In vitro suppression of lymphocyte activation in patients with seasonal allergic rhinitis and pollen-related asthma by cetirizine or azelastine in combination with ginkgolide B or astaxanthin

Novel strategies are evaluated for management of allergic rhinitis and asthma in patients co-afflicted with both disorders. It is hypothesized that the platelet activating factor receptor antagonist ginkgolide B (GB) and the carotenoid antioxidant astaxanthin (ASX) interact with antihistamines cetirizine dihydrochloride (CTZ) and azelastine (AZE) to potentiate their ability to downregulate potentially pathological immune activation. Peripheral blood mononuclear cells from asthmatics and healthy subjects, cultured 24 hours with 50 μg/ml phytohemaglutinin (PHA) or PHA plus each drug are analyzed by flow cytometry for expression of CD25+ or HLA-DR+ by CD3+ (T cells). Results are reported as stimulation indices for CD3+CD25+ (SICD3+CD25+) and CD3+HLA-DR+ (SICD3+HLADR+) cells in cultures treated with PHA alone, versus cultures treated with both PHA and drugs. Optimal suppression of activated cells was observed in cultures stimulated with ASX 10-6 M + CTZ 10-6 M (SICD3+CD25+, p = 0.016; SICD3+HLADR, p = 0.012); ASX 10-6 M + AZE 10-6 M (SICD3+CD25+, p = 0.012; SICD3+HLADR, p = 0.015); GB 10-6 M + CTZ 10-6 M (SICD3+CD25+, p = 0.024, SICD3+HLADR+, p = 0.019). Results demonstrate improved activity of antihistamines by 2 phytochemicals, suggesting dosing strategies for animal trials of ASX- or GB-augmented formulations for seasonal allergic rhinitis and asthma.

Role of haeme oxygenase-1 in resolution of oxidative stress-related pathologies: focus on cardiovascular, lung, neurological and kidney disorders

The present review examines the role of the cytoprotective enzyme haeme oxygenase-1 (HO-1) in adaptive responses to inflammatory disease and explores strategies for its clinical use, with particular emphasis on use of therapeutic use of the enzyme using phytochemical inducers of HO-1 such as extracts of Ginkgo biloba, curcumin, and flavonoids extracted from seeds of the sour cherry (Prunus cerasus). This laboratory has identified strategies by which combinations of dietary phytochemicals may be configured to synergistically strengthen immunoregulatory mechanisms that normally prevent inflammation from leading to disease. A major focus of this research initiative has been HO-1, which is capable of substantially reducing oxidative stress by several mechanisms. HO-1 metabolizes haeme that accumulates in tissues because of red blood cell turnover. Two products of this degradation - carbon monoxide (CO) and bilirubin - have potent capacity for reducing oxidative stress and for counteracting its effects. A description will be provided of how HO-1 products maintain healthy tissue function and remediate oxidative tissue damage. This will be explored in four major organ systems, including the cardiovascular system, the lungs, the central nervous system and the kidneys. Particular focus will be given to the physiological coordination of cardiovascular functions mediated by CO produced by HO-1 and to nitric oxide (NO), a gaseous second messenger expressed by nitric oxide synthetase. A major unifying theme of the present review is an exploration of the potential use of dietary phytochemical formulations as tools for the clinical application of HO-1 in therapeutic reduction of oxidative stressors, with resultant improved treatment of inflammatory pathologies.

Inhibition of cardiac leptin expression after infarction reduces subsequent dysfunction

Leptin is known to exert cardiodepressive effects and to induce left ventricular (LV) remodelling. Nevertheless, the autocrine and/or paracrine activities of this adipokine in the context of post-infarct dysfunction and remodelling have not yet been elucidated. Therefore, we have investigated the evolution of myocardial leptin expression following myocardial infarction (MI) and evaluated the consequences of specific cardiac leptin inhibition on subsequent LV dysfunction. Anaesthetized rats were subjected to temporary coronary occlusion. An antisense oligodesoxynucleotide (AS ODN) directed against leptin mRNA was injected intramyocardially along the border of the infarct 5 days after surgery. Cardiac morphometry and function were monitored by echocardiography over 11 weeks following MI. Production of myocardial leptin and pro-inflammatory cytokines interleukin (IL)-1β and IL-6 were assessed by ELISA. Our results show that (1) cardiac leptin level peaks 7 days after reperfused MI; (2) intramyocardial injection of leptin-AS ODN reduces early IL-1β and IL-6 overexpression and markedly protects contractile function. In conclusion, our findings demonstrate that cardiac leptin expression after MI could contribute to the evolution towards heart failure through autocrine and/or paracrine actions. The detrimental effect of leptin could be mediated by pro-inflammatory cytokines such as IL-1β and IL-6. Our data could constitute the basis of new therapeutic approaches aimed to improve post-MI outcome.

The role of exogenous carbon monoxide in the recovery of post-ischemic cardiac function in buffer perfused isolated rat hearts

Isolated rat hearts were perfused for 10 min with oxygenated buffer and equilibrated with carbon monoxide (CO) of 0.001% and 0.01% before the induction of 30 min global ischemia followed by 120 min of reperfusion. These concentrations of CO significantly improved the post-ischemic recovery of coronary flow (CF), aortic flow (AF), and left ventricular developed pressure (LVDP). The improvement in recovery reflected in the reduction of infarct size and the incidence of reperfusion-induced ventricular fibrillation (VF). Thus, hearts subjected to 0.001% and 0.01% of CO exposure via the perfusion buffer, infarct size was reduced from the CO-free control value of 39% +/- 5% to 21% +/- 3% (*p<0.05) and 18% +/- 4% (*p<0.05), respectively. In the presence of 0.001% and 0.01% CO, the incidence of VF was also reduced from its control value of 92% to 17% (*p<0.05) and 17% (*p<0.05), respectively. Increasing the CO exposure to 0.1% in the buffer, all hearts showed VF combined with ventricular tachycardia or bradycardia and various rhythm disturbances indicating the direct toxic effects of CO on the myocardium. The results show that cardioprotective concentrations (0.01% and 0.001%) of exogenous CO related to an increase in cGMP levels and guanylate cyclase activities.

Cardioprotection with white wine

The cardioprotective effects of red wine have been attributed to several polyphenolic antioxidants including resveratrol and proanthocyanidins. The goal of the present study was to determine whether white wines could also provide cardioprotection. Three different white wines (white wine #1, #2 and #3) were chosen for this study. Ethanol-free extracts of the wines were prepared by vacuum evaporation. Rats weighing approximately 200 g were given either 50 mg/kg or 100 mg/kg of each wine extract for 3 weeks. The rats were anesthetized and sacrificed and their hearts were excised for the preparation of isolated working rat heart. All hearts were subjected to 30 min of global ischemia followed by 2 h of reperfusion. Cardiac function including heart rate, left ventricular developed pressure (LVDP), maximum first derivative of developed pressure (LVdp/dtmax), left ventricular systolic pressure (LVSP), left ventricular end diastolic pressure (LVEP), aortic flow (AF) and coronary flow (CF) were continuously monitored and myocardial infarct size was measured at the end of the experiments. The results of our study demonstrated that among the three different white wines, only white wine #2 conferred cardioprotection as evidenced by improved postischemic ventricular recovery compared with controls. The same white wine at a dose of 50 mg/kg also showed improvement in postischemic contractile recovery but the differences compared with controls were not significant. The amount of malondialdehyde production from these hearts was lower than that found in control hearts, indicating reduced formation of reactive oxygen species in white wine #2-treated rats. In vitro studies using a chemiluminescence technique revealed that white wine #2 scavenged both superoxide anions and hydroxyl radicals. The results of our study demonstrate that white wine #2 provided cardioprotection and the cardioprotective effect of the wine can be attributed, at least in part, to its ability to function as an in vivo antioxidant.

Benefits of resveratrol in women's health

Resveratrol and trans-resveratrol are powerful phytoestrogens, present in the skins of grapes and other plant foods and wine, which demonstrate a broad spectrum of pharmacological and therapeutic health benefits. Phytoestrogens are naturally occurring plant-derived nonsteroidal compounds that are functionally and structurally similar to steroidal estrogens, such as estradiol, produced by the body. Various studies, reviewed herein, have demonstrated the health benefits of phytoestrogens in addressing climacteric syndrome including vasomotor symptoms and postmenopausal health risks, as well as their anticarcinogenic, neuroprotective and cardioprotective activities and prostate health and bone formation promoting properties. Conventional HRT drugs have been demonstrated to cause serious adverse effects including stroke and gallbladder disease, as well as endometrial, uterine and breast cancers. Recent research demonstrates that trans-resveratrol binds to human estrogen receptors and increases estrogenic activity in the body. We investigated the effects of protykin, a standardized extract of trans-resveratrol from Polygonum cuspidatum, on cardioprotective function, the incidence of reperfusion-induced arrhythmias and free radical production in isolated ischemic/reperfused rat hearts. The rats were orally treated with two different daily doses of protykin for 3 weeks. Coronary effluents were measured for oxygen free radical production by electron spin resonance (ESR) spectroscopy in treated and drug-free control groups. In rats treated with 50 and 100 mg/kg of protykin, the incidence of reperfusion-induced ventricular fibrillation was reduced from its control value of 83% to 75% (p < 0.05) and 33% (p < 0.05), respectively. Protykin was seen to possess cardioprotective effects against reperfusion-induced arrhythmias through its ability to reduce or remove the reactive oxygen species in ischemic/reperfused myocardium. Taken together, these data suggest that trans-resveratrol supplementation may be a potential alternative to conventional HRT for cardioprotection and osteoporosis prevention and may confer other potential health benefits in women.

Non-specific caspase inhibition reduces infarct size and improves post-ischaemic recovery in isolated ischaemic/reperfused rat hearts

Myocardial ischaemia and reperfusion lead to myocardial cell death due, at least in part, to apoptotic mechanisms. Although cysteinyl aspartate-specific proteinase (caspase) activation is a major event and the most-cited culprit in the development of apoptosis, its potential contribution to ischaemic myocardial cell death is largely unknown. To study the role of caspase activation, isolated rat hearts (n=6 per group) were subjected to 30 min coronary artery occlusion followed by 120 min reperfusion. A non-selective [0.1 or 0.5 microM acetyl-Tyr-Val-Ala-Asp chloromethylketone (YVAD-cmk)] or selective caspase inhibitors [0.07 or 0.2 microM acetyl-Asp-Glu-Val-Asp-cmk (Ac-DEVD-cmk, caspase-3 inhibitor); 0.07 or 0.2 microM benzoxycarbonyl-Leu-Glu-OMe-His-Asp(OMe)-fluoromethylketone (z-LEHD-fmk, caspase-9 inhibitor)] were added to the perfusate at the start of reperfusion. Non-selective caspase inhibition with 0.1 or 0.5 microM YVAD-cmk limited infarct size: (21 +/- 4%, P<0.05; 17 +/- 3%, P<0.05, respectively) compared with the ischaemic/reperfused control (32 +/- 5%). In hearts treated with 0.1 or 0.5 microM caspase II non-selective inhibitor, the fraction of terminal-deoxynucleotidyl-transferase deoxyuridine nick end labelling (TUNEL)-positive myocyte nuclei in the infarcted zone was reduced from the ischaemic/reperfused non-treated control of 11.2 +/- 2.1% to 6.2 +/- 1.6% (P<0.05) and 1.2 +/- 0.2% (P<0.05), respectively. The recovery of post-ischaemic cardiac function (coronary flow, aortic flow and left-ventricular developed pressure) improved significantly with the application of the non-selective caspase inhibitor as well. In hearts perfused with specific caspase inhibitors (caspase-3 and caspase-9) there was no significant reduction in the infarct size, no improvement in post-ischaemic cardiac function and no reduction of apoptotic cell death. We conclude that non-specific inhibition of caspases may be therapeutically beneficial in myocardial ischaemia/reperfusion-induced damage, while selective caspase inhibitors may fail to prevent such reperfusion-induced injury in our model system.

Grape seed proanthocyanidin reduces cardiomyocyte apoptosis by inhibiting ischemia/reperfusion-induced activation of JNK-1 and C-JUN

The mechanism of cardioprotection with red wine consumption was studied by examining the antideath signaling cascade of one of the principle components of red wine, proanthocyanidins. Grape seed proanthocyanidin extract (GSPE) was administered orally (100 mg/kg/d) supplemented with regular diet for 3 weeks to a group of rats while the other group was given the regular diet only for the same period of time. After 3 weeks, rats were sacrificed, hearts excised, and perfused via Langendorff mode. After stabilization, hearts were perfused in the working mode for baseline measurement of contractile function. Hearts were then made globally ischemic for 30 min followed by 2 h of reperfusion. Contractile function was continuously monitored during reperfusion, and free radical production was examined by electron spin resonance (ESR) technique. Cardiomyocyte apoptosis was examined by TUNEL staining in conjunction with an antibody against myocin heavy chain to specifically detect myocytes. Induction of JNK-1 and c-fos proteins was studied by Western blot analysis using respective antibodies followed by densitometric scanning. The results indicated significant induction of JNK-1 and c-fos proteins in the ischemic/reperfused myocardium, which was inhibited by the proanthocyanidin extract. In concert, GSPE significantly reduced the appearance of apoptotic cardiomyocytes in the ischemic/reperfused hearts. GSPE also significantly reduced the appearance of the reactive oxygen species in the hearts. Improved postischemic contractile recovery was achieved with GSPE suggesting its cardioprotective action. The results of this study indicated that GSPE functioned as an in vivo antioxidant, and its cardioprotective properties may be at least partially attributed to its ability to block antideath signal through the inhibition of proapoptotic transcription factor and gene, JNK-1 and c-Jun.

Functional and biochemical evidence for capsaicin-induced neural endothelin release in isolated working rat heart

In isolated working rat heart, capsaicin elicited a concentration-dependent constriction of coronary arteries accompanied by decline of all cardiac parameters recorded (heart rate, coronary and aortic flow, left ventricular developed pressure, and first derivative of left ventricular developed pressure). The following evidence suggests that capsaicin-induced changes are mediated by endothelin of neural origin: (1) the capsaicin (10 nM)-evoked decrease in coronary flow resulting in deterioration of cardiac functions was mimicked by endothelin (0.1 nM); (2) the selective endothelin ET(A) receptor antagonist, cyclo (D-alpha-aspartyl-L-propyl-D-valyl-L-leucyl-D-tryptophyl) (1 microM), abolished the cardiac effects provoked by capsaicin (10 nM); (3) reduction of extracellular Ca2+ concentration from 2.4 to 1.2 or 0.6 mM inhibited the cardiac effects of capsaicin (10 nM) but not those induced by endothelin (0.1 nM); (4) perfusion of the heart with 0.1% (v/v) Triton X-100 damaged the endothelium and reversed the enhancement of coronary flow evoked by bethanechol (1 microM), decreased the basal flow, but was without effect on capsaicin-induced coronary constriction; (5) in response to capsaicin challenge (10-100 nM), the endothelin concentration measured in coronary effluent by means of radioimmunoassay increased up to sevenfold but remained unchanged in the presence of 0.6 mM Ca2+; (6) no reduction of coronary flow was induced by capsaicin (100 nM) applied to the heart of rats which were desensitised by capsaicin (150 mg/kg). It is concluded that, in the rat heart, capsaicin acting on VR1 capsaicin receptors elicits a release of endothelin from the sensory nerve terminals.

Regulation of ventricular fibrillation by heme oxygenase in ischemic/reperfused hearts

We have assessed the relationship between reperfusion-induced ventricular fibrillation (VF) and heme oxygenase (HO) mRNA expression using northern blotting, reverse transcription-polymerase chain reaction (RT-PCR), and enzyme activity in isolated working ischemic/reperfused rat hearts. Isolated hearts were subjected to 30 min of global ischemia followed by 120 min of reperfusion. Upon reperfusion with VF, cardiac function was registered (n = 6 in each group), and HO mRNAs and enzyme activities were measured at the end of reperfusion in hearts that showed VF or did not develop VF. The expression of HO-1 mRNA (about fourfold) was observed in ischemic/reperfused nonfibrillated myocardium in comparison with the nonischemic control hearts. In those hearts when VF was developed, the expression of HO-1 mRNA was not observed in comparison with the nonischemic control myocardium. The results measured by RT-PCR and enzyme analysis support the data obtained by northern blotting. In additional studies, we decided to approach the question from a different angle. Thus, the purpose of our work was also to study the role of HO expression and enzyme activity in electrically fibrillated hearts without the ischemic/reperfused protocol. To simulate the period of 10 min of reperfusion-induced VF, hearts were electrically fibrillated, then defibrillated, and perfused for an additional 110 min, and HO-1 mRNA expression and enzyme activities were determined. Thus, electrically induced VF resulted in about 60%, 60%, and 70% reduction in HO-1 mRNA expression, RT-PCR signal intensity, and enzyme activity, respectively, compared with the nonfibrillated ischemic/reperfused group. In conclusion, our data provide evidence that the development of reperfusion-induced VF inhibits HO-1 mRNA expression and enzyme activity in both electrically fibrillated myocardium and ischemic/reperfused fibrillated hearts. The results clearly show that HO-1 mRNA expression and enzyme activity were increased in ischemic/reperfused nonfibrillated myocardium, suggesting that interventions that are able to increase HO-1 mRNA expression and enzyme activity may prevent the development of VF.

Effects of oxidative stress on the expression of antioxidative defense enzymes in spontaneously hypertensive rat hearts

Little is known concerning the effect of oxidative stress on the expression of antioxidative enzymes in the decompensated cardiac hypertrophy of spontaneously hypertensive rats (SHR), considered as a model of dilative cardiomyopathy in man. Superoxide dismutase (SOD), catalase, and glutathione peroxidase (GPx) were characterized in isolated perfused hearts of 18 month old SHR and the age-matched normotensive control Wistar-Kyoto (WKY) rats, before and after 30 min infusion of 25 microM H(2)O(2). After infusion of H(2)O(2), aortic flow decreased in WKY from 26.2 +/- 2.2 to 16.0 +/- 0.8 ml/min (p <.05) but not in SHR (18.2 +/- 1.9 vs. 20.7 +/- 2.2 ml/min). This protection was related to the higher myocardial activities of GPx, MnSOD and CuZnSOD in SHR, compared with those of the WKY group. Although total SOD activity in the SHR fell after H(2)O(2) exposure (to 1.81 +/- 0.13 from 3.56 +/- 0.49 U/mg of protein), catalase activity increased (to 2.46 +/- 0.34 from 1.56 +/- 0.29 k min(-1)mg(-1)protein), compared with the pre-infusion period (p <.05 in each case). In additional studies, hearts were subjected to 30 min of global ischemia followed by 30 min of reperfusion. The results obtained in ischemic/reperfused hearts show the same changes in enzyme activities measured as it was observed in H(2)O(2) perfused hearts, indicating that oxidative stress is independent of the way it was induced. The higher catalase activity derived from elevated mRNA synthesis. The antioxidative system in dilative cardiomyopathic hearts of SHR is induced, probably due to episodes of oxidative stress, during the process of decompensation. This conditioning of the antioxidative potential may help overcome acute stress situations caused by reactive oxygen species in the failing myocardium.

Effect of transdermal nitroglycerin on glucose-stimulated insulin release in healthy male volunteers

BACKGROUND

Morpholinosydnonimine, a nitric oxide (NO) donor, has been reported to inhibit insulin release in isolated pancreatic islets. We studied whether transdermal application of nitroglycerin, another NO donor widely used for angina prophylaxis, influenced glucose-stimulated insulin release in healthy, young, male volunteers.

METHODS AND RESULTS

Oral glucose tolerance tests [(OGTT) 75 g glucose in 200 mL of water) were performed in the presence of placebo patches or nitroglycerin-releasing 'active' patches (approx. 0.4 mg hour-1 nitroglycerin) in the same patients with a 2-week intertest interval. Venous blood samples were taken before and 15, 30, 60, 90, 120 and 180 min after the glucose load and evaluated for plasma glucose level and immunoreactive insulin responses (radioimmunoassay). Glucose-stimulated maximum increase in plasma insulin immunoreactivity were 36.3 +/- 5 and 78.8 +/- 6.1 mU mL-1 (P < 0.05) in the presence of active and placebo patches, respectively. Nevertheless, both fasting and postload blood glucose levels were the same at either patch. Active patches significantly decreased blood pressure with a marginal increase in heart rate.

CONCLUSION

We conclude that inhibition of glucose-stimulated insulin release by transdermal nitroglycerin without causing hyperglycaemia may serve as a novel component of the antianginal mechanism of action of nitrates.

Cardioprotective effects of the calcineurin inhibitor FK506 and the PAF receptor antagonist and free radical scavenger, EGb 761, in isolated ischemic/reperfused rat hearts

Effects of the calcineurin inhibitor FK506, the platelet-activating factor (PAF) antagonist, and free radical scavenger Ginkgo biloba extract, EGb 761, and their combination on reperfusion-induced ventricular fibrillation (VF), ventricular tachycardia (VT), and recovery of cardiac function were studied after 30 min of global ischemia followed by 2 h of reperfusion in isolated rat hearts. In the first series of studies, rats received a daily (oral) dose of 0, 1, 5, 10, 20, or 40 mg/kg/day FK506 for 10 days. FK506 dose-dependently reduced the incidence of reperfusion-induced total (irreversible plus reversible) VF from a value of 92% for untreated animals to 92% (NS), 83% (NS), 67% (NS), 33% (p<0.05), and 25% (p<0.05), for doses of 1-40 mg/kg/day, respectively, with effects on incidence of VT showing the same pattern. FK506, between 20 and 40 mg/kg/day, also resulted in significant recovery of postischemic cardiac function. In the second series of studies, rats were treated with EGb 761 alone or in combination with FK506. Whereas no significant reduction in arrhythmias or improvement in cardiac function resulted from a single intervention of EGb 761 at 25 mg/kg/day, combined treatment of rats with 25 mg/kg/day of EGb 761 and 1 or 5 mg/kg/day of FK506 resulted in a reduction in total and irreversible VF of 92% and 92% to 42% (p<0.05) and 33% (p<0.05), 25% (p<0.05) and 8% (p<0.05), respectively, versus untreated control animals, paralleled by similar effects on the incidence of VT and accompanied by significant improvements in postischemic cardiac function. Our results demonstrate a novel cardioprotective characteristic of FK506 and suggest that combination therapy by using FK506 plus EGb 761 synergistically improves postischemic cardiac function, while reducing the incidence of reperfusion-induced VF and VT, which may expand the clinical utility of FK506 and allow therapy with FK506 at lower doses than are currently useful.

Classic preconditioning decreases the harmful accumulation of nitric oxide during ischemia and reperfusion in rat hearts

BACKGROUND

The role of NO in the mechanism of preconditioning is not understood. Therefore, we studied the effect of preconditioning and subsequent ischemia/reperfusion on myocardial NO content in the presence of an NO synthase (NOS) inhibitor.

METHODS AND RESULTS

Isolated working rat hearts were subjected to preconditioning protocols of 3 intermittent periods of rapid pacing or no-flow ischemia of 5 minutes' duration each followed by a test 30 minutes of global no-flow ischemia and 15 minutes of reperfusion. Test ischemia/reperfusion resulted in a deterioration of myocardial function and a considerable increase in cardiac NO content as assessed by electron spin resonance. Preconditioning improved postischemic myocardial function and markedly decreased test ischemia/reperfusion-induced NO accumulation. In the presence of 4.6 micromol/L N(G)-nitro-L-arginine (LNA), basal cardiac NO content decreased significantly, although test ischemia/reperfusion-induced functional deterioration and NO accumulation were not affected in nonpreconditioned hearts. However, the protective effects of preconditioning on both test ischemia/reperfusion-induced functional depression and NO accumulation were abolished. When 4.6 micromol/L LNA was administered after preconditioning, it failed to block the effect of preconditioning. In the presence of 46 micromol/L LNA, ischemia/reperfusion-induced NO accumulation was significantly decreased and postischemic myocardial function was improved in nonpreconditioned hearts.

CONCLUSIONS

Our results show that (1) although NO synthesis by the heart is necessary to trigger classic preconditioning, preconditioning in turn attenuates the accumulation of NO during ischemia/reperfusion, and (2) blockade of ischemia/reperfusion-induced accumulation of cardiac NO by preconditioning or by an appropriate concentration of NOS inhibitor alleviates ischemia/reperfusion injury as demonstrated by enhanced postischemic function.

The protective effect of EGb 761 in isolated ischemic/reperfused rat hearts: a link between cardiac function and nitric oxide production

This study was conducted to evaluate the effect of Ginkgo biloba extract (EGb 761) on the nitric oxide (NO) production in relation to the recovery of postischemic cardiac function in isolated working rat hearts. Rats were orally treated with various doses (25, 50, 75, and 100 mg/kg/day) of EGb 761 for 10 days. Hearts were isolated in "working mode" and subjected to 30-min ischemia followed by 120 min of reperfusion. EGb 761 inhibited NO production measured by electron spin-resonance spectroscopy (ESR), and improved the recovery of postischemic cardiac function (coronary flow, aortic flow, left ventricular developed pressure and its first derivative) in the ischemic/reperfused myocardium. Thus in rats treated with 25, 50, 75, and 100 mg/kg/day of EGb 761 and in hearts subjected to 30-min ischemia followed by 120 min of reperfusion, aortic flow was increased from its postischemic drug-free control value of 8.0+/-0.4 to 8.6+/-0.4 ml/min (NS), 17.3+/-0.9 ml/min (p<0.05), 21.5+/-1.1 ml/min (p<0.05), and 23.6+/-1.2 ml/min, respectively. The same recovery in postischemic coronary flow, left ventricular developed pressure, and its first derivative also was observed. In the initial phase of reperfusion, NO production measured by ESR was reduced by 85% in the 75 mg/ kg/day of EGb 761-treated group in comparison with the drug-free ischemic/reperfused hearts. Inducible NO synthase (iNOS) messenger RNA (mRNA) measured by reverse transcription-polymerase chain reaction (RT-PCR) also was reduced by 41 and 58% in the groups treated with 75 and 100 mg/kg/day of EGb 761, respectively. Our findings show that EGb 761 directly acts as an NO scavenger and concomitantly inhibits the expression of iNOS mRNA. Thus, EGb 761 may act as a potent inhibitor of NO production under the condition of ischemia/reperfusion, improving the recovery of postischemic cardiac function.

Interplay between nitric oxide and CGRP by capsaicin in isolated guinea-pig heart

Capsaicin at a concentration of 10(-7)m induced a significant increase in heart rate and increased coronary flow in isolated Langendorff-perfused guinea-pig hearts. This effect was completely blocked by 30 microm of N(omega)-nitro-L-arginine methyl ester (L-NAME), an inhibitor of nitric oxide synthase. Additional incubation with 3 m m L-Arg antagonized the inhibitory effect of L-NAME. In the presence of 1 microm of a human calcitonin gene-related peptide fragment (hCGRP 8-37), a CGRP-receptor antagonist, L-Arg was without effect. We conclude that a capsaicin-induced increase in coronary flow and heart rate is dependent from an interplay between CGRP and NO in guinea-pig hearts. 1999 Academic Press.

Heme oxygenase and cardiac function in ischemic/reperfused rat hearts

We investigated whether the expression of heme oxygenase (HO) isozymes was related to the occurrence of ventricular fibrillation (VF) induced by ischemia/reperfusion in nondiabetic and diabetic myocardium. To study the role of HO-1 and HO-2 mRNA expression in VF, isolated hearts obtained from nondiabetic and 8-week diabetic rats were subjected to 30 min of ischemia followed by 2 h of reperfusion. Expression of HO-1 and HO-2 mRNA was studied in fibrillated and nonfibrillated myocardium using Northern blotting and reverse transcription polymerase chain reaction (RT-PCR). The effect of zinc protoporphyrin IX (Zn-PPIX), a potent inhibitor of HO activity, on HO activity was also studied in ischemic/reperfused hearts. Upon reperfusion, an expression of HO-1 was observed in nonfibrillated myocardium. HO-1 mRNA expression was significantly reduced in hearts showed VF. Zn-PPIX (5 microM) treatment reduced HO activity from its control values of 398+/-27 (in nondiabetics) and 370+/-20 pmol bilirubin/h (in diabetics) to 69+/-14 (in nondiabetics, p<.05) and 60+/-11 pmol bilirubin/h (in diabetics, p<.05), respectively, and all hearts, upon reperfusion, showed VF in both nondiabetic and diabetic subjects. HO-2 expression was unchanged in nonfibrillated and fibrillated myocardium. Postischemic function showed no correlation with the expression of these genes. Our data show that the mechanism(s) of ischemia/reperfusion-induced VF involves the downregulation of HO-1 mRNA and a reduction in HO activity. Furthermore, the mechanism(s) of VF at molecular level involving HO isozymes does not show a significant difference between nondiabetics and diabetics.

Interaction between capsaicin and nitrate tolerance in isolated guinea-pig heart

Capsaicin-induced increases in heart rate and coronary flow were blocked by N(G)-nitro-L-Arg-methyl ester (30 mM) in Langendorff-perfused guinea-pig hearts. Neither heart rate nor coronary flow changed by capsaicin in hearts from animals made tolerant to the hypotensive effect of 30 microg/kg nitroglycerin by the administration of 50 mg/kg nitroglycerin subcutaneously 4 times a day over 3 days. We conclude that the effector function of sensory nerves may deteriorate in nitrate tolerance.

Role of nitric oxide and TPEN, a potent metal chelator, in ischaemic and reperfused rat isolated hearts

1. The role of nitric oxide (NO) was studied in the control of ischaemic/reperfused cardiac function and the effect of N,N,N',N'-tetrakis-[2-pyridylmethyl]-ethylenediamine (TPEN), a potent metal chelator, on the regulation of cardiac NO formation. 2. Rat isolated working hearts were subjected to 30 min ischaemia and reperfusion. The incidence of reperfusion-induced ventricular fibrillation (VF), ventricular tachycardia (VT) and the recovery of cardiac function were measured. Nitric oxide was detected by electron spin resonance (ESR) spectroscopy. 3. With 5.0, 7.5 and 10.0 mumol/L of TPEN administered prior to ischaemia, the drug produced a reduction in the incidence of VF from its control value of 100% to 25% (P < 0.05), 17% (P < 0.05) and 8% (P < 0.05), respectively. The incidence of VT followed the same pattern. 4. When TPEN was given at the moment of reperfusion, a reduction in the incidence of VF and VT was still observed. Reduction in the incidence of VF and VT was reflected in the improvement of cardiac function both in the pre- and post-ischaemic TPEN-treated groups. 5. TPEN reduced basal cardiac NO content and prevented the accumulation of NO during ischaemia/reperfusion. 6. The results show that TPEN exerts beneficial effects on postischaemic cardiac function and dysrhythmias in relation to inhibition of the accumulation of NO in ischaemic/reperfused myocardium.

Preconditioning of rat heart with monophosphoryl lipid A: a role for nitric oxide

Preconditioning with monophosphoryl lipid A (MLA) protects rabbit hearts from prolonged ischemic reperfusion injury by a mechanism involving inducible nitric oxide synthase (iNOS) activation. This study was undertaken to determine whether MLA also could precondition rat hearts in a similar manner. Rats were injected with two different doses of MLA (300 microg/kg or 450 microg/kg i.v.) or vehicle (control), and after 24 hr the animals were sacrificed for preparation of isolated perfused rat hearts. Hearts were then perfused by working mode, and then made ischemic for 30 min followed by 30 min of reperfusion. Another group of hearts were treated simultaneously with a nitric oxide (NO) blocker, L-nitro-arginine-methyl-ester (L-NAME) (10 mg/kg) and MLA (450 microg/kg). For arrhythmia studies, 12 hearts were used in each group (total, 48 hearts). Cardiac functions were examined in a separate group of 24 hearts (n = 6/group). MLA-treated hearts (either dose) were tolerant to ischemic reperfusion injury as evidenced by improved postischemic ventricular recovery [coronary flow (ml/min) 19.1 +/- 0.8 (300 microg/kg MLA), 22.6 +/- 1.0 (450 microg/kg MLA) vs. 15.9 +/- 0.7 (control); aortic flow (ml/min) 20.7 +/- 1.8 (300 microg/kg MLA), 25.8 +/- 1.4 (450 microg/kg MLA) vs. 11. 0 +/- 0.8 (control); left ventricular developed pressure (kPa) 13.3 +/- 0.6 (300 microg/kg MLA), 14.6 +/- 0.2 (450 microg/kg MLA) vs. 10. 3 +/- 0.7 (control)]. Incidences of ventricular fibrillation and ventricular tachycardia were decreased compared with the control group only in the 450 microg/kg dose of MLA-treated hearts (92% to 33%). Pretreatment of the hearts with L-NAME inhibited the preconditioning effect of MLA. To examine the induction of the iNOS expression, RNAs were extracted from the control and MLA-treated hearts (after 2, 4,6, 8, 12 and 24 hr of treatment) and Northern blot analyses were performed with a specific cDNA probe for iNOS. A single band of approximately 4.6 kb corresponding to iNOS mRNA was detected after 4 hr of MLA treatment, whereas the maximal iNOS expression was found between 6 and 8 hr of MLA treatment. The results of this study demonstrated that MLA induced the expression of iNOS and protected the myocardium from ischemic reperfusion injury which is blocked by an inhibitor of NO synthesis, which suggests a role of NO in MLA-mediated cardioprotection.

Induction of iNOS gene expression by monophosphoryl lipid A: a pharmacological approach for myocardial adaptation to ischemia

Using the concept that exposing a cell to an adverse environment (stress) results in the stimulation of its endogenous defense system, hearts have been adapted to ischemia by exposing them to diverse stresses. Recently, 24-h pretreatment of monophosphoryl lipid A (MLA), a chemically modified derivative of endotoxin, was found to render the hearts more tolerant to ischemic reperfusion injury. Since nitric oxide has recently been implicated in myocardial preservation and since inducible nitric oxide synthetase (iNOS) was originally characterized in macrophages and shown to be maximally induced by bacterial lipopolysaccharides (endotoxin), we sought to determine whether MLA mediates its cardioprotective effects through the iNOS expression. For this, rats were injected with MLA (300 micrograms/kg) or vehicle (control), and after 24 h the animals were sacrificed and the isolated working hearts were made ischemic for 30 min followed by 30 min of reperfusion. MLA-treated hearts were found to be tolerant to ischemic reperfusion injury as evidenced by improved postischemic ventricular recovery. After 30 min of reperfusion, left ventricular developed pressure (LVDP) and its maximum first derivative (LVmaxdp/dt) were 13.3 +/- 0.3 kPa and 537 +/- 13 kPa/s, respectively, in the MLA-treated group, as compared with 10.2 +/- 0.4 kPa (p < 0.05) and 447 +/- 11 kPa/s (p < 0.05), respectively, for the control group. Aortic flow and coronary flow were 20.1 +/- 1.4 ml/min and 19.1 +/- 0.8 ml/min, respectively, in the MLA group, as compared with 9.5 +/- 0.8 ml/min (p < 0.05) and 15.9 +/- 0.7 ml/min (p < 0.05), respectively, for the untreated group. To examine the induction of the iNOS expression, RNAs were extracted from the control and MLA-treated hearts (after 2, 4, 6, 8, 12 and 24 h of treatment) and Northern blot analysis was performed using specific cDNA probe for iNOS. A single band of approximately 4.6 kb corresponding to iNOS mRNA was detected after 4 h of MLA treatment, while the maximal iNOS expression was found between 6-8 h of MLA treatment. The results of this study demonstrate that MLA induces the expression of iNOS and protects the myocardium from ischemic reperfusion injury.

Ischemic preconditioning triggers phospholipase D signaling in rat heart

Recent studies have indicated that repeated brief episodes of ischemia and reperfusion render the myocardium more tolerant to subsequent lethal ischemic injury. In view of the previous observations that ischemia-reperfusion potentiates phospholipase D signaling and that such signaling is beneficial for the heart, we investigated whether a similar phospholipase D signaling is responsible for the beneficial effects associated with repeated ischemia and reperfusion. Using an isolated perfused working rat heart model, we demonstrated that four brief episodes of 5 min of ischemia and 10 min of reperfusion reduced the incidence of ventricular arrhythmias, enhanced the postischemic ventricular performance, and decreased the release of creatine kinase from the reperfused heart, with simultaneous activation of phospholipase D generating the second messengers diacylglycerol and phosphatidic acid and leading to the translocation and activation of protein kinase C. The specific antiphospholipase D antibody blocked the activation of phospholipase D and attenuated the generation of diacylglycerol and phosphatidic acid and activation of protein kinase C. In concert, phospholipase D inhibition increased the incidence of ventricular arrhythmias, blocked the beneficial effects of preconditioning on the ventricular performance, and increased the amount of creatine kinase release from the coronary effluent. The results of this study indicate that repeated brief episodes of ischemia and reperfusion exert beneficial effects on the intact rat heart by triggering the activation of a phospholipase D signaling mechanism.

Extracellular Mg++ manipulation prevents the proarrhythmic activity of cromakalim in ischemic/reperfused diabetic hearts

Cromakalim, an adenosine triphosphate-sensitive potassium channel opener, shows proarrhythmic activity at moderate doses (1-10 micromol/liter) in the ischemic and reperfused myocardium. We studied the effects of extracellular Mg++ ([Mg++]o) on the incidence of reperfusion-induced ventricular fibrillation and ventricular tachycardia in isolated working hearts (n = 12 in each group) subjected to 20 min of global ischemia followed by 30 min of reperfusion, a model eliciting a low incidence of reperfusion arrhythmias, obtained from 8-wk streptozotocin-induced diabetic rats. Cromakalim, at a concentration of 3 micromol/liter, perfused 5 min before the induction of ischemia and throughout reperfusion increased the incidence of ventricular fibrillation and ventricular tachycardia from their drug-free diabetic control values of 25 and 42% ([Mg++]o = 1.2 mmol/liter) to 92% (P < .05) and 100% (P < .05), respectively. Glibenclamide at a concentration of 3 micromol/liter prevented the proarrhythmiac activity of cromakalim. Increasing concentration of [Mg++]o to 2.4, 3.6 and 4.8 mmol/liter in the perfusion buffer, the arrhythmogenic effect of cromakalim was also abolished. Thus, with 2.4, 3.6 and 4.8 mmol/liter of [Mg++]o perfused before the administration of cromakalim and the onset of ischemia, the incidence of reperfusion-induced ventricular tachycardia was reduced from 92% (in cromakalim treated group) to 67%, 42% (P < .05), and 25% (P < .05), respectively. The incidence of reperfusion-induced ventricular tachycardia showed the same pattern. Elevated [Mg++]o prevented the cromakalim-induced cellular Na+ gain and K+ loss, measured by atomic absorption spectrophotometer. [Mg++]o could prevent the proarrhythmic activity of cromakalim, and the use of cromakalim as an antihypertensive or antiischemic agent may be of particular concern in the population of postischemic diabetic subjects who are known to be at high risk of sudden coronary death.

Effects of Ginkgo biloba extract and preconditioning on the diabetic rat myocardium

Effects of preconditioning and Ginkgo biloba extract (EGb 761) were studied in isolated nondiabetic and diabetic ischaemic and re-perfused rat hearts. Hearts were randomly divided into five groups in both the age-matched non-diabetic and the 8-week streptozotocin-induced diabetic groups: Group I, hearts were subjected to 30 min of global ischaemia followed by 30 min of re-perfusion; Group II, one cycle of preconditioning consisting of 5 min ischaemia and 10 min re-perfusion before the induction of 30 min of ischaemia and 30 min of re-perfusion; Group III, two cycles of preconditioning; Group IV, three cycles; and Group V, four cycles before the onset of 30 min ischaemia followed by 30 min of re-perfusion. Four cycles of ischaemic preconditioning resulted in a reduction of arrhythmias in non-diabetic rats. Thus, in non-diabetics, the incidence of ventricular fibrillation and tachycardia fell from 92% and 100% (no preconditioning) to 33% (p < 0.05) and 42% (p < 0.05), respectively. Four cycles of preconditioning failed to reduce the incidence of re-perfusion arrhythmias in diabetic subjects. Preconditioning reduced the formation of oxygen free radicals measured by electron spin resonance spectroscopy, but the recovery of cardiac function was low in all non-diabetic and diabetic preconditioned groups. EGb 761 at 25 and 50 mg/kg improved cardiac function in non-preconditioned and preconditioned non-diabetic and diabetic hearts. During re-perfusion in the four-cycle preconditioned non-diabetic and diabetic groups, the amount of free radicals was reduced approximately by 50 and 70% using 25 and 50 mg/kg of EGb 761, respectively. EGb 761 improved cardiac function after ischaemia in both non-preconditioned and preconditioned non-diabetic and diabetic rats. Our data suggest that diabetes could abolish the precondition-induced protection.

The role of protein kinase in C ischemic/reperfused preconditioned isolated rat hearts

Protein kinase C (PKC) has been implicated in the preconditioning-induced cardiac protection in ischemic/reperfused myocardium. We studied the effect of PKC inhibition with calphostin C (25, 50, 100, 200, 400, and 800 nM), a potent and specific inhibitor of PKC, in isolated working nonpreconditioned and preconditioned ischemic/reperfused hearts. In the nonpreconditioned groups, all hearts underwent 30 min of normothermic global ischemia followed by 30 min of reperfusion. In the preconditioned groups, hearts were subjected to four cycles of ischemic preconditioning by using 5 min of ischemia followed by 10 min reperfusion, before the induction of 30 min ischemia and reperfusion. At low concentrations of calphostin C (25, 50, and 100 nM), the PKC inhibitor had no effect on the incidence or arrhythmias or postischemic cardiac function in the nonpreconditioned ischemic/reperfused groups. With 200 and 400 nM of calphostin C, a significant increase in postischemic function and a reduction in the incidence of arrhythmias were observed in the nonpreconditioned ischemic/reperfused groups. Increasing the concentration of calphostin C to 800 NM, the recovery of postischemic cardiac function was similar to that of the drug-free control group. In preconditioned hearts, lower concentrations (< 100 nM) of calphostin C did not change the response of the myocardium to ischemia and reperfusion in comparison to the preconditioned drug-free myocardium. Two hundred and 400 nM of the PKC inhibitor further reduced the incidence of ventricular fibrillation (VF) from the preconditioned drug-free value of 50% to 0 (p < 0.05) and 0 (p < 0.05), respectively, indicating that the combination of the two, preconditioning and calphostin C, affords significant additional protection. Increasing the concentration of calphostin C to 800 nM blocked the cardioprotective effect of preconditioning (100% incidence of VF). The recovery of cardiac function was similarly improved at calphostin C doses of 200 and 400 nM and was reduced at 800 nM (p < 0.05). With 200 and 400 nM of calphostin C, both cytosolic and particulate PKC activity were reduced by approximately 40 and 60%, respectively, in both preconditioned and preconditioned/ischemic/reperfused hearts. The highest concentration of calphostin C (800 nM) resulted in almost a complete inhibition of cytosolic (100%) and particulate (85%) PKC activity correlated with the abolition of preconditioning-induced cardiac protection. In conclusion, calphostin C protects the ischemic myocardium obtained from intact animals, provides significant additional protection to preconditioning at moderate doses, and blocks the protective effect of preconditioning at high concentrations. The dual effects of calphostin C appear to be strictly dose and "enzyme inhibition" related.

The evolution of diabetic response to ischemia/reperfusion and preconditioning in isolated working rat hearts

OBJECTIVE

Studies have shown that the diabetic heart exhibits abnormalities in cellular ion transport, which can affect susceptibility to reperfusion-induced ventricular fibrillation (VF), tachycardia (VT) and functional derangements. It has been shown that "preconditioning" renders the heart very resistant to a subsequent prolonged ischemic episode. This phenomenon has been extensively studied in healthy myocardium, but such a study has not been previously done in diseased (hypertrophic or myopathic) hearts.

METHODS

We studied the incidence of reperfusion-induced VF, VT, cardiac function, and ion shifts (Na+, K+, Ca2+, and Mg2+) induced by ischemia/reperfusion in isolated hearts from rats with streptozotocin-induced diabetes. Following 2, 4, 6, and 8 weeks of diabetes, hearts were isolated and subjected to 30 min global ischemia followed by reperfusion.

RESULTS

In the 2-week diabetic group the total incidence of VF and VT was reduced from their non-diabetic age-matched control value of 100 and 100% to 42 (P < 0.05) and 42% (P < 0.05), respectively. Such a reduction in the incidence of VF and VT was not observed with progressive diabetes (4, 6, and 8 weeks). In the 2-week diabetics, the reduction in the VF and VT was reflected in the improvement of postischemic function, the reduction of ischemia and reperfusion-induced Na+ and Ca2+ gains, and the prevention in K+ and Mg2+ loss. This diabetes-induced initial protection was not seen in the 4- and 6-week diabetics, and a deterioration of postischemic function was observed in the 8-week diabetics. Four cycles of preconditioning, each consisting of 5 min ischemia followed by 10 min reperfusion, failed to reduce the incidence of VF and VT, improve cardiac function, and prevent ion shifts induced by 30 min ischemia followed by 30 min reperfusion in 4- and 8-week diabetics.

CONCLUSIONS

In the early phase of diabetes the heart is more resistant to ischemia/reperfusion than the non-diabetic heart. Preconditioning does not afford protection against a prolonged period of ischemia in diabetics, indicating that preconditioning may be a "healthy heart phenomenon".

Diabetes and ATP-sensitive potassium channel openers and blockers in isolated ischemic/reperfused hearts

The incidence of reperfusion ventricular fibrillation (VF) and tachycardia (VT), heart function and the maldistribution of cardiac cations were studied in isolated ischemic/reperfused hearts obtained from streptozotocin-induced diabetic rats. Effects of an ATP-sensitive potassium (KATP) channel opener, cromakalim, and a KATP channel blocker, glibenclamide, also were studied. After 2 and 8 weeks of diabetes, hearts were isolated and subjected to 30 min of ischemia followed by reperfusion. After 2 weeks of diabetes, the incidence of VF and VT was reduced from their nondiabetic control values of 100 and 100 to 42% (P < .05) and 50% (P < .05), respectively. The reduction in VF and VT was not observed with progressive diabetes and after 8 weeks cardiac failure developed. In the 8-week diabetics, the development of cardiac failure was reflected in the aggravation of heart function (26, 16 and 17% reductions in aortic flow, left ventricular developed pressure and first derivative of developed pressure, respectively), and ion shifts (56 and 71% accumulation in cellular Na+ and Ca++, respectively, and 15% loss in cell K+) before the induction of ischemia. After ischemia/reperfusion, these changes were pronounced in diabetic groups. Cromakalim aggravated and glibenclamide attenuated the incidence of arrhythmias, contractile function and ion shifts induced by ischemia/reperfusion in diabetic hearts. The data show that the use of KATP channel openers as anti-ischemic agents may be of particular concern in the population of postinfarction diabetic patients who are known to be at high risk of sudden coronary death.

Alpha-1 adrenergic receptor agonist-induced preconditioning in isolated working rat hearts

The aim of this study was to determine whether pharmacologic preconditioning, without a short episode of myocardial hypoxia or ischemia, could improve myocardial function after a prolonged period of ischemia. Isolated rat hearts were perfused with .01, .1 or 1 mg/L of phenylephrine for 5 min followed by a 10-min washout period (preconditioning) before the induction of 30 min of normothermic global ischemia and 30 min of reperfusion. Hearts preconditioned with increasing concentrations of phenylephrine (an alpha-1 adrenergic receptor agonist) produced a reduction in the incidence of reperfusion-induced ventricular fibrillation (VF) and ventricular tachycardia (VT). Preconditioning of the hearts with the highest dose of phenylephrine (1.0 mg/L), after 30 min of ischemia, reduced the incidence of reperfusion-induced VF and VT from their nonpreconditioned control values of 87% and 100% to 33% (P < .05) and 50% (P < .05), respectively. After 30 min of ischemia, the recovery of myocardial function was significantly improved in phenylephrine-preconditioned groups. Thus, .1 and 1.0 mg/L of phenylephrine increased aortic flow from its nonpreconditioned control value of 10.8 +/- .9 ml/min to 22.4 +/- 2.4 ml/min (P < .05) and 26.5 +/- 1.5 ml/min (P < .05), respectively. Phenylephrine (1.0 mg/L) preconditioning significantly reduced ischemia/reperfusion-induced tissue Na+ and Ca2+ gains and prevented K+ and Mg2+ loss measured by an atomic absorption spectro-photometer. Our results show that alpha-1 adrenergic stimulation (preconditioning) can prevent postischemic abnormalities in intracellular ions, reperfusion arrhythmias, and contractile function without the inhibition of O2 delivery.

Myocardial salvage by 1-O-hexadecyl-Sn-glycerol: possible role of peroxisomal dysfunction in ischemia reperfusion injury

A recent study demonstrated biochemical and structural alterations of peroxisomes in rat kidney after ischemia/reperfusion. We examined whether peroxisomes play any role in the pathophysiology of myocardial ischemia/reperfusion injury. Isolated perfused rat heart was made ischemic for 30 min by terminating coronary flow (CF), followed by 30-min reperfusion. Experiments were divided into two groups; the experimental group received 1-O-hexadecyl-Sn-glycerol (chimyl alcohol) (25, 50, and 100 microM) before ischemia, and the control group received an equivalent amount of saline. Two of the experimental groups (50 and 100 microM) demonstrated improved postischemic myocardial performance, as demonstrated by accelerated recovery in left ventricular developed pressure (LVDP) and CF, as well as reduction in the incidence of ventricular fibrillation (VF). However, because the heart rate (HR) was significantly reduced in the 100-microM chimyl alcohol group, subsequent studies were performed with 50 microM chimyl alcohol as the optimal dose. Chimyl alcohol (50 microM) also reduced cellular injury, as evidenced by reduced creatine kinase (CK) release, and decreased development of oxidative stress, as evidenced by reduced formation of malonaldehyde (MDA). Peroxisomal catalase activity was decreased in the control group after ischemia/reperfusion, and chimyl alcohol treatment restored the activity of the enzyme. Our results indicate that chimyl alcohol, a precursor of ether-linked phosphoglyceride biosynthesis, can reduce myocardial ischemia/reperfusion injury, possibly by restoring catalase activity and reducing oxidative stress through synthesis of ether lipids, suggesting a possible role of peroxisomal disorder in ischemia/reperfusion injury.

Myocardial salvage by chimyl alcohol: possible role of peroxisomal dysfunction in reperfusion injury

The results of this study suggest that reperfusion of ischemic myocardium may lead to the peroxisomal disorder both functionally and biochemically. An alkyl glycerol such as chimyl alcohol can protect the ischemic heart from the reperfusion injury probably by enhancing the plasmalogen synthesis.

Ginkgo biloba extract (EGb 761) improves postischemic function in isolated preconditioned working rat hearts

BACKGROUND

We studied the effect of preconditioning and Gikgo biloba extract (EGb 761) in relation to the recovery of contractile function after global ischemia in the isolated working rat heart.

METHODS

Hearts (n = 12 in each group) were randomly divided into five groups: In group I, hearts were subjected to 30 min of normothermic global ischemia followed by 30 min of reperfusion; in group II, they were subjected to one cycle of preconditioning consisting of 5 min ischemia and 10 min reperfusion before the induction of 30 min of ischemia and 30 min of reperfusion; group III hearts underwent two cycles of preconditioning; group IV hearts underwent three cycles of preconditioning; and group hearts underwent four cycles of preconditioning before the onset of 30 min ischemia followed by 30 min of reperfusion.

RESULTS

Ventricular fibrillation (total) and ventricular tachycardia (no preconditioning) both fell from 100% to 50% (P < 0.05) after four cycles of preconditioning. In relation to ventricular fibrillation, preconditioning significantly reduced the formation of oxygen free radicals, measured by electron spin resonance spectroscopy (ESR), but recovery of cardiac function was low in all preconditioned groups. Because of the relatively low incidence of arrhythmias (50% ventricular fibrillation and 50% ventricular tachycardia) and relatively low cardiac function in Group V, EGb 761, a free-radical scavenger, was chosen to improve myocardial contractile function in preconditioned hearts. Fifty and 100 mg/kg of EGb 761 (per os) significantly improved coronary flow, aortic flow, left ventricular developed pressure (LVDP), and the first derivative of LVDP (LVDdP/dtmax) in the four-cycle preconditioned group. Thus, after 30 min of reperfusion, aortic flow was improved from 11.6 +/- 0.9 ml/min to 19.7 +/- 1.2 ml/min (P < 0.05) with a dose of 50 mg/kg of EGb 761 and to 22.0 +/- 1.5 ml/min (P < 0.05) with a dose 100 mg/kg of EGb 761, in the four-cycle preconditioned group. During reperfusion, the formation of free radicals was reduced by approximately 50 and 60% using 50 mg/kg and 100 mg/kg of EGb 761, respectively, when compared with the four-cycle preconditioned drug-free control group.

CONCLUSION

We have demonstrated that EGb 761 can improve contractile function after global ischemia in the isolated working rat heart by reducing the formation of oxygen free radicals, and we have shown that this protection is additive to that of ischemia-induced preconditioning.

Effects of preconditioning on reperfusion arrhythmias, myocardial functions, formation of free radicals, and ion shifts in isolated ischemic/reperfused rat hearts

The effects of preconditioning on development of reperfusion-induced ventricular fibrillation (VF), ventricular tachycardia (VT), free radical formation, and ion shifts, particularly those of Na, K, Ca, and Mg, were studied in isolated rat heart. Hearts were randomly divided into four groups: group I, aerobically perfused time-matched controls with no preconditioning or ischemia; group II, hearts subjected to 30-min global ischemia followed by 30-min reperfusion; group III, hearts subjected to one cycle of preconditioning, consisting of 5-min global ischemia plus 10-min reperfusion, followed by 30-min global ischemia plus 30-min reperfusion; and group IV, hearts subjected to four cycles of preconditioning (5-min ischemia plus 10-min reperfusion) followed by 30-min ischemia plus 30-min reperfusion. The incidences of VF and VT were reduced from their nonpreconditioned ischemic values of 100 and 100% in group II to 83 and 92% in group III and to 33% (p < 0.05) and 41% (p < 0.05) in group IV, respectively. Maximum malondialdehyde formation, as an indirect marker of free radicals, was observed after 30-min ischemia followed by 10-min reperfusion (0.72 +/- 0.1 nmol/ml) in the nonpreconditioned ischemic group (protocol II). One and four cycles of preconditioning reduced formation of malondialdehyde from the nonpreconditioned ischemic value of 0.72 +/- 0.1 to 0.35 +/- 0.02 and 0.26 +/- 0.02 nmol/ml (p < 0.05), respectively. The same trend was observed when free radical formation was directly detected by salicylic acid.(ABSTRACT TRUNCATED AT 250 WORDS)

Adenosine triphosphate-sensitive potassium channel blocking agent ameliorates, but the opening agent aggravates, ischemia/reperfusion-induced injury. Heart function studies in nonfibrillating isolated hearts

OBJECTIVES

This study was conducted to elucidate the role of the adenosine triphosphate (ATP)-sensitive potassium channel blocking agent glibenclamide and the opener cromakalim in the mechanism of reperfusion-induced injury.

BACKGROUND

Recently, ATP-sensitive potassium channel openers have been proposed to reduce ischemia/reperfusion-induced injury, including arrhythmias and heart function. Thus, one might hypothesize that pharmacologic agents that enhance the loss of potassium ions in the myocardium through ATP-sensitive potassium channels would be arrhythmogenic, and agents that interfere with tissue potassium ion loss would be antiarrhythmic.

METHODS

Isolated "working" guinea pig hearts and phosphorus-31 nuclear magnetic resonance spectroscopy were used to study the recovery of myocardial function and phosphorus compounds after 30, 40 and 50 min of normothermic global ischemia followed by reperfusion in untreated control and glibenclamide- and cromakalim-treated groups.

RESULTS

After 30 min of ischemia, 1, 3, 10 and 30 mumol/liter of glibenclamide dose-dependently reduced the incidence of reperfusion-induced ventricular fibrillation (total) from its control value of 92% to 75%, 33% (p < 0.05), 33% (p < 0.05) and 42% (p < 0.05), respectively. The incidence of ventricular tachycardia followed the same pattern. A reduction of arrhythmias was also observed after 40 and 50 min of ischemia followed by reperfusion in the glibenclamide-treated hearts. Cromakalim, at the same concentrations, did not reduce the incidence of reperfusion-induced arrhythmias. During reperfusion, glibenclamide (3 and 10 mumol/liter) improved the recovery of coronary blood flow, aortic flow, myocardial contractility and tissue ATP and creatine phosphate content, but cromakalim failed to ameliorate the recovery of postischemic myocardium compared with that in the drug-free control hearts.

CONCLUSIONS

The preservation of myocardial potassium ions and phosphorus compounds by glibenclamide can improve the recovery of postischemic function, but the use of ATP-sensitive potassium channel openers as antihypertensive or antiarrhythmic agents may be of particular concern in those postinfarction patients who are known to be at high risk for sudden cardiac death.

Potassium channel openers and blockers: do they possess proarrhythmic or antiarrhythmic activity in ischemic and reperfused rat hearts?

Cromakalim is a member of the new antihypertensive drug family possessing an action that involves an increased K efflux in vascular and cardiac muscle. We studied the contribution of opening of ATP-sensitive K channel to the development of reperfusion-induced arrhythmias and myocardial ion shifts, particularly that of Na, K, Ca and Mg in isolated rat hearts. After 30 min of global ischemia, cromakalim (1 to 30 microM) failed to reduce reperfusion arrhythmias. On the postischemic-reperfused myocardium in a subset of hearts unresponsive to reperfusion-induced arrhythmias (duration of ischemia was reduced to 25 min), cromakalim treatment was associated with a higher incidence of reperfusion ventricular fibrillation (VF) and ventricular tachycardia (VT) as compared to the controls (100% VF and 100% VT in treated vs. 41% VF and 50% VT in controls, P < .05). Proarrhythmic effects of cromakalim were also reflected in a maldistribution of myocardial ions. At concentrations of 3, 10 and 30 microM of glibenclamide, a K channel blocker, a significant reduction in the incidence of reperfusion-induced VF and VT was observed, and an attenuation in the maldistribution of myocardial ion contents induced by ischemia/reperfusion was found. The reduction in myocardial contractility was detected at relatively high concentrations (10 and 30 microM) in both cromakalim- and glibenclamide-treated groups. The proarrhythmic effect of cromakalim (30 microM) was abolished by 3 microM of glibenclamide, suggesting that the increased tendency to develop reperfusion arrhythmias is associated with the cromakalim-induced K efflux.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of extracellular magnesium manipulation on reperfusion-induced arrhythmias and myocardial ion shifts in isolated ischemic reperfused rat hearts

Isolated rat hearts were subjected to global ischemia followed by reperfusion, and a reduction in the incidence of reperfusion-induced ventricular fibrillation and ventricular tachycardia was brought about by increasing the extracellular Mg concentration in the perfusion buffer. Thus the incidence of ventricular fibrillation was reduced from its control value of 100% in 1.2 mM Mg to 83% by 2.4 mM Mg (P = N.S.), to 42% by 3.6 mM Mg (P < .05), to 17% by 4.8 mM Mg (P < .001) and to 17% by 9.6 mM Mg (P < .001). The corresponding values for ventricular tachycardia were 100% (control, 1.2 mM Mg) vs. 92% (P = N.S.), 50% (P < .05), 25% (P < .01) and 25% (P < .01), respectively. In further studies, extracellular Ca was reduced by 50% (1.2 mM) in the perfusion buffer just before ischemia and during reperfusion. The incidence of ventricular fibrillation was reduced from its control value of 83% in 1.2 mM Mg to 75% by 1.8 mM Mg (P = N.S.), to 33% by 2.4 mM Mg (P < .05), to 17% by 3.6 mM Mg (P < .01) and to 8% by 4.8 mM Mg (P < .01). The incidence of ventricular tachycardia followed the same pattern. Myocardial Na, K, Ca and Mg were measured by atomic absorption spectrophotometer after the removal of ions from the extracellular space. In controls, 30 min of ischemia resulted in 3- and 4-fold accumulation of myocardial Na and Ca, respectively, and during reperfusion these values were similar to the values for 30-min ischemia.(ABSTRACT TRUNCATED AT 250 WORDS)

Pacing-induced ventricular fibrillation leading to oxygen free radical formation in aerobically perfused rat hearts

The objective of this study was to determine whether electrically-induced ventricular fibrillation can elicit oxygen free radical formation, even in the absence of ischemia and reperfusion. Rat hearts (n = 8 in each group) were perfused aerobically at 37 degrees C and ventricular fibrillation was induced by pacing (20 Hz, 1200 beats/min) for 10 min, during which time no changes in coronary flow rates were observed. In this study, electron spin resonance (ESR) studies using the spin trap 5,5-dimethyl-1-pyrroline-N-oxide (DMPO) demonstrated the formation of oxygen free radicals consisting of 1:2:2:1 quartet with peak concentration at the 3rd min of fibrillation in non-ischemic electrically fibrillating hearts. Since there were no significant changes in coronary flow rates during ventricular fibrillating (22.3 +/- 1.3 ml/min in control vs 22.3 +/- 0.9 ml/min in pacing-induced fibrillating group), the formation of oxygen free radicals could not be attributed to a pacing-induced ischemic event. In additional studies, hearts were paced by 10 Hz (600 beats/min), to demonstrate whether ventricular tachycardia could elicit free radical formation. In these experiments the genesis of oxygen free radicals was not observable after 1 min, 5 min, and 10 min of tachycardia, but a small amount of OH. radicals was detected at the 3rd min of ventricular tachycardia. When DMPO was infused into the heart giving a final perfusate concentration of 2.5 mmoles/litre during the pacing-induced fibrillation period, myocardial function (aortic flow, cardiac output, left ventricular developed pressure, first derivative of left ventricular developed pressure, and end-diastolic pressure) was significantly improved after the postfibrillating period. In conclusion, our studies clearly show that electrically-induced ventricular fibrillation is capable of eliciting free radical formation even in the absence of ischemia and reperfusion, and the cardioprotective effect of the spin trap is directly originated from its free radical trapping property and not from the other pharmacological activities of DMPO.

Effects of SOD, catalase, and a novel antiarrhythmic drug, EGB 761, on reperfusion-induced arrhythmias in isolated rat hearts

Effects of superoxide dismutase (SOD), catalase, EGB 761 (Tanakan), and their combination on reperfusion-induced ventricular fibrillation (VF), tachycardia (VT), and the formation of oxygen free radicals were studied after 30 min of global ischemia followed by reperfusion in isolated rat hearts. In the first series of studies, rats received a daily dose of 10(4), 2 x 10(4), or 5 x 10(4) U/kg of SOD (i.v.); 2.5 x 10(4), 5 x 10(4), or 10(5) U/kg of catalase (i.v.); and 25, 50, 100, or 200 mg/kg of EGB 761 (per os), respectively, for 10 d (chronic administration). Neither SOD nor catalase alone reduced the incidence of reperfusion arrhythmias, but EGB 761 dose-dependently reduced the incidence of such arrhythmias. The coadministration of SOD (5 x 10(4) U/kg) with catalase (5 x 10(4) U/kg) significantly reduced the incidence of VF and VT. The same reduction in the incidence of VF and VT was observed when SOD (5 x 10(4) U/kg) was given in combination with EGB 761 (50 mg/kg). In the second series of studies, hearts were isolated and perfused with 5 x 10(4) U/l of SOD plus 5 x 10(4) U/l of catalase (acute treatment), and the incidence of reperfusion-induced VF and VT was significantly reduced. The combination of SOD (5 x 10(4) U/l) with EGB 761 (50 mg/l) also reduced the incidence of VF and VT. In these experiments, we studied the time course of oxygen radical formation using 5,5-dimethyl-pyrroline-N-oxide (DMPO), a spin trap, and it was found that EGB 761 (200 mg/l) or the coadministration of EGB 761 (50 mg/l) with SOD (5 x 10(4) U/l) almost completely abolished the formation of oxygen radicals during reperfusion measured by electron spin resonance (ESR) spectroscopy. Although SOD or catalase alone significantly reduced the formation of oxygen radicals, these drugs failed to prevent the development of reperfusion arrhythmias, while their combination significantly attenuated both the formation of free radicals and the incidence of reperfusion-induced arrhythmias. Our results indicate that the combination therapy may synergistically reduce the formation of free radicals and the incidence of reperfusion-induced VF and VT.

Comparisons of ESR and HPLC methods for the detection of OH. radicals in ischemic/reperfused hearts. A relationship between the genesis of free radicals and reperfusion arrhythmias

In this study we compared two methods, electron spin resonance (ESR) spectroscopy and high performance liquid chromatography (HPLC), which are currently used to detect directly hydroxyl radical (OH.) formation in the ischemic and reperfused heart. Isolated buffer-perfused rat hearts were subjected to 30 min of normothermic global ischemia followed by 30 min of reperfusion. 5,5-Dimethyl-pyrroline-N-oxide (DMPO) was used as a spin-trap agent to detect OH. radicals by ESR and HPLC. In additional HPLC studies, salicylic acid was infused into the heart for the detection of OH. radicals. In all studies, the effects of superoxide dismutase (SOD) and catalase (CAT) on the OH. generation were examined. The results of our studies indicate that, irrespective of the method, OH. was always detected when an ischemic heart was reperfused and showed ventricular fibrillation. The OH. concentration increased dramatically between 60 and 90 sec of reperfusion, peaked between 180 and 210 sec, and then progressively decreased. In all cases, both SOD and CAT were able to reduce the formation of OH. radicals, with SOD being relatively more effective. Our results indicate that OH. was produced only in the fibrillating hearts that peaked between 180 and 210 sec (1.64 +/- 0.09 nmol/mL measured by ESR), but not in the non-fibrillating hearts. Although SOD or CAT reduced the OH. formation, they had no effects on the incidence of reperfusion-induced ventricular fibrillation (VF) and ventricular tachycardia (VT). However, when SOD (5 x 10(4) IU/L) was coadministered with CAT (5 x 10(4) IU +/- L), the incidence of reperfusion-induced VF (total) and VT was reduced from their control value of 92 and 100 to 33 (P < 0.05) and 50% (P < 0.05), respectively. The results of this study indicate that the HPLC method, as well as ESR, can be used to detect OH. formation in ischemic/reperfused hearts. Because of the convenience, reproducibility and greater sensitivity, the HPLC technique may be more suitable for OH. detection. Our results further suggest the potential therapeutic value of the combination therapy of SOD and CAT for the reduction of reperfusion-induced VF and VT.

Does the antiarrhythmic effect of DMPO originate from its oxygen radical trapping property or the structure of the molecule itself?

Using the isolated perfused rat heart with transient (30 min) normothermic global ischemia, it was shown that DMPO (5,5-dimethyl-pyrroline-N-oxide), an organic spin trap agent designed specifically to trap free radicals, dramatically reduced the vulnerability of the myocardium to reperfusion-induced ventricular fibrillation (VF) and ventricular tachycardia (VT). DMPO (concentration range 30-500 mumol/l) infused in the heart at the moment and during the first 10 min of reperfusion exerted a dose-dependent antiarrhythmic effect. Thus, the doses of 30, 100, and 500 mumol/l of DMPO reduced the incidence of reperfusion-induced VF and VT from their control values of 100% and 100% to 83% and 91%, 50% (p < 0.05) and 67%, 25% (p < 0.01) and 50% (p < 0.05), respectively. Furthermore, the recovery of myocardial function was improved during postischemic reperfusion. A modification in the molecular structure of DMPO leading to HMIO (1,2,2,4,5,5-hexamethyl-3-imidazoline-oxide), so-called inactive DMPO which does not trap free radicals in the presence of a radical generating system or in the effluent of reperfused hearts, failed to reduce the incidence of reperfusion-induced arrhythmias or improve the recovery of postischemic reperfused myocardium. These findings suggest that the free radical trapping properties of DMPO or the effects of the formed DMPO-OH, a stable nitroxyl radical adduct, are responsible for the reduction of reperfusion-induced arrhythmias, and not the molecular structure of DMPO itself. Finally, it is of interest to note that the detection of free radicals was observed in fibrillating hearts, but not in nonfibrillating hearts. This consideration should be taken into account when making therapeutic interventions and risk assessments of a radical scavenger in this setting.