Low-dose calcium antagonists reduce energy demand and cellular damage of isolated hearts during both ischemia and reperfusion

Differential effects of eplerenone versus amlodipine on muscle metaboreflex function in hypertensive humans

Numerous studies have demonstrated that sympathetic nervous system overactivation during exercise in hypertensive rodents and humans is due, in part, to an exaggerated reflex response known as the exercise pressor reflex. Our prior studies have implicated a key role of mineralocorticoid receptor activation in mediating an augmented exercise pressor reflex in spontaneously hypertensive rats, which is mitigated by blockade with eplerenone. However, the effect of eplerenone on exercise pressor reflex has not been assessed in human hypertension. Accordingly, the authors performed a randomized crossover study to compare the effects of eplerenone to another antihypertensive drug from a different class amlodipine on sympathetic nerve activity (SNA) in 14 patients with uncomplicated hypertension. The authors found that amlodipine unexpectedly augmented the increase in SNA during the second minute of isometric handgrip, which persisted into the post‐exercise circulatory arrest period (∆ SNA, from rest of 15 ± 2 vs. 9 ± 2 vs. 10 ± 2 bursts/min, amlodipine vs. baseline vs. eplerenone, respectively, p < .01), suggesting an exaggerated muscle metaboreflex function. Eplerenone did not alter sympathetic responses to exercise or post‐exercise circulatory arrest in the same hypertensive individuals. In conclusions, our studies provide the first direct evidence for a potentially unfavorable potentiation of muscle metaboreflex by amlodipine during isometric handgrip exercise in hypertensive patients whereas eplerenone has no significant effect. Our study may have clinical implications in terms of selection of antihypertensive agents that have the least detrimental effects on sympathetic neural responses to isometric exercise.

A calcium channel blocker nifedipine distorts the effects of nano-zinc oxide on metal metabolism in the marsh frog Pelophylax ridibundus

Global decline of amphibian populations causes particular concern about their vulnerability to novel environmental pollutants, including engineering nanomaterials and pharmaceutical products. We evaluated the bioavailability of nanoform of zinc oxide (n-ZnO) in frog Pelophylax ridibundus and determined whether co-exposure to a common pharmaceutical, a calcium-channel blocker nifedipine (Nfd) can affect this bioavailability. Male frogs were exposed for 14 days to the tap water (Control) and n-ZnO (3.1 μM), Zn²⁺ (3.1 μM, as a positive control for n-ZnO exposures), Nfd (10 μM), and combination of n-ZnO and Nfd (n-ZnO + Nfd) in environmentally-relevant concentration. Exposure to Zn²⁺ or n-ZnO led to up-regulation of metal-binding proteins, metallothioneins (MTs) in the liver and Zn-carrying vitellogenin-like proteins in the blood plasma. Notably, upregulation of MTs by Zn²⁺ or n-ZnO exposures combined with increased binding of Zn and Cu to MTs. This was associated with the more reducing conditions in the liver tissue indicated by elevated lactate to pyruvate ratio. Nfd suppressed the binding of Zn and Cu to MTs and led to a decrease in Lactate/Pyruvate ratio and elevated protein carbonylation indicating pro-oxidant conditions. Redox status parameters were not directly related to DNA fragmentation, nuclear abnormalities or suppression of cholinesterase activity indicating that factors other than oxidative stress are involved in cytotoxicity of different pollutants and their combinations. Furthermore, activity of Phase I biotransformation enzyme (CYP450 oxidase measured as EROD) was elevated in Nfd-containing exposures and in Zn²⁺ exposed frogs. Tyrosinase-like activity in the frog liver was strongly stimulated by Zn²⁺ but suppressed by n-ZnO, Nfd and n-ZnO + Nfd. These findings show that Nfd modulates homeostasis of essential metals in amphibians and emphasize that physiological consequences of combined n-ZnO and Nfd exposures are difficult to predict based on the mechanisms of single stressors.

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.

Pharmacological preconditioning by diazoxide downregulates cardiac L-type Ca(2+) channels

BACKGROUND AND PURPOSE

Pharmacological preconditioning (PPC) with mitochondrial ATP-sensitive K(+) (mitoK(ATP) ) channel openers such as diazoxide, leads to cardioprotection against ischaemia. However, effects on Ca(2+) homeostasis during PPC, particularly changes in Ca(2+) channel activity, are poorly understood. We investigated the effects of PPC on cardiac L-type Ca(2+) channels.

EXPERIMENTAL APPROACH

PPC was induced in isolated hearts and enzymatically dissociated cardiomyocytes from adult rats by preincubation with diazoxide. We measured reactive oxygen species (ROS) production and Ca(2+) signals associated with action potentials using fluorescent probes, and L-type currents using a whole-cell patch-clamp technique. Levels of the α(1c) subunit of L-type channels in the cellular membrane were measured by Western blot.

KEY RESULTS

PPC was accompanied by a 50% reduction in α(1c) subunit levels, and by a reversible fall in L-type current amplitude and Ca(2+) transients. These effects were prevented by the ROS scavenger N-acetyl-L-cysteine (NAC), or by the mitoK(ATP) channel blocker 5-hydroxydecanoate (5-HD). PPC significantly reduced infarct size, an effect blocked by NAC and 5-HD. Nifedipine also conferred protection against infarction when applied during the reperfusion period. Downregulation of the α(1c) subunit and Ca(2+) channel function were prevented in part by the protease inhibitor leupeptin.

CONCLUSIONS AND IMPLICATIONS

PPC downregulated the α(1c) subunit, possibly through ROS. Downregulation involved increased degradation of the Ca(2+) channel, which in turn reduced Ca(2+) influx, which may attenuate Ca(2+) overload during reperfusion.

Enhancement of amlodipine cardioprotection by quercetin in ischaemia/reperfusion injury in rats

Objectives

To investigate the possible modification of the cardioprotective effect of amlodipine when co-administered with quercetin in myocardial ischaemia/reperfusion-induced functional, metabolic and cellular alterations in rats.

Methods

Oral doses of amlodipine (15 mg/kg) and quercetin (5 mg/kg), alone or in combination, were administered once daily for 1 week. Rats were then subjected to myocardial ischaemia/reperfusion (35min/10min). Heart rates and ventricular arrhythmias were recorded during ischaemia/reperfusion progress. At the end of reperfusion, activities of plasma creatine kinase (CK) and cardiac myeloperoxidase were determined. In addition, cardiac contents of lactate, ATP, thiobarbituric acid reactive substances (TBARS), reduced glutathione (GSH) and total nitrate/nitrite (NOx) were estimated. Finally, histological examination was performed to visualize the protective cellular effects of different pretreatments.

Key findings

Combined therapy provided significant improvement in the amlodipine effect toward preserving cardiac electrophysiologic functions, ATP and GSH contents as well as reducing the elevated plasma CK, cardiac TBARS and NOx contents.

Conclusion

Quercetin could add benefits to the cardioprotective effect of amlodipine against injury induced in the heart by ischaemia/reperfusion.

Modulation of cortical nitric oxide synthase, glutamate, and redox state by nifedipine and taurine in PTZ-kindled mice

PURPOSE

Correlation between pentylenetetrazol (PTZ)-induced kindling and the cortical nitric oxide synthase (NOS), intracellular calcium [Ca2+]i, glutamate, and free radicals was studied in mice, as well as the modulatory action of nifedipine and taurine on these parameters.

METHODS

Male Swiss albino mice were used. Mice in one group received a single convulsive dose of PTZ (50 mg/kg, i.p), and were killed 24 h later. To induce kindling, PTZ was injected in a subconvulsive dose (40 mg/kg, i.p.) every other day for 3 weeks. One kindled group was used as control, whereas two other groups were injected 30 min before PTZ with either nifedipine (30 mg/kg, i.p) or taurine (100 mg/kg, i.p). All three kindled groups were killed 24 h after the last injection.

RESULTS

Compared with normal control group, PTZ-kindled mice had significantly higher levels of [Ca2+]i, malonaldehyde (MDA), NOS, and lactate dehydrogenase (LDH) but had lower levels of superoxide dismutase (SOD) and reduced glutathione (GSH). Acute seizures of the same intensity did not induce these alterations, indicating their link to the kindling phenomenon and not to seizure activity. The effect of taurine, known as an antioxidant, was more pronounced than that of the Ca2+-channel blocker, nifedipine. The first drug reversed the PTZ-kindled action on [Ca2+]i, NOS, LDH, GSH, and SOD, whereas nifedipine restored only LDH and GSH levels. However, both drugs did not restore the elevated MDA level.

CONCLUSIONS

This study suggests that free radicals, as well as NOS, are implicated in PTZ-induced kindling, and that antioxidants could play a role in controlling the accompanying changes.

Cardioprotective effects of lowering oxygen tension after aortic unclamping on cardiopulmonary bypass during coronary artery bypass grafting

The effect on myocardial reperfusion injury of reducing oxygen tension during reperfusion on cardiopulmonary bypass (CPB) in coronary artery bypass grafting (CABG) was examined at the same time as the influence of diltiazem during CPB was evaluated. A prospective, randomized trial evaluated the hemodynamic and myocardial metabolic recovery in 3 groups of patients undergoing elective CABG; subjects were randomly allocated on the basis of oxygen tension during reperfusion after aortic unclamping: group 1 (n=10) hyperoxic reperfusion (oxygen tension [PO2]=450-550 mmHg); group 2 (n=10): hyperoxic reperfusion and subsequent continuous infusion of diltiazem (0.5 microg/kg); group 3 (n=10): lowering reperfusate PO2 (PO2=200-250 mmHg). Hemodynamic and myocardial metabolic measurements were taken at 6 preset times: before starting the surgical procedure and at 30 min and 3, 9, 21, and 45 h after discontinuation of CPB. The cardiac index in the lowering reperfusate PO2 group was higher than that of the hyperoxic reperfusion groups at 30 min and 3 h after CPB, and malondialdehyde and troponin-T were significantly lower at 30 min and 3 h, respectively. In comparison with the hyperoxic + diltiazem group, the hemodynamic and myocardial recovery in the lowering reperfusate PO2 group was improved for about 3 h after CPB. Reduced oxygen tension during reperfusion after aortic unclamping on CPB is more effective against myocardial injury than a calcium antagonist in the short term. It is a convenient and safe management technique that can reduce morbidity and mortality, especially in the severely compromised heart.

l-carnosine and verapamil inhibit hypoxia-induced expression of hypoxia inducible factor (HIF-1 alpha) in H9c2 cardiomyoblasts

Contractile failure of myocardial cells is a common cause of mortality in ischemic heart disease. In response to hypoxic conditions, cells upregulate the activity of hypoxia-inducible factor 1 (HIF-1) and express a number of genes encoding proteins that either enhance O (2)delivery or increase cellular ATP levels. HIF-1 is a heterodimer of bHLH-PAS proteins, HIF-1 alpha and HIF-1 beta. Both subunits are constitutively expressed under normoxic conditions, but HIF-1 alpha levels are kept low by proteolytic degradation, then stabilized under conditions of low O (2)by a mechanism that is poorly understood. Here we tested the hypothesis that expression of HIF-1 alpha in cardiac cells may be affected by two known cardioprotective agents. We tested l-carnosine, a naturally occurring dipeptide which has been shown to improve myocardial contractility during hypoxia, and verapamil, a calcium channel blocker frequently prescribed for the treatment of heart disease. The levels of HIF-1 alphamRNA remained relatively stable during time course hypoxia (1% O (2)) in H9c2 cardiomyoblasts, then increased slightly after 24 h. In cells pretreated with 1 microM carnosine, the levels of mRNA were transiently reduced, but then increased after 24 h similar to the controls. The levels of HIF-1 alpha protein increased rapidly in H9c2 cells within 30 min of hypoxia, but this induction was significantly reduced in cells treated with either carnosine or verapamil. In addition, treatment of cells with these agents further reduced the low levels of HIF-1 under normoxic conditions. These results suggest that l-carnosine and verapamil may affect the regulated proteolytic degradation of HIF-1 alpha in heart cells during hypoxia.