Inhibition of methyldigoxin-induced arrhythmias by pentadecapeptide BPC 157: a relation with NO-system.

Pentadecapeptide BPC 157 (GEPPPGKPADDAGLV, MW 1419) reversed congestive heart failure and various arrhythmias, influenced the NO-system and showed no proarrhythmic effect. In therapy analogy, we challenged rats with digitalis, to show attenuation by BPC 157 and the relation between the NO-system and digitalis toxicity. (i). BPC 157 prophylactic effect. Development of cumulative intravenous digitalis toxicity, BPC 157 (50 microg, 10 microg, 10 ng/kg applied intravenously immediately before a methyldigoxin increment regimen (2.0/1.5/1.5/1.0 mg/kg at 15 min-intervals, total dose 6.0 mg/kg/45 min)) reduced the number of ventricular premature beats, prolonged the time before onset of ventricular tachycardia, reduced ventricular tachycardia and AV-block duration (microg-regimes) or reduced mainly the AV-block duration (ng-regimen). (ii). BPC 157 therapy. Advanced methyldigoxin toxicity (6.0 mg/kg i.v. bolus). BPC 157 applied at the 20th second of the grade 3 AV-block shortened AV-blocks, mitigated a further digitalis toxicity course. Ventricular tachycardias were either avoided (50 microg), or markedly reduced (10 microg, 10 ng). Fatal outcome was either avoided (50 microg), reduced (10 microg), or only delayed (10 ng) (iii) BPC 157, L-NAME, l-arginine, L-NAME+l-arginine application. L-NAME-application (5 mg/kg i.p.) aggravated methyldigoxin-arrhythmias. l-arginine (200 mg/kg i.p.) alone had no effect but blunted L-NAME-exaggeration (L-NAME+l-arginine). In this respect, BPC 157 (50 microg/kg i.p.) was prophylactically and therapeutically more effective: the antagonism of L-NAME with BPC 157 produced an effect similar to BPC 157 alone. In conclusion, digitalis-induced arrhythmias in rats could be prevented and counteracted by pentadecapeptide BPC 157, mainly through an interaction with the NO-system.

Selective inhibition of brain Na,K-ATPase by drugs.

The effect of drugs from the class of cardiac (methyldigoxin, verapamil, propranolol), antiepileptic (carbamazepine), sedative (diazepam) and antihistaminic (promethazine) drugs on Na,K-ATPase activity of plasma membranes was studied in rat brain synaptosomes. Methyldigoxin in a concentration of 0.1 mmol/l inhibits enzyme activity by 80 %. Verapamil, propranolol and promethazine in concentrations of 20, 20 and 2 mmol/l respectively, entirely inhibit the ATPase activity. Carbamazepine and diazepam in concentrations of 0.02-60 mmol/l have no effect on the activity of this enzyme. According to the drug concentrations that inhibit 50 % of enzyme activity (IC(50)), the potency can be listed in the following order: methyldigoxin promethazine verapamil ? propranolol. From the inhibition of commercially available purified Na,K-ATPase isolated from porcine cerebral cortex in the presence of chosen drugs, as well as from kinetic studies on synaptosomal plasma membranes, it may be concluded that the drugs inhibit enzyme activity, partly by acting directly on the enzyme proteins. Propranolol, verapamil and promethazine inhibitions acted in an uncompetitive manner. The results suggest that these three drugs may contribute to neurological dysfunctions and indicate the necessity to take into consideration the side effects of the investigated drugs during the treatment of various pathological conditions.

[Disturbances of rhythm and atrio-ventricular conduction in digitalis overdose. Case reports]. / Zaburzenia rytmu i przewodzenia przedsionkowo-komorowego wystepujace przy przedawkowaniu naparstnicy. Opis przypadków.

Three cases of patients with symptoms of digitalis overdosage were presented. The principal manifestations included complex supraventricular dysrhythmias and atrio-ventricular conduction disturbances. In the discussion a special attention was paid to digitalis dosage. Multiple factors influencing plasma concentration of digitalis including pharmacokinetics, bioavailability and drug interactions with glycosides were described. Short review of toxic manifestations of digitalis was made and the treatment of digitalis intoxication was outlined.

[Effect of amiloride and its derivative dichlorobenzamil on guinea pig atria: interaction with other inotropic mechanisms]. / Efecto de la amilorida y su derivado diclorobenzamil sobre la auricula aislada del acure (Cavia porcellus): interaccion con otras maniobras inotropicas.

The inotropic and chronotropic effects of Amiloride (AMI) and Dichloro-benzamil Amiloride (DBC-AMI) were studied on the guinea pig isolated atria, also, the interaction between these drugs and Beta-methyl-Digoxin (BM-DIGO), epinephrine and low extracellular potassium (1 mM). AMI (10(-3) M) has a negative chronotropic and positive inotropic effects, not dependent on the autonomic system. DCB-AMI has a bimodal effect on the contractile force: increases it at low concentrations but causes a decrease at concentrations higher than 10(-6) M. The effect of AMI on the sinus frequency is unchanged by BM-DIGO. AMI (10(-3) M) decreases the inotropic effect of BM-DIGO and increases the toxic concentration of this drug on isolated tissues. The dose-response curve to epinephrine was not changed by AMI. Similar results were obtained using DCB-AMI (2 x 10(-7) M). The positive inotropic effect obtained by low extracellular potassium (1 mM) was not altered by AMI. The activity of the Mg(++)-dependent, Na+/K+ ATPase measured in the microsomal fraction obtained from guinea pig heart was diminished (10%) by AMI (10(-3) M). The drug did not affect the inhibition of the enzyme induced by ouabain. In conclusion, our experiments show multiple effects of AMI and DCB-AMI on the guinea pig heart. The inhibition of the Na+/Ca++ exchange explains them only partially. A slow channel blocking effect appears fundamental to interpret our results.

Efecto de la amilorida y su derivado diclorobenzamil sobre la auricula aislada del acure (Cavia porcellus): interaccion con otras maniobras inotropicas / Effect of amiloride and dichlorobenzamil derivative in the guinea pig atria: interaction with other inotropic mechanisms

Se estudiaron los efectos cronotrópico e inotrópico de la Amilorida (AMI) y la dicloro-benzamil-Amilorida (DCB-AMI) sobre las aurículas aislada del acure, así como la interacción de estas drogas con la beta-metil-digoxina (BM_DIGO), la epinefrina y la disminución del potasio extracelular (de 4 a 1 mM). La AMI (1 mM) causa un efecto inotrópico positivo y cronotrópico negativo, independientes del sistema autonómico. La DCB-AMI causa um efecto bimodal sobre la fuerza de contracción: la aumenta a bajas dosis pero la disminuye a concentraciones mayores de 10(-6) M. También disminuye levemente la frecuencia sinusal. El efecto de la AMI sobre el automatismo sinusal no es alterado por la BM-DIGO. En cambio, la AMI ((10(-3 M) disminuye el efecto inotrópico positivo de la BM-DIGO e incrementa la dosis tóxica en preparaciones aisladas. La curva dosis-respuesta a la epinefrina no varía en presencia de AMI. Resultados similares se obtuvieron con DCB-AMI (2 x 10(-7 M). El incremento de contractilidad que se observa al disminuir la concentración extracelular de potasio a 1 mM no se altera en presencia de AMI. La actividad de la Na+/K+ ATPasa dependiente de Mg++ de la fracción microsomal obtenida del corazón del acure disminuye en 10 por ciento aproximadamente en presencia de AMI (1nM). Por otra parte, el efecto inhibitorio sobre la enzima obtenido con ouabaína no varía con esta droga. En conclusión, nuestros resultados sugieren múltiples efectos de la AMI y DCB-AMI sobre el corazón del acure. La inhibición del intercambiador Na+/Ca++ explica solo parte de ellos; el bloqueo de los canales lentos parece fundamental para explicar nuestras observaciones.

Digoxin transfer across the isolated placenta is influenced by maternal and fetal albumin concentrations.

The aim of this study was to evaluate the influence of different maternal and fetal albumin concentrations on the transplacental transfer and the placental tissue accumulation of digoxin. Digoxin passage across the isolated lobules of 15 human placentae was calculated from repeated fetal and maternal perfusate samples, and placental tissue digoxin concentrations were measured at the end of the experiments. Metildigoxin (Lanitop) was added to the maternal medium at a concentration of 5.70 +/- 0.73 ng mL-1, and maternal and fetal perfusate albumin (BSA) concentrations were kept equal either at a high concentration of 21 g L-1 (Group I; n = 5) or at a low concentration of 3 g L-1 (Group III; n = 5), or differed with a materno-fetal gradient of 21:3 g L-1 (Group II; n = 5). In the experiments with low maternal albumin concentrations (Group III), digoxin concentrations in the maternal circuit decreased to 3.56 ng mL-1, whereas digoxin concentrations in the fetal circuit reached 2.59 ng mL-1 over a 3-h period. With maternal BSA concentrations of 21 g L-1 (Group I and Group II), the decrease in digoxin concentration in the maternal circuit was lower (P < 0.05), and digoxin tissue concentrations at the end of the experiments were smaller (0.45 +/- 0.07 and 0.42 +/- 0.03 v. 0.82 +/- 0.32 ng mg-1 protein, Group I and Group II v. Group III respectively; P < 0.05). Comparing only those lobules with similar high concentrations of maternal protein, fetal BSA concentrations of 21 g L-1 resulted in a greater increase in digoxin concentrations in the fetal circuit (end-feto to initial-maternal digoxin concentrations of 0.44 +/- 0.08 v. 0.37 +/- 0.04 ng mg-1 protein (Group I v. Group II respectively), although this was not significant. The data suggest that maternal and fetal serum albumin concentrations may have an influence on transplacental digoxin transfer, and this should be considered when treating fetuses with cardiac disease transplacentally with glycosides.

[The electrocardiogram of the guinea pig. Changes induced by beta-methyl digoxin acute administration]. / El electrocardiograma del acure. Cambios inducidos por la admistración aguda de beta-metil digoxina.

In this study we describe the normal electrocardiogram of the Guinea pig (Cavia porcellus), including the correlation between cardiac frequency and the Q-T interval. We studied the acute changes induced by an intraperitoneal dose of beta-methyl digoxin (0.2 mg). The drug produced a significant decrease in cardiac frequency and a significant prolongation of the P-R interval. It did not change the QRS duration or its position on the frontal plane. The Q-T interval, corrected by cardiac frequency, showed a tendency to decrease with treatment, but this change did not reach significance. The drug caused characteristic changes in ventricular repolarization: the T wave changed its polarity and S-T segment shifted to negative potential (between 0.05 and 0.15 mV). The possible origin of these observation is discussed.

[Effect of the in vivo administration of beta-methyldigoxin on the Na, K-ATPase measured in different tissues of guinea pigs]. / Effecto de la beta-metil digoxina, administrada in vivo, sobre la actividad de la Na,K-ATPasa de diferentes tejidos de acure.

We measured the activity of the Na,K ATPase, Mg dependent and inhibited by ouabain, in microsomal fractions obtained from guinea pig myocardium and kidney, as weel as red cell ghosts. A group of animal was treated with beta-methyl digoxin (0.2 mg intraperitoneally) about one hour before obtaining the tissues. The control group received no medication. The plasma of both group, control and treated, had similar potassium concentrations (4.3 +/- 0.87 mM and 4.3 +/- 0.66 mM, respectively). The plasma digoxin concentrations from treated animals was always high (76.4 +/- 34.1 ng/ml). The Na,K-ATPase activity in the microsomal fraction from treated animals decreased by 28.7% in myocardium and by 27.7% in red cell ghosts, in comparison to the enzime activity measured in control animals. On the other hand, the Na/K activity obtained in kidney microsomal fraction did not change with treatment. We then measured the Na,K-ATPase activity in the red cell ghosts and microsomal fractions obtained from myocardium and kidney of untreated Guinea pigs. Adding digoxin in vitro (1 x 10(-9) M to 1 x 10(-3) M) we obtained, in myocardial fractions, a 50% maximal inhibition; the digoxin concentration causing half maximal effect (DI50) was 7 x 10(-5) M. In the kidney microsomal fraction we measured a 66% maximal inhibition of the enzime activity and DI50 was 2 x 10(-6) M. For red cell ghosts the maximal enzime inhibition was 34% and the DI50 was 1 x 10(-5) M. In conclusion, in the Guinea pig, the acute in vivo administration of beta-methyl digoxin causes a parallel inhibition of the Na,K-ATPase from myocardial fractions and red cell ghosts. We measured no significant change in the kidney microsomal fractions. We propose the determination of red cell Na,K-ATPase activity as possible indicator of digitalis effect on humans treated with these drugs.

El electrocardiograma del acure. Cambios inducidos por la administracion aguda de b-metil digoxina / The electrocardiogram of the guinea pig. Changes induced by the beta-methyl digoxin acute administration

In this study we describe the normal electrocardiogram of the Guinea pig (Cavia porcellus), including the correlation between cardiac frequency and the Q-T interval. We studied the acute changes induced by an intraperitoneal dose of beta-methyl digoxin (0.2 mg). The drug produced a significant decrease in cardiac frequency and a significant prolongation of the P-R interval. It did not change the QRS duration or its position on the frontal plane. The Q-T interval, corrected by cardiac frequency, showed a tendency to decrease with treatment, but this change did not reach significance. The drug caused characteristic changes in ventricular repolarization: the T wave changed its polarity and S-T segment shifted to negative potential (between 0.05 and 0.15 mV). The possible origin of these observation is discussed

Beta-methyl digoxin: a better absorbable digoxin.

Since Megges and Repke [1961] showed that acetylation of the hydroxyl groups in the aglycone or the sugar side chain of the digitalis molecule results in a derivative with enhanced and more complete absorption from the gastrointestinal tract, several new compounds resulting from acetylation or methylation of digoxin molecule have been developed. Beta-methyl digoxin (beta-methyl digoxin) is a methyl derivative (methyl group in position 4 of the digitoxose residue) of digoxin. Enhanced and more complete gastrointestinal absorption of tritium labeled beta-methyl digoxin [Rennekamp et al. 1972] has been confirmed. Weiss et al. [1975], based on the serum levels following oral administration, calculated that to achieve comparable levels, digoxin dose would have to be increased by 1.55 times compared to that of beta-methyl digoxin. These and other studies supported an earlier notion that beta-methyl digoxin was a better and desirable cardiotropic agent than the digoxin. Comparison of cardiac effects using equivalent doses of the two compounds however, showed no difference [Das et al. 1977]. Following oral administration, the serum glycoside levels to beta-methyl digoxin indeed were significantly greater than those with digoxin. However, these differences in serum levels were not of sufficient magnitude to influence detectable cardiac inotropic effects, hence, the search for a better digoxin should continue.

Amplification of serotonin-induced contractions of isolated porcine coronary arteries after pretreatment with therapeutic doses of beta-methyldigoxin.

The present experiments demonstrate that after pretreatment of isolated porcine coronary arteries with therapeutic (2.5 X 10(-9) M) was well as with toxic (10(-6) M) doses of beta-methyldigoxin the serotonin-induced contractions were significantly amplified. Since serotonin released from destroyed thrombocytes may be one of the triggering factors eliciting coronary spasms, caution must be taken in the use of digitalis in coronary disease of spastic origin.

Determination of the onset of beta-methyl-digoxin action by potentiation of the adenosine response in guinea pigs.

The onset of beta-methyl-digoxin action was investigated by the potentiation of the adenosine response in guinea pigs and rats, and compared with that of digoxin and dipyridamole. A number of i.v. infusions of adenosine were given to determine the mean control adenosine response and its 95% confidence limits. After oral administration of the drugs, successive infusions of adenosine were continued until a drug-induced potentiation of the adenosine response was observed. The time of appearance of the potentiated adenosine response was marked as the onset of action of the drugs. The onset of action in guinea pigs was 9 to 12 min for 0.2 to 0.4 mg/kg of beta-methyl-digoxin, 90 to 100 min for 0.2 mg/kg of digoxin and 25 min for 5 mg/kg of dipyridamole. The maximal potentiation was 48.8 to 53.8% at 18 to 21 min for beta-methyl-digoxin, 74.5% at 130 min for digoxin and 74.8% at 80 min for dipyridamole. Adenosine infused i.v. into rats produced heart block, as in guinea pigs. However, in rats, the adenosine response was not potentiated by beta-methyl-digoxin and digoxin. Dipyridamole at a dose as high as 200 mg/kg produced 25.8% potentiation at 36 min after oral administration to rats.

Effects of vasoactive drugs on fluoride-induced contractions of vascular smooth muscle in calcium-free solution.

Cumulative dose-response curves were obtained for contractions induced by fluoride in bovine facial veins and arteries in the presence and absence of external Ca (Cao). In 1.4 mmol/l Cao the threshold for contractions was lower for veins than for the arteries, i.e. at 1 mmol/l vs. 2 mmol/l F-. After Ca withdrawal from the external medium, the ED50 values for veins and arteries were shifted from 2.2 to 10 and from 4.5 and 8.5 mmol/l F-, respectively. Several vasodilators (order of potency to relax veins: caffeine less than verapamil less than sulmazole less than sodium nitroprusside less than papaverine) were investigated for their ability to inhibit contractions induced by F- in Ca2+-free solution. None of them was able to counteract F- induced contractions in Ca2+-free solutions. Furosemide and beta-methyldigoxine were also ineffective. However, nitroprusside, sulmazole and papaverine were able to relax strips pretreated with Ca2+-free solutions. By contrast, contractions of depolarized veins induced by F- in Ca2+-free solutions were significantly, though transiently, inhibited by 10 mmol/l ammonium ions. The vasodilators tested in this study seem thus to act by inhibiting Ca influx at some level of the membrane, while F- may act by mobilizing Ca ions from some unidentified, cellular pools not accessible to the drugs tested in this study.

[Cardiac effects of a single daily dose of 0.15 mg and 0.20 mg of beta-methyldigoxin]. / Die kardialen Effekte täglicher Einmaldosen von 0,15 mg und 0,20 mg beta-Methyldigoxin.

In this placebo-controlled study the cardiac effects of once daily doses of beta-methyl digoxin 0.15 mg and 0.20 mg were evaluated using noninvasive methods. In double-blind fashion, 3 groups of 15 healthy volunteers each took 0.15 mg, or 0.20 mg beta-methyl digoxin, or placebo for a period of 14 days. On the first 2 days, all volunteers received a double amount of tablets for digoxin loading. Before the start of the study and 12 h after the last dose, the following parameters were recorded: electrocardiogram (QTc, T wave amplitude), systolic time intervals (STI) (QS2c, PEP, PEPc, LVETc), and impedance cardiogram (Heather index). The mean digoxin serum concentrations were 0.648 ng/ml and 0.975 ng/ml respectively for the two doses. The typical glycoside effects were seen and there was shortening of the STI (QS2c: - 12 ms/ - 14 ms resp.), flattening of the T wave, and a rise in the Heather index. The variations between baseline values and the 2 doses were statistically significant (p less than 0.05). In most parameters, the more intense effects corresponded with the higher serum level from the 0.20 mg dose; however, the difference between the 2 doses was not statistically significant. In conclusion, the results of this study show that a positive digitalis effect is demonstrable following the relatively small dose of beta-methyl digoxin 0.15 mg once daily under long-term application in healthy volunteers.

Abolition of digitalis tachyarrhythmias by caffeine.

Digitalis-induced ventricular tachyarrhythmias (VTAs) are believed to be due to oscillatory afterpotentials (OAPs) generated by an oscillatory release of calcium from the sarcoplasmic reticulum (SR). Caffeine blocks the calcium uptake into the SR and then may influence VTAs by depleting the SR stores of calcium. We studied the action of digitalis and caffeine, singly and in combination, in the isolated guinea pig heart perfused by means of a modified Langendorff apparatus. Digitalis (beta-methyldigoxin 1.27 X 10(-6) M) caused VTAs and ventricular fibrillation (VF) in all the hearts. Caffeine alone decreased heart rate but never caused VTAs. With the administration of digitalis and caffeine (1 mM), VTAs rarely developed and VF never occurs. With digitalis and higher concentration of caffeine (10 mM), neither VTAs nor VF were observed. In hearts with complete atrioventricular block, digitalis increased the ventricular rate from 143 +/- 10 to 270 +/- 13 beats/min (n = 8) in 12 +/- 1.9 min and provoked the appearance of multiple ventricular pacemakers. The addition of 10 mM caffeine to the digitalis-containing solution reduced the ventricular rate to 171 +/- 12 beats/min (P less than 0.001 vs. digitalis alone, not significant vs. control, n = 8) and abolished the digitalis-induced multiple pacemakers. Ventricular asystole was occasionally observed during the perfusion with digitalis + 10 mM caffeine. Caffeine alone did not modify the diastolic pressure, whereas caffeine and digitalis rapidly increase it. These results represent indirect evidence to support that SR plays an important role in the origin of the digitalis-induced VTAs.

Interaction between verapamil and beta-methyldigoxin. Study by 86Rubidium uptake in erythrocytes.

Digoxin and Verapamil may often be used in association in heart diseases; we tested whether this coadministration increases digitalis activity. Ten patients with failing heart were given 0.10 mg of beta-methyldigoxin, twice a day, for nine days; then they received in addition 80 mg of Verapamil, four times a day, for seven days. Digoxin activity was measured on the eighth, ninth and 16th days of treatment by 86Rubidium uptake in erythrocytes. The steady-state concentration was 0.91 +/- 0.13 ng/ml; during the coadministration the concentration rose to 1.23 +/- 0.16 ng/ml (an increase of 35.12%). The change was significant (p less than 0.001). The mechanism of this increase is unknown: it is important that there exists an increase in digitalis activity and not only a haematic elevation.