Efecto de la hidralazina sobre la vasoconstricción pulmonar hipóxica en la arteria pulmonar principal de rata / Effect of the hydralazine on the hypoxia lung vaso constriction in the main lung artery of rat

Estudiamos la vasoconstricción inducida por hipoxia (VPH) en la arteria pulmonar (AP) de la rata, así como el efecto que tienen sobre esta el verapamil (VE) y la hidralazina (HZ). Se montaron anillos de AP de ratas Sprague-Dawley adultas, de 3 mm de longitud, en un baño con solución de Kreb's-Henseleit, a 37º C, pH= 7,3-7,4 y burbujeada con 95 por ciento O2 5 por ciento CO2. Se aplicaron 2 gramos de tensión basal. Luego de estabilización se indujo contracción de la preparación con norepinefrina (NE), 3X10 M. Durante la meseta se cambió el burbujeo por 95 por ciento N2, 5 por ciento CO2 y se obtuvo la VPH sobrepuesta. Luego de relajar la preparación en normoxia, se añadió HZ (5 X 10 M) y media hora después se contrajo nuevamente con NE y se indujo VPH. Esta respuesta disminuyó significativamente en presencia de HZ, pero no en presencia de verapamil (1 X 10 M), cuando se añadió en un protocolo similar. Conclusión: la VPH no es alterada por VE pero se reduce significativamente en presencia de HZ

Efecto de distintas maniobras inotrópicas sobre la potenciación post-reposo en aurícula izquierda aislada de ratas / Effect of differrent inotrophics manoeuvre on the post-rest in isolation left atrium of rats

Se estudió la potenciación post-reposo (PPR) en aurículas izquierdas de rata, en un baño con solución de tyrode, a 35ºC, burbujeadas con 95 por ciento 02: 5 por ciento CO2. La estimulación basal (1Hz) se interrumpió por períodos de 2,4,8,64,128 segundos y se obtuvo una curva de potenciación de la contracción en función del intervalo de reposo (IR). En condiciones control la contracción fue aumentando con IR hasta los 32 S y luego se mantuvo estable. Un aumento de [Ca2+]e de 1,7 a 3,4mM, no cambió esta cinética. La disminución de [Ca2+]e a 0,85 mM disminuyó la contracción basal (CB) pero se mantuvo la PPR. La disminución de [Na+]e, de 145 a 55mM, aumentó la CB e inhibió la PPR. El cd2+ (0,02mM) y Ni2+ (0,2mM) disminuyeron CB sin variar la PPR. El añadir Mn2+ (0,2mM) fue la única maniobra inotrópica que cambió la cinética de la PPR, ya que no fue incrementado hasta los 128s de intervalo de reposo sin llegar a estabilizarse. Conclusiones: la PPR depende del Ca2+ contenido en el SER. Su cinética varió cuando se añadió Mn al baño, lo que sugiere que este bloqueante puede alterar el movimiento del Ca2+ dentro del RS

[Measurement of serum amiodarone by protein precipitation followed by high performance liquid chromatography with ultraviolet detection]. / Cuantificación de amiodarona en suero mediante precipitación de proteínas seguida de cromatografía liquida de alta resolución con detección ultravioleta.

Our aim was to develop a quantitative method for serum amiodarone measurement using high performance liquid chromatography with ultraviolet photometric detection. We studied previous reports in the literature in order to obtain a simpler method to be used routinely in our TDM unit. Sample preparation was based on protein precipitation adding 2 parts of acetonitrile to 1 part of serum, followed by vortex-agitation for 45 s, incubation at 24 degrees C for 5 min, and centrifugation at 6000 x g for 2 min. Twenty microliters of the supernatant was directly injected into the chromatographic system. A microBondapak CN RP column (3.9 x 150 mm) at 45 degrees C, with a mobile phase consisting of KH2PO4 10 mM/methanol/acetonitrile (40:37:23 v/v/v), pH 3.5, were used. Eluting with a flow rate of 0.6 mL/mm the retention time of amiodarone was approximately 4.9 min. Detection was performed at 242 nm and the quantification was made by peak height comparison with external standards. The mass/response ratio is linear (r2 > 0.99) within a mass range of 2.96 to 18,930 ng of injected amiodarone, which exceeds the requirements for the monitoring of serum levels (0.3 to 6.0 micrograms/mL). Sample storage should be done with acetonitrile-extracted sera at -16 degrees C to avoid degradation. The method is very efficient, linear, sensitive and specific but it also simpler and cheaper than others reported in the literature.

[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.

Variation of flow propagation velocity with age.

Flow propagation velocity is a new color Doppler M-mode measurement of left ventricular filling characteristics. This study was designed to establish normal values for this measurement in healthy individuals and to compare these findings with pulsed Doppler transmitral velocities. Complete M-mode, two-dimensional, and Doppler echocardiographic studies were performed on 64 volunteers between 21 and 79 years of age. Significant negative correlations (p < 0.001) with age were noted for flow propagation velocity (r = -0.59), peak early diastolic filling velocity (r = -0.65), and peak early diastolic filling/peak atrial filling ratio (r = -0.80). Positive correlations (p < 0.001) with age were observed for peak atrial filling velocity (r = 0.50) and atrial filling velocity integral (r = 0.71). Flow propagation velocity decreased by 44% between the youngest and oldest age groups. We conclude that flow propagation velocity is influenced by age and that it compares favorably with transmitral Doppler indices of left ventricular filling in this regard. These age-related alterations are present in healthy individuals, in the absence of any apparent cardiovascular disease.

[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.

[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.

Rate-dependent changes in excitability of depressed cardiac Purkinje fibers as a mechanism of intermittent bundle branch block.

When the heart rate is accelerated, rate-dependent intraventricular block may occur. This block has been attributed to abnormal action potential prolongation in a diseased conducting pathway. Less often, intraventricular block develops during slowing of the heart rate and has been explained in terms of phase 4 depolarization in potentially automatic cells within the diseased fascicle. We tested these hypotheses in isolated bundles of Purkinje fibers placed in a three-chambered tissue bath. In one group of experiments, conditions of localized injury and depressed excitability were mimicked by superfusing the central segment with sucrose solution. Action potentials were initiated in the proximal segment while the slope of phase 4 of cells in the distal end was controlled by intracellular ramps of current of either polarity. In these preparations, phase 4 depolarization facilitated rather than retarded propagation across the depressed segment, even at takeoff potentials as low as -45 mV. In a second group, depressed excitability was induced by exposing the three fiber segments to Tyrode's solution that contained high concentrations of KCl and CaCl2 or isoproterenol (0.1 microgram/ml). Under these conditions, Purkinje fibers did not undergo phase 4 depolarization and did not generate abnormally prolonged action potentials. These preparations showed a biphasic time dependence of conduction during premature stimulation or in response to changes in the basic cycle length. Conduction impairment and block were manifest at either side of an optimal interval or cycle length. Our results suggest that phase 4 depolarization and abnormally prolonged action potentials are not necessary conditions for intermittent block. Both tachycardia and bradycardia-dependent intraventricular conduction abnormalities may be associated with time-dependent variations in the excitability of depolarized conducting fibers as well as in the amplitude of the slow responses generated by these fibers. These alterations can be explained in terms of regulation of slow inward current by the intracellular calcium concentration.

Effects of lidocaine on conduction through depolarized canine false tendons and on a model of reflected reentry.

Reflected reentry was produced in canine false tendons, mounted in a three-chamber bath, in which the central fiber segment was partially depolarized with an "ischemic" solution to provide an area of impaired conduction. Lidocaine (3-5 mg/l) added to the central chamber further impaired conduction; consequently, reflections were obtained at lower frequencies and over a wider range of stimulation cycle lengths. Complete block followed drug exposure in some preparations. At moderate stimulation rates, the drug-induced shift of the frequency-dependence of manifest reflected reentries was either arrhythmogenic or antiarrhythmic. The action of lidocaine can be explained on the basis of effects on depressed fast or slow response activity at the boundary regions of the ischemic gap. Under slow response conditions, in false tendons homogeneously exposed to a solution containing 20 mM K+ and 9 mM Ca++, lidocaine delayed propagation or induced complete block. In fibers mounted in a single sucrose gap, the drug increased the current required to reach threshold without significant changes in resting potential, threshold voltage or input resistance. The effect of lidocaine on threshold current was lost in Na+-deficient solutions. Thus, lidocaine impairs conduction through K+-depolarized false tendons, an effect that may be related to the Na+ background current.

Electrophysiological effects of insulin on normal and depressed cardiac tissues.

The electrophysiological effects of insulin were studied in canine false tendons (FT) and papillary muscles from kittens and rats. Insulin caused hyperpolarization (2-8 mV) and an increase in action potential (AP) amplitude. However, the rate of rise and duration of the AP, the slope of phase 4 depolarization and conduction velocity were unchanged in the normal tissues. In preparations depressed spontaneously or by stretch or low pH (6.7), hyperpolarization was larger than observed in normal tissues. Insulin partially normalized electrophysiological parameters under these conditions but not in the presence of anoxia (95% N2). The membrane resistances of normal canine FT and kitten papillary muscles were not changed by insulin. Blockade of K channels by CsCl doubled hyperpolarization induced by the hormone. Insulin effects were abolished by cold (21 degrees C), ouabain (3-9 X 10(-7) M), or acetylstrophanthidin (0.5-3 X 10(-6) M). Overdrive hyperpolarization was enhanced by insulin. These experiments suggest that insulin-induced hyperpolarization is mediated by activation of the electrogenic Na pump and not by a change in membrane conductance.

Effects of current flow on pacemaker activity of the isolated kitten sinoatrial node.

The dynamic behavior of the cardiac pacemaker in response to single or to periodically repeated perturbations was studied using kitten sinoatrial (SA) nodal strips mounted in a sucrose gap. Sustained stepwise applications of current across the gap produce lasting variations in pacemaker cycle length that depend on current magnitude and polarity, but not on the phase of the pacemaker period at the time of the input. Brief current pulses, whether hyperpolarizing or depolarizing, may abbreviate or prolong the immediately affected cycle depending on their timing. These changes result in phase shifts of the subsequent discharges, but they do not alter the pacemaker period permanently. The phasic effects of brief current pulses can be described by a phase response curve (PRC), which is a plot of the phase shift as a function of the position of the stimulus in the pacemaker cycle. PRCs were constructed for inputs of different polarity and several strengths and durations. The behavior of the sinus nodal pacemaker when interacting with period perturbing inputs, such as vagal stimulation or electrotonic depolarization, can be predicted on the basis of the phase response curve.