Inotropic response of stunned hypertrophied myocardium: responsiveness of hypertrophied and normal postischemic isolated rat hearts to calcium and dopamine stimulation

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

BACKGROUND

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

MATERIAL AND METHODS

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

RESULTS

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

CONCLUSION

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

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

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

ECG-gated 18F-FDG positron emission tomography

AIM

18F-fluorodeoxyglucose (18F-FDG)-positron emission tomography (PET) provides information about myocardial glucose metabolism to diagnose myocardial viability. Additional information about the functional status is necessary. Comparison of tomographic metabolic PET with data from other imaging techniques is always hampered by some transfer uncertainty and scatter. We wanted to evaluate a new Fourier-based ECG-gated PET technique using a high resolution scanner providing both metabolic and functional data with respect to feasibility in patients with diseased left ventricles.

METHODS

Forty-five patients with coronary artery disease and at least one left ventricular segment with severe hypokinesis or akinesis at biplane cineventriculography were included. A new Fourier-based ECG-gated metabolic 18F-FDG-PET was performed in these patients. Function at rest and 18F-FDG uptake were examined in the PET study using a 36-segment model.

RESULTS

Segmental comparison with ventriculography revealed a high reliability in identifying dysfunctional segments (> 96%). 18F-FDG uptake of normokinetic/hypokinetic/akinetic segments was 75.4 +/- 7.5, 65.3 +/- 10.5, and 35.9 +/- 15.2% (p < 0.001). In segments > or = 70% 18F-FDG uptake no akinesia was observed. No residual function was found below 40% 18F-FDG uptake. An additional dobutamine test was performed and revealed inotropic reserve (viability) in 42 akinetic segments and 45 hypokinetic segments.

CONCLUSION

ECG-gated metabolic PET with pixel-based Fourier smoothing provides reliable data on regional function. Assessment of metabolism and function makes complete judgement of segmental status feasible within a single study without any transfer artefacts or test-to-test variability. The results indicate the presence of considerable amounts of viable myocardium in regions with an uptake of 40-50% 18F-FDG.

Effects of intracoronary calcium chloride on regional oxygen balance and mechanical function in normal and stunned myocardium in dogs

BACKGROUND

Brief myocardial ischaemia has been demonstrated to result in mechanical and coronary endothelial dysfunction, in which calcium may play a role. We examined whether the mechanical and vascular responses to calcium are altered in postischaemic, reperfused myocardium.

METHODS

Regional myocardial oxygen consumption (MVO2), mechanical function and coronary blood flow (CBF) in response to calcium chloride (0.10, 0.25, 0.50 and 0.75 mg ml(-1) of CBF) directly infused into the left anterior descending (LAD) artery were determined before (normal) and 30 min after a 15-min-period of LAD occlusion (stunned) in an open-chest canine model. Percentage segment shortening (%SS) and percentage postsystolic shortening (%PSS) in the LAD territory were determined using ultrasonic crystals and CBF using a Doppler transducer. Myocardial extraction of oxygen (EO2) and lactate (Elac) was calculated.

RESULTS

The infusion of calcium chloride resulted in dose-dependent increases in %SS and MVO2 but did not affect %PSS in normal myocardium. These changes were accompanied by parallel increases in CBF, resulting in no change in EO2. In stunned myocardium, the responses to calcium chloride were not significantly altered, with the exception of a reduction in %PSS. However, ischaemia and reperfusion itself significantly reduced %SS and Elac and increased %PSS.

CONCLUSIONS

These data suggest that calcium chloride improves regional systolic and diastolic function both in normal and stunned myocardium. Calcium chloride is unlikely to cause direct coronary vasoconstriction or to deteriorate regional mechanical function in postischaemic myocardium.