Long-term treatment with nipradilol, a nitric oxide-releasing beta-adrenergic blocker, enhances postischemic recovery and limits infarct size

Long-term inorganic nitrate administration protects against myocardial ischemia-reperfusion injury in female rats

BACKGROUND

The favorable effects of nitrate against myocardial ischemia-reperfusion injury (MIRI) have primarily focused on male rats and in short term. Here we determine the impact of long-term nitrate intervention on baseline cardiac function and the resistance to MIRI in female rats.

METHODS

Female Wistar rats were randomly divided into untreated and nitrate-treated (100 mg/L sodium nitrate in drinking water for 9 months) groups (n = 14/group). At intervention end, levels of serum progesterone, nitric oxide metabolites (NOx), heart NOx concentration, and mRNA expressions of NO synthase isoforms (NOS), i.e., endothelial (eNOS), neuronal (nNOS), and inducible (iNOS), were measured. Isolated hearts were exposed to ischemia, and cardiac function indices (CFI) recorded. When the ischemia-reperfusion (IR) period ended, infarct size, NO metabolites, eNOS, nNOS, and iNOS expression were measured.

RESULTS

Nitrate-treated rats had higher serum progesterone (29.8%, P = 0.013), NOx (31.6%, P = 0.035), and higher heart NOx (60.2%, P = 0.067), nitrite (131%, P = 0.018), and eNOS expression (200%, P = 0.005). Nitrate had no significant effects on baseline CFI but it increased recovery of left ventricular developed pressure (LVDP, 19%, P = 0.020), peak rate of positive (+ dp/dt, 16%, P = 0.006) and negative (-dp/dt, 14%, P = 0.014) changes in left ventricular pressure and decreased left ventricular end-diastolic pressure (LVEDP, 17%, P < 0.001) and infarct size (34%, P < 0.001). After the IR, the two groups had significantly different heart nitrite, nitrate, NOx, and eNOS and iNOS mRNA expressions.

CONCLUSIONS

Long-term nitrate intervention increased the resistance to MIRI in female rats; this was associated with increased heart eNOS expression and circulating progesterone before ischemia and blunting ischemia-induced increased iNOS and decreased eNOS after MIRI.

Chronic β1-adrenoceptor blockade impairs ischaemic tolerance and preconditioning in murine myocardium

β-adrenoceptor antagonists are commonly used in ischaemic heart disease (IHD) patients, yet may impair signalling and efficacy of 'cardioprotective' interventions. We assessed effects of chronic β1-adrenoceptor antagonism on myocardial resistance to ischaemia-reperfusion (IR) injury and the ability of cardioprotective interventions [classic ischaemic preconditioning (IPC); novel sustained ligand-activated preconditioning (SLP)] to reduce IR injury in murine hearts. Young male C57Bl/6 mice were untreated or received atenolol (0.5g/l in drinking water) for 4 weeks. Subsequently, two cardioprotective stimuli were evaluated: morphine pellets implanted (to induce SLP, controls received placebo) 5 days prior to Langendorff heart perfusion, and IPC in perfused hearts (3×1.5min ischaemia/2min reperfusion). Atenolol significantly reduced in vivo heart rate. Untreated control hearts exhibited substantial left ventricular dysfunction (~50% pressure development recovery, ~20mmHg diastolic pressure rise) with significant release of lactate dehydrogenase (LDH, tissue injury indicator) after 25min ischaemia/45min reperfusion. Contractile dysfunction and elevated LDH were reduced >50% with IPC and SLP. While atenolol treatment did not modify baseline contractile function, post-ischaemic function was significantly depressed compared to untreated hearts. Atenolol pre-treatment abolished beneficial effects of IPC, whereas SLP protection was preserved. These data indicate that chronic β1-adrenoceptor blockade can exert negative effects on functional IR tolerance and negate conventional IPC (implicating β1-adrenoceptors in IR injury and IPC signalling). However, novel morphine-induced SLP is resistant to inhibition by β1-adrenoceptor antagonism.

Landiolol Enhances Effect of Ischemic Preconditioning in Isolated Rabbit Hearts

The effect of the ultra-short-acting beta blocker, landiolol, on ischemic preconditioning was examined in isolated rabbit hearts. Ischemic preconditioned hearts received 2 episodes of 5 min each of global ischemia and reperfusion. The left anterior descending coronary artery was occluded for 1 hour and reperfused for 1 hour. Left ventricular end-systolic and end-diastolic pressures and infarct size were measured. Seven control hearts had no drug infused. Four groups of 6 hearts each were pretreated with 1 or 3 μM of landiolol or a combination of 1 or 3 μM landiolol and ischemic preconditioning. A further group of 6 hearts had ischemic preconditioning without landiolol. Ischemic preconditioning significantly reduced left ventricular end-diastolic pressure and infarct size compared to the controls. Landiolol alone did not change left ventricular end-diastolic pressure or infarct size, but landiolol 3 μM and ischemic preconditioning decreased left ventricular end-diastolic pressure more than preconditioning alone. These data suggest that pre-ischemic landiolol infusion may enhance the cardioprotective effect of ischemic preconditioning.

Effects of Ischemic Preconditioning in Human Heart

BACKGROUND

The aim of this study is to investigate the effects of ischemic preconditioning (IP) on myocardium and the level of nitric oxide (NO) in patients undergoing aorta-coronary bypass surgery.

METHODS

Twenty consecutive patients with coronary artery disease were subjected into two equal groups; the IP group and the control group. Following the onset of cardiopulmonary bypass in the study group, hearts were preconditioned with two 3-minute periods of cross-clamping separated by 2 minutes of reperfusion. In the control group, cardiopulmonary bypass was continued for 10 minutes without using cross-clamp. Arterial and coronary sinus blood samples were used to determine serum NO, malondialdehyde (MDA), creatine phosphokinase-MB (CKMB), and lactate dehydrogenase (LDH) levels. Need for defibrillation after cross-clamp removal, ECG changes, postoperative arrhythmias, ejection fraction, and fractional shortening rates were recorded as hemodynamic data.

RESULTS

Serum NO level was higher in the study group 5 minutes after aortic clamp removal (199.3 +/- 92.7 vs. 112.2 +/- 35.8 micromol; p = 001). Serum MDA (2.55 +/- 0.4 vs. 4.06 +/- 0.5; etamol/ml; 5 minutes after the aortic clamp removal; p = 0.0002); CK-MB (22.8 +/- 2.5 vs. 37.4 +/- 4.1; U/L 12 hours after the operation, p < 0.0001), and LDH (501.8 +/- 46.7 vs. 611.4 +/- 128.3; IU/L 48 hours after the operation, p = 0.02) levels were significantly lower in the preconditioned group when compared with the control group. Also, need for electrical defibrillation was significantly lower in the study group; Ejection fraction (64.3 +/- 6.3 vs. 57.6 +/- 7.6; p = 0.04) and fractional shortening (31.7 +/- 3.9 vs. 26.2 +/- 4.0; p = 0.04) rates were better in the study group postoperatively.

CONCLUSIONS

These data may suggest that cardioprotection by ischemic preconditioning offers higher NO production, a lower myocardial ischemia, and better functional recovery of the hearts in coronary artery surgery patients.

Nitric oxide-releasing drugs

Pharmacological compounds that release nitric oxide (NO) have been useful tools for evaluating the broad role of NO in physiology and therapeutics. NO deficiency has been implicated in the genesis and evolution of several disease states. Both medical needs and commercial opportunities have fostered attempts to modulate NO in the human body for therapeutic gain. Strategies for NO modulation encompass antiinflammatory, sexual dysfunction, and cardiovascular indications. Apart from newly developed drugs, several commonly used cardiovascular drugs exert their beneficial action, at least in part, by modulating the NO pathway. This review discusses the fundamental pharmacological properties and mechanisms of action of NO-releasing drugs. Some of these compounds may enter in the clinical arena providing important therapeutic benefits in human diseases.

Ischemic preconditioning is not cardioprotective in senescent human myocardium

BACKGROUND

Cellular and functional changes secondary to aging could impair myocardial tolerance to ischemia and affect the heart's response to ischemic preconditioning.

METHODS

We investigated the impact of cardiac aging on preconditioning in right atrial trabeculae of adult patients (< or = 55 years) and senescent patients (> or = 70 years) with coronary artery disease. Specimens were subjected to 30 minutes of simulated ischemia (hypoxic substrate-free superfusion) with and without 5 minutes of ischemic pretreatment. Postischemic contractile recovery was measured and expressed as percentage of base line force values.

RESULTS

During the reoxygenation period, trabeculae of adult patients but not those of senescent patients improved after ischemic preconditioning. After 40 minutes of reoxygenation, preconditioned adult trabeculae developed 57% +/- 5% of their preischemic force (nonpreconditioned control 44% +/- 5%, p < 0.01), senescent trabeculae recovered to 44% +/- 4% (control 45% +/- 3%). Especially myocardium from adult patients with Canadian Cardiovascular Society (CCS) stage III angina pectoris treated with ACE inhibitors recovered well (70% +/- 7%; control 50% +/- 8%, p < 0.01), contrasting with trabeculae from patients with CCS stage II angina (44% +/- 5%; control 40% +/- 10%). Ischemia-inducible Hsp70 (human heat shock protein) was additionally measured after reoxygenation. Total Hsp70 mRNA was elevated in preconditioned myocardium along with its contractile recovery (r = 0.33, p = 0.07). Because the control transcription, analyzing 18S rRNA and beta-actin, was reduced by ischemia but recovered in preconditioned trabeculae, relative Hsp70 mRNA was not altered.

CONCLUSIONS

Our data indicate that ischemic preconditioning has no beneficial effect on the postischemic functional recovery of senescent human myocardium.