Sphingolipid metabolism and its relationship with cardiovascular, renal and metabolic diseases.

Sphingolipids (sphingomyelin, glycolipids, gangliosides) are located in cell membranes, plasma, and lipoproteins. In patients with cardiovascular, renal, and metabolic diseases, the profile of sphingolipids and their metabolites (ceramide, sphingosine, and sphingosine-1-phosphate) is modified, and these changes may explain the alterations in some cellular responses such as apoptosis. Furthermore, sphingosine and sphingosine-1-phosphate have been suggested to prevent COVID-19. This review also briefly mentions the techniques that allow us to study sphingolipids and their metabolites.

Los esfingolípidos (esfingomielina, glucolípidos y gangliósidos) se localizan en las membranas celulares, el plasma y las lipoproteínas. En pacientes con enfermedades cardiovasculares, renales y metabólicas, el perfil de los esfingolípidos y sus metabolitos (ceramida, esfingosina y esfingosina-1-fosfato) se modifica, y estos cambios pueden explicar las alteraciones en algunas respuestas celulares, como la apoptosis. Además, se ha sugerido que la esfingosina y la esfingosina-1-fosfato previenen la COVID-19. En esta revisión también se mencionan brevemente las técnicas que permiten el estudio de los esfingolípidos y sus metabolitos.

Antiarrhythmic and cardioprotective effects of remifentanil in anesthetized dogs.

OBJECTIVE: To study the antiarrhythmic effect of remifentanil in experimental arrhythmias in dogs. METHODS: We used dogs weighing 12 kg-18 kg anesthetized with 30 mg/kg sodium pentobarbital given intravenously. Ventricular arrhythmia, ventricular fibrillation and death were induced with digoxin (9 microg/kg/min). In another model, two types of arrhythmia were induced in the right atrium, one of them with aconitine crystals placed on the right atrium and the other was induced in the basement of the right atrium by electrical stimulation. The potential antiarrhythmic action of remifentaniL was investigated in ventricular and atrial arrhythmias by the administration of an intravenous bolus after toxic signs were evident. Thus, two arrhythmias with different mechanisms were generated. Leads DII, unipolar left intraventricular and right atrial leads, and left ventricular pressure were used to record control tracings and tracings in presence of remifentanil, during ventricular arrhythmia. RESULTS: Remifentanil abolished toxic effects of digoxin, it eliminated the A-V dissociation and ventricular extrasystoles, reverting to sinus rhythm in each case. Remifentanil extended the time to reach lethal doses from 63.25 +/- 11.3 to 100 +/- 11.8 min. These effects were blocked by naloxone (0.01 microg/kg) applied before remifentanil. In the two arrhythmias model, remifentanil suppressed both, ectopic focus and atrial flutter. CONCLUSIONS: Remifentanil elicits antiarrhythmic and cardioprotective effects in experimental ventricular arrhythmias induced by digoxin and in a model of two atrial arrhythmias induced by aconitine and by electrical stimulation.

Metabolismo de los esfingolípidos y su relación con las enfermedades cardiovasculares, renales y metabólicas / Sphingolipid metabolism and its relationship with cardiovascular, renal and metabolic diseases

Resumen Los esfingolípidos (esfingomielina, glucolípidos y gangliósidos) se localizan en las membranas celulares, el plasma y las lipoproteínas. En pacientes con enfermedades cardiovasculares, renales y metabólicas, el perfil de los esfingolípidos y sus metabolitos (ceramida, esfingosina y esfingosina-1-fosfato) se modifica, y estos cambios pueden explicar las alteraciones en algunas respuestas celulares, como la apoptosis. Además, se ha sugerido que la esfingosina y la esfingosina-1-fosfato previenen la COVID-19. En esta revisión también se mencionan brevemente las técnicas que permiten el estudio de los esfingolípidos y sus metabolitos.

Abstract Sphingolipids (sphingomyelin, glycolipids, gangliosides) are located in cell membranes, plasma, and lipoproteins. In patients with cardiovascular, renal, and metabolic diseases, the profile of sphingolipids and their metabolites (ceramide, sphingosine, and sphingosine-1-phosphate) is modified, and these changes may explain the alterations in some cellular responses such as apoptosis. Furthermore, sphingosine and sphingosine-1-phosphate have been suggested to prevent COVID-19. This review also briefly mentions the techniques that allow us to study sphingolipids and their metabolites.

Vulgarenol, a sesquiterpene isolated from Magnolia grandiflora, induces nitric oxide synthases II and III overexpression in guinea pig hearts.

Vulgarenol, a sesquiterpene isolated from Magnolia grandiflora flower petals, decreased coronary vascular resistance in the Langendorff isolated and perfused heart model, when compared to the control group [(15.2 x 10(7) +/- 1.0 x 10(7)) dyn s cm(-5) vs. (36.8 x 10(7) +/- 1.2 x 10(7)) dyn s cm(-5)]. Our data suggest that this coronary vasodilator effect probably involved inducible and endothelial nitric oxide synthase overexpression (6.8 and 4.2 times over control, respectively), which correlated with increases in nitric oxide release [(223 +/- 9) pmol mL(-1) vs. (61 +/- 11) pmol mL(-1)] and in cyclic guanosine monophosphate production [(142 +/- 8) pmol mg(-1) of tissue vs. (44 +/- 10) pmol mg(-1) of tissue], as compared to control values. This effect was antagonized by 3 microm gadolinium(III) chloride, 100 microM N-nitro-L-arginine methyl ester, and 10 microM 1H-[1,2,4]oxadiazolo[4,2-a]quinoxalin-1-one. Hence, the vulgarenol-elicited coronary vasodilator effect could be mediated by the nitric oxide-soluble guanylyl cyclase pathway.

[Viscum album aqueous extract induces inducible and endothelial nitric oxide synthases expression in isolated and perfused guinea pig heart. Evidence of the coronary vasodilation mechanism]. / El extracto acuoso de viscum album induce la expresión de las sintasas de oxido nítrico inducible y endotelial en corazón aislado y perfundido de cobayo. Evidencia del mecanismo de vasodilatación coronaria.

The pharmacological effect of a Viscum album aqueous extract was evaluated on the Langendorff isolated and perfused heart model in normotense male guinea pig hearts. Coronary vascular resistance, left intraventricular pressure, nitric oxide release in the perfusion liquid, cyclic guanosine monophosphate production, and analysis of inducible and endothelial nitric oxide synthases expression by Western Blot in ventricular tissue were recorded in absence and presence of blockers and inhibitors, such as 3 microM gadolinium chloride, 100 microM N(omega)-nitro-L-arginine methyl ester and 10 microM 1H-[1,2,4]oxadiazolo[4,2-a]quinoxalin-1-one. V. album aqueous extract exerts a significant decrease in the coronary vascular resistance, which courses with significant increases in nitric oxide and cyclic guanosine monophosphate production. Analysis of the expression of both nitric oxide synthases revealed that this extract significantly induces the expression of both isoforms in guinea pig hearts. These effects were inhibited by the presence of blockers and inhibitors. The coronary vasodilation induced by the extract is mediated by the nitric oxide/soluble guanylyl cyclase pathway. In addition, this extract shows a positive inotropic effect which that is tyramine-mediated by means of beta1-adrenergic stimulation.

Peroxisome proliferator-activated receptor-α stimulation by clofibrate favors an antioxidant and vasodilator environment in a stressed left ventricle.

BACKGROUND: Arterial high blood pressure is a risk factor for target organ damage; the most susceptible organs are the arteries, brain, kidneys, and heart. The damage mechanisms include oxidative stress and renin-angiotensin system (RAS) overactivity. Therefore, our aim was to study whether clofibrate-induced peroxisome proliferator-activated receptor-alpha (PPAR-α) stimulation is able to prevent alterations in cardiac functioning derived from RAS overstimulation in the left ventricle of rats with hypertension secondary to aortic coarctation and to improve antioxidant defenses. METHODS: Male Wistar rats were assigned to Control (Sham)- or aortic coarctation-surgery and further divided to receive (1 or 21 days) vehicle, clofibrate (100mg/kg), captopril (20mg/kg), or clofibrate+captopril. The left ventricle was obtained to measure: angiotensin II and -(1-7), AT1 and AT2 receptors, angiotensin converting enzyme (ACE)-1 and -2, and MAS receptor; the activity and expression of superoxide dismutase, catalase, endothelial nitric oxide synthase, the production of reactive oxygen species (ROS) and peroxidated lipids; as well as ex vivo cardiac functioning. RESULTS: Clofibrate decreased angiotensin II, AT1 receptor and ACE expression, and raised angiotensin-(1-7), AT2 receptor, ACE-2 expression, superoxide dismutase and endothelial nitric oxide synthase participation. These effects promoted lower coronary vascular resistance and improved mechanical work compared to aortic coarctated vehicle-treated rats. CONCLUSIONS: Clofibrate-induced PPAR-α stimulation changes the angiotensin II receptor profile, favors the ACE2/angiotensin-(1-7)/AT2 receptor axis decreasing the vasoconstrictor environment, activates the antioxidant defense, and facilitates endothelial nitric oxide synthase activity favoring vasodilation. This may represent a protection for the stressed heart.

[Mechanism of cellular toxicity induced by digitalis compounds. Study with ouabain]. / Mecanismo de toxicidad celular inducida por digitálicos. Estudio con ouabaína.

UNLABELLED: The toxic effect of digitalis compounds at cell level produces an intracellular Ca2+ overload and a decrease in intracellular concentrations of K+. Since Ca2+ and K+ are critical modulators of life and death, the purpose of this study was to explore the cell death pathway activated through the ionic imbalance provoked by digitalis intoxication. We present results of cell toxicity in a study performed with ouabain acting on a HeLa cells culture and on guinea pig heart myocites under ouabain intoxication. RESULTS: In tissue culture, ouabain produced inhibition of cell viability in a time and dose dependent manner. Through ethidium-bromide staining, nuclear condensation and fragmentation were observed. The electrophoretic analysis of nuclear DNA in agarose gel showed a degradation pattern characteristic of apoptosis. In histologic sections of guinea pig heart under ouabain intoxication (50-60% of lethal doses), in situ cell death was detected by in situ DNA TUNEL labeling. We conclude that the electrical and physiologic imbalance produced by toxic doses of ouabain activates mechanisms that cause cell death via apoptosis in heart myocites and fast growing cells.

[Study of Magnolia grandiflora extracts in guinea pigs cardiac muscle]. / Estudio de los extractos de Magnolia grandiflora sobre el músculo cardíaco de cobayo.

Several extracts from diverse Magnolia grandiflora varieties were pharmacological evaluated in the cardiac muscle. From March to July, flowers and leaves from Magnolia grandiflora, native from the National Institute of Cardiology "Ignacio Chávez", from north, west, and orient zones from Mexico City, and from Puebla, Colima and Chiapas states were collected. They were separately processed and the extracts were obtained by maceration with ethanol-water (1:3 v/v) at 4 degrees C during two weeks. Qualitative analysis was accomplished with thin-layer, column and high-performance liquid chromatographies (HPLC). Functional and molecular analysis was made by specific chemical reactivity and by protonic magnetic resonance (RMN 1H). Pharmacological evaluation was completed in isolated and perfused male guinea pigs hearts. Extracts, fractions, and compounds were administrated by serial bolus in a gradual dose-response curves study in which left intraventricular pressure and coronary perfusion pressure were recorded, evaluating by such the positive inotropic and vasodilator effects of Magnolia grandiflora extracts. Vulgarenol and 2-p-hydroxyphenyl-2-hydroxy-ethylamine were isolated and identified, and the obtained results suggest that its positive inotropic and vasodilator effects are owed to these substances, being complemented by magnograndiolide and tyramine.

[Study of the relation between the electromolecular characteristics of digitalis compounds and their pharmacological action]. / Estudio de la relación entre las características electromoleculares de los digitálicos y su acción farmacológica.

In spite their reduced therapeutic index, digitalis-type drugs continue being used for treating diseases such as congestive heart failure and chronic atrial fibrillation. Thanks to the development of several methods, their structural determination has been feasible, so, structural modifications have been worked out to modulate their toxicity. Several reports realizes that efficacy for these digitalis-type drugs lies on the electronegativity centered on the steroidal moiety (D-ring) generated by either lactone and hydroxyl substituents attached to the steroidal moiety. In this work, we report how electronegativity, and so structural conformation, does modify their pharmacological properties, e.g., inotropism and safety margin. Thus, we evaluated a series of eleven drugs derived from digitoxigenin, named -OH, -Lac, D-01, D-02, D-03, D-07, D-14, D-15, D-20, D-21 and D-22, with groups that substitute both lactone and hydroxyl groups on the steroidal D-ring. Electronegativity and conformational energy were determined by Duhamm's method. The pharmacological evaluation for these drugs was accomplished in guinea pigs isolated hearts (according to the model proposed by Langendorff) and dog's isolated heart (as established by Starling's in vivo model). The results may suggest that digitalis-like action lies on the substituents attached to the D-ring. Positive inotropic effect and therapeutic index are related with increases in electronegativity as well with decreases in rotational and translational energies; therefore, these molecular properties have such importance for the digitalis efficacy.

Simultaneous determination of angiotensins II and 1-7 by capillary zone electrophoresis in plasma and urine from hypertensive rats.

We describe the procedure developed for the simultaneous detection and quantification of angiotensin II and angiotensin-(1-7), by capillary zone electrophoresis with UV detection by photodiode-array, at a wavelength of 200 nm, in the plasma and urine from hypertensive rats. Optimal separation was achieved with a 100mM boric acid+3mM tartaric acid+10 fM gold (III) chloride electrolyte solution at pH 9.80. The applied voltage was 30 kV and the capillary temperature was kept constant at 20 degrees C. The method was over the concentration range of 0.01-500 pmol/mL. All determination coefficients were higher or equal to 0.9985. Limits of detection and quantification for angiotensin II were 0.0110 pmol/mL (S/N=3) and 0.0195 pmol/mL (S/N=5), respectively. While for angiotensin-(1-7), the limits were 0.0112 pmol/mL (S/N=3) and 0.0193 pmol/mL (S/N=5), respectively. The present method offers a time-saving way to simultaneous determination of angiotensin II and angiotensin-(1-7), since it can be completed in 10 min, compared to other methodologies reported in the literature for capillary electrophoresis and liquid chromatography, which require more than 1h for analysis of complex matrices, such as plasma and urine. The procedure is illustrated by experiments that quantify simultaneously angiotensin II and angiotensin-(1-7) in plasma and urine from hypertensive and normotensive rats, with and without antihypertensive treatment. The levels of angiotensin II and angiotensin-(1-7) detected in the experimental model, resulted in a recovery of 99.00-106.01% and a reproducibility of less than 10%. The proposed analytical method is a use full tool for the simultaneous detection of angiotensin II and angiotensin-(1-7) implicated in vascular remodeling in pathologies such as hypertension.

Capillary zone electrophoretic determination of cytochrome c in mitochondrial extracts and cytosolic fractions: Application to a digitalis intoxication study.

We describe a capillary zone electrophoretic procedure with photodiode-array detection for the determination of the apoptogenic protein cytochrome c in cytosolic fractions and mitochondrial extracts from guinea pig hearts. Optimal separation was achieved with a 100mM phosphates electrolyte solution at pH 2.05. The applied voltage was 25kV and the capillary temperature was kept constant at 25+/-0.5 degrees C. The method was linear over the concentration range of 0.2-600pM. All determination coefficients were higher or equal to 0.9989. Limits of detection and quantitation were 0.06pM (S/N=3) and 0.21pM (S/N=10), respectively. The present method offers a time-saving way to determine cytochrome c since it can be completed in 12min, compared to a time scale of days for Western blotting methods, or hours for ELISA-based methods. The procedure is illustrated by experiments that quantify cytochrome c released under control conditions and in a digitalis intoxication experimental animal model, in which cytochrome c content was successfully determined and was found to be (mean+/-standard deviation): control cytosol (0.48+/-0.01pM), digitalis-intoxicated cytosol (0.85+/-0.01pM), control mitochondria (1.11+/-0.1pM) and digitalis-intoxicated mitochondria (0.75+/-0.02pM). Recovery results ranged from 98.4 to 110.2%. Hence, the proposed analytical method could be useful to elucidate the digitalis intoxication mechanism as well as the role of cytochrome c in mediating apoptosis.

Antiarrhythmic and cardioprotective effects of remifentanil in anesthetized dogs / Efectos antiarrítmicos y cardioprotectores de remifentanil en perros anestesiados

OBJECTIVE: To study the antiarrhythmic effect of remifentanil in experimental arrhythmias in dogs. METHODS: We used dogs weighing 12 kg-18 kg anesthetized with 30 mg/kg sodium pentobarbital given intravenously. Ventricular arrhythmia, ventricular fibrillation and death were induced with digoxin (9 microg/kg/min). In another model, two types of arrhythmia were induced in the right atrium, one of them with aconitine crystals placed on the right atrium and the other was induced in the basement of the right atrium by electrical stimulation. The potential antiarrhythmic action of remifentaniL was investigated in ventricular and atrial arrhythmias by the administration of an intravenous bolus after toxic signs were evident. Thus, two arrhythmias with different mechanisms were generated. Leads DII, unipolar left intraventricular and right atrial leads, and left ventricular pressure were used to record control tracings and tracings in presence of remifentanil, during ventricular arrhythmia. RESULTS: Remifentanil abolished toxic effects of digoxin, it eliminated the A-V dissociation and ventricular extrasystoles, reverting to sinus rhythm in each case. Remifentanil extended the time to reach lethal doses from 63.25 +/- 11.3 to 100 +/- 11.8 min. These effects were blocked by naloxone (0.01 microg/kg) applied before remifentanil. In the two arrhythmias model, remifentanil suppressed both, ectopic focus and atrial flutter. CONCLUSIONS: Remifentanil elicits antiarrhythmic and cardioprotective effects in experimental ventricular arrhythmias induced by digoxin and in a model of two atrial arrhythmias induced by aconitine and by electrical stimulation.

El extracto acuoso de viscum album induce la expresión de las sintasas de oxido nítrico inducible y endotelial en corazón aislado y perfundido de cobayo. Evidencia del mecanismo de vasodilatación coronaria / Viscum album aqueous extract induces inducible and endothelial nitric oxide synthases expression in isolated and perfused guinea pig heart. Evidence of the coronary vasodilation mechanism

The pharmacological effect of a Viscum album aqueous extract was evaluated on the Langendorff isolated and perfused heart model in normotense male guinea pig hearts. Coronary vascular resistance, left intraventricular pressure, nitric oxide release in the perfusion liquid, cyclic guanosine monophosphate production, and analysis of inducible and endothelial nitric oxide synthases expression by Western Blot in ventricular tissue were recorded in absence and presence of blockers and inhibitors, such as 3 microM gadolinium chloride, 100 microM N(omega)-nitro-L-arginine methyl ester and 10 microM 1H-[1,2,4]oxadiazolo[4,2-a]quinoxalin-1-one. V. album aqueous extract exerts a significant decrease in the coronary vascular resistance, which courses with significant increases in nitric oxide and cyclic guanosine monophosphate production. Analysis of the expression of both nitric oxide synthases revealed that this extract significantly induces the expression of both isoforms in guinea pig hearts. These effects were inhibited by the presence of blockers and inhibitors. The coronary vasodilation induced by the extract is mediated by the nitric oxide/soluble guanylyl cyclase pathway. In addition, this extract shows a positive inotropic effect which that is tyramine-mediated by means of beta1-adrenergic stimulation.

Estudio de los extractos de Magnolia grandiflora sobre el músculo cardíaco de cobayo / Study of Magnolia Grandiflora extracts in guinea pigs cardiac muscle

Se evaluó farmacológicamente los extractos de diversas variedades de Magnolia grandiflora sobre el músculo cardíaco. Se recolectó en el período de marzo a julio hojas y flores de Magnolia grandiflora nativa del Instituto Nacional de Cardiología "Ignacio Chávez", de la zona norte, poniente y oriente del Distrito Federal, de los estados de Puebla, Colima y Chiapas. Éstas se procesaron por separado y los extractos se obtuvieron por maceración con una mezcla de etanol-agua (1:3 v/v) a 4°C durante dos semanas. El análisis cualitativo se realizó por cromatografía en capa fina, columna y de líquidos de alta resolución (CLAR). El análisis funcional y molecular se efectuó por reactividad química específica y resonancia magnética protónica (RMN ¹H). La evaluación farmacológica se realizó en corazones aislados de cobayo macho. Los extractos, fracciones y compuestos se administraron en bolos seriados bajo un estudio de curvas dosis-respuesta gradual en donde se midió la presión intraventricular izquierda y la presión de perfusión coronaria, evaluando así el efecto inotrópico positivo y vasodilatador de los extractos de Magnolia grandiflora. Se identificó y aisló vulgarenol y 2-p-hidroxifenil-2-OH-etilamina, por lo que los resultados sugieren que su efecto vasodilatador e inotrópico positivo, se deben a la presencia de estas sustancias, las cuales se complementan con magnograndiólido y tiramina.

Several extracts from diverse Magnolia grandiflora varieties were pharmacological evaluated in the cardiac muscle. From March to July, flowers and leaves from Magnolia grandiflora, native from the National Institute of Cardiology "Ignacio Chávez", from north, west, and orient zones from Mexico City, and from Puebla, Colima and Chiapas states were collected. They were separately processed and the extracts were obtained by maceration with ethanol-water (1:3 v/v) at 4°C during two weeks. Qualitative analysis was accomplished with thin-layer, column and high-performance liquid chromatographies (HPLC). Functional and molecular analysis was made by specific chemical reactivity and by protonic magnetic resonance (RMN ¹H). Pharmacological evaluation was completed in isolated and perfused male guinea pigs hearts. Extracts, fractions, and compounds were administrated by serial bolus in a gradual dose-response curves study in which left intraventricular pressure and coronary perfusion pressure were recorded, evaluating by such the positive inotropic and vasodilator effects of Magnolia grandifloraextracts. Vulgarenol and 2-p-hydroxyphenyl-2-hydroxy-ethylamine were isolated and identified, and the obtained results suggest that its positive inotropic and vasodilator effects are owed to these substances, being complemented by magnograndiolide and tyramine.

Estudio de la relación entre las características electromoleculares de los digitálicos y su acción farmacológica / Relationship between the electromolecular properties of digitalis compounds and their pharmacological properties

Pese a su reducido margen de seguridad, los digitálicos siguen utilizándose en el tratamiento de la insuficiencia cardiaca congestiva y la fibrilación auricular crónica. Con el descubrimiento de su estructura, se han realizado remodelaciones para disminuir su toxicidad. Investigaciones recientes reportan que la eficacia digitálica radica en la electronegatividad del anillo "D" esteroideo, generada por la lactona e hidroxilo que poseen estos compuestos. En el presente trabajo, damos cuenta de la importancia que tiene esta propiedad molecular, que aunada a la conformación estructural, dan lugar a cambios significativos en las propiedades farmacológicas como el inotropismo y el margen de seguridad. Así, evaluamos una serie de once compuestos derivados de digitoxigenina, con grupos que sustituyen sobre el anillo "D" al hidroxilo y/o la lactona, los cuales denominamos -OH, -Lac, D-01, D-02, D-03, D-07, D-14, D-15, D-20, D-21 y D-22. La electronegatividad y la energía conformacional de cada compuesto se determinaron por el método Duhamm. El estudio farmacológico se realizó en corazones aislados de cobayo con base en el modelo de Langendorff y, en corazón de perro conforme al modelo cardiopulmonar de Starling. Los resultados permiten observar que la modulación de la acción digitálica está centrada, estructuralmente, en los sustituyentes de la fracción "D". El efecto inotrópico positivo y el margen de seguridad, medido como el cociente de la dosis tóxica sobre la dosis inotrópica, están relacionados con el aumento de electronegatividad y con una disminución de las energías rotacional y translacional que definen la conformación molecular; en consecuencia, estas propiedades son imprescindibles en la eficacia digitálica.

In spite their reduced therapeutic index, digitalis-type drugs continue being used for treating diseases such as congestive heart failure and chronic atrial fibrillation. Thanks to the development of several methods, their structural determination has been feasible, so, structural modifications have been worked out to modulate their toxicity. Several reports realizes that efficacy for these digitalis-type drugs lies on the electronegativity centered on the steroidal moiety (D-ring) generated by either lactone and hydroxyl sub-stituents attached to the steroidal moiety. In this work, we report how electronegativity, and so structural conformation, does modify their pharmacological properties, e.g., inotropism and safety margin. Thus, we evaluated a series of eleven drugs derived from digitoxigenin, named -OH, -Lac, D-01, D-02, D-03, D-07, D-14, D-15, D-20, D-21 and D-22, with groups that substitute both lactone and hydroxyl groups on the steroidal D-ring. Electronegativity and conformational energy were determined by Duhamm's method. The pharmacological evaluation for these drugs was accomplished in guinea pigs isolated hearts (according to the model proposed by Langendorff) and dog's isolated heart (as established by Starling's in vivo model). The results may suggest that digitalis-like action lies on the substituents attached to the D-ring. Positive inotropic effect and therapeutic index are related with increases in electronegativity as well with decreases in rotational and traslational energies; therefore, these molecular properties have such importance for the digitalis efficacy. (Arch Cardiol Mex 2003; 73:11-17).