Levitra (vardenafil) Info

The present study showed that administering vardenafil at reperfusion decreased infarct size in rat isolated hearts. Although vardenafil was protective at 10nM, we were surprised to find that the protective effect was lost at higher concentrations. So far, we have no explanation for this observation. We could show that protection by vardenafil at 10nM was dependent on the activity of GC and the cGMP-dependent kinase PKG. Furthermore, vardenafil was found to be protective in a model of TMRE-stained cardiomyocytes exposed to calcium stress with a selective calcium ionophore. The cell model allowed the additional use of the highly specific PKG inhibitory peptides DT-2 and DT-3 to further support a role for PKG.

Canadian Vardenafil and other PDE-5 inhibitors are established drugs in the treatment of erectile dysfunction in men. PDE enzymes hydrolyse the phosphodiester bond of the cyclic nucleotides cAMP and cGMP, which serve as second messengers in various cellular functions. Therefore, PDE inhibition can elevate intracellular cAMP or cGMP concentration, depending on their substrate specificity. Type-5 PDEs predominantly metabolize cGMP and are localized in many tissues, including canine and mouse ventricular myocytes. In the heart, increasing intracellular cGMP via the addition of a cell-permeable cGMP analogue leads to reduced infarct size after ischemia/reperfusion with either pretreatment or treatment at reperfusion. Therefore, it seemed only logical that indirect cGMP elevation via PDE-5 inhibition would show similar effects. Ockaili et al. (2002) were the first to show that sildenafil administered before ischemia reduced myocardial infarct size in an in situ rabbit heart model. Later, similar results could be shown for other PDE-5 inhibitors, such as vardenafil and tadalafil, in various models.

However, PDE-5 inhibitors also proved to be effective not only when given before ischemia, as preconditioning agents, but also when applied at reperfusion, as postconditioning agents. Salloum et al. (2007) reported a marked reduction in infarct size in rabbit hearts in situ when sildenafil professional or vardenafil professional was administered at reperfusion. In the present study, we confirmed these data for cheap vardenafil in rat isolated hearts with approximately the same concentration of the drug used in the earlier study. In our hands, administration of 10nM vardenafil at reperfusion was clearly protective and this protection was lost when vardenafil (generic levitra) was used at higher concentrations of 100nM or 1μM. A similar pattern could be seen in the myocytes. This somewhat surprising result was in agreement with a report from du Toit et al. (2005), where they observed clear infarct size reduction with a pretreatment of 50nM sildenafil, whereas doubling the concentration to 100nM removed this protective effect. One disadvantage of the in situ rabbit model is the confounding effect of the blood-pressure-lowering effects of an elevated dose of PDE-5 inhibitors. This disadvantage is not present in our constant pressure Langendorff model. We did see a significant increase in coronary flow at high, nonprotective vardenafil concentrations (1μM) but there was no effect on coronary flow at the protective concentration of 10nM.

At present, we cannot explain the loss of protection by vardenafil (generic Levitra) at higher concentration, leading to a bell-shaped dose–response curve. Nevertheless, recent evidence suggests that cGMP is highly compartmentalized within the cell. Hence, it might be possible that vardenafil increases cGMP first in a compartment leading to protection, whereas higher concentrations of vardenafil increases cGMP concentrations in another compartment which counteracts these effects. Obviously, further experiments are necessary to prove this concept.

We also tested whether vardenafil acts through PKG activation. Although vardenafil (Levitra Professional) is highly selective for PDE-5, which in turn is selective for cGMP, it is still possible that cAMP might be involved in its cardioprotection at reperfusion, either through direct modification via PDE-5 or through its interaction with cGMP. There are also reports of a putative negative feedback mechanism of PKG and PKA phosphorylating and, hence, inactivating PDE-5 and leading to an elevated cGMP level. We found that the selective PKG inhibitor KT-5823 could fully abolish the vardenafil-induced protection. Nevertheless, taking into account that PKA levels in the heart are relatively high compared with those of PKG, we cannot rule out any effects of PKA either directly or via PDE-5 phosphorylation. To further confirm the role of PKG, we developed a cell model of intracellular calcium stress mirroring the detrimental calcium increase occurring at reperfusion. HL-1 cardiomyocytes were stained with TMRE, and it is well accepted that a loss in TMRE fluorescence is correlated with a loss of mitochondrial membrane potential (ψm), which in turn presumably indicates mPTP opening. As expected, when vardenafil (Generic Levitra) was added in a preconditioning-like manner before the calcium ionophore, we found cells less prone to calcium-induced depolarization of ψm. The highly selective PKG inhibitory peptides DT-2 and DT-3 totally abolished this protective effect. Unfortunately, although the DT peptides are able to enter a single cell due to their membrane translocation sequence, they were found to be ineffective when infused into a whole heart because they were trapped in the endothelial cells and failed to reach the myocytes. Staining the myocytes with PI instead of TMRE showed more viable cells in the vardenafil-treated group dependent on PKG and, hence, provided additional evidence for vardenafil’s protective effects. PKG activity was also increased in these cells after exposure to vardenafil (Levitra).

Garlid’s group could show that activated PKG causes the opening of the mKATP channels that are instrumental in cardioprotection, and additionally present evidence that mKATP and mPTP interact at the mitochondrial level via PKC. Salloum et al. (2007) also provided evidence that mKATP is involved in protection by vardenafil at reperfusion. Thus, our findings fit well with these earlier results, putting PKG in between the cGMP increase via PDE-5 inhibition and mKATP and mPTP at the mitochondrial level.

Taken together, we have shown that the PDE-5 inhibitor vardenafil significantly reduces ischemia/reperfusion injury when administered at reperfusion in an isolated rat heart model and a cell model of calcium-induced mPTP formation, and that this protection was dependent on GC and PKG. PKG activity was increased after exposure to vardenafil (Levitra Plus). There is still an unmet clinical need for interventions that make the heart resistant to infarction in the setting of acute myocardial infarction. PDE-5 inhibitors may be excellent candidates for a cardioprotectant that can be given just before reperfusion.