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S Herzig

Publications and source records attributed to S Herzig.

At least 55 records · Page 3Linked to original sources

Informed consent for phase I studies: evaluation of quantity and quality of information provided to patients.

BACKGROUND: The process by which patients are informed and their consent is obtained in phase I trials has thus far been only marginally studied. Since 1986 we have followed an oral procedure, consisting of three consecutive conversations in which the investigator responsible for phase I studies, the research nurse and the patients' relatives and/or friends also participate, followed by the patients signing of a written consent form. It is required that six items of information considered essential by our staff be conveyed to patients by the responsible investigator. Meerwein's model, which defines three main dimensions of the informing process (the information itself, the emotional and interactive aspects), has been studied to ascertain whether it can be applied to evaluate the quality of the information proffered. METHODS: Thirty-two conversations were taped, transcribed and evaluated by one psychiatrist and one psychologist. A quantitative analysis of information was performed by calculating the number of patients to whom the essential items of information had been conveyed. The qualitative analysis was performed by rating on a five-point scoring system, from 1 (very bad) to 5 (excellent), the three dimensions of the informing process for each patient and by calculating for each dimension the mean score of the constituent items. RESULTS: Complete information about the characteristics of the phase I drug and the modalities of the treatment and follow up was given to almost 80% of the patients. All but one of the items of the information dimension scored 3.5 or higher, with the one related to the assessment by the doctor of the patient's understanding at the end of the consultation scoring less than 3 in 53% of the patients. All items of the emotional dimension scored higher than 3.5. Greater difficulty was encountered by the physician with the interactive dimension, the lowest mean scores being reported on the items related to the doctor's awareness of the indirectly expressed anxieties of the patients. In 71% of the consultations the three dimensions of information scored more than 3 and balanced one another, indicating a successful consultation by the Meerwein model. CONCLUSIONS: The informed consent procedure applied was satisfactory from a quantitative point of view, and the main items of information were acceptable to the patients. Meerweins's model proved to be applicable and useful for identifying pitfalls in communication. Greater attention should be paid to the indirect messages and implied criticisms of the patients to improve their participation in decision making. Physicians should become more skillful in providing adequate information and improve their methods of communication.

Adolescent↗

Derivatives of 3-digitoxigenone amidinohydrazone: synthesis and effect on the digitalis receptor of several species. Part 7: Compounds with positive inotropic activity.

2-Digitoxigenone amidinohydrazone (1), a compound with known digitalis-like activity, and Schiff bases 2-11 of 3-digitoxigenone were synthesized and tested pharmacologically in order to further determine possible structural requirements at the 3-position of digitalis compounds. The inotropic activity was screened using guinea-pig atria, and the interaction with the digitalis receptor was further examined using [3H]ouabain binding to cardiac membranes from guinea pig, rat, pit and man. All compounds revealed activities intermediate between 3-digitoxigenone and ouabain, and the potency of the derivatives covered approximately one order of magnitude. The absolute potency varied among species, but the rank order of potency was rather similar, yielding good correlations between species. This indicates no pronounced preference of these compounds for a particular (Na+/K+)-ATPase isoform of any of the species studied.

Animals↗

On the cardiac contractile, biochemical and electrophysiological effects of cantharidin, a phosphatase inhibitor.

Cantharidin concentration dependently increased the force of contraction in isolated guinea pig papillary muscles (1-100 microM). The positive inotropic effect is accompanied by a reduction in time to peak tension and relaxation time. Cantharidin did not exert a positive chronotropic effect in spontaneously beating right atria. L-type calcium channel currents of guinea pig cardiomyocytes were moderately increased by cantharidin (by about 20%), both at the whole-cell level (2 mM Ca2+) and at the single channel level (70 mM Ba2+). There was a correspondingly small increment of single channel availability. Additionally, a larger proportion of single-channel sweeps displayed high open probability-gating (so-called mode 2-gating). Cantharidin inhibited both type 1 and type 2A phosphatase activity in phosphatases purified from guinea pig ventricles [IC50 2.70 (2.06-3.53) and 0.13 (0.05-0.34) microM, n = 5-6, with 95% confidence intervals, respectively]. In isolated [32P]-labeled guinea pig ventricular cardiomyocytes, cantharidin (10 microM) increased the phosphorylation state of phospholamban (to 210% of control), the inhibitory subunit of troponin (to 155% of control), C-protein (to 156% control) and various additional proteins. It is concluded that the effects of cantharidin are likely mediated by increasing the phosphorylation state of several regulatory proteins. Furthermore, cantharidin might be an economical tool to investigate the function of phosphatases in model organ systems.

Animals↗

[Sotalol].

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Arrhythmias, Cardiac↗

Functional interaction between local anaesthetics and calcium antagonists in guineapig myocardium: 1. Cardiodepressant effects in isolated organs.

Both local anaesthetics and calcium antagonists depress cardiac function. Therefore, we have studied the interaction of these compounds in the isolated myocardium of guineapigs. The negative inotropic effect of various local anaesthetics was investigated in left atria in the absence or presence of nitrendipine 10(-7) mol litre-1 (n = 7-8 in each group). In addition, the effect of bupivacaine was studied in the presence of several calcium antagonists. The factor by which the negative inotropic potency (EC50) of local anaesthetics was enhanced significantly in the presence of nitrendipine varied from mean 1.2 (SD 0.2) (benzocaine) to 3.0 (0.6) (bupivacaine). The EC50 of bupivacaine was lowered by all calcium antagonists. The potentiation factor varied from 1.4 (0.4) (verapamil) to 3.3 (0.6) (nifedipine). The effects of benzocaine (n = 12) and bupivacaine (n = 11) on the working heart were assessed either alone or after pretreatment with nifedipine 10(-8) mol litre-1. The effects of benzocaine on contractility remained unaltered in the presence of nifedipine, whereas the negative inotropic effect of bupivacaine increased significantly (for example, a 20% reduction in left ventricular maximum dP/dt occurred with bupivacaine 1.75 (0.16) x 10(-6) mol litre-1 alone compared with 1.1 (0.22) x 10(-6) mol litre-1 when combined with nifedipine). We conclude that the effects of some local anaesthetics, for example bupivacaine, on cardiac contractility are enhanced in the presence of calcium antagonists. The relevance of this interaction in patients remains to be determined.

Anesthetics, Local↗

Functional interaction between local anaesthetics and calcium antagonists in guineapig myocardium: 2. Electrophysiological studies with bupivacaine and nifedipine.

The negative inotropic effect of local anaesthetics is potentiated by several calcium antagonists in guineapig myocardium [1]. Therefore, we studied which effects on cardiac ionic currents could be responsible for this interaction. Concentration-response curves for bupivacaine were studied in isolated guineapig atria and papillary muscles (slow action potentials). Effects on action potentials were assessed in the absence (n = 7 atria, n = 8 papillary muscles) or presence of nifedipine (8 x 10(-8) mol litre-1 in n = 8 atria, 10(-8) mol litre-1 in n = 8 papillary muscles). The effect on the Ca2+ current was assessed directly using the patch-clamp technique in guineapig ventricular myocytes. Bupivacaine reduced contractile force and upstroke velocity of atrial action potentials. Only the negative inotropic effect was potentiated in the presence of nifedipine. Force and upstroke velocity of slow action potentials were diminished by bupivacaine. Both variables were affected at significantly smaller concentrations of bupivacaine when given in combination with nifedipine. The Ca2+ current was reduced significantly by bupivacaine 5 x 10(-5) mol litre-1 (mean -18 (SD 7)%, n = 9). Its effect was accentuated in the presence of nifedipine 10(-9) mol litre-1 (-47 (4)%, n = 7). Bupivacaine 3 x 10(-4) mol litre-1 given alone exerted a comparable effect (-53 (4)%, n = 4). Variables indicative of Ca2+ channel function (contractile force, upstroke of slow but not normal action potentials, Ca2+ inward current) revealed potentiation of the effects of bupivacaine by nifedipine.

Action Potentials↗

Pharmacological characterization of positive inotropic derivatives of 4-amino-7-methyl-1,8-naphthyridine-3-carboxylic acid.

The positive inotropic effect of a series of 4-amino-7-methyl-1,8-naphthyridine-3-carboxylic acid derivatives was compared with the effects of known inotropic agents (ouabain, dihydroouabain, isoproterenol, adrenaline, histamine and isobutylmethylxanthine) in guinea-pig atrial and ventricular myocardial preparations. With respect to their functional effects, the 1,8-naphthyridine compounds are clearly different from drugs acting on the cAMP system, whereas several similarities with cardiac glycoside effects were found. Their ability to inhibit [3H]ouabain binding in guinea-pig cardiac membranes correlates well with their effects on myocardial contractile force. However, the latter effect was exerted by tenfold lower concentrations. The dissimilarities found between the 1,8-naphthyridines and digitalis may be due to a different type of interaction with the binding site on the (Na(+) + K+)-ATPase.

Animals↗

Biochemical and electrophysiological mechanisms of the positive inotropic effect of calyculin A, a protein phosphatase inhibitor.

Calyculin A (CyA; 1 microM) increased the force of contraction in isolated guinea pig papillary muscles to 144% of control without affecting contraction parameters. The effect of CyA on L-type calcium channels was assessed in cell-attached patches of guinea pig ventricular cardiomyocytes. Unitary Ba++ current recordings revealed that CyA at micromolar concentrations enhanced channel availability almost 2-fold, whereas the duration of individual openings and closures remained unchanged. In whole-cell recordings with Ca++ as the charge carrier, intracellular dialysis of 1 microM CyA enhanced peak current to a similar extent. In homogenates from guinea pig ventricles, 1 microM CyA completely inhibited phosphorylase phosphatase activity. In isolated [32P]-labeled guinea pig ventricular cardiomyocytes, 1 microM CyA increased the phosphorylation state of phospholamban (to 267% of control), that of the inhibitory subunit of troponin (to 182% of control) and those of various additional proteins. We conclude that the effects of CyA are likely to be mediated by increasing the phosphorylation state of several regulatory proteins.

Animals↗

Mechanisms of beta-adrenergic stimulation of cardiac Ca2+ channels revealed by discrete-time Markov analysis of slow gating.

Individual cardiac Ca2+ channels cycle slowly between a mode of gating in which the channel is available to open, and one in which the channel remains silent. The regulation of this multisecond cycling process by isoproterenol was investigated by single-channel recording and the development of a discrete-time Markov model that describes the slow switching among modes in terms of (de) phosphorylation reactions. The results provide evidence that isoproterenol increases Ca2+ channel activity by a reciprocal regulatory mechanism: not only is the phosphorylation rate of the channel increased, but also the dephosphorylation rate decreased. The discrete-time Markov formalism should prove useful as a general tool for understanding the mode switching demonstrated by a number of ionic channels.

1-Methyl-3-isobutylxanthine↗

Evidence for physiological functions of protein phosphatases in the heart: evaluation with okadaic acid.

Okadaic acid exerts a positive inotropic effect in cardiac preparations. We studied whether the positive inotropic effect of okadaic acid in cardiac preparations could be due to phosphatase inhibition and whether this inhibition affects the phosphorylation of cardiac proteins. In papillary muscles from guinea pigs, 30 microM okadaic acid increased force of contraction to 175% of predrug value. In isolated guinea pig ventricular cardiomyocytes, okadaic acid augmented single Ca(2+)-channel currents by enhancing channel availability. In homogenates from ventricles, 1 microM okadaic acid completely inhibited phosphorylase a phosphatase activity. In isolated 32P-labeled ventricular cardiomyocytes, 30 microM okadaic acid increased phosphorylation of phospholamban (PLB) and troponin inhibitor (TnI) to 325 and 284% of control, respectively. Furthermore, 30 microM okadaic acid increased phosphorylation of a hitherto unknown 23-kDa protein to 352% of control. It is concluded that the effects of okadaic acid could be mediated by increasing the phosphorylation state of several proteins including PLB, a 23-kDa protein, and TnI.

Animals↗

Pattern of interaction between dihydropyridine calcium antagonists and cationic amphiphilic drugs in isolated guinea-pig left atria.

The pharmacodynamic interaction between dihydropyridine calcium antagonists and several cationic amphiphilic agents with respect to their negative inotropic action has been studied in isolated guinea-pig left atria. (+/-)-Bepridil (CAS 64706-54-3), (+/-)-cis-diltiazem (CAS 33286-22-5), falipamil (CAS 77862-92-1), (+/-)-gallopamil (CAS 16662-47-2), lidocaine (CAS 6108-05-0), procainamide (CAS 614-39-1), or quinidine (CAS 50-54-4) were added at fixed concentrations. Afterwards, concentration-response curves for nifedipine (CAS 21829-25-4), the S-enantiomer niguldipine.HCl and its R-enantiomer dexniguldipine.HCl (CAS 113165-32-5), (+/-)-nimodipine (CAS 66085-59-4) (+/-)-nitrendipine (CAS 39562-70-4), or (+/-)-isradipine (CAS 75695-93-1) were obtained. In most cases, a left-ward shift in the concentration-response curve of the dihydropyridine was observed. The extent of this shift varied between dihydropyridines, and it depended on the catamphiphilic compound present. A high correlation was found between the different dihydropyridines, when comparing the extent of displacement of their concentration-response curves by the various catamphiphilic test compounds. Although quantitative differences exist between the different dihydropyridines, they are affected in potency by other compounds with a rather similar pattern. Accordingly, some general predictions about the interactions of a given dihydropyridine might be possible using limited datasets.

Animals↗

Potentiation of cardiodepressive action among calcium antagonists from different classes: evidence for a mechanism at the single calcium channel level.

The ability of calcium antagonists and antiarrhythmic agents to potentiate the negative inotropic effects of calcium antagonists was investigated in guinea-pig left atria. The potency of nitrendipine was enhanced by several amphiphilic agents by one order of magnitude or more (by pretreatment with quinidine or bepridil). The effect of preincubation with bepridil was investigated for a larger number of dihydropyridines. Only some of them were potentiated like nitrendipine. There was no potentiation between any two members of the same chemical group, i.e. between two dihydropyridines or two catamphiphilic calcium antagonists. The interaction between bepridil and nitrendipine was studied in more detail. In atria, its extent was influenced by several conditions, such as the stimulus frequency, the incubation temperature, or the extracellular K+ concentration. In measurements of whole-cell calcium currents in guinea-pig myocytes, the interaction was found to take place in a quantitatively similar manner. At the single channel level, an enhancement of the effects could also be demonstrated. It appears here that both drugs interact by binding to the same channel molecule. We conclude that the interaction may be due to 1.: an amphiphilic drug (like bepridil) binding to the channel very transiently and thus briefly favouring the inactivated channel state, which means that 2.: the other drug (like nitrendipine) has a higher chance to be bound because of its high affinity towards inactivated channels. Alternative explanations are also discussed.

Animals↗

Enantioselectivity of asocainol studied at different conditions: a novel approach to check the feasibility of molecular models of antiarrhythmic drug action.

In terms of the "guarded receptor" hypothesis, changes in potency of Na+ channel blocking drugs reflect alterations in drug access to and/or egress from a compartment facing a binding site with constant affinity. Potency is therefore assumed to be determined by changes in drug diffusion, its mobility in the electric field, protonation etc. Hence, the potencies of enantiomers, i.e. compounds with identical physicochemical properties, should be influenced in a parallel manner by the condition. To test this prediction, actions of the enantiomers of the stereoselective antiarrhythmic drug asocainol were compared at various membrane potentials and stimulus frequencies. Several experimental models indicative of Na+ channel block were used: the elevation of the rectangular pulse stimulation threshold (RPT) and the suppression of alternating-current induced arrhythmia (ACT) were studied in guinea-pig atria. The reduction of the upstroke velocity of action potentials was measured in guinea-pig papillary muscles. The inhibition of whole-cell Na+ currents was investigated in isolated guinea-pig ventricular myocytes. In all these assays, (+)-asocainol was more potent than the (-)-enantiomer. Lowering the membrane potential and/or increasing the stimulus frequency enhanced the effects of both enantiomers. However, over a certain range of conditions, the potency of (+)-asocainol was more markedly affected than that of (-)-asocainol, indicating that the eudismic ratio between potencies of the two drugs is not constant. Accordingly, these findings are inconsistent with the guarded receptor hypothesis.

Action Potentials↗

Marked dependence of the cardiac effects of gallopamil on the extracellular K(+)-concentration.

1. In guinea-pig Langendorff hearts, the negative inotropic effect of the calcium antagonist gallopamil is shifted by 15-fold to the left, when the extracellular K(+)-concentration is raised from 2.7 to 8.1 mM. 2. In papillary muscles, the ability of gallopamil to shorten the action potential (AP) markedly depends on K+: 100-fold lower gallopamil concentrations were required at 10.8 mM, compared to 2.7 mM. 3. In isolated myocytes, a change in the holding potential from -90 to -70 mV displaces the gallopamil dose-response curve to block Ca2+ currents leftward by only 6-fold. 4. Tetraethylammonium (TEA, 10 mM) mimics the mitigating effect of low K+ on the gallopamil-induced AP-shortening. Hence, the K(+)-dependence of gallopamil may be comprised of modulation of Ca(2+)-channel and K(+)-channel blocking effects.

Action Potentials↗

Frequency- and potential-dependency of the negative inotropic action of various dihydropyridine and non-dihydropyridine calcium antagonists.

Transmembrane voltage and beat frequency are important determinants of the action of several organic calcium antagonists. This is well-known for the cationic amphiphilic calcium antagonists. We intended to assess the functional impact of these phenomena in cardiac muscle with special regard to dihydropyridines. Therefore, concentration-response curves were constructed in isolated guinea-pig left atria for the negative inotropic effect of various compounds. The dihydropyridines nifedipine, racemic nitrendipine, nisoldipine, and felodipine, and the enantiomers of isradipine were investigated at different stimulation frequencies (1 Hz, 2.5 Hz, 4.5 Hz), and at different extracellular K+ concentrations (2.7 mM, 5.4 mM, 10.8 mM). These drugs were compared with the cationic amphiphilic compounds gallopamil, verapamil and diltiazem. The potency of some dihydropyridines, particularly nitrendipine, could be modulated to a remarkable extent, covering several orders of magnitude. The potential-dependency of the drugs depended on stimulus frequency and ranged from less than a half to two orders of magnitude. At 2.5 Hz, the rank order of extent of potential-dependency was gallopamil greater than nitrendipine greater than diltiazem greater than verapamil = (+)-isradipine greater than (-)-isradipine greater than or equal to nisoldipine greater than or equal to felodipine = nifedipine. Based on data obtained from binding studies in intact atria and from patch-clamp measurements of calcium current blockade, a mathematical model was used which describes the observed potency changes.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

Diastolic tension and contraction amplitude in calcium-loaded rat ventricular myocardium are differently affected by drugs.

1. To obtain a measure of drug effects on myocardial function during diastole, the following experimental protocol was designed: rapid electrical stimulation (5 Hz) at high Ca02+ caused an elevated diastolic tension, which could be subjected to drug-induced alterations. 2. Antiarrhythmic drugs (quinidine, propafenone, procainamide, mexiletine) were able to lower diastolic force without appreciably decreasing contraction amplitude. Calcium antagonists (nifedipine, verapamil) lowered both parameters in parallel. 3. Veratridine and Bay K 8644 both enhanced diastolic tension, but only Bay K 8644 concomitantly elevated contraction amplitude. 4. These findings may be explained when taking into account differential actions of sodium- and calcium channel modulating drugs, respectively, on cellular Ca2+ movements. In quantitative terms, the non-linear dependence of myocardial force on Cai2+ also had to be considered.

3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethy↗

The positive inotropic drugs DPI 201-106, BDF 9148, and veratridine increase ouabain toxicity and [3H]ouabain binding in guinea pig heart.

The interaction of three positive inotropic compounds, which are modulators of sodium channels, with the cardiac glycoside ouabain was investigated in isolated guinea pig atria. In the presence of DPI 201-106 (3 x 10(-7) M), of its new acetidine derivative BDF 9148 (10(-7) M), or of veratridine (10(-6) M), the threshold ouabain concentration to induce toxicity was lowered by a factor of 2. This effect can be explained by the observation that specific equilibrium [3H]ouabain binding in intact atria was elevated by these compounds in the appropriate concentrations. The binding results were analyzed by means of a previously established model of "positive cooperative ouabain binding to intact myocardium," which describes the relationship between cellular sodium homeostasis and ouabain binding. The extent to which the compounds increased ouabain binding was in good quantitative agreement with the observed shift in the threshold concentration of ouabain toxicity. The increase of specific [3H]ouabain binding is likely initiated by a gain in cytosolic sodium. It takes place at the cellular level only, since a direct enhancement of [3H]ouabain binding to isolated cardiac membranes was not found. In conclusion, at least under some conditions, new inotropic drugs acting as sodium channel modulators can increase the risk of digitalis toxicity.

Animals↗

Modulation of ouabain binding in beating ventricular myocardium from guinea-pigs: effects of lidocaine and monensin.

To further elucidate the interdependence between digitalis sensitivity and the cellular Na+ load, the influence of two Na+ load modifying drugs, monensin and lidocaine, on the concentration-dependence of ouabain binding and ouabain effects was studied in beating ventricular strips from guinea-pig heart. Monensin (3 x 10(-6)M), a Na+ ionophore known to elevate Na+ influx, enhanced 3H-ouabain binding (by approximately 40%) as well as the ouabain effect at non-toxic ouabain concentrations, and it shifted the threshold for toxicity towards threefold lower ouabain concentrations. Lidocaine (2 x 10(-4)M), a Na+ channel blocker, lowered ouabain binding by about one third, and it extended the ouabain concentration range tolerated without toxicity by a factor of three. In the concentrations used, neither compound exerted any direct effect on ouabain binding studied in isolated cardiac membranes. The binding data obtained in the muscle strips were well fitted by a mathematical model which quantifies the dependence of ouabain binding on the underlying (Na+ +K+)-ATPase activity. These findings provide evidence for an indirect drug-induced modulation of ouabain binding via the interference with the cellular Na+ load.

Animals↗