Digitalis Drugs Research Articles

A Review on: Digitalis Purpurea

Digitalis contain cardiac glycosides and used in the treatment of congestive heart failure. Digitalis drug obtain from Digitalis Purpurea L. belongs to family scrophulariaceae. 200 years ago William Withering discover the use of digitalis in CHF treatment in 1785.In 18th century a controversy has existed about the benefits and risks of digitalis in patients with heart problems. Active component of digitalis classified as cardiac glycosides and cardiotonic steroids. The term "digitalis" or "cardiac glycosides" are used to refer to any of steroids or steroid glycosides compound which exert characteristic positively inotropic and electrophysiological effect on heart. In 20th century digitalis and its derivatives specially, digoxin is used in treatment of CHF. Cardiac glycosides are used in therapy of CHF since William Withering identify their uses. Digitalis purpurea is not only use in treatment of CHF also has wound healing, antioxidant and cytotoxic activity. In 1990 most prescribed drug is digoxin. It shows intermediate duration of action. Digoxin is use for its rate control in atrial fibrillation in the presence of marginal blood pressure. The introduction of diuretic provide an alternative more effective and safer for treatment of CHF.
 Keywords: CHF., Digitalis Purpurea L

Pharmaceutical care of chloroquine phosphate in elderly patients with coronavirus pneumonia (COVID-19).

Pharmaceutical care of chloroquine phosphate in elderly patients with coronavirus pneumonia (COVID-19).

The sodium pump and digitalis drugs: Dogmas and fallacies.

The sodium pump (Na/K‐ATPase) is a plasma membrane enzyme that transports Na+ and K+ against their physiological gradients in most eukaryotic cells. Besides pumping ions, the enzyme may also interact with neighboring proteins to activate cell signaling pathways that regulate cell growth. Digitalis drugs, useful for the treatment of heart failure and atrial arrhythmias, inhibit the pumping function of Na/K‐ATPase and stimulate its signaling function. In the current field of research on the sodium pump and digitalis drugs, some issues that are commonly accepted to be well established are not so, and this may impede progress. Here, several such issues are identified, their histories are discussed, and their open discussions are urged. The covered unsettled questions consist of (a) the suggested hormonal role of endogenous digitalis compounds; (b) the specificity of Na/K‐ATPase as the receptor for digitalis compounds; (c) the relevance of the positive inotropic action of digitalis to its use for the treatment of heart failure; (d) the conflicting findings on digitalis–induced signaling function of Na/K‐ATPase; and (e) the uncertainties about the structure of Na/K‐ATPase in the native cell membrane.

The clinical efficacies of Milrinone on cardiac function and blood-gas analytic indices in elderly patients with chronic heart failure

Objective To investigate the clinical efficacies of Milrinone on cardiac function and blood-gas analytic indices in elderly patients with chronic heart failure. Methods During January 2013 to December 2016, 50 elderly patients with chronic congestive heart failure admitted into the First People's Hospital of Qingdao Economic and Technological Development Zone were randomly selected and divided into the observation group (n=25) and the control group (n=25). The control group was given conventional treatment including diuretics, ACEI/ARBs, vasodilators, β-adrenergic receptor inhibitors and digitalis drugs, as well as anti-infection, fluid intake treatment and inhibiting the excessive activation of nerve-endocrine system.And Milrinone was taken as add-on to the therapy of control group in observation group.The changes in cardiac function, blood-gas analysis indices and adverse reactions were compared between the two groups. Results The total improvement rate of cardiac function was significantly higher in the observation group than in control group (92.0% vs.76.0%, χ2=5.446, P<0.05). The cardiac function indices, blood-gas analysis index and the level of CRP were significantly improved after treatment versus before treatment in both groups(all P<0.05). And these improvements were significantly more superior in observation group than in control group (P<0.05). Conclusions Milrinone can significantly improve the clinical efficacies in elderly patients with chronic heart failure.It can also improve the blood-gas indices and alleviate clinical symptoms, which seems to deserve more clinical application and promotion. Key words: Milrinone; Heart failure; Heart function tests; Blood-gas analysis

Comparison of Digitalis Sensitivities of Na+/K+-ATPases from Human and Pig Kidneys.

Digitalis drugs are selective inhibitors of the plasma membrane Na+/K+-ATPase. There are many studies on molecular mechanisms of digitalis interaction with purified pig kidney enzyme, with the tacit assumption that it is a good model of human kidney enzyme. However, previous studies on crude or recombinant human kidney enzymes are limited, and have not resulted in consistent findings on their digitalis sensitivities. Hence, we prepared comparably purified enzymes from human and pig kidneys and determined inhibitory constants of digoxin, ouabain, ouabagenin, bufalin, and marinobufagenin (MBG) on enzyme activity under optimal turnover conditions. We found that each compound had the same potency against the two enzymes, indicating that (i) the pig enzyme is an appropriate model of the human enzyme, and (ii) prior discrepant findings on human kidney enzymes were either due to structural differences between the natural and recombinant enzymes or because potencies were determined using binding constants of digitalis for enzymes under nonphysiological conditions. In conjunction with previous findings, our newly determined inhibitory constants of digitalis compounds for human kidney enzymes indicate that (i) of the compounds that have long been advocated to be endogenous hormones, only bufalin and MBG may act as such at kidney tubules, and (ii) beneficial effects of digoxin, the only digitalis with extensive clinical use, does not involve its inhibitory effect on renal tubular Na+/K+-ATPase.

Epidural anesthesia for cesarean section for pregnant women with rheumatic heart disease and mitral stenosis.

Pregnancy increases stress on the circulation of parturient with mitral stenosis secondary to rheumatic heart disease and increases the risk of peripartum heart failure, especially during delivery. This study investigated the epidural anesthesia management for cesarean section in pregnant women with rheumatic heart disease and mitral stenosis. 48 parturients with rheumatic heart disease and mitral stenosis that had cesarean section deliveries with epidural anesthesia in the Union Hospital, Fujian Medical University (Fuzhou, China) from Jan 2002 to Dec 2012 were retrospectively analyzed. Heart rate (HR), systolic arterial pressure (SAP), diastolic arterial pressure (DAP), mean arterial pressure (MAP), central venous pressure (CVP), fluid intake volume and fluid output volume (blood loss+urine volume) were analyzed. Medication included digitalis drugs for heart failure or potential heart failure, digoxin and furosemide for chronic congestive heart failure and beta blockers for arrhythmia. Frequent premature ventricular contractions were treated with lidocaine and propafenone. Dexamethasone was administered when heart failure occurred during less than 37weeks gestation. HR, SAP, DAP, MAP and CVP were significantly increased at the time of delivery. The fluid intake volume was more elevated in the NYHA III-IV group of parturients than the NYHA I-II group, while fluid output volume was less. All parturients survived. Epidural anesthesia was applied successfully for cesarean sections for parturients with rheumatic heart disease and mitral stenosis.

Drug safety associated with the change of digitalis drug in Norway

BACKGROUND In 2011, following a period with delivery problems, the only registered digitoxin drug in Norway was replaced with digoxin. As a result, approximately 21000 patients had to replace digitoxin with digoxin. There are important pharmacokinetic differences between digitoxin and digoxin (the general term for both drugs is digitalis), which must be taken into account when changing therapy. The aim of this study was to investigate compliance of drug security, during the transition from digitoxin to digoxin in Norway.MATERIAL AND METHOD Enquiries addressed to the Norwegian Poison Information Centre and reports of fatal adverse effects to the Regional Drug Information Centres (RELIS) regarding intake of digitalis were analysed. Serum concentrations of digitoxin and digoxin analyzed at Oslo University Hospital were reviewed. All data sources were reviewed for the years 2010-2014 and patients > 20 years were included.RESULTS The total number of enquiries addressed to the Norwegian Poison Information Centre, fatal adverse drug reactions reported to RELIS, and patient samples in the toxic range analyzed at Oslo University Hospital increased from 2012, timewise related to the transition to digoxin.INTERPRETATION Despite extensive information from the Norwegian Medicines Agency, a small, transient increase was observed in the number of overdoses and reported deaths from digitalis related to change in therapy. The cause of the overdose was in many cases unknown. This study revealed several cases of incorrect dosage, simultaneous use of digitoxin and digoxin, and washout time that was insufficient or lacking before initiation of digoxin.

Digitalis-induced cell signaling by the sodium pump: On the relation of Src to Na+/K+-ATPase

In addition to performing its essential transport function, the sodium pump also activates multiple cell signaling pathways in response to digitalis drugs such as ouabain. Based mainly on cell-free studies with mixtures of purified Src kinase and Na+/K+-ATPase, a well-advocated hypothesis on how ouabain initiates the activation of signaling pathways is that there is a preexisting physiological complex of inactive Src bound to the α-subunit of Na+/K+-ATPase, and that ouabain binding to this subunit disrupts the bound Src and activates it. Because of the published disagreements of the results of such cell-free experiments of two other laboratories, our aim was to attempt the resolution of these discrepancies. We reexamined the effects of ouabain, vanadate, and oligomycin on mixtures of Src, Na+/K+-ATPase, Mg2+, and ATP as specified in prior studies; and assayed for Src-418 autophosphorylation as the measure of Src activation. In contrast to the findings of the proponents of the above hypothesis, our results showed similar effects of the three inhibitors of Na+/K+-ATPase; indicating that Src activation in such experiments is primarily due to the ATP-sparing effect of the ATPase inhibitor on the mixture of two enzymes competing for ATP. We conclude that there is no solid evidence for direct molecular interaction of Src with Na+/K+-ATPase under physiological conditions.

Selective atrial profibrotic signalling in mice and man

This editorial refers to ‘Molecular basis of selective atrial fibrosis due to overexpression of transforming growth factor-β1’ by D. Rahmutula et al. , pp. 769–779, this issue. Although oral anticoagulation can prevent the majority of strokes in patients with atrial fibrillation (AF) if used as recommended in treatment guidelines,1 patients with AF receiving optimal therapy still die prematurely, and are frequently hospitalized.2 Hence, we need a deeper understanding of the mechanisms behind AF in patients to develop better treatment. Most of the currently used treatments for AF were initially developed to treat ventricular heart disease, e.g. angiotensin-converting enzyme inhibitors, digitalis, beta-adrenoceptor blockers, spironolactone, and most antiarrhythmic drugs. Understanding electrophysiological differences between the atria and ventricles have allowed the recent development of atrial antiarrhythmic drugs (dronedarone, vernakalant), with others undergoing clinical development. Catheter ablation of AF also illustrates how the understanding of an atrial arrhythmia mechanism, i.e. focal firing in and around the pulmonary veins, helped develop a specific AF treatment. In this issue of Cardiovascular Research , Rahmutula et al. 3 characterize a molecular pathway leading to selective atrial fibrosis. By analysing human atrial and ventricular tissues, they identified an atrial preponderance of transforming growth factor-β (TGF-β) expression, and higher atrial TGF-β …

Different roles of the cardiac Na+/Ca2+-exchanger in ouabain-induced inotropy, cell signaling, and hypertrophy

Previous studies have shown that digitalis drugs, acting as specific inhibitors of cardiac Na(+)/K(+)-ATPase, not only cause positive inotropic effects, but also activate cell signaling pathways that lead to cardiac myocyte hypertrophy. A major aim of this work was to assess the role of Na(+)/Ca(2+)-exchanger, NCX1, in the above two seemingly related drug effects. Using a mouse with ventricular-specific knockout (KO) of NCX1, ouabain-induced positive inotropy that was evident in isolated wild-type (Wt) hearts was clearly reduced in KO hearts. Ouabain also increased Ca(2+) transient amplitudes in Wt myocytes, but not in KO myocytes. Ouabain-induced activations of ERK 1/2 were noted in Wt myocytes, but not in KO myocytes; however, ouabain activated PI3K1A and Akt in both Wt and KO myocytes. Protein synthesis rate, as a measure of hypertrophy, was increased by ouabain in Wt and KO myocytes; these drug effects were prevented by a PI3K inhibitor but not by a MEK/ERK inhibitor. Hypertrophy caused by ET-1, but not that induced by ouabain, was accompanied by upregulation of BNP gene in Wt and KO myocytes. The findings indicate 1) the necessity of NCX1 for positive inotropic action of ouabain; 2) the irrelevance of NCX1 and ERK 1/2 activation to ouabain-induced hypertrophy; and 3) that hypertrophy caused by ouabain through the activation of PI3K1A/Akt pathway is likely to be beneficial to the heart.

Current Status of Rate Control for Clinical Management of Patients with Atrial Fibrillation

Clinical management of patients with AF involves the following objectives: prevention of thromboembolism, rate control of heart rate, correction of rhythm disturbance, and symptom relief. For patients with symptomatic AF lasting many days, initial therapy may be anticoagulation and rate control, while the long-term goal may be to restore sinus rhythm. If rate control offers inadequate symptomatic relief, restoration of sinus rhythm becomes a clear long-term goal. Randomized trials such as AFFIRM and RACE comparing outcomes of rhythm vs. rate control managements in AF patients found that rate control is not inferior to rhythm control for prevention of cardiovascular morbidity. AF-CHF trial in AF patients with heart failure also showed a similar outcome. Patients with a rapid ventricular response usually need control of their ventricular rate. This can be achieved by oral administration of β-blockers, non-dihydropyridine calcium channel antagonists, or digitalis. Current guidelines of AF management recommend β-blockers as a first line to control their ventricular rate. The combination of a β-blocker and digitalis may be beneficial in patients with heart failure. β-blockers may be especially useful in the presence of high adrenergic tone occurring in association with AF. During chronic treatment β-blockers have been shown to be effective and safe in several studies compared with placebo, digitalis, and other drugs.

Preconditioning by Subinotropic Doses of Ouabain in the Langendorff perfused Rabbit Heart

Short exposure to low concentrations of digitalis drugs like ouabain protects the rat heart against ischemia/reperfusion injury through the activation of the Na/K-adenosine triphosphatase (ATPase)/Src receptor complex and subsequent stimulation of key intracellular cardioprotective signals. Rat Na/K-ATPase, however, is relatively insensitive to digitalis, and it is not known if similar results could be obtained in species with higher sensitivity. Thus, to determine whether ouabain pretreatment protects against ischemic injury and activates the Na/K-ATPase signaling cascade in a species with cardiac glycoside sensitivity comparable to humans, the present study was conducted in the rabbit model. In Langendorff perfused rabbit hearts, 20-minute exposure to 500-nM ouabain resulted in positive inotropy as evidenced by a significant increase in +dP/dt, and this increase was accompanied by the activation of several well-characterized downstream mediators of the cardiac Na/K-ATPase receptor pathway, including Src, Akt, ERK1/2, and protein kinase Cepsilon. A short (4 minutes) administration of a subinotropic dose of ouabain (100 nM) followed by an 8-minute washout before 30 minutes of global ischemia and 120 minutes of reperfusion resulted in protection against cell death, as evidenced by a significant decrease in infarct size. These data indicate that ouabain administration activates the Na/K-ATPase signaling cascade and protects against ischemic injury in a species with high cardiac Na/K-ATPase sensitivity.

Dual activity of the H1-H2 domain of the (Na++K+)-ATPase

(Na++K+)-ATPase is a target receptor of digitalis (cardiac glycoside) drugs. It has been demonstrated that the H1-H2 domain of the α-subunit of the (Na++K+)-ATPase is one of the digitalis drug interaction sites of the enzyme. Despite the extensive studies of the inhibitory effect of digitalis on the (Na++K+)-ATPase, the functional property of the H1-H2 domain of the enzyme and its role in regulating enzyme activity is not completely understood. Here we report a surprise finding: instead of inhibiting the enzyme, binding of a specific monoclonal antibody SSA78 to the H1-H2 domain of the (Na++K+)-ATPase elevates the catalytic activity of the enzyme. In the presence of low concentration of ouabain, monoclonal antibody SSA78 significantly protects enzyme function against ouabain-induced inhibition. However, higher concentration of ouabain completely inactivates the (Na++K+)-ATPase even in the presence of SSA78. These results suggest that the H1-H2 domain of the (Na++K+)-ATPase is capable of regulating enzyme function in two distinct ways for both ouabain-sensitive and -resistant forms of the enzyme: it increases the activity of the (Na++K+)-ATPase during its interaction with an activator; it also participates in the mechanism of digitalis or ouabain-induced inhibition of the enzyme. Understanding the dual activity of the H1-H2 domain will help better understand the structure–function relationships of the (Na++K+)-ATPase and the biological processes mediated by the enzyme.

Kardiomyopathie bei Hypocalcämie

A 48-year-old woman developed a hypocalcaemic cardiomyopathy, the hypocalcaemia being due to hypoparathyroidism after three previous thyroid operations for goitre with tracheal compression. She had signs of severe cardiac failure, but no tetany. She was put on calcium and vitamin D3 medication which raised calcium concentration. The cardiac status improved, as did the radiological and echocardiographic findings, without the patient having received any diuretics, digitalis or afterload lowering drugs.

Identification of a PKCε-dependent regulation of myocardial contraction by epicatechin-3-gallate

In this study, the effects of tea catechins and tea theaflavins on myocardial contraction were examined in isolated rat hearts using a Langendorff-perfusion system. We found that both tea catechins and theaflavins had positive inotropic effects on the myocardium. Of the tested chemicals, epicatechin-3-gallate (ECG) and theaflavin-3,3'-digallate (TF(4)) appear to be the most effective tea catechin and theaflavin, respectively. Further studies of ECG-induced positive inotropy revealed the following insights. First, unlike digitalis drugs, ECG had no effect on intracellular Ca(2+) level in cultured adult cardiac myocytes. Second, it activated PKCepsilon, but not PKCalpha, in the isolated hearts as well as in cultured cells. Neither a phospholipase C (PLC) inhibitor (U73122) nor the antioxidant N-acetyl cysteine (NAC) affected the ECG-induced activation of PKCepsilon. Third, inhibition of PKCepsilon by either chelerythrine chloride (CHE) or PKCepsilon translocation inhibitor peptide (TIP) caused a partial reduction of ECG-induced increases in myocardial contraction. Moreover, NAC was also effective in reducing the effects of ECG on myocardial contraction. Finally, pretreatment of the heart with both CHE and NAC completely abolished ECG-induced inotropic effects on the heart. Together, these findings indicate that ECG can regulate myocardial contractility via a novel PKCepsilon-dependent signaling pathway.

Association of PI3K-Akt signaling pathway with digitalis-induced hypertrophy of cardiac myocytes

Our previous studies on cardiac myocytes showed that positive inotropic concentrations of the digitalis drug ouabain activated signaling pathways linked to Na(+)-K(+)-ATPase through Src and epidermal growth factor receptor (EGFR) and led to myocyte hypertrophy. In view of the known involvement of phosphatidylinositol 3-kinase (PI3K)-Akt pathways in cardiac hypertrophy, the aim of the present study was to determine whether these pathways are also linked to cardiac Na(+)-K(+)-ATPase and, if so, to assess their role in ouabain-induced myocyte growth. In a dose- and time-dependent manner, ouabain activated Akt and phosphorylation of its substrates mammalian target of rapamycin and glycogen synthase kinase in neonatal rat cardiac myocytes. Akt activation by ouabain was sensitive to PI3K inhibitors and was also noted in adult myocytes and isolated hearts. Ouabain caused a transient increase of phosphatidylinositol 3,4,5-trisphosphate content of neonatal myocytes, activated class IA, but not class IB, PI3K, and increased coimmunoprecipitation of the alpha-subunit of Na(+)-K(+)-ATPase with the p85 subunit of class IA PI3K. Ouabain-induced activation of ERK1/2 was prevented by Src, EGFR, and MEK inhibitors, but not by PI3K inhibitors. Activation of Akt by ouabain, however, was sensitive to inhibitors of PI3K and Src, but not to inhibitors of EGFR and MEK. Similarly, ouabain-induced myocyte hypertrophy was prevented by PI3K and Src inhibitors, but not by an EGFR inhibitor. These findings 1) establish the linkage of the class IA PI3K-Akt pathway to Na(+)-K(+)-ATPase and the essential role of this linkage to ouabain-induced myocyte hypertrophy and 2) suggest cross talk between these PI3K-Akt pathways and the signaling cascades previously identified to be associated with cardiac Na(+)-K(+)-ATPase.

Digitalis‐induced activation of the sodium pump‐linked survival pathways in cardiac myocytes

Partial inhibition of cardiac Na+/K+-ATPase (sodium pump) by nontoxic concentrations of ouabain and related digitalis drugs is known to cause transactivation of Src/EGFR, activation of Ras/Raf/MEK/ERK1/2 cascade, transcriptional regulation of growth-related genes, and myocyte hypertrophy.( L. Liu et al, AJP, 284, C1560, 2003; and Refs therein). To explore the nature of this drug-induced growth, we have used cultured neonatal and adult rat cardiac myocytes, and examined the possibility of other specific kinases as downstream effectors of digitalis interaction with Na+/K+-ATPase. Stress-activated MAPKs, JNKs and P38 kinase, were not affected by myocyte exposure to nontoxic concentrations of ouabain. However, the PI3K/Akt cascade, and its downstream branches, were strongly activated by these ouabain concentrations; and this ouabain effect was blocked by PI3K inhibitors wortmannin and LY-294002. The ouabain-induced hypertrophy of the neonatal myocytes was also prevented by PI3K inhibitors. These finding suggest that in cardiac myocytes, the protein kinase signaling pathways regulated by digitalis are more similar to the survival pathways associated with physiological hypertrophy, rather than those involved in pathological hypertrophy. (Supported by NIH Grant HL-36573)

Congestive Heart Failure: Pharmacological Agents and the Potential of BType Natriuretic Peptide

Congestive heart failure (CHF) is a life-threatening cardiovascular disease that is increasing in prevalence. It is a common cause of death and is accompanied by high direct and indirect costs for treatment. The current situation faced by patients and the medical community with regard to this ailment is one of high mortality, repeated hospitalizations, and combination therapies. The various classes of pharmacological agents that are currently used for patients suffering from CHF include angiotensin converting enzyme (ACE) inhibitors, angiotensin receptor blockers (ARBs), aldosterone antagonists, beta-blockers, calcium channel blockers (CCBs), digitalis drugs, diuretics, inotropic agents, nitrates, and vasodilators. While these agents are all important therapeutic tools in the treatment of CHF, the prognosis for patients with CHF remains poor. Thus improvement of the current pharmacological armamentarium is greatly needed. An endogenous peptide, B-type natriuretic peptide (BNP), has been increasingly utilized in the setting of acute CHF since its approval in 2001. This peptide, or a derivative thereof, has great potential for the treatment of patients at various stages in the progression of heart failure. This review provides an overview of current pharmacological strategies in CHF and addresses potential future developments in the use of BNP for the treatment of CHF.

The Na/K-ATPase-mediated signal transduction as a target for new drug development

The Na/K-ATPase, or Na+ pump, is a member of the P-type ATPase superfamily. In addition to pumping ions, the Na/K-ATPase is a receptor that not only regulates the function of protein kinases, but also acts as a scaffold, capable of tethering different proteins into a signalplex. The signaling Na/K-ATPase resides in caveolae and forms a "binary receptor" with the tyrosine kinase Src. Endogenous cardiotonic steroids and digitalis drugs such as ouabain act as agonists and provoke this binary receptor, resulting in tyrosine phosphorylation of the proteins that are either associated with, or in close proximity to, the signaling Na/K-ATPase. Subsequently, this initiates protein kinase cascades including ERKs and PKC isozymes. It also increases mitochondrial production of reactive oxygen species (ROS) and regulates intracellular calcium concentration. Like other receptors, activation of the Na/K-ATPase/Src by ouabain induces the endocytosis of the plasma membrane Na/K-ATPase. Significantly, this newly appreciated signaling function of the Na/K-ATPase appears to play an important role in the pathogenesis of many cardiovascular diseases, therefore serving as an important target for development of novel therapeutic agents.

Digitalis-Induced Signaling by Na+/K+-ATPase in Human Breast Cancer Cells

Because beneficial effects of digitalis treatment in breast cancer patients have been suggested by epidemiological studies, we explored the mechanism of the growth inhibitory effects of these drugs on the estrogen receptor-negative human breast cancer cell line MDA-MB-435 s. Ouabain concentrations (100 nM or lower) that caused less than 25% inhibition of the pumping function of Na+/K+-ATPase had no effect on cell viability but inhibited proliferation. At the same concentrations, ouabain 1) activated Src kinase and stimulated the interaction of Src and Na+/K+-ATPase with epidermal growth factor receptor (EGFR); 2) caused a transient and then a sustained activation of extracellular signal-regulated kinases 1 and 2 (ERK1/2); 3) increased the expression of p21Cip1 but decreased that of p53; and 4) activated c-Jun NH2-terminal kinase (JNK) but not p38 kinase. These data, in conjunction with our previous findings on the signaling role of Na+/K+-ATPase in other cells, suggest that ouabain-induced activation/transactivation of Src/EGFR by Na+/K+-ATPase leads to activation of ERK1/2, the resulting increase in the level of cell cycle inhibitor p21Cip1, and growth arrest. Cooperation of JNK with ERK1/2 in this process is also suggested. Digoxin and digitoxin concentrations close to or at the therapeutic plasma levels had effects on proliferation and ERK1/2 similar to those of ouabain, supporting the proposed potential value of digitalis drugs for the treatment of breast cancer.