Herbal medicines today and the roots of modern pharmacology

The transformation of digitalis from a folk medicine, foxglove, to a modern drug, digoxin, illustrates principles of modern pharmacology that have helped make drugs safer and more effective. Digitalis was improved because its preparation was standardized, first by bioassay and then by chemical methods; however, few of today's herbs are standardized by methods that can ensure a consistent product and, hence, consistent safety and efficacy profiles. Many herbs have been evaluated in randomized, controlled trials, and several-St. John's wort and ginkgo, for example-are apparently effective. Yet, many trials of herbs have limited value because of poor design, small samples, and, above all, use of products of uncertain composition and consistency. The uncertain composition of many herbal products raises questions about their safety, as does evidence indicating that herbs may have harmful interactions with prescription drugs. Such adverse effects of herbs are probably underreported. Meanwhile, systematic studies, such as those identifying adverse reactions to drugs, are hindered because herbal preparations are not standardized-one brand of St. John's wort, for example, will differ chemically from another-and, unlike for prescription drugs, there are no databases linking herb consumption to later medical problems. Since herbal medicines are regulated as dietary supplements, they are not subject to the premarketing regulatory clearance required for drugs. The burden of proof is on the U.S. Food and Drug Administration to show a dietary supplement is unsafe, unlike for drugs, which cannot be approved until the manufacturer has demonstrated safety and effectiveness.

Endogenous digitalis-like Na+, K+-ATPase inhibitors, and brain function

Digitalis-like compounds are recently identified steroids synthesized by the adrenal gland, which resemble the structure of plant cardiac glycosides. These compounds, like the plant steroids, bind to and inhibit the activity of the Na+, K+-ATPase. The possible function of the endogenous digitalis-like compounds has to be evaluated in view of the presence of different isoforms of the Na+, K+-ATPase, which differ in their sensitivity to digitalis. This review focuses on recent published data on the Na+, K+-ATPase inhibitors, the digitalis-like compounds, regarding their structure, biosynthesis and secretion from the adrenal gland, physiological role and pathological implications in diseases such as hypertension and depression. Emphasis is given to studies describing the involvement of these compounds in brain function.

Digitalis-like factor response to hyperinsulinemia accompanying a euglycemic hyperinsulinemic clamp or oral glucose tolerance test

Many studies of essential hypertension find evidence of insulin resistance in the same individuals, leading some to postulate a hypertensive role for insulin. However, the mechanisms by which insulin might exert a hypertensive effect are not fully resolved. An endogenous sodium pump inhibitor or digitalis-like factor (DLF) has been proposed as a hypertensive agent and its plasma concentrations are elevated in hypertension and in Type II diabetes, where insulin levels are elevated. Hence, we studied the effect of insulin on DLF using two approaches to achieve hyperinsulinemia. Normotensive men and women underwent a hyperinsulinemic, euglycemic clamp (40 mU/m2/min insulin, 40 mU = 1.6 x 10(-6) g) in which plasma insulin concentration was kept at high, but physiologic levels. Serum DLF (measured as inhibition of [Na,K]ATPase activity) and insulin levels were measured at baseline and every 30 min throughout the 2 hr clamp. Additionally, other subjects underwent an oral glucose tolerance test (OGTT) as a second means of increasing insulin levels. Insulin and DLF levels were measured prior to and hourly for 3 hours after receiving 100 gm of oral glucose. Serum DLF increased significantly during the clamp from a baseline of 4.6 +/- 0.81 to a peak of 8.7 +/- 1.2% inhibition (p=0.001). Comparison of the baseline and peak DLF levels with concomitant plasma insulin levels revealed a significant correlation (R=0.60, p=0.003). During the OGTT, DLF levels rose from a baseline of 2.4 +/- 1.0 to a peak level of 5.0 +/- 0.4%, p = 0.04. These results suggest that DLF, a factor that can cause vascular smooth muscle contraction and potentially influence blood pressure, is increased by hyperinsulinemia and provides a mechanism by which insulin may increase blood pressure.

The management of heart failure--an overview

National and international societies have issued guidelines on the management of heart failure: The European Society of Cardiology, WHO, ACC/AHA Task Force Report, US Department of Health and Human Services, German Society of Cardiology. The therapeutic approaches to heart failure have undergone considerable changes during the last few years. The guidelines have to be updated almost yearly due to new results from prospective randomized studies. Although an agreement could be reached with respect to general measures and drug treatment, no agreement on mechanical devices, pacemakers and surgical interventions has been reached. The basis for medical treatment of chronic heart failure depends on diuretics, digitalis, ACE inhibitors, and beta-blockers. Calcium antagonists and other positive inotropic drugs, other than digitalis, should be avoided as far as possible. Thiazides, loop diuretics and aldosterone antagonists are needed for acute and chronic treatment of heart failure, alone or in combination (diuretic resistant heart failure!). Digitalis glycosides are needed in patients with atrial fibrillation with a fast ventricular rate or atrial flutter and in patients with systolic dysfunction, large hearts and symptomatic failure class NYHA III and IV. However, digitalis does not convert atrial fibrillation to sinus rhythm. Today there is no question that ACE inhibitors improve the prognosis of all patients with heart failure in all stages, if ejection fraction is reduced. Therefore, most patients after myocardial infarction or after having experienced pump failure due to myocarditis or cardiomyopathy are treated with ACE inhibitors and diuretics. The beneficial effects of ACE inhibitors seem to be most pronounced the worse the situation is. Relative risk reductions (mortality!) between 10% and 40% have been published depending on the severity of symptomatic left ventricular dysfunction. Those patients with high absolute risk have more to gain than those with low risk for any given "risk reduction", of course. Recent studies also indicate that most high risk cardiac patients profit from ACE inhibitors even if pump function is normal (i.e., patients with coronary heart disease, diabetes mellitus, cerebral vascular disease, hypertension) (15). AT1 antagonists can substitute for ACE inhibitors, if the latter are not tolerated due to cough. Up to now, beta-blocking agents apart from diuretics seem to be the best investigated drugs in heart failure. Large controlled studies with bisoprolol, carvedilol and metoprolol in addition to diuretics, digitalis and ACE inhibitors convincingly yielded positive results in chronic left ventricular failure patients. Reduction of mortality by 35% and even of sudden cardiac deaths by 40% have been proven beyond doubt. Thus, heart failure patients today should also receive beta-blocking agents in all stages of the disease. In the era of controlled prospective studies (evidence-based medicine), physicians are well advised to use only drugs that have been proven beneficial in large controlled studies.

Cardiovascular activity of a methanolic extract of Digitalis purpurea spp. heywoodii

The paper deals with the effects of a glycosidal extract of Digitalis heywoodii, ssp. of Digitalis purpurea L., (Schrophulariaceae) grown in Badajoz (Spain), on isolated cardiac auricle of rabbits, urinary excretion of rats, as well as its emetic effect in pigeons. These effects using vehicle (propylene glycol-ethanol-water, 40:10:50) and digoxin as standards are presented. The extract at concentrations of 20 and 40 microg/ml produced an increase in the contraction force of auricles in a dose-dependent way. At doses of 15 and 30 mg/kg a slight diuretic and natriuretic effect was observed. The active dose range for emesis was 0.5-4 mg/kg and a decrease of the emesis time within 10 min of injection in dose-dependent manner was obtained. The pharmacological activity of the extract is related to gitoxin derivatives (digitalinum verum and strospeside), the most abundant compounds obtained from the leaves of Digitalis purpurea spp. heywoodii.

The actions of digitalis leaf preparations and of cardiac glycosides on the isolated right ventricle of the guinea pig

A method is described for recording kymographically the systolic contraction and the resting length of the electrically stimulated, isolated right ventricle of the guinea pig. Two samples of Digitalis purpurea leaf and a sample of Digitalis lanata have been assayed in terms of the Third International Standard of D. purpurea using metameters dependent on changes in the systolic contractions and resting length of the muscle and the time elapsing before the changes occur. In a similar manner digitoxin and ouabain have been assayed in terms of digoxin. The results are compared with those obtained by slow intravenous infusion of the preparations into guinea pigs. The potencies derived from the two methods are in close agreement in the case of the digitalis leaf preparations. Digitoxin, however, is more active than digoxin on the ventricle preparation irrespective of the metameter used and less active by the slow infusion method, while ouabain has the same activity as digoxin on the ventricle and twice the activity by the infusion method. The results for ouabain on the ventricle using the different metameters, are homogenous, those for digitoxin are not. There is little difference between the general actions of the three glycosides on the ventricle but each glycoside is capable of producing different effects on systolic contraction and resting length depending on the dose employed. The possible mechanisms responsible for these effects are discussed.

The role of digitalis in the treatment of heart failure

Over the past 200 years, digoxin has been commonly used to treat patients with congestive heart failure. Clinical trials have demonstrated the benefits of the use of digoxin on exercise tolerance, ejection fraction, and neurohormone production. The Digoxin Investigators Group trial has recently provided strong evidence for the long-term benefits of digoxin on morbidity for patients with heart failure. This article will review the evidence of the benefits of digoxin and its current role in the treatment of patients with congestive heart failure.

Chemical structure and pharmacological activity of some derivatives of digitoxigenin and digoxigenin

A series of derivatives of digitoxigenin and digoxigenin were prepared and tested for toxicity in the cat and the guinea-pig and on the isolated heart of the 48-hr chick embryo, and for inotropic activity on the cat isolated papillary muscle and the guinea-pig Langendorff heart. The order of relative potency of the compounds remained the same whether they were tested for toxicity or for positive inotropic activity. There are three molecular centres in the cardiac aglycone that are linked closely with cardiac activity. These are: (a) an OH at carbon-3 which can be combined as a glycoside, thus enhancing activity, or esterified or oxidized, producing compounds of lower activity; the maximum intensity of the inotropic response was reduced in the less potent compounds; (b) a 14-beta-OH associated with a cis C-D ring junction, alteration of which abolished activity; (c) an unsaturated cyclobutenolide ring which cannot be reduced without a great decrease in activity.

Studies on digitalis. VI. Reduction of the oxygen debt after exercise with digoxin in cardiac patients without heart failure

Three patients with acquired valvular heart disease and cardiac enlargement who were able to perform normal everyday activity without difficulty in the absence of digitalis therapy were exercised while receiving a placebo and again while receiving digoxin. Digoxin administration did not produce a significant change in body weight or in the subjective condition of the individuals. Varying degrees of exercise were performed on a treadmill in a Metabolic Chamber and oxygen consumption was measured cotinuously before, during, and after the period of exercise, utilizing a continuous gas flow paramagnetic oxygen analyzer. The oxygen debt that developed during digoxin administration was compared to that observed during placebo administration.

In all patients the oxygen debt was smaller during the period of digoxin administration, although the external work performed was identical. In the first patient, following a 7-minute walk, the oxygen debt was 53 per cent more and following a 10-minute walk it averaged 40 per cent more while not receiving digoxin than when receiving this drug. In the second subject the oxygen debt following a 7-minute walk was 34 per cent more and following 10-minute walk it averaged 74 per cent more when he was not receiving digoxin than when receiving this drug. In the third subject the oxygen debts were 46 per cent and 41 per cent greater following 10- and 15- minute walks respectively, when she was not receiving digoxin.

The accumulation of a smaller oxygen debt following exercise while these subjects were receiving digoxin indicates that the functional status of their circulatory system was improved by the drug. It would appear that digitalis administration is beneficial to at least some patients who have cardiac disease and enlarged hearts and some decrease in cardiac reserve without signs or symptoms of heart failure.