Repeated exercise stress testing identifies early and late preconditioning

Short-term exercise-induced protection of cardiovascular function and health: why and how fast does the heart benefit from exercise?

Regular exercise training has potent and powerful protective effects against the development of cardiovascular disease. These cardioprotective effects of regular exercise training are partly explained through the effects of exercise on traditional cardiovascular risk factors and improvement in cardiac and vascular health, which take several weeks to months to develop. This review focuses on the observation that single bouts of exercise may also possess an underrecognized, clinically useful form of immediate cardioprotection. Studies, performed in both animals and humans, demonstrate that single or short-term exercise-induced protection (SEP) attenuates the magnitude of cardiac and/or vascular damage in response to prolonged ischaemia and reperfusion injury. This review highlights preclinical evidence supporting the hypothesis that SEP activates multiple pathways to confer immediate protection against ischaemic events, reduce the severity of potentially lethal ischaemic myocardial injury, and therefore act as a physiological first line of defence against injury. Given the fact that the extent of SEP could be modulated by exercise-related and subject-related factors, it is important to recognize and consider these factors to optimize future clinical implications of SEP. This review also summarizes potential effector signalling pathways (i.e. communication between exercising muscles to vascular/cardiac tissue) and intracellular pathways (i.e. reducing tissue damage) that ultimately confer protection against cardiac and vascular injury. Finally, we discuss potential future directions for designing adequate human and animal studies that will support developing effective SEP strategies for the (multi-)diseased and aged individual. KEY POINTS: Single or short-term exercise-induced protection (SEP) attenuates the magnitude of cardiac and/or vascular damage in response to prolonged ischaemia and reperfusion injury (IR injury). SEP activates multiple pathways to confer cardiac protection, which develops remotely at the site of the activated muscle by release of circulating molecules, which transfer towards activation of intramyocardial signalling that promotes cell survival during episodes of IR injury. SEP represents an attractive intervention in aged individuals and in those with co-morbidities. The immediate protection, low cost and simplicity to increase the 'dose' of SEP offers unique opportunities in the clinical applications of SEP.

Short term exercise‐induced protection of cardiovascular function and health: Why and how fast does the heart benefit from exercise?

Abstract

Regular exercise training has potent and powerful protective effects against the development of cardiovascular disease. These cardioprotective effects of regular exercise training are partly explained through the effects of exercise on traditional cardiovascular risk factors and improvement in cardiac and vascular health, which take several weeks to months to develop. This review focuses on the observation that single bouts of exercise may also possess an underrecognized, clinically useful form of immediate cardioprotection. Studies, performed in both animals and humans, demonstrate that single or short‐term exercise‐induced protection (SEP) attenuates the magnitude of cardiac and/or vascular damage in response to prolonged ischaemia and reperfusion injury. This review highlights preclinical evidence supporting the hypothesis that SEP activates multiple pathways to confer immediate protection against ischaemic events, reduce the severity of potentially lethal ischaemic myocardial injury, and therefore act as a physiological first line of defence against injury. Given the fact that the extent of SEP could be modulated by exercise‐related and subject‐related factors, it is important to recognize and consider these factors to optimize future clinical implications of SEP. This review also summarizes potential effector signalling pathways (i.e. communication between exercising muscles to vascular/cardiac tissue) and intracellular pathways (i.e. reducing tissue damage) that ultimately confer protection against cardiac and vascular injury. Finally, we discuss potential future directions for designing adequate human and animal studies that will support developing effective SEP strategies for the (multi‐)diseased and aged individual.

Key points

Single or short‐term exercise‐induced protection (SEP) attenuates the magnitude of cardiac and/or vascular damage in response to prolonged ischaemia and reperfusion injury (IR injury).

SEP activates multiple pathways to confer cardiac protection, which develops remotely at the site of the activated muscle by release of circulating molecules, which transfer towards activation of intramyocardial signalling that promotes cell survival during episodes of IR injury.

SEP represents an attractive intervention in aged individuals and in those with co‐morbidities. The immediate protection, low cost and simplicity to increase the ‘dose’ of SEP offers unique opportunities in the clinical applications of SEP.

Mechanisms Involved in Cardioprotection Induced by Physical Exercise

Significance: Regular exercise training can reduce myocardial damage caused by acute ischemia/reperfusion (I/R). Exercise can reproduce the phenomenon of ischemic preconditioning, due to the capacity of brief periods of ischemia to reduce myocardial damage caused by acute I/R. In addition, exercise may also activate the multiple kinase cascade responsible for cardioprotection even in the absence of ischemia. Recent Advances: Animal and human studies highlighted the fact that, besides to reduce risk factors related to cardiovascular disease, the beneficial effects of exercise are also due to its ability to induce conditioning of the heart. Exercise behaves as a physiological stress that triggers beneficial adaptive cellular responses, inducing a protective phenotype in the heart. The factors contributing to the exercise-induced heart preconditioning include stimulation of the anti-radical defense system and nitric oxide production, opioids, myokines, and adenosine-5'-triphosphate (ATP) dependent potassium channels. They appear to be also involved in the protective effect exerted by exercise against cardiotoxicity related to chemotherapy. Critical Issues and Future Directions: Although several experimental evidences on the protective effect of exercise have been obtained, the mechanisms underlying this phenomenon have not yet been fully clarified. Further studies are warranted to define precise exercise prescriptions in patients at risk of myocardial infarction or undergoing chemotherapy.

High-intensity interval training recuperates capacity of endogenous thrombin generation in heart failure patients with reduced ejection fraction

OBJECTIVE

Consumptive coagulopathy is associated with increased mortality in patients with heart failure (HF). Physical activity influences the risk of major vascular thrombotic events. This study investigates how high-intensity interval training (HIIT) affects the capacity of endogenous thrombin generation (TG) by modulating circulatory procoagulant microparticles (MPs) in HF patients.

METHODS

Thirty-eight HF patients with reduced ejection fraction (HFrEF) and 38 age- and gender-matched normal counterparts (NC) were recruited into this study. The HFrEF group performed HIIT (3-min intervals at 40% and 80%VO_2peak) on a bicycle ergometer for 30 min/day, 3 days/week for 12 weeks, whereas the NC group did not receive any form of intervention. Plasma TG kinetics, procoagulant MPs, coagulation-related factors, and oxidative stress/proinflammatory status were analyzed.

RESULTS

The HFrEF group exhibited (i) less endogenous thrombin potential (ETP) and TG rate, (ii) lower concentration/activity of tissue factor (TF) and counts of TF-rich MPs derived from blood cells, and (iii) higher vascular endothelial shedding and plasma myeloperoxidase and interleukin-6 concentrations, compared to the NC group did. However, HIIT elevated TG rate and TF concentration/activity in plasma, as well as, TF-rich MP counts derived from blood cells in patients with HFrEF. Moreover, the exercise regimen also decreased vascular endothelial shedding and plasma myeloperoxidase and interleukin-6 concentrations in HFrEF patients.

CONCLUSION

HFrEF reduces the capacity of endogenous TG in plasma, which is associated with decreased (or consumed) circulatory procoagulant MP levels. However, HIIT alleviates HFrEF-declined endogenous TG capacity and vascular endothelial damage through recuperating TF-related coagulation activity and suppressing oxidative stress/proinflammatory status.

Ischaemic conditioning and targeting reperfusion injury: a 30 year voyage of discovery

To commemorate the auspicious occasion of the 30th anniversary of IPC, leading pioneers in the field of cardioprotection gathered in Barcelona in May 2016 to review and discuss the history of IPC, its evolution to IPost and RIC, myocardial reperfusion injury as a therapeutic target, and future targets and strategies for cardioprotection. This article provides an overview of the major topics discussed at this special meeting and underscores the huge importance and impact, the discovery of IPC has made in the field of cardiovascular research.

Exercise-induced ischemic preconditioning and the potential application to cardiac rehabilitation: a systematic review

Exercise-induced ischemic preconditioning (IPC) can be assessed by the results of the second of sequential exercise tests. Exercise-induced IPC is quantified by using the time to 1-mm ST-segment depression, the rate-pressure product at 1-mm ST-segment depression, the maximal ST-segment depression, and the rate-pressure product at the peak of exercise. Few studies reported whether exercise-induced IPC could be used in cardiovascular rehabilitation. A systematic review of the literature limited to human studies was performed using electronic databases, and the main key words were ischemic preconditioning, warm-up phenomenon, and exercise. After careful review, 38 articles were included in the systematic review. This review summarizes the molecular pathways of IPC and describes the first window of protection induced by sequential exercise tests, as well as the effect of medication on exercise-induced IPC. A section on the exercise protocol, mode of exercise, and intensity provides understanding as to what is needed for clinicians to induce IPC with sequential stress tests. The final section of the review is a discussion of the potential use of exercise-induced IPC in a cardiovascular rehabilitation setting. Even if exercise-induced IPC is a well-documented phenomenon, additional studies are needed in order to more fully understand its use in rehabilitation.

Cardioprotection acquired through exercise: the role of ischemic preconditioning

A great bulk of evidence supports the concept that regular exercise training can reduce the incidence of coronary events and increase survival chances after myocardial infarction. These exercise-induced beneficial effects on the myocardium are reached by means of the reduction of several risk factors relating to cardiovascular disease, such as high cholesterol, hypertension, obesity etc. Furthermore, it has been demonstrated that exercise can reproduce the "ischemic preconditioning" (IP), which refers to the capacity of short periods of ischemia to render the myocardium more resistant to subsequent ischemic insult and to limit infarct size during prolonged ischemia. However, IP is a complex phenomenon which, along with infarct size reduction, can also provide protection against arrhythmia and myocardial stunning due to ischemia-reperfusion. Several clues demonstrate that preconditioning may be directly induced by exercise, thus inducing a protective phenotype at the heart level without the necessity of causing ischemia. Exercise appears to act as a physiological stress that induces beneficial myocardial adaptive responses at cellular level. The purpose of the present paper is to review the latest data on the role played by exercise in triggering myocardial preconditioning.

Biomarkers for ischemic preconditioning: finding the responders

Ischemic preconditioning is emerging as an innovative and novel cytoprotective strategy to counter ischemic vascular disease. At the root of the preconditioning response is the upregulation of endogenous defense systems to achieve ischemic tolerance. Identifying suitable biomarkers to show that a preconditioning response has been induced remains a translational research priority. Preconditioning leads to a widespread genomic and proteonomic response with important effects on hemostatic, endothelial, and inflammatory systems. The present article summarizes the relevant preclinical studies defining the mechanisms of preconditioning, reviews how the human preconditioning response has been investigated, and which of these bioresponses could serve as a suitable biomarker. Human preconditioning studies have investigated the effects of preconditioning on coagulation, endothelial factors, and inflammatory mediators as well as on genetic expression and tissue blood flow imaging. A biomarker for preconditioning would significantly contribute to define the optimal preconditioning stimulus and the extent to which such a response can be elicited in humans and greatly aid in dose selection in the design of phase II trials. Given the manifold biologic effects of preconditioning a panel of multiple serum biomarkers or genomic assessments of upstream regulators may most accurately reflect the full spectrum of a preconditioning response.

Acute effects of continuous and interval low-intensity exercise on arterial stiffness in healthy young men

PURPOSE

To examine and compare systemic arterial stiffness responses in humans to acute continuous and interval low-intensity exercise.

METHODS

Fifteen healthy young men (21.2 ± 0.4 years) underwent non-exercise control (CON), continuous exercise (CE), and interval exercise trial (IE) in a randomized balanced self-control crossover design. Systemic arterial stiffness (Cardio-ankle vascular index, CAVI) was measured at baseline (BL), immediately after (0 min) and 40 min after exercise in CE and IE trials, and at corresponding time points in CON trial. Subjects cycled continuously for 30 min at 35 % heart rate reserve after BL measurement in CE trial, whereas in IE trial, subjects cycled two bouts of 15-min separated by a 20-min rest at the same intensity.

RESULTS

There were no significant CAVI changes with time in CON trial (6.7 ± 0.1, 6.7 ± 0.1, 6.6 ± 0.1 at BL, 0 and 40 min, respectively). In CE trial, CAVI decreased immediately after exercise (0 min) and returned to baseline after 40 min of recovery (6.5 ± 0.1, 5.5 ± 0.2, 6.4 ± 0.1 at BL, 0 and 40 min, respectively). IE elicited similar CAVI reduction from 6.7 ± 0.1 at baseline to 5.6 ± 0.2 at 0 min: however, CAVI at 40 min remained significantly low compared to that of CON trial at corresponding time point (6.0 ± 0.1 vs. 6.6 ± 0.1, P < 0.001).

CONCLUSION

Both acute continuous and interval low-intensity exercise elicits transient improvement in systemic arterial stiffness in humans. Despite equivalent exercise intensity and duration, interval exercise resulted in improved arterial stiffness for longer duration.

Hypotheses, rationale, design, and methods for evaluation of ischemic preconditioning assessed by sequential exercise tests in diabetic and non-diabetic patients with stable coronary artery disease--a prospective study

BACKGROUND

Ischemic preconditioning is a powerful mechanism of myocardial protection and in humans it can be evaluated by sequential exercise tests. Coronary Artery Disease in the presence of diabetes mellitus may be associated with worse outcomes. In addition, some studies have shown that diabetes interferes negatively with the development of ischemic preconditioning. However, it is still unknown whether diabetes may influence the expression of ischemic preconditioning in patients with stable multivessel coronary artery disease.

METHODS/DESIGN

This study will include 140 diabetic and non-diabetic patients with chronic, stable coronary artery disease and preserved left ventricular systolic function. The patients will be submitted to two sequential exercise tests with 30-minutes interval between them. Ischemic parameters will be compared between diabetic and non-diabetic patients. Ischemic preconditioning will be considered present when time to 1.0 mm ST-segment deviation is greater in the second of two sequential exercise tests. Exercise tests will be analyzed by two independent cardiologists.

DISCUSSION

Ischemic preconditioning was first demonstrated by Murry et al. in dog's hearts. Its work was reproduced by other authors, clearly demonstrating that brief periods of myocardial ischemia followed by reperfusion triggers cardioprotective mechanisms against subsequent and severe ischemia. On the other hand, the demonstration of ischemic preconditioning in humans requires the presence of clinical symptoms or physiological changes difficult to be measured. One methodology largely accepted are the sequential exercise tests, in which, the improvement in the time to 1.0 mm ST depression in the second of two sequential tests is considered manifestation of ischemic preconditioning.Diabetes is an important and independent determinant of clinical prognosis. It's a major risk factor for coronary artery disease. Furthermore, the association of diabetes with stable coronary artery disease imposes worse prognosis, irrespective of treatment strategy. It's still not clearly known the mechanisms responsible by these worse outcomes. Impairment in the mechanisms of ischemic preconditioning may be one major cause of this worse prognosis, but, in the clinical setting, this is not known. The present study aims to evaluate how diabetes mellitus interferes with ischemic preconditioning in patients with stable, multivessel coronary artery disease and preserved systolic ventricular function.

Effects of interval and continuous exercise training on CD4 lymphocyte apoptotic and autophagic responses to hypoxic stress in sedentary men

Exercise is linked with the type/intensity-dependent adaptive immune responses, whereas hypoxic stress facilitates the programmed death of CD4 lymphocytes. This study investigated how high intensity-interval (HIT) and moderate intensity-continuous (MCT) exercise training influence hypoxia-induced apoptosis and autophagy of CD4 lymphocytes in sedentary men. Thirty healthy sedentary males were randomized to engage either HIT (3-minute intervals at 40% and 80%VO_2max, n=10) or MCT (sustained 60%VO_2max, n=10) for 30 minutes/day, 5 days/week for 5 weeks, or to a control group that did not received exercise intervention (CTL, n=10). CD4 lymphocyte apoptotic and autophagic responses to hypoxic exercise (HE, 100W under 12%O₂ for 30 minutes) were determined before and after various regimens. The results demonstrated that HIT exhibited higher enhancements of pulmonary ventilation, cardiac output, and VO₂ at ventilatory threshold and peak performance than MCT did. Before the intervention, HE significantly down-regulated autophagy by decreased beclin-1, Atg-1, LC3-II, Atg-12, and LAMP-2 expressions and acridine orange staining, and simultaneously enhanced apoptosis by increased phospho-Bcl-2 and active caspase-9/-3 levels and phosphotidylserine exposure in CD4 lymphocytes. However, five weeks of HIT and MCT, but not CTL, reduced the extents of declined autophagy and potentiated apoptosis in CD4 lymphocytes caused by HE. Furthermore, both HIT and MCT regimens manifestly lowered plasma myeloperoxidase and interleukin-4 levels and elevated the ratio of interleukin-4 to interferon-γ at rest and following HE. Therefore, we conclude that HIT is superior to MCT for enhancing aerobic fitness. Moreover, either HIT or MCT effectively depresses apoptosis and promotes autophagy in CD4 lymphocytes and is accompanied by increased interleukin-4/interferon-γ ratio and decreased peroxide production during HE.

Exercise does not increase cyclooxygenase-2 myocardial levels in young or senescent hearts

Increased myocardial cyclooxygenase-2 (COX-2) activity is essential for late phase ischemic preconditioning (IPC). Currently unknown is whether cardioprotection elicited by exercise also involves elevated myocardial COX-2 activity. This investigation tested whether aerobic exercise elevates myocardial COX-2 protein content or enzyme activity in young and senescent male Fisher 344 rats assigned to sedentary or cardioprotective endurance exercise treatments (3 consecutive days of treadmill exercise, 60 min/day @ approximately 70% VO(2)max). Assay of cardiac COX-2 protein content, catalytic activity, and inducible nitric oxide synthase (iNOS) protein content reveal that exercise did not alter COX-2 activity (PGE(2), p = 0.866; PGF1alpha, p = 0.796) or protein levels (p = 0.397) within young or senescent hearts. In contrast, myocardial iNOS, an up-stream mediator of COX-2 expression, was over-expressed by an average of 37% in aged hearts (p = 0.005), though iNOS was not influenced by exercise. Findings reveal exercise does not elevate cardiac COX-2 activity and suggests that mechanisms responsible for cardioprotection differ between IPC and aerobic exercise.

Stress test with dual isotope studies for the documentation of classical ischemic preconditioning

OBJECTIVES

We investigated whether myocardial perfusion imaging (MPI) can demonstrate the effect of classical preconditioning.

METHODS

21 patients with documented coronary artery disease (stenosis>or=70%) underwent two exercise stress tests (EST) with concomitant MPI, using TL-201 for the first and tetrofosmin-Tc-99m for the second. A third MPI was performed at rest, using Tc-99m. Total defect score was derived by summing tracer uptake in a 17 segments left ventricle model, graded on a 5-point scale. Tomographic images were also analyzed quantitatively, to derive the total defect size.

RESULTS

Maximum ST depression did not differ significantly between the two EST (2.2+/-1 vs 2.2+/-1 mm, p=NS), however in the second EST longer times for onset of ischemic changes (228+/-94 vs 265+/-103 s, p=0.01) and appearance of angina (282+/-153 vs 328+/-177 s, p=0.04) were observed. Exercise perfusion abnormalities were significantly lower in the second MPI, in terms of both total defect score (19.2+/-11.5 vs 10+/-10.4, p<0.0001) and total defect size (28.3+/-16.9 vs 13.8+/-15.8, p<0.0001).

CONCLUSION

Significant improvement in perfusion pattern was demonstrated in the second MPI, accompanied by delayed appearance of ischemic manifestations. The improvement in myocardial perfusion extends far beyond the changes that can be attributed to differences in myocardial uptake between tracers, reflecting the effect of classical preconditioning.

Correlation of modification of heart rate recovery with adaptation to myocardial ischemia in a model of sequential exercise testings

BACKGROUND

Heart rate recovery (HRR) has been identified as a reliable predictor of cardiac mortality, correlated with autonomic tone. In a model of sequential exercise testings, we investigated the reproducibility of HRR and the association between HRR modification and myocardial adaptation to ischemia.

METHODS

We studied 128 patients (mean age 62 +/- 9 years, 83% males) with angiographically documented coronary artery disease (CAD) and a first positive exercise testing, who agreed to undergo a second exercise testing after 24 hours.

RESULTS

HRR was increased from 25 +/- 10 beats/min at the first exercise testing to 30 +/- 13 beats/min at the second exercise testing (P < 0.001). Thereafter, participants were divided into two groups: Group I comprised 88 patients who presented augmentation of the HRR in the first compared to the second exercise testing, while group II comprised 40 patients who presented unchanged or reduced HRR. The rate-pressure product (RPP) at 1 mm ST-segment depression (ischemic threshold) at the second compared to the first exercise testing were significantly improved in group I patients (2345 +/- 3429 mmHg/min), while it was worsened in group II patients (-630 +/- 2510 mmHg/min) (P < 0.001).

CONCLUSIONS

In a model of sequential exercise testings, myocardial adaptation to exercise-induced ischemia was associated with favorable modification of HRR.

Diabetes and the heart: could the diabetic myocardium be protected by preconditioning?

Both type 1 and type 2 diabetes (insulin-dependent and non-insulin dependent diabetes, respectively) are associated with increased risk for microvascular and macrovascular complications including retinopathy, neuropathy, nephropathy and atherosclerosis. Type 2 diabetes markedly increases the risk for cardiovascular morbidity and mortality, which has major public health implications. In this review, molecular mechanisms pertaining to diabetes-induced heart pathology are addressed.

Treadmill exercise test with dual isotope scintigraphy documents the second window of preconditioning in humans

BACKGROUND

In experimental studies, two windows of preconditioning have been identified, one lasting 1-2h and a second one (SWOP) starting 24h later and lasting 3-4 days. We sought to document SWOP in humans, using scintigraphy as an objective method of imaging.

METHODS

Nineteen male patients, aged 62+/-7 years with documented coronary artery disease underwent two treadmill exercise tests (at baseline and 30 h later) and three tomographic perfusion studies (during the first exercise test, during the redistribution phase 4 h later and during the second exercise test 30 h later) with two different isotopes. Thallium-201 (TL) was used for the assessment of the first exercise and the redistribution phase, whereas technetium 99m tetrofosmin (TET) was used 30 h later for the evaluation of SWOP. Both exercise tests terminated at the same time-point. The distribution of TL and TET uptake was analyzed qualitatively using a 5-point scale on a 17-segment myocardial model. Perfusion score was derived by summing the uptake of all segments, while total perfusion defect by subtracting the polar map of the first exercise test from that of the second exercise test.

RESULTS

Anginal symptoms were reported by 13 of 19 patients (68%) in the first test versus only 2 of 19 patients (11%) in the second one (p=0.001). The mean maximum ST segment depression was significantly reduced in the second test (from 1.58+/-0.73 to 0.82+/-1.07, p<0.01). Similarly, the perfusion score was reduced from 21.0+/-7.4 to 14.2+/-5.7 in the second test (p<0.01) and the total defect size from 24+/-16 to 12+/-14 (p<0.01).

CONCLUSION

The myocardial perfusion improvement during the second exercise study confirms objectively the existence of SWOP in humans.

Exercise modulates platelet-nasopharyngeal carcinoma cell aggregation and subsequent tissue factor and matrix metalloproteinase activities

Interaction between platelet and carcinoma cell contributes to pathogenesis of cancer-related thrombosis and metastasis. This study investigated whether physical exercise affects platelet-nasopharyngeal carcinoma cell (NPC) interaction and platelet-promoted tissue factor (TF) and matrix metalloproteinase (MMP) activities of NPC. Thirty sedentary men performed on three occasions moderate-intensity exercise [MIE, 60% maximal oxygen consumption (V(.)o(2max)) for 40 min] and high-intensity exercise (HIE, up to V(.)o(2max)), with and without warm-up exercise (WUE, 60% V(.)o(2max) for 20 min) on a bicycle ergometer. Before and immediately after exercise, platelet-NPC aggregation, the TF, MMP-2 and MMP-9 expressions and activities, and TF pathway inhibitor (TFPI) and tissue inhibitor of MMP-1 levels of NPC and platelet were measured. The results of this study demonstrated that HIE enhanced platelet-NPC aggregation in the presence of fibrinogen and was accompanied by increased platelet-promoted TF activity, expression of NPC, decreased platelet-promoted MMP-2 and MMP-9 activities, and TFPI release of NPC, whereas these alterations to HIE on platelet-NPC interactions were ameliorated by WUE pretreatment. Conversely, MIE reduced the formation of platelet-NPC aggregates, but did not change the TF, TFPI, MMP-2, MMP-9, tissue inhibitor of MMP activities, and/or levels of NPC mediated by platelet. It is concluded that HIE may enhance aggregation and coagulation and reduce MMP bioactivity related to platelet-NPC interactions, by raising the binding affinity to fibrinogen and TF activity and expression and lowering TFPI release and MMP-2 and -9 activities. These effects on HIE diminish after WUE. However, MIE minimizes the risk of thrombosis induced by platelet-NPC interactions.

Role of the cyclooxygenase pathway in the protection against postischemic stunning in conscious sheep

OBJECTIVE

There are controversial reports in conscious animals regarding the role of cyclooxygenase-2 in late preconditioning (LP). This study analyzed the effect of COX-2 involvement in non-preconditioned hearts (NP) and in mediation of LP protection against stunning in conscious sheep submitted to a prolonged reversible ischemia.

METHODS

Six groups were considered: NP: 12 min ischemia and 120 min reperfusion; LP consisting of six periods of 5 min-ischemia-5 min reperfusion 24 h before the 12 min ischemia; NP and LP with either the non-selective COX-1 and COX-2 inhibitor, aspirin (20 mg/kg), or the specific COX-2 inhibitor, celecoxib (3 mg/kg) before the 12 min ischemic period.

RESULTS

Mean postischemic wall thickening fraction (as % of preischemic values) improved from 49.6 +/- 4.0% in NP to 72.5 +/- 3.5% in LP (p < 0.01) and a similar protection was obtained with aspirin and celecoxib in NP hearts (p < 0.01). Neither aspirin nor celecoxib administration prior to the prolonged ischemia on day 2 abrogated LP improvement of postischemic dysfunction. Moreover, LP with aspirin improved the protective response (80.7 +/- 2.6%) over that obtained with aspirin in NP hearts (66.6 +/- 4.7%, p < 0.05). This effect was not obtained with celecoxib.

CONCLUSIONS

Aspirin and celecoxib showed that COX-2 has a detrimental effect on mechanical cardioprotection in NP hearts of conscious sheep submitted to a prolonged reversible ischemia, and does not seem to participate as mediator of LP. Aspirin revealed a similar COX-1 deleterious action, since only when both COX-1 and COX-2 were inhibited, LP was put in evidence adding functional improvement over that obtained in NP hearts treated with aspirin.