischemia-reperfusion injury in hypertrophied hearts

The beneficial effects of N-(2-mercaptopropionyl)-glycine (MPG) against ischemia-reperfusion injury in normotensive animals have been previously studied. Our objective was to test the action of MPG during ischemia and reperfusion in hearts from spontaneously hypertensive rats (SHR). Isolated hearts from SHR and age-matched normotensive rats Wistar Kyoto (WKY) were subjected to 50-min global ischemia (GI) and 2-hour reperfusion (R). In other hearts MPG 2mM was administered during 10 min before GI and the first 10 min of R. Infarct size (IS) was assessed by TTC staining technique and expressed as percentage of risk area. Postischemic recovery of myocardial function was assessed. Reduced glutathione (GSH), thiobarbituric acid reactive substances (TBARS) and SOD cytosolic activity - as estimators of oxidative stress and MnSOD cytosolic activity - as an index of (mPTP) opening were determined. In isolated mitochondria H(2)O(2)-induced mPTP opening was also measured. The treatment with MPG decreased infarct size, preserved GSH levels and decreased SOD and MnSOD cytosolic activities, TBARS concentration, and H(2)O(2) induced-mPTP opening in both rat strains. Our results show that in both hypertrophied and normal hearts an attenuation of mPTP opening via reduction of oxidative stress appears to be the predominant mechanism involved in the cardioprotection against reperfusion injury MPG-mediated.

Participation of mitochondrial permeability transition pore in the effects of ischemic preconditioning in hypertrophied hearts: role of NO and mitoKATP

BACKGROUND

The mitochondrial permeability transition pore (mPTP) plays an important role in ischemia-reperfusion in normotensive animals. Our study aims to define their participation in the ischemic preconditioning (IP) in hypertrophied hearts and to assess the role played by NO and mitochondrial ATP-dependent K channels (mitoKATP).

MATERIAL AND METHODS

Isolated hearts from spontaneously hypertensive rats (SHR) and age-matched normotensive rats Wistar Kyoto (WKY) were subjected to 35-min or 50-min global ischemia (GI) followed by 2-hour reperfusion (R). IP was induced by a single cycle of 5-min GI and 10-min R (IP1) or three cycles of 2-min GI and 5-min R (IP3) applied before to prolonged ischemia. L-NAME (NOS inhibitor) or 5-HD (mitoKATP blocker) to investigate the role played by NO and mitoKATP, respectively were administered. Infarct size (IS), myocardial function, reduced glutathione (GSH) - as marker of oxidative stress and MnSOD cytosolic activity - as an index of mPTP opening were determined.

RESULTS

IP1 significantly decreased the IS in WKY hearts at both ischemia duration times. In SHR, IP1 decreased the IS observed in GI35 but it did not modify that detected at 50-min GI, which was limited by IP3. IP preserved GSH content and decreased MnSOD cytosolic activity in both rat strains. These protective effects were annulled by L-NAME and 5-HD for both ischemic periods in SHR, whereas in WKY they were only effective for 50-min GI.

CONCLUSION

Our data demonstrate that the cardioprotection achieved by ischemic preconditioning in hearts from SHR hearts involves an attenuation of mPTP opening NO and mitoKATP-mediated.

In vivo key role of reactive oxygen species and NHE-1 activation in determining excessive cardiac hypertrophy

Growing in vitro evidence suggests NHE-1, a known target for reactive oxygen species (ROS), as a key mediator in cardiac hypertrophy (CH). Moreover, NHE-1 inhibition was shown effective in preventing CH and failure; so has been the case for AT1 receptor (AT1R) blockers. Previous experiments indicate that myocardial stretch promotes angiotensin II release and post-translational NHE-1 activation; however, in vivo data supporting this mechanism and its long-term consequences are scanty. In this work, we thought of providing in vivo evidence linking AT1R with ROS and NHE-1 activation in mediating CH. CH was induced in mice by TAC. A group of animals was treated with the AT1R blocker losartan. Cardiac contractility was assessed by echocardiography and pressure-volume loop hemodynamics. After 7 weeks, TAC increased left ventricular (LV) mass by ~45% vs. sham and deteriorated LV systolic function. CH was accompanied by activation of the redox-sensitive kinase p90(RSK) with the consequent increase in NHE-1 phosphorylation. Losartan prevented p90(RSK) and NHE-1 phosphorylation, ameliorated CH and restored cardiac function despite decreased LV wall thickness and similar LV systolic pressures and diastolic dimensions (increased LV wall stress). In conclusion, AT1R blockade prevented excessive oxidative stress, p90(RSK) and NHE-1 phosphorylation, and decreased CH independently of hemodynamic changes. In addition, cardiac performance improved despite a higher work load.

Myocardial reperfusion injury: reactive oxygen species vs. NHE-1 reactivation

BACKGROUND/AIMS

Flow restoration to ischemic myocardium reduces infarct size (IS), but it also promotes reperfusion injury. A burst of reactive oxygen species (ROS) and/or NHE-1 reactivation were proposed to explain this injury. Our study was aimed to shed light on this unresolved issue.

METHODS

Regional infarction (40 min-ischemia/2 hs-reperfusion) was induced in isolated and perfused rat hearts. Maximal doses of N-(2-mercaptopropionyl)-glycine (MPG 2mmol/L, ROS scavenger), cariporide (10μmol/L, NHE-1 inhibitor), or sildenafil (1μmol/L, phosphodiesterase5A inhibitor) were applied at reperfusion onset. Their effects on IS, myocardial concentration of thiobarbituric acid reactive substances (TBARS), ERK1/2, p90(RSK), and NHE-1 phosphorylation were analyzed.

RESULTS

All treatments decreased IS ∼ 50% vs. control. No further protection was obtained by combining cariporide or MPG with sildenafil. Myocardial TBARS increased after infarction and were decreased by MPG or cariporide, but unaffected by sildenafil. In line with the fact that ROS induce MAPK-mediated NHE-1 activation, myocardial infarction increased ERK1/2, p90(RSK), and NHE-1 phosphorylation. MPG and cariporide cancelled these effects. Sildenafil did not reduce the phosphorylated ERK1/2-p90(RSK) levels but blunted NHE-1 phosphorylation suggesting a direct dephosphorylating action.

CONCLUSIONS

1) Reperfusion injury would result from ROS-triggered MAPK-mediated NHE-1 phosphorylation (and reactivation) during reperfusion; 2) sildenafil protects the myocardium by favouring NHE-1 dephosphorylation and bypassing ROS generation.

High resistance to lipid peroxidation of bird heart mitochondria and microsomes: Effects of mass and maximum lifespan

The aim of this investigation was to study the connection between body size, fatty acid composition and sensitivity to lipid peroxidation of heart mitochondria and microsomes isolated from different size bird species: manon (Lonchura striata), quail (Coturnix coturnix var japonica), pigeon (Columba livia), duck (Cairina moschata) and goose (Anser anser), representing a 372-fold range of body mass. Fatty acids of total lipids were determined using gas chromatography and lipid peroxidation was evaluated with a chemiluminescence assay. The fatty acids present in heart organelles of the different bird species analyzed showed a small number of significant allometric trends. In mitochondria, from the individual fatty acid data, palmitoleic acid (C16:1 n7) increased allometrically (r=0.878), while stearic acid (C18:0) was negatively related to body mass (r=-0.903). Interestingly, none of the calculated fatty acid variables, the average fatty acid saturated, monounsaturated, polyunsaturated (PUFA) and the unsaturation index (UI) was established to show significant body size-related variations. In heart microsomes, the content of C18:0 was significantly smaller (r=-0.970) in the birds of greater size. A significant allometric increase in linoleic acid (C18:2 n6) (r=0.986), polyunsaturated (r=0.990) and UI (r=0.904) was observed in the larger birds. The total n6 fatty acids of heart mitochondria did not show significant differences when it was correlated to body mass of the birds. Moreover, positive allometric relationships were shown for microsomes. The total n3 fatty acids of heart mitochondria and microsomes indicated no significant correlations to body mass of birds. The C16:1 n7, C18:0 in mitochondria and C18:0, C18:2 n6, PUFA, UI and PUFA n6 in microsomes showed significant differences when they were correlated to maximum life span (MLSP) of birds. As light emission=chemiluminescence originated from heart organelles was not statistically significant, a lack of correlation between the sensitivity to lipid peroxidation and body size or maximum life span was obtained. These results indicate that the high resistance of bird hearts to the attack by free radicals is body size-independent and would be related to the preservation of cardiac function.

Na+/H+ exchanger-1 inhibitors decrease myocardial superoxide production via direct mitochondrial action

The possibility of a direct mitochondrial action of Na(+)/H(+) exchanger-1 (NHE-1) inhibitors decreasing reactive oxygen species (ROS) production was assessed in cat myocardium. Angiotensin II and endothelin-1 induced an NADPH oxidase (NOX)-dependent increase in anion superoxide (O(2)(-)) production detected by chemiluminescence. Three different NHE-1 inhibitors [cariporide, BIIB-723, and EMD-87580] with no ROS scavenger activity prevented this increase. The mitochondria appeared to be the source of the NOX-dependent ROS released by the "ROS-induced ROS release mechanism" that was blunted by the mitochondrial ATP-sensitive potassium channel blockers 5-hydroxydecanoate and glibenclamide, inhibition of complex I of the electron transport chain with rotenone, and inhibition of the permeability transition pore (MPTP) by cyclosporin A. Cariporide also prevented O(2)(-) production induced by the opening of mK(ATP) with diazoxide. Ca(2+)-induced swelling was evaluated in isolated mitochondria as an indicator of MPTP formation. Cariporide decreased mitochondrial swelling to the same extent as cyclosporin A and bongkrekic acid, confirming its direct mitochondrial action. Increased O(2)(-) production, as expected, stimulated ERK1/2 and p90 ribosomal S6 kinase phosphorylation. This was also prevented by cariporide, giving additional support to the existence of a direct mitochondrial action of NHE-1 inhibitors in preventing ROS release. In conclusion, we report a mitochondrial action of NHE-1 inhibitors that should lead us to revisit or reinterpret previous landmark observations about their beneficial effect in several cardiac diseases, such as ischemia-reperfusion injury and cardiac hypertrophy and failure. Further studies are needed to clarify the precise mechanism and site of action of these drugs in blunting MPTP formation and ROS release.

An allometric study of fatty acids and sensitivity to lipid peroxidation of brain microsomes and mitochondria isolated from different bird species

The objective of this investigation was to examine the relationship between body size, fatty acid composition and sensitivity to lipid peroxidation of mitochondria and microsomes isolated from the brain of different size bird species: manon, quail, pigeon, duck and goose, representing a 372-fold range of body mass. Fatty acids of total lipids were determined using gas chromatography and lipid peroxidation was evaluated using a chemiluminescence assay. The allometric study of the fatty acids present in brain mitochondria and microsomes of the different bird species showed a small number of significant allometric trends. In mitochondria the percentage of monounsaturated fatty acids, was significantly lower in the larger birds (r=-0.965; P<0.008). The significant allometric increase in 18:2 n-6; linoleic acid (r=0.986; P<0.0143), polyunsaturated (r=0.993; P<0.007) and total unsaturated (r=0.966; P<0.034) in brain microsomes but not in mitochondria may indicate a preferential incorporation of this fatty acid in the brain endoplasmic reticulum of the larger bird species. The brain of all birds studied had a high content of docosahexaenoic acid. However brain mitochondria but not microsomes isolated from all the birds analyzed showed a significant decrease of arachidonic and docosahexaenoic acids during lipid peroxidation. The allometric analyses of chemiluminescence were not statistically significant. In conclusion our results show absence of correlation between the sensitivity to lipid peroxidation of brain mitochondria and microsomes with body size and maximum life span.

Cardioprotective effects of stretch are mediated by activation of sarcolemmal, not mitochondrial, ATP-sensitive potassium channels

To determine whether sarcolemmal and/or mitochondrial ATP-sensitive potassium (K(ATP)) channels (sarcK(ATP), mitoK(ATP)) are involved in stretch-induced protection, isolated isovolumic rat hearts were assigned to the following protocols: nonstretched hearts were subjected to 20 min of global ischemia (Is) and 30 min of reperfusion, and before Is stretched hearts received 5 min of stretch + 10 min of no intervention. Stretch was induced by a transient increase in left ventricular end-diastolic pressure (LVEDP) from 10 to 40 mmHg. Other hearts received 5-hydroxydecanoate (5-HD; 100 microM), a selective inhibitor of mitoK(ATP), or HMR-1098 (20 microM), a selective inhibitor of sarcK(ATP), before the stretch protocol. Systolic function was assessed through left ventricular developed pressure (LVDP) and maximal rise in velocity of left ventricular pressure (+dP/dt(max)) and diastolic function through maximal decrease in velocity of left ventricular pressure (-dP/dt(max)) and LVEDP. Lactate dehydrogenase (LDH) release and ATP content were also measured. Stretch resulted in a significant increase of postischemic recovery and attenuation of diastolic stiffness. At 30 min of reperfusion LVDP and +dP/dt(max) were 87 +/- 4% and 92 +/- 6% and -dP/dt(max) and LVEDP were 95 +/- 9% and 10 +/- 4 mmHg vs. 57 +/- 6%, 53 +/- 6%, 57 +/- 10%, and 28 +/- 5 mmHg, respectively, in nonstretched hearts. Stretch increased ATP content and did not produce LDH release. 5-HD did not modify and HMR-1098 prevented the protection achieved by stretch. Our results show that the beneficial effects of stretch on postischemic myocardial dysfunction, cellular damage, and energetic state involve the participation of sarcK(ATP) but not mitoK(ATP).

CARDIOPROTECTIVE EFFECTS OF A NON-ALCOHOLIC EXTRACT OF RED WINE DURING ISCHAEMIA AND REPERFUSION IN SPONTANEOUSLY HYPERTENSIVE RATS

1. We reported recently the cardioprotection conferred by a non-alcoholic extract of Cabernet-Sauvignon red wine (RWE) against alterations derived from ischaemia and reperfusion in normotensive rats. The aim of the present study was to assess the effects of RWE on ischaemia/reperfusion injury in hearts isolated from spontaneously hypertensive rats (SHR). 2. After stabilization, rat isovolumic perfused hearts were exposed to a 20 min global ischaemic period followed by 30 min reperfusion in the absence (ischaemic control (IC) hearts) or presence of RWE infused prior to ischaemia and early in reperfusion. In other hearts, N(G)-nitro-L-arginine methyl ester (L-NAME), an inhibitor of nitric oxide synthase, was administered prior to RWE infusion (L-NAME + RWE). 3. Left ventricular developed pressure (LVDP), dP/dt(max) and left ventricular end-diastolic pressure (LVEDP) were used to assess myocardial function. 4. At the end of reperfusion, LVDP and dP/dt(max) decreased to 47 +/- 9 and 46 +/- 9% of baseline values, respectively, in IC. Treatment with the RWE significantly improved systolic postischaemic recovery (LVDP = 85 +/- 8%; dP/dt(max) = 83 +/- 5%) and attenuated the increase in LVEDP (23 +/- 6 and 53 +/- 8 mmHg in RWE and IC, respectively; P < 0.05). 5. In the L-NAME + RWE group, L-NAME completely abolished the systolic and diastolic protection induced by RWE (LVDP = 44 +/- 13%; dP/dt(max) = 43 +/- 13%; LVEDP = 60 +/- 10 mmHg). 6. These data are the first demonstration that a non-alcoholic extract of Cabernet-Sauvignon red wine protects SHR hearts from systolic and diastolic alterations induced by ischaemia and reperfusion through a nitric oxide-dependent mechanism.

Comparative effects of ischemic pre and postconditioning on ischemia-reperfusion injury in spontaneously hypertensive rats (SHR)

Brief episodes of myocardial ischemia-reperfusion applied early in reperfusion may attenuate the reperfusion injury, strategy called ischemic postconditioning (IPO). Our objective was to examine the effects of IPO compared with ischemic preconditioning (IP) on postischemic myocardial dysfunction in spontaneously hypertensive rats (SHR). Isolated hearts from SHR and normotensive WKY rats were subjected to the following protocols: (1) Ischemic control (IC): global ischemia 20 min (GI20) and reperfusion 30 min (R). (2) IPO: three cycles of R30sec-IG30sec at the onset of R; (3) IP: a cycle of IG5-R10 previous to GI20, (4) IPO in the presence of chelerythrine, an inhibitor of protein kinase C (PKC). Systolic and diastolic function were assessed through developed pressure (LVDP) and end diastolic pressure (LVEDP), respectively. Lipid peroxidation was estimated by thiobarbituric reactive substance (TBARS) concentration. IPO significantly improved postischemic dysfunction. At the end of R, LVDP recovered to 87 +/- 7% in WKY and 94 +/- 7% in SHR vs. 55 +/- 11% and 58 +/- 12% in IC hearts. LVEDP reached values of 24 +/- 6 mmHg for WKY and 24 +/- 3 mmHg for SHR vs. 40 +/- 8 and 42 +/- 5 mmHg in IC hearts. Similar protection was achieved by IP. TBARS contents of SHR hearts were significantly diminished by IP and IPO. PKC inhibition aborted the protection of myocardial function and attenuated the diminution of lipid peroxidation conferred by IPO. These data show that IPO was as effective as IP in improving the postischemic dysfunction of hearts from SHR hearts, and that this cardioprotection appears to be associated with a diminution of ROS-induced damage involving the PKC activation.

Na+/H+ exchanger inhibition at the onset of reperfusion decreases myocardial infarct size: role of reactive oxygen species

BACKGROUND

A burst of reactive oxygen species and activation of Na+/H+ exchanger take place at the beginning of reperfusion. The aim of this study was to assess the possible interrelation of the inhibition of Na+/H+ exchanger and reactive oxygen species about the determination of myocardial infarct size.

METHODS

Isolated rat hearts were submitted to 40 min of coronary occlusion and 2 h of reperfusion. Infarct size was determined through triphenyltetrazolium chloride staining technique and was expressed as a percentage of risk area. Lipid peroxidation, as a marker of oxidative stress, was estimated by the concentration of thiobarbituric reactive substances.

RESULTS

Treatment during the first 20 min of reperfusion with a selective inhibitor of Na+/H+ exchanger 1 isoform, HOE 642 (cariporide; 10 microM), significantly diminished infarct size (15.1+/-2.4% vs. 31+/-2% in untreated hearts). The administration of a "scavenger" of hydroxyl radical, N-(2-mercaptopropionyl)-glycine (2 mM), decreased infarct size in an extent similar to that of cariporide (18+/-3%). The combination cariporide+N-(2-mercaptopropionyl)-glycine did not produce additional protection (17+/-1.7%). Each intervention [HOE 642 or N-(2-mercaptopropionyl)-glycine] and its combination improved the postischemic recovery of myocardial systolic and diastolic functions in a similar extent. The content of the thiobarbituric reactive substances of untreated hearts (1012+/-144 nmol/g) decreased to 431+/-81, 390+/-82, and 433+/-41 after cariporide, N-(2-mercaptopropionyl)-glycine, and cariporide+N-(2-mercaptopropionyl)-glycine treatments, respectively.

CONCLUSIONS

The present data support the conclusion that the cardioprotective effect of cariporide is associated with diminution of oxidative stress.

Cardioprotective effects of Ilex paraguariensis extract: evidence for a nitric oxide-dependent mechanism

AIM

To examine the effects of an Ilex paraguariensis (Ip) extract on postischemic alterations derived from 20 min of global ischemia and 30 min of reperfusion.

METHODS

Isolated rat hearts were treated 10 min before ischemia and the first 10 min of reperfusion with Ip 30 microg/ml. In other hearts, chelerythrine (1 microM), a protein kinase C blocker, or l(G)-nitro l-arginine methyl ester (l-NAME), a nitric oxide synthase inhibitor, were administered prior to Ip infusion. Left ventricular developed pressure (LVDP), +dP/dt(max), -dP/dt(max), and left ventricular end diastolic pressure (LVEDP) were used to assess myocardial function. Thiobarbituric acid reactive substances (TBARS) were measured.

RESULTS

Ip treatment produced an improvement of postichemic recovery (LVDP=96+/-8%; +dP/dt(max)=95+/-10%; -dP/dt(max)=90+/-12% vs. 57+/-6%, 53+/-6% and 57+/-8%, respectively, in untreated hearts) and an attenuation of the increase of LVEDP and TBARS content. Chelerythrine did not modify and l-NAME abolished the protection induced by Ip.

CONCLUSIONS

These data are the first demonstration that Ip extract attenuates the myocardial dysfunction provoked by ischemia and reperfusion and that this cardioprotection involves a diminution of oxidative damage through a nitric oxide-dependent mechanism.

Effects of different fractions of a red wine non-alcoholic extract on ischemia-reperfusion injury

We have recently demonstrated the cardioprotective effects of a non-alcoholic extract of Argentinian red wine (RWE) on ischemia-reperfusion injury. The aim of the present study was to assess the relative contribution of four phenolic fractions separated from RWE by liquid/liquid extraction with solvents of decreasing hydrophobicity, to the myocardial protection achieved by the original extract. Isovolumic perfused rat hearts treated with each fraction 10 min before ischemia and the first 10 min of reperfusion were submitted to a 20-min global ischemic period followed by 30 min of reperfusion. The treatment with the fraction rich in polymeric proanthocyanidins (fraction IV = aqueous residue) significantly improved the postischemic recovery of left ventricular developed pressure (LVDP) and +dP/dt (max) (111 +/- 5% and 117 +/- 6% vs 61 +/- 4%, 62 +/- 5% , respectively, detected in control hearts) and abolished the increase of left ventricular end diastolic pressure (LVEDP) (8 +/- 2 mmHg vs 42 +/- 4 mmHg in untreated hearts). However, the fraction rich in anthocyanins (III: butanol) elicited a cardioprotective action weaker than the original extract. On the other hand, the representative of either resveratrol or flavan-3-ols and flavonols (fractions I and II) failed to induce this type of response. LDH release and TBARS concentration were significantly lowered after treatment with fraction IV alone. These data show that the fraction rich in polymeric proanthocyanidins exerts a protective effect against myocardial alterations derived from ischemia and reperfusion comparable to the original RWE. This beneficial effect can be correlated to the ability of that fraction to attenuate the degree of lipid peroxidation.

Fatty acid composition and lipid peroxidation induced by ascorbate-Fe2+ in different organs of goose (Anser anser)

Many reports have demonstrated that birds show a low degree of fatty acid unsaturation and lipid peroxidation compared with mammals of similar body size. The aim of the present study was to examine fatty acid profiles, non-enzymatic lipid peroxidation and vitamin E levels of mitochondria and microsomes obtained from liver, heart and brain of goose (Anser anser). The unsaturated fatty acid content found in mitochondria and microsomes of all tissues examined was approximately 60% with a prevalence of C18:1 n9 + C18:2 n6 = 50%. The 20:4 n6 + C22:6 n3 content was significantly higher in brain organelles (approx. 16%) compared with mitochondria and microsomes of liver and heart (approx. 4%). Whereas these organelles were not affected when subjected to lipid peroxidation, brain mitochondria were highly affected, as indicated by the increase in chemiluminescence and a considerable decrease of arachidonic and docosahexaenoic acids. These changes were not observed during lipid peroxidation of brain microsomes. Vitamin E content was higher in liver and heart than in brain mitochondria (1.77 +/- 0.06 and 1.93 +/- 0.13 vs. 0.91 +/- 0.09 nmol/mg protein). The main conclusion of this paper is that a lower degree of unsaturation of fatty acids in liver and heart mitochondria and a higher vitamin E level than in brain mitochondria protect those tissues against lipid peroxidation.

Comparison of the effects of different magnesium administration times on infarct size

BACKGROUND

The protection of high magnesium on infarct size remains controversial.

OBJECTIVE

To examine the effects of magnesium administered before ischemia or early in reperfusion on infarct size in a rat model of global ischemia

METHODS

Isolated rat hearts were submitted to 40 min of normothermic global ischemia and 2 h of reperfusion. After 20 min of stabilization, four protocols were performed: ischemic control (IC) hearts; 15 mM of magnesium chloride administered 15 min before ischemia (MgI); 15 mM of magnesium chloride administered during the first 15 min of reperfusion (MgR); or 15 mM magnesium plus 5 mM calcium (Mg+Ca) before ischemia. Infarct size was measured by triphenyltetrazolium staining. Contractile function was assessed by left ventricular developed pressure and the maximal velocity of rise of left ventricular presssure.

RESULTS

The infarct size in IC hearts was 44+/-5%. In MgI and MgR hearts, the infarct diminished to 4.5+/-1.5% and 18+/-4%, respectively. In Mg+Ca hearts, the protection was also obtained (19+/-3%). Myocardial function also improved significantly by magnesium treatment. At the end of reperfusion, left ventricular developed pressure and maximal velocity of rise of left ventricular pressure values were 23+/-6% and 22+/-3% in MgI; and 10+/-3% and 9+/-2.6% in MgR versus 2+/-0.7% and 2.3+/-0.8% in IC hearts, respectively.

CONCLUSION

The treatment with magnesium either before ischemia or early in reperfusion has an infarct size limiting effect in a model of global ischemia. This protective effect is partially due to its calcium antagonistic action.

Cardioprotection from ischemia/reperfusion induced by red wine extract is mediated by K(ATP) channels

The objective was to analyze the mechanism of the protection induced by a nonalcoholic extract of red wine (RWE) on ischemia/reperfusion injury. Isovolumic perfused rat hearts were exposed after stabilization to a 20-min global ischemic period followed by 30 min of reperfusion in absence and presence of RWE infused prior to ischemia and early in reperfusion. In other hearts, 5-hydroxydecanoate (5-HD, 100 microM), a selective mitochondrial K(ATP) blocker, chelerythrine (1 microM), a protein kinase C blocker, or >L(G)-nitro->L-arginine methyl ester (>L-NAME), a nitric oxide synthase inhibitor, was administered prior to RWE infusion. Left ventricular developed pressure (LVDP), +dP/dtmax, and left ventricular end-diastolic pressure (LVEDP) were used to assess myocardial function. The lactate dehydrogenase release during reperfusion was measured. After the ischemic period, LVDP decreased to 61 +/- 4% and +dP/dtmax to 62 +/- 5% of baseline values at the end of reperfusion. The infusion of RWE resulted in a complete recovery of systolic function (LVDP = 102 +/- 4%; +dP/dtmax = 101 +/- 4%) and in an attenuation of the increase of LVEDP (20 +/- 3 mm Hg versus 42 +/- 4 mm Hg, p < 0.05). The treatment with RWE did not produce lactate dehydrogenase release during reperfusion. 5-HD and chelerythrine completely abolished the protection induced by RWE (mechanical and enzymatic). >L-NAME partially abolished the systolic improvement induced by RWE but returned lactate dehydrogenase loss to ischemic control values. The diastolic protection afforded by RWE was not altered by >L-NAME. These data are the first demonstration that mitochondrial K channels and nitric oxide are involved in the protection against ischemia/reperfusion conferred by a nonalcoholic RWE.

[Post-ischemic myocardial protection with Cabernet-Sauvignon red wine]

The objective was to assess the action of two Argentine (from Mendoza) non-alcoholic red wine extracts (Cabernet-Sauvignon (CS) and a generic control (G)) on myocardial stunning that follows the reperfusion period. In the isolated isovolumically perfused rat heart the recovery of systolic and diastolic functions after 20 min of global ischemia were assessed through left ventricular developed pressure (LVDP) and end diastolic pressure (EDP), respectively. After 30 min of reperfusion LVDP recovered to 66 +/- 7% in control ischemic hearts. The administration of non-alcoholic extract of CS not of G wine significantly increased the post-ischemic recovery (101 +/- 4%, p < 0.05) of the hearts. The ischemic contracture was not modified by either of the wines. However, during reperfusion the CS, not the G wine, decreased significantly the increase in EDP observed in control ischemic hearts. These results present experimental evidence that the non-alcoholic extracts of CS and not of G Argentine red wine induces protection of postischemic myocardial function.

[The Na+/Ca2+ exchanger as responsible for myocardial stunning]

Our objective was to assess the participation of Na+/H+ exchanger (NHE) and Na+/Ca2+ exchanger (NCX) on systolic and diastolic alterations of myocardial stunning. Isolated perfused rat hearts were submitted to 20 min of global ischemia (Is) followed by 30 min of reperfusion (R). This protocol was repeated after treatment before ischemia and/or early in R. with HOE 642 1 microM, a specific blocker of NHE-1 and KB-R7943 1 microM the novel inhibitor of the reverse mode of NCX. In control ischemic hearts the contractility assessed through +dP/dtmax recovered approximately 60%. When the NHE blockade was performed before is or early in R the postischemic recovery reached 100%. The blockade of the reverse mode of NCX only improved significantly the recovery when administered before is and early in R (95 +/- 7%). The ischemic contracture decreased when the treatment with both blockers was performed before Is. During R the increase of end diastolic pressure (EDP) observed in control ischemic hearts (at 30 min of R, EDP value was 44 +/- 4 mmHg) diminished significantly by NHE (24 +/- 6 and 12 +/- 2 mmHg when the blocker was administered before or after Is) and NCX blockade performed before and after is (12 +/- 6 mmHg). These results indicate that the activation of the reverse mode of NCX secondary to the NHE activation during ischemia and reperfusion is the mechanism responsible for the Ca2+ overload involved in the diminution of contractility that characterizes myocardial stunning.

Is the protection against ischemia induced by red wine linked to its antioxidant capacity?

OBJECTIVE

To establish whether the total antioxidant capacity of nonalcoholic extracts of three Argentine red wines (RWE) is correlated with their protection against ischemia-reperfusion injury.

ANIMALS AND METHODS

The antioxidant properties of three RWE were determined using different free radical-generating systems. To examine the effects of these RWE during a 20 min global ischemic period followed by 30 min of reperfusion, isolated rat hearts received 50 mug/mL of RWE 1 (cabernet-sauvignon), RWE 2 (malbec) or RWE 3 (a commercial mixture of cabernet-sauvignon, malbec and merlot) 10 min before and after ischemia. Left ventricular developed pressure (LVDP), maximal velocity of rise of left ventricular pressure (+dP/dt(max)) and left ventricular end-diastolic pressure (LVEDP) were used to assess contractility and diastolic function.

RESULTS

All RWE inhibited lipid peroxidation induced by the Cl(4)C/NADPH system in a similar proportion (42+/-4%, 47+/-9% and 43+/-14% for RWE 1, RWE 2 and RWE 3, respectively). The scavenging activity of superoxide anion and 2,2-diphenyl-1-picryl-hydrazyl radical was about the same with the three RWE. In hearts without RWE treatment, LVDP and +dP/dt(max) were 61+/-4% and 62+/-5%, respectively, at the end of the reperfusion period. Infusion of RWE 1 and RWE 2 significantly improved postischemic recovery (LVDP and +dP/dt(max) were 102+/-4% and 101+/-4% for RWE 1 and 92+/-5% and 91+/-5% for RWE 2, respectively) and attenuated the increase of LVEDP. RWE 3 did not improve either systolic or diastolic dysfunction.

CONCLUSION

These data show that although the three non-alcoholic RWE exhibit a similar total antioxidant capacity, only two of them protect the heart against myocardial stunning, suggesting that the protective effect is not primarily linked to the anti-oxidant properties of the extracts.

Comparison of the protective effects of ischemic preconditioning and the Na+/H+ exchanger blockade

The protective effects of ischemic preconditioning (IP) and Na+/H+ exchanger blockade (NHEb) by two blockers [ethylisopropylamiloride (EIPA) and HOE 642] were compared in the isovolumic perfused rat heart. The impairment in systolic and diastolic function detected in control ischemic hearts (C) exposed to 20 min of ischemia and 30 min of reperfusion was diminished in similar extent by IP and by NHEb with EIPA and HOE 642. At the end of the reperfusion period +dP/dtmax values were 57+/-9% in C hearts and 94+/-6%, 82+/-6% and 104+/-6% after IP and NHEb with EIPA and HOE 642, respectively. A depletion of ATP levels detected in C hearts after reperfusion (from 20.2+/-0.8 micromol/g dry weight before ischemia to 6.9+/-0.7 micromol/g dry weight) was partially prevented by both IP and NHEb with EIPA (9.2+/-0.7 micromol/g dry weight and 11.1+/-0.5 micromol/g dry weight, respectively). The ischemic contracture (IC), assessed by the left ventricular end diastolic pressure (LVEDP), observed in C hearts (35+/-4 mmHg) was not decreased by IP (40+/-4 mmHg) but it was prevented by NHEb (18+/-4 mmHg and 10+/-3 mmHg with EIPA and HOE 642, respectively). The ATP levels at the end of the ischemic period were similar in C and IP hearts (4.1+/-0.2 micromol/g dry wt vs. 3.3+/-0.4 micromol/g dry wt) but they were significantly higher after NHEb with HOE 642 (7.0+/-1.0 micromol/g dry wt). PKC inhibition by chelerythrine abolished the protection induced by IP after reperfusion although not the improvement induced by NHEb with EIPA. According to the present results, we can conclude that despite the fact that IP and NHEb are protecting the postischemic function in a similar magnitude, both interventions are different in terms of modifying IC that develops during the ischemic period. IC was prevented by NHEb whereas it was not by IP. Furthermore, IP protection and not that obtained by NHEb is abolished by PKC.

Is stunning prevented by ischemic preconditioning?

In a model of global ischemia in the isolated perfused rat heart, a 20 min ischemic period followed by 30 min of reperfusion induces a decrease in isovolumic developed pressure (LVDP) and +dP/dtmax to 61+/-6% and 61+/-7% of baseline, respectively. Left ventricular end-diastolic pressure (LVEDP) increases to 36+/-4 mmHg at the end of the reperfusion period. No significant necrotic area as assessed by triphenyltetrazolium chloride (TTC) was detected at the end of the reperfusion period. By an immunohistochemical method using antiactin monoclonal antibodies 10.8+/-1.9% of unstained cells were detected in the stunned hearts and 10.3+/-1.2% in control hearts. Preceding the ischemic episode with a cycle of 5 min of ischemia followed by 10 min of reperfusion (ischemic preconditioning) protected contractile function. LVDP and +dP/dtmax now stabilized at 89+/-5% and 94+/-5% of baseline respectively. LVEDP was 20+/-2 mmHg at the end of the reperfusion period. The protection of contractile dysfunction after 20 min of ischemia was achieved also by early reperfusion of low Ca2+-low pH perfusate. With this intervention LVDP stabilized at 87+/-5% of baseline. LVEDP was 12+/-2 mmHg at the end of the reperfusion period. A positive inotropic intervention induced by a modified postextrasystolic potentiation protocol at the end of the reperfusion period increases LVDP to levels higher than baseline in the stunned hearts. However, these values were less than those obtained in control hearts. Ischemic preconditioning significantly increased the maximal inotropic response. Therefore, ischemic preconditioning diminishes the contractile dysfunction of early stunning.

Biphasic changes in relaxation following reperfusion after myocardial ischemia

The present study provides evidences of left ventricular diastolic alterations following reperfusion in a model of global ischemia. Isolated perfused rabbit and rat hearts, were subjected to ischemia for 15 and 20 min respectively, followed by 30 min of reperfusion. In rabbit heart at the end of the reperfusion period, isovolumic left ventricular developed pressure (LVDP) and +dP/dtmax stabilized at 55 +/- 3% and 60 +/- 2% of preischemic values respectively and, in rat heart LVDP = 61 +/- 8% and +dP/dtmax = 57 +/- 9% of preischemic values. Stunned heart was then obtained from both species. Left ventricular end diastolic pressure (LVEDP) values stabilized at the end of reperfusion period at values higher than preischemic conditions in both species (38.9 +/- 4.4 mmHg and 30.3 +/- 3.1 mmHg in rabbit and rat respectively). The time constant of relaxation (T) increased early in reperfusion in both species, but then decreased and stabilized at the end of reperfusion period at values lower than preischemic values. The ratio between both maximal velocities (+P/-P), also showed a transitory impairment in relaxation, followed by normalization and stabilization at values lower than preischemic values. This biphasic pattern in relaxation was detected in both species. The changes in relaxation were dissociated from the diastolic compliance and could be the result of a transitory calcium overload and/or sarcoplasmic reticulum dysfunction. The faster myocardial relaxation at the end of reperfusion period is consistent with the decreased myofilament sensitivity, which characterizes the stunned myocardium.

Chronic nifedipine treatment diminishes cardiac inotropic response to nifedifine: functional upregulation of dihydropyridine receptors

Chronic treatment with nifedipine induces up-regulation of functional active Ca2+ channels in cardiac muscle membranes. Adult male New Zealand White rabbits (NZW) were treated with nifedipine (20 mg/day) for 25 days. In isovolumic perfused hearts at constant coronary flow and heart rate (HR) the left ventricular developed pressure (LVDP) and its first derivative (dP/dt) were monitored. Basal contractility and contractility at different end-diastolic volumes (EDV) were higher in nifedipine-treated animals, with no changes in diastolic chamber stiffness. Dose response to nifedipine in pretreated animals showed less decrease in contractility than in controls [ED50 = 1.09 +/- 0.09 x 10-7 (control) and 1.55 +/- 0.17 x 10-7 M nifedipine (treated) (p < 0.05)]. Ca2+ channel density was assessed by specific binding at the dihydropyridine receptor with [methyl-3H]PN 200-110. In cardiac membranes, maximal binding capacity (Bmax) was 269 +/- 38 (n = 7, control) and 429 +/- 46 fmol/mg protein (n = 7, treated) (p < 0.05), without significant changes in dissociation constant. In addition, we noted no changes in dihydropyridine (DHP) binding sites in aortic membranes. Our results offer a possible explanation for the lack of decrease in contractility despite the persistent hypotensive effect in hypertensive patients during chronic treatment with nifedipine.

Protective effect of nifedipine on myocardial stunning in isolated rabbit hearts: role of high energy phosphates stores

The aim of the present study was to evaluate the effects of a single dose of nifedipine on myocardial stunning in isolated rabbit hearts. Hearts from rabbits pretreated with a single dose of 20 mg of nifedipine (NIF group) 1-4 h before isolation were compared to control hearts in their response to 15 min of global ischemia (37 degrees C) followed by 30 min of reperfusion. Both experimental groups showed similar baseline cardiac contractility. At the end of the reperfusion period in the control group, isovolumic left ventricular developed pressure (LVDP) and +dP/dtmax had stabilized at 45 +/- 2 and 48 +/- 2% of preischemic values respectively and in the NIF group LVDP stabilized at 63 +/- 6 and +dP/dtmax at 66 +/- 6% (P < 0.05 with respect to the control group). Left ventricular end diastolic pressure (LVEDP) values were significantly lower at the end of reperfusion in the NIF group compared to the controls (36.8 +/- 5.5 mmHg vs 53.4 +/- 3.9 mmHg, P < 0.05). The early impairment of the time constant of relaxation (tau) observed in control hearts was attenuated by pretreatment with nifedipine (control delta tau = 55 +/- 10 ms; NIF group delta tau = 29 +/- 5 ms, P < 0.05). Tissue ATP and creatine phosphate (CP) levels in the control group at the end of reperfusion were 6.9 +/- 0.7 and 8.7 +/- 0.7 mumol/g dry tissue, respectively; in the NIF group ATP and CP levels were significantly higher, 9.2 +/- 0.7 and 11.5 +/- 0.9 mumol/g dry tissue respectively (P < 0.05). Creatine kinase (CK) and lactate dehydrogenase (LDH) leakage during reperfusion were significantly higher in the control group (CK = 120 +/- 15 mU/ml and LDH = 60 +/- 8 mU/ml) compared to the NIF group (CK = 82 +/- 5 mU/ml and LDH = 41 +/- 2 mU/ml, P < 0.05). Our results demonstrate that pretreatment with a single oral dose (20 mg) of nifedipine attenuates systolic and diastolic functional alterations as well as the metabolic impairment associated with stunning in the isolated rabbit heart.

Adenosine and dipyridamole mimic the effects of ischemic preconditioning

The effects of preconditioning, adenosine and dipyridamole in protecting the systolic and diastolic alterations of myocardial stunning in rabbit hearts were studied. Isovolumic left ventricular developed pressure (LVDP), and end diastolic pressure (LVEDP) were measured. The time constant of relaxation (T) was calculated. Isolated rabbit hearts were subject to 15 min of global ischemia (37 degrees C) followed by 30 min of reperfusion. LVDP and LVEDP stabilized to 55 +/- 5% and 320 +/- 28% of control values respectively (stunned group) T increased early in reperfusion (from 48.2 +/- 3.9 to 97.2 +/- 10 ms P < 0.05) but returned to control value late in reperfusion. When hearts were preconditioned by a single cycle of 5 min of ischemia LVDP and LVEDP stabilized at 89 +/- 3% and 162 +/- 34% of preischemic values respectively (P < 0.05 with respect to stunned group). The change in T was attenuated (62 +/- 6 ms at 5 min of reperfusion, P < 0.05 with respect to stunned group). Hearts treated either with adenosine (800 micrograms/min) or the nucleoside transport blocker dipyridamole (4 micrograms/min) previously to the ischemia, recovered their LVDP to 86 +/- 1% and 82 +/- 3% of preischemic values, respectively (P < 0.05 with respect to stunned group). Adenosine and dipyridamole also attenuated the increase in LVEDP (195 +/- 12% and 197 +/- 10% respectively, P < 0.05 with respect to stunned group).(ABSTRACT TRUNCATED AT 250 WORDS)

Chronic administration of nifedipine induces upregulation of dihydropyridine receptors in rabbit heart

In rabbits chronically pretreated with nifedipine (20 mg/day for 25 days), we demonstrate upregulation of Ca2+ channels in mammalian heart (maximal binding capacity = 222 +/- 14 and 421 +/- 55 fmol/mg protein for control and treated, respectively; P < 0.05) without significant changes in dissociation constant. No changes in calcium sensitivity or maximal force were detected by pretreatment with nifedipine in chemically skinned fibers. Cardiac contractility at different extracellular Ca2+ concentrations was similar in control and pretreated animals. This upregulation of Ca2+ channels in mammalian heart offers an explanation for the lack of significant negative inotropic effect after chronic administration of nifedipine.

Chronic administration of nicardipine attenuates myocardial stunning in isolated rabbit hearts

The purpose of this study was to evaluate the effects of the chronic administration of a calcium channel blocker, nicardipine, on systolic and diastolic alterations occurring during myocardial stunning in isolated rabbit hearts. Rabbits were pretreated with nicardipine 20 mg (O.I.D.) for 30 days. Then hearts were isolated (group II) and compared with control hearts (group I) in their response to 20 min of global ischemia and 30 min of reperfusion. Coronary flow and heart rate were kept constant. Left ventricular isovolumic developed pressure (LVDP), its first derivative (dP/dt), and end diastolic pressure (LVEDP) were measured. After isolation, no statistically significant changes were detected in LVDP, +dP/dtmax, LVEDP, or coronary resistance in hearts of rabbits with or without the pharmacological intervention. Early after the onset of reperfusion, LVDP and +dP/dtmax partially recovered in a similar way in groups I and II. Late in reperfusion LVDP stabilized at 48 +/- 7% in group I and 71 +/- 6% in group II (P < 0.05) and +dP/dtmax stabilized at 56 +/- 7% and 79 +/- 6% (P < 0.05), respectively. Diastolic dysfunction was manifested by a 217 +/- 39% increase in LVEDP (P < 0.05) in group I, and 140 +/- 31% in group II (P < 0.05). The isovolumic relaxation time constant (tau, tau) increased from 70 +/- 5 to 151 +/- 27 ms (P < 0.05), and from 66 +/- 6 to 97 +/- 10 ms. (NS) in groups I and II, respectively at 5 min of reperfusion. This relaxation parameter returned to normal values in the late reperfusion.(ABSTRACT TRUNCATED AT 250 WORDS)

Dissociation between myocardial relaxation and diastolic stiffness in the stunned heart: its prevention by ischemic preconditioning

The effects of myocardial stunning and ischemic preconditioning on left-ventricular developed pressure and end-diastolic pressure (diastolic stiffness) as well as on coronary-perfusion pressure were examined in isolated isovolumic rabbit hearts. The isovolumic relaxation was evaluated, and the time constant of pressure decay during the isovolumic period was calculated. Our experimental protocol comprised: 1) myocardial stunning-global ischemia (15 min) followed by reperfusion (30 min); 2) myocardial stunning-global ischemia (20 min) followed by reperfusion (30 min); and 3) ischemic preconditioning--a single cycle of brief global ischemia and reperfusion (5 min each), before a second ischemic period, of 20-min duration. There was no effect upon systolic and diastolic parameters when 15 and 20 minutes of ischemia were evaluated. In both stunned groups the left ventricular developed pressure first recovered to near control values, but then stabilized at only 60% of the control values. Whereas the isovolumic relaxation time constant was increased after 5 min of reperfusion, and return to control values at late reperfusion, the end diastolic pressure remained elevated during the entire period. Values of dP/dV calculated at common pressure levels, were used as a second index of diastolic stiffness. They were increased after stunning, as also was the coronary perfusion pressure. When the heart was preconditioned with a single episode of ischemia, the systolic and diastolic alterations were completely abolished. We thus concluded that diastolic abnormalities incurred by myocardial stunning consist in both an increase in diastolic stiffness and an early impairment of isovolumic relaxation.(ABSTRACT TRUNCATED AT 250 WORDS)

The effects of hypocapnic alkalosis on the myocardial contractility of isovolumic perfused rabbit hearts

During acute respiratory alkalosis myocardial contractility first increases but then decreases towards control levels. The mechanism of this response was investigated in isovolumic perfused rabbit hearts. Developed pressure (DP) and its first derivative (dP/dt) were measured before, during and after hypocapnia induced by equilibrating the perfusate with 2% CO2 rather than the 5% used in control. pH of the perfusate (pHo) changed from 7.36 +/- .02 to 7.71 +/- .01. After about 20 s, an increase in DP of about 20% was detected. This increase in contractility is followed by a partial recovery towards control levels. After the partial recovery a new mechanical steady state is reached in about 2 min. Neither 5-[N-ethyl-N-isopropyl]amiloride (EIPA) 10(-6) M, a blocker of the Na+/H+ exchanger, nor 4,4'-diisothiocyanatostilbene-2-2'-disulfonic acid (SITS) 10(-4) M, or 5-[aminosulfonyl]-4-chloro-2-[(2-furanylmethyl)-amino] benzoic acid (furosemide) 10(-4) M, blockers of Cl-/HCO3- exchanger, abolished the recovery in contractility towards control levels. The recovery was not abolished by replacing 50% of extracellular Cl- concentration by either sulfate or gluconate. The lack of blockade of this mechanical recovery in spite of the intervention performed suggests a mechanism other than the exchangers as the cause of the biphasic changes.