Protective effect of diltiazem against ischemia-induced decreases in regional myocardial flow in rat heart

The effect of mebudipine on cardiac function and activity of the myocardial nitric oxide system in ischaemia-reperfusion injury in rats

Objectives

Previous studies have suggested that failure of the synthesis of nitric oxide is involved in the pathophysiology of myocardial ischaemia–reperfusion injury. In this study, we investigated the effect of mebudipine, a new dihydropyridine calcium channel blocker, on cardiac function and activity of the myocardial nitric oxide system in ischaemia–reperfusion injury in isolated rat hearts.

Methods

Forty male Wistar rats (250–300 g) were divided into four groups (n = 10): sham, control, vehicle and drug groups. The animals were anesthetised with sodium pentobarbital (6 mg/kg intraperitoneal). The hearts were quickly removed, mounted on a Longendorff apparatus and perfused with Krebs-Henseleit solution under constant pressure at 37°C. After 20 min stabilisation period, the ischaemic groups received 30 min global ischaemia and 120 min reperfusion. For the drug and vehicle groups, before ischaemia the hearts were perfused with mebudipine (10^-3 µM) or ethanol-enriched solution (0.01%) for 25 min, respectively. Myocardial function, and creatine kinase, lactate dehydogenase and total nitric oxide metabolite (nitrite and nitrate) levels were analysed.

Results

Cardiac functions had recovered significantly in the mebudipine group (p < 0.01). Furthermore, mebudipine remarkably reduced the levels of lactate dehydogenase and creatine kinase in the coronary effluent and increased myocardial nitric oxide metabolite levels compared with the control group.

Conclusion

Our results indicate that mebudipine reduced the intensity of myocardial ischaemia–reperfusion injury, and that activation of the myocardial nitric oxide system played an important role in this regard.

Protective Effect of Diltiazem on Hepatic Ischemia-Reperfusion Injury in Rats by Improving Liver Tissue Blood Flow

BACKGROUND

Cytosolic calcium ions are known to play an important role in ischemia-reperfusion (IR) injury. However, the protective effect of calcium channel blockers remains controversial in liver IR injury. Moreover, calcium channel blockers improve hepatic IR injury not due to blocking an increase in hepatic calcium concentration. Therefore, we hypothesized that calcium antagonists protected a liver from IR injury by a vasodilatory action rather than by the inhibition of an increase in Ca2+ within parenchymal cells. This study evaluated the effects of diltiazem, a calcium channel blocker, on liver energy metabolism and blood flow after IR injury.

METHODS

Twenty-seven rats underwent hepatic ischemia for 30 minutes followed by 60 minutes of reperfusion. The animals were allocated into group C (without drug); group D5 (diltiazem, 5 microg/kg per min); or group D10 (diltiazem, 10 microg/kg per min). Diltiazem was infused before laparotomy and then throughout the experiment.

RESULTS

After 60 minutes of reperfusion, liver tissue blood flow and ATP concentrations were significantly higher in group D10 than the other animals (both, P < .05). Changes in ATP values strongly correlated those observed in blood flow (R = 0.80, P < .001).

CONCLUSION

Diltiazem improved ATP-generating capacity during reperfusion by improving liver tissue blood flow. An improvement in hepatic tissue perfusion may be a therapeutic strategy for liver IR injury.

Subendocardial and subepicardial pressure–flow relations in the rat heart in diastolic and systolic arrest

Ischemic heart disease is more apparent in the subendocardial than in subepicardial layers. We investigated coronary pressure-flow relations in layers of the isolated rat left ventricle, using 15 microm microspheres during diastolic and systolic arrest in the vasodilated coronary circulation. A special cannula allowed for selective determination of left main stem pressure-flow relations. Arterio-venous shunt flow was derived from microspheres in the venous effluent. We quantitatively investigated the pressure-flow relations in diastolic arrest (n=8), systolic arrest at normal contractility (n=8) and low contractility (n=6). In all three groups normal and large ventricular volume was studied. In diastolic arrest, at a perfusion pressure of 90 mmHg, subendocardial flow is larger than subepicardial flow, i.e., the endo/epi ratio is approximately 1.2. In systolic arrest the endo/epi ratio is approximately 0.3, and subendocardial flow and subepicardial flow are approximately 12% and approximately 55% of their values during diastolic arrest. The endo/epi ratio in diastolic arrest decreases with increasing perfusion pressure, while in systole the ratio increases. The slope of the pressure-flow relations, i.e., inverse of resistance, changes by a factor of approximately 5.3 in the subendocardium and by a factor approximately 2.2 in the subepicardium from diastole to systole. Lowering contractility affects subendocardial flow more than subepicardial flow, but both contractility and ventricular volume changes have only a limited effect on both subendocardial and subepicardial flow. The resistance (inverse of slope) of the total left main stem pressure-flow relation changes by a factor of approximately 3.4 from diastolic to systolic arrest. The zero-flow pressure increases from diastole to systole. Thus, coronary perfusion flow in diastolic arrest is larger than systolic arrest, with the largest difference in the subendocardium, as a result of layer dependent increases in vascular resistance and intercept pressure. Shunt flow is larger in diastolic than in systolic arrest, and increases with perfusion pressure. We conclude that changes in contractility and ventricular volume have a smaller effect on pressure-flow relations than diastolic-systolic differences. A synthesis of models accounting for the effect of cardiac contraction on perfusion is suggested.

Autologous mesenchymal stem cell transplantation induce VEGF and neovascularization in ischemic myocardium

Neovascularization induced by vascular endothelial growth factor (VEGF) represents an appealing approach for treating ischemic heart disease. However, VEGF therapy has been associated with transient therapeutic effects and potential risk for hemangioma growth. Adult mesenchymal stem cells (MSCs) derived from bone marrow are a promising source for tissue regeneration and repair. In order to achieve a safe and persistent angiogenic effect, we have explored the potential of autologous MSCs transplantation to enhance angiogenesis and cardiac function of ischemic hearts. One week after myocardial infarction induced by occlusion of left anterior descending artery, autologous MSCs expanded in vitro was administrated intramyocardially into the infarct area of the same donor rats. By 2 months, MSCs implantation significantly elevated VEGF expression levels, accompanied by increased vascular density and regional blood flow in the infarct zone. The neovascularization resulted in a decreased apoptosis of hypertrophied myocytes and markedly improved the left ventricular contractility (ejection fraction: 79.9+/-7.6% vs. 37.2+/-6.9% in control animals). Therefore, mechanisms underlying MSCs improvement of cardiac functions may involve neovascularization induced by differentiation of MSCs to endothelial cells and para-secretion of growth factors, in addition to the apoptosis reduction and previously reported cardiomyocytes regeneration. Two months after cell transplantation, there are significant improvement of left ventricular function. Hence, autologous MSCs transplantation may represent a promising therapeutic strategy free of ethical concerns and immune rejection, for neovascularization in ischemic heart diseases.

Commonly used numbers of microspheres affect cardiac vascular resistance

The main goal of the study was to examine how the microsphere technique affects the hemodynamics and mitochondrial energy status of the Langendorff-perfused rat heart. The hearts were perfused at a constant flow with Tyrode solution. NADH videofluorometry of the surface of the left ventricle was used to record the mitochondrial energy status as indication of regional ischemia. The effects of seven successive (separated by 10 min) injections of 0.1 ml of saline or (0.05% Tween 20; polysorbate 20, Sigma-Aldrich, St. Louis, MO, U.S.A.) or (0.05% Tween 20 + microspheres) were studied. The number of microspheres per injection were: #1 (2,500), #2 (5,000), #3 (10,000), #4 (20,000), #5 (40,000), #6 (40000), and #7 (80000). The anti-aggregation agent Tween always caused a biphasic response in perfusion pressure. Compared with the Tween effect, the injection of microspheres caused an initial change (mm Hg) in perfusion pressure of #1 (-10), #2 (NS), #3 (NS), #4 (+7.5), #5 (+12.3), #6 (+14.4), #7 (+18.3), and a delayed change (10 min after injection) of #1 (-22.2), #2 (-6.0), #3 (-4.1), #4 (-4.5), #5 (NS), #6 (NS), and #7 (+5.9). The microspheres caused a significant delayed increase in NADH only for injection #6 and #7. Similar results were found for different durations of the input function or when hearts were perfused at constant perfusion pressure. In hearts without flow reserve (10 microM adenosine), Tween injections were without effect, whereas three successive injections of 60,000 microspheres each only caused increases in perfusion pressure and NADH. The data demonstrate that in hearts with flow reserve present, even very low numbers of microspheres (2,000/g heart) cause large decreases in perfusion pressure without obvious signs of ischemia. When flow reserve was exhausted by either microsphere loading or adenosine addition, microspheres only caused increases in perfusion pressure and resulted in detectable ischemia (NADH). It is concluded that microspheres affect the vascular resistance of the heart and that these effects are flow reserve dependent.