Convallatoxin promotes apoptosis and inhibits proliferation and angiogenesis through crosstalk between JAK2/STAT3 (T705) and mTOR/STAT3 (S727) signaling pathways in colorectal cancer

BACKGROUND

Aberrant activation of STAT3 is frequently encountered and promotes survival, cellular proliferation, migration, invasion and angiogenesis in tumor cell. Convallatoxin, triterpenoid ingredient, exhibits anticancer pharmacological properties.

PURPOSE

In this work, we investigated the anticancer potential of convallatoxin and explored whether convallatoxin mediates its effect through interference with the STAT3 activation in colorectal cancer cells.

METHODS

In vitro, the underlying mechanisms of convallatoxin at inhibiting STAT3 activation were investigated by homology modeling and molecular docking, luciferase reporter assay, MTT assay, RT-PCR, Western blotting and immunofluorescence assays. Changes in cellular proliferation, apoptosis, migration, invasion and angiogenesis were analyzed by EdU labeling assay, colony formation assay, flow cytometry assay, wound-healing assay, matrigel transwell invasion assay and tube formation assays. And in vivo, antitumor activity of convallatoxin was assessed in a murine xenograft model of HCT116 cells.

RESULTS

Convallatoxin decreased the viability of colorectal cancer lines. Moreover, convallatoxin reduced the P-STAT3 (T705) via the JAK1, JAK2, and Src pathways and inhibited serine-727 phosphorylation of STAT3 via the PI3K-AKT-mTOR-STAT3 pathways in colorectal cancer cells. Interestingly, we discovered the crosstalk between mTOR and JAK2 in mTOR/STAT3 and JAK/STAT3 pathways, which collaboratively regulated STAT3 activation and convallatoxin play a role in it. Convallatoxin also downregulated the expression of target genes involved cell survival (e.g., Survivin, Bcl-xl, Bcl-2), proliferation (e.g., Cyclin D1), metastasis (e.g., MMP-9), and angiogenesis (e.g., VEGF). Indeed, we found that convallatoxin inhibited tube formation, migration, and invasion of endothelial cells, and inhibited the proliferation. Finally, in vivo observations were confirmed by showing antitumor activity of convallatoxin in a murine xenograft model.

CONCLUSION

The result of the current study show that convallatoxin promotes apoptosis and inhibits proliferation and angiogenesis through crosstalk between JAK2/STAT3 (T705) and mTOR/STAT3 (S727) signaling pathways in colorectal cancer cells and indicate that convallatoxin could be a valuable candidate for the development of colorectal cancer therapeutic.

[Nonspecific effect of Na+/K(+)-ATPase inhibition with strophanthin or under hypothermia in rat heart]

Electron probe microanalysis was applied to study the kinetics of changes in potassium and sodium concentration in muscle cells of isolated heart from Wistar rat during experimental ischemia. Hypoxic perfusion without glucose was shown to evoke the potassium deficiency and sodium accumulation in cardiac myocells. Short-term action (10 min) of strophanthin (0.1 mM/l) recovered Na/K balance in ischemic myocells. Hypothermic perfusion exhibited the opportunity to conserve the cytoplasmic elemental contents in the state corresponding to the beginning of low temperature (4 degrees C) operation.

Convallatoxin, a dual inducer of autophagy and apoptosis, inhibits angiogenesis in vitro and in vivo

Autophagy and apoptosis are important processes that control cellular homeostasis and have been highlighted as promising targets for novel cancer therapies. Here, we identified convallatoxin (CNT), isolated from Antiaris toxicaria, as a dual inducer of autophagy and apoptosis. CNT exerts cytotoxic effects on a number of cancer and normal cell lines and induces apoptosis by increasing caspase-3 and poly ADP ribose polymerase (PARP) cleavage. Moreover, dose- and time-dependent autophagic activity was detected in CNT-treated cells, and mammalian target of rapamycin (mTOR)/p70S6K signal pathway inhibition was observed. Notably, CNT inhibits human umbilical vein endothelial cell (HUVEC) growth and exerts anti-angiogenic activity in vitro and in vivo. Collectively, these results demonstrate that the naturally occurring compound, CNT, is a novel anti-angiogenic compound via dual inducing of autophagy and apoptosis.

Experience-based behavioral and chemosensory changes in the generalist insect herbivore Helicoverpa armigera exposed to two deterrent plant chemicals

Behavioral and electrophysiological responses of larvae of the polyphagous moth species Helicoverpa armigera to two plant-derived allelochemicals were studied, both in larvae that had been reared on a diet devoid of these compounds and in larvae previously exposed to these compounds. In dual-choice cotton leaf disk and pepper fruit disk arena assays, caterpillars reared on a normal artificial diet were strongly deterred by strychnine and strophanthin-K. However, caterpillars reared on an artificial diet containing strychnine were insensitive to strychnine and strophanthin-K. Similarly, caterpillars reared on an artificial diet containing strophanthin-K were also desensitized to both deterrent chemicals. Electrophysiological tests revealed that the deterrent-sensitive neurons in taste sensilla on the maxillae of caterpillars reared on each deterrent-containing diet displayed reduced sensitivity to the two chemicals compared with the caterpillars reared on normal diets. We conclude that the experience-dependent behavioral plasticity was partly based on the reduced sensitivity of taste receptor neurons and that the desensitization of taste receptor neurons contributed to the cross-habituation to the two chemicals.

Cytotoxic effects of cardiac glycosides in colon cancer cells, alone and in combination with standard chemotherapeutic drugs

Cardiac glycosides have been reported to exhibit cytotoxic activity against several different cancer types, but studies against colorectal cancer are lacking. In a screening procedure aimed at identifying natural products with activity against colon cancer, several cardiac glycosides were shown to be of interest, and five of these were further evaluated in different colorectal cancer cell lines and primary cells from patients. Convallatoxin (1), oleandrin (4), and proscillaridin A (5) were identified as the most potent compounds (submicromolar IC50 values), and digitoxin (2) and digoxin (3), which are used in cardiac disease, exhibited somewhat lower activity (IC50 values 0.27-4.1 microM). Selected cardiac glycosides were tested in combination with four clinically relevant cytotoxic drugs (5-fluorouracil, oxaliplatin, cisplatin, irinotecan). The combination of 2 and oxaliplatin exhibited synergism including the otherwise highly drug-resistant HT29 cell line. A ChemGPS-NP application comparing modes of action of anticancer drugs identified cardiac glycosides as a separate cluster. These findings demonstrate that such substances may exhibit significant activity against colorectal cancer cell lines, by mechanisms disparate from currently used anticancer drugs, but at concentrations generally considered not achievable in patient plasma.

The effects of sodium pump inhibitors on sensory ganglion neurite growth

The effects of sodium pump inhibitors of the cardiac glycoside family (strophanthin K and digoxin) on neurite growth in the sensory ganglia of chick embryos (10-12 days) were studied in organotypic tissue cultures. These experiments produced the first evidence that these medicinal agents have marked neurite-suppressing actions. Their effects on sensory ganglion neurite growth were dose-dependent. At 1.10(-6) M, strophanthin K and digoxin completely blocked sensory ganglion neurite growth. Addition of study compounds to the medium at a concentration of 1.10(-7) M decreased the area index of the experimental explants to a level significantly below that of the controls, by a mean of 45%. These strophanthin K and digoxin concentrations were comparable with those at which endogenous digitalis-like factors are present in the systemic circulation. These results provide evidence that cardiac glycosides can produce the directed regulation of nervous tissue growth by affecting the signal transducer Na+, K+-ATPase.

[Effects of digoxin and corglycon on ion currents in neuronal membrane of snail (Lymnaea stagnalis)]

The results of endocellular dialysis membrane potential monitoring show that cardiac glycosides digoxin and corglycon in concentration from 10(-12) to 10(-6) M influence the sodium, calcium and potassium ion currents in isolated snail (Lymnaea stagnalis) neurons in reversible and slightly dose-dependent manner. In low concentration (10(-12) - 10(-8) M) both substances increased all ionic currents by up to 5%, while in higher concentrations both drugs led to the suppression of ion currents. The most pronounced decrease (up to 26% relative to control) was observed for sodium ion current under the action of digoxin in a concentration of 10(-6) M. The process of slow potassium currents inactivation was accelerated by corglycon in a concentration of 10(-6) M. Digoxin caused a shift in the current - voltage curve maximum by 5 - 10 mV to the right on the potential axis. Generally, digoxin in comparison to corglycon produced less activating and more suppressing effect on the membrane ion currents studied.

[Effect of Na(+), K(+)-pump inhibitors on the sensory ganglia neurite growth]

Inhibitors of Na(+), K(+)-pump belonging to the class of cardiac glycosides were investigated in organotypic tissue culture of dorsal root ganglia cells of 10-12 days old chicken embryos. The data obtained show that the application of cardiac glycosides (strophantin K and digoxin) in a wide range of concentrations controls the neurite growth in sensory neurons in the dose-dependent manner. It was shown, that at the concentrations of cardiac glycoside exceeding 1 x 10(-6) M the growth of neurites was totally inhibited. Our data indicate that cardiac glycoside have the down-regulation effect on the neurite growth. The data obtained indicate that the Na(+), K(+)-ATPase is involved in the control of the process of neurite growth as a signal transducer.

[Strophanthin induced changes in the ion currents of Lymnaea stagnalis and Planorbis corneus neurons]

Experiments on isolated neurons of Lymnaea stagnalis and Planorbis corneus using the intracellular dialysis and fixed membrane potential techniques showed that strophanthin G in a concentration range from 10(-11) to 10(-6) M produce dolse-dependent reversible suppression of the ion currents in potassium, calcium, and sodium channels. At the maximum concentration (10(-6) M), the maximum suppression (up to 55% of that in the control) was observed for the calcium ion current. At the minimum concentration (10(-12) M), the drug did not influence the sodium ion current, but slightly (approximately by 5%) increased the calcium and potassium ion currents. In addition, strophanthin accelerated the inactivation of slow potassium ion currents.

[The effect of hypothermia on kinetic characteristics of the rat brain synaptic membrane Na,K-ATPase]

The effect of profound hypothermia (acute or prolonged) on Km for ATP, Vm and strophanthine K affinity to Na,K-ATPase in the rat brain synaptosomal membranes was investigated. The temperature dependence of Na,K-ATPase activity in temperature range 5-40 degrees C was also studied. Hypothermia decreases Km and Vm, and increases affinity of strophanthine K to the enzyme. There are two linear sections in Arrhenius plots ofNa,K-ATPase activity. Hypothermia does not change position of the break point in Arrhenius plots. The mechanisms and biological significance of the changes revealed are discussed.

[Comparative analysis of the cardiac glycosides action on the growth of the cardiac tissue explants]

The method of organotypical cell culture was used. The long-term cell culture of cardiac embryonic tissue of 10-12-days old chicken was investigated. The effects of ouabaine, strophantin K and digoxin on the growth of cardiac tissue explant were measured. The ouabain concentration which stimulates activity of Na+, K+-ATPase as the signal transducer, was determined. It was equal to 10(-10) M. Strophantin K and digoxin stimulate growth of cardiac tissue in concentration equal to 10(-16) M and 10(-18) M, resp. The data obtained show that application of cardiac glycosides led to control of cardiac tissue growth in dose-dependent manner. We hypothesize that alpha3 isoform of Na+, K+-ATPase is a signal transducer that controls the cardiac cell metabolism and growth.

Electromechanical properties of Purkinje fiber strands isolated from human ventricular endocardium

BACKGROUND

Abnormalities in the regulation of intracellular Ca2+ were observed in cardiac cells obtained from failing human hearts. However, the electromechanical properties and pharmacologic responses of human ventricular Purkinje fibers have not been well characterized.

METHODS

Strands of free-running Purkinje fibers and/or trabecular muscle fibers with a diameter of around 1.5 mm were removed from the endocardial surface of ventricles obtained from 16 transplant recipient hearts. Action potential (AP) was detected by conventional microelectrode techniques and twitch force by a force-displacement transducer.

RESULTS

The human Purkinje fiber strands as revealed by histologic examination were composed of Purkinje cells and the surrounding ventricular muscle cells. In well-polarized Purkinje fibers (mean +/- SE of maximum diastolic potential [MDP] = -85 +/- 1 mV) showing fast-response AP (Phase 0 Vmax >100 V/sec), the cardiotonic agents isoproterenol and strophanthidin (1 to 2 micromol/liter) accelerated the slope of diastolic depolarization and induced delayed afterdepolarization but not spontaneous APs. Steady-state contraction and the post-rest potentiation of contraction (PRPC) were similar in both Purkinje fibers and ventricular muscles, but inotropic agents induced tachyarrhythmia only in Purkinje fibers. In partially depolarized Purkinje fibers (MDP <-70 mV) with slow-response AP, isoproterenol and/or strophanthidin readily induced automatic and triggered rhythms.

CONCLUSIONS

Accumulation of excessive cytosolic Ca2+ in the presence of cardiotonic agents could lead to tachyarrhythmias in Purkinje fibers, but rarely in ventricular muscles of failing human hearts.

Selective inhibition of sodium-calcium exchanger by SEA-0400 decreases early and delayed after depolarization in canine heart

The sodium-calcium exchanger (NCX) was considered to play an important role in arrhythmogenesis under certain conditions such as heart failure or calcium overload. In the present study, the effect of SEA-0400, a selective inhibitor of the NCX, was investigated on early and delayed afterdepolarizations in canine ventricular papillary muscles and Purkinje fibres by applying conventional microelectrode techniques at 37 degrees C. The amplitude of both early and delayed afterdepolarizations was markedly decreased by 1 microM SEA-0400 from 26.6+/-2.5 to 14.8+/-1.8 mV (n=9, P<0.05) and from 12.5+/-1.7 to 5.9+/-1.4 mV (n=3, P<0.05), respectively. In enzymatically isolated canine ventricular myocytes, SEA-0400 did not change significantly the L-type calcium current and the intracellular calcium transient, studied using the whole-cell configuration of the patch-clamp technique and Fura-2 ratiometric fluorometry. It is concluded that, through the reduction of calcium overload, specific inhibition of the NCX current by SEA-0400 may abolish triggered arrhythmias.

[Some mechanisms of adenosine protective effect in the "calcium paradox"]

A possibility of preventing the "calcium paradox" with the aid of adenosine was studied as well as some mechanisms of adenosine effect upon the heart in case of the "calcium paradox". Adenosine was found to suppress release of amino acids from the heart in perfusion with calcium-free medium, to efficiently prevent disorders in the energy-dependent functions of mitochondrion and myoglobin release from the heart in reperfusion with Ca2+ -containing solution. Adenosine was also found to increase 2-10-fold lactate release from the heart. Adenosine seems to be able to activate glycolysis. Iodine acetate was shown to completely suppress the adenosine ability to decrease amino acid release from the heart perfused with calcium-free medium. Under conditions of iodine acetate blocking of glycolysis was found to possess no protective properties against cytolysis in the "calcium paradox". The heart mitochondria isolated in the end of the experiment revealed low values of free or phosphorylating respiration and complete dissociation of oxidation. Also a protective effect of adenosine in inhibition of Na+, K+ -ATPhase with Strophantinum, was studied.

The interaction of carbachol and strophantin on the electrical and mechanical events in electrically driven strips of guinea pig left atria

We compared the electrophysiological and the mechanical actions of the cholinergic agonist carbachol (CARB) and the digitalis glycoside strophantin (STR) in a study on the electrically driven strips of guinea pig left atria. The respective control values for the resting membrane potential (RMP), action potential amplitude (APA), action potential duration at 20%, 50%, and 90% repolarization levels (APD20,50,90), and time to peak tension (TtPt) were of the order of 61.1 +/- 1.69 nmV, 104.64 +/- 1.28 mV, 28.5 +/- 1.22 msec, 51.0 +/- 1.51 msec, 106.91 +/- 3.81 msec, and 60.1 +/- 1.09 msec. Exposure to CARB (2 x 10(-7) M) rapidly reduced contractility, TtPt, APD, and APA to exceptionally lower levels within the initial 5 minutes and gradually caused a slight hyperpolarization in RMP. Strophantin (1 x 10(-7) M) caused contractility and RMP to increase slightly, APD and APA to reduce less markedly, but did not significantly affect TtPt. Under the influence of combined CARB/STR, the effect of CARB on the contraction amplitude (CA), TtPt, APD, and APA was attenuated and that on RMP was significantly potentiated (p < 0.05), whereas the effects of STR on CA, TtPt, APD, and APA were reversed (p < 0.05), and the effect on RMP was augmented. The action potential duration was less responsive to STR at all depolarization levels with respect to those of CARB and combined CARB/STR. Although the correlation between the time course of APD-20 and APD-90 for STR was poor, the correlation for CARB and combined CARB/STR was highly significant (r > 0.95). The correlation between the effects of CARB on CA and APD-90 was high but poor for the effect of combined CARB/STR. Striking to note is that the rate of induction of contractile changes with CARB (d(delta)/dt = 1.39 +/- 0.05%/sec), and its washout was more rapid (p < 0.05) in comparison to the rate of changes in APD-90 (0.98 +/- 0.05%/sec). This result, however, was not observed with combined CARB/STR. From the results we concluded that CARB and STR act as antagonists when used in combination, with the exception that only the effect on RMP was additive, with asignificant discordance between the rates of induction of effects on CA and APD-90, with the former being more rapid.

Effects of epinephrine and calcium on the electrogram of the ouabainized frog heart

The effects of bound ouabain on the electrogram of the isolated frog heart are antagonized by epinephrine and potentiated by calcium. Ouabainized hearts also develop increased ventricular automatism (paroxysmal tachycardia, flutter and fibrillation) in the presence of large concentrations of calcium but not of epinephrine. The actions of both epinephrine and calcium are readily reversed by washing the tissue with normal Ringer's solution.

Myocardial dysfunction and male mortality in peroxisome proliferator-activated receptor alpha knockout mice overexpressing lipoprotein lipase in muscle

Free fatty acids (FFA) are liberated from triglyceride-rich lipoproteins by lipoprotein lipase (LPL) and are considered to be a principal energy source for the heart. The peroxisome proliferator-activated receptor alpha (PPARalpha) is a key regulator of FFA catabolism. To investigate its role in cardiac muscle metabolism, transgenic mice overexpressing LPL in skeletal and cardiac muscle were bred on a PPARalpha knockout background. Fifty-five percent of male animals lacking PPARalpha and overexpressing LPL died within 4 months after birth. In contrast, females of this genotype stayed alive. Deceased animals exhibited cardiopulmonary congestion but had no increase of neutral lipids in the heart. Changes in plasma glucose, FFA, lactate, and triglycerides did not clearly account for gender-specific differences in mortality; however, they indicated a critical role for PPARalpha during fasting. Analysis of cardiac function revealed that in isolated perfused hearts, left ventricular developed pressure (a measure of contractility) was markedly lower in PPARalpha knockout mice overexpressing LPL compared with controls. Glucose uptake of isolated perfused hearts was significantly higher in PPARalpha knockout mice with both normal or increased LPL expression. However, uptake of FFA was not different among genotypes. In contrast, fasted FFA levels were significantly lower in cardiac muscle of PPARalpha knockout mice with normal LPL expression (-26%) and PPARalpha knockout mice overexpressing LPL (-38%) compared with controls. Our results indicate a critical role for PPARalpha in myocardial pump function and suggest that mouse models combining different genetic effects such as PPARalpha knockout mice overexpressing muscle LPL may be useful to study cardiomyopathies.

Interactions of cationic drugs and cardiac glycosides at the hepatic uptake level: studies in the rat in vivo, isolated perfused rat liver, isolated rat hepatocytes and oocytes expressing oatp2

This paper deals with a crucial mechanism for interaction of basic drugs and cardiac glycosides at the hepatic uptake level. Available literature data is provided and new material is presented to picture the differential transport inhibition of bulky (type2) cationic drugs by a number of cardiac glycosides in rat liver. It is shown that the so called organic anion transporting peptide 2 (oatp2) is the likely interaction site: differential inhibition patterns as observed in oocytes expressing oatp2, could be clearly identified also in isolated rat hepatocytes, isolated perfused rat liver and the rat in vivo. The anticipation of transport interactions at the hepatic clearance level should be based on data on the relative affinities of interacting substrates for the transport systems involved along with knowledge on the pharmacokinetics of these agents as well as the chosen dose regimen in the studied species. This review highlights the importance of multispecific tranporter systems such as OATP, accommodating a broad spectrum of organic compounds of various charge, implying potential transport interactions that can affect body distribution and organ clearance.

[Cardiotropic activity of total bufadienolides from the poison of Central Asian toad Bufo viridis]

The sum of bufadienolides (bacagin) isolated from the poison of Bufo viridis toad occurring in Central Asia produces a selective strophanthin-K-like action upon the heart function, increasing myocardial contractility, retarding cardiac rhythm, and positively influencing the parameters of myocardial metabolism. The mechanism of realization of the positive ionotropic effect of bacagin is probably related to the ability of increasing the basal level of cytosol calcium at the expense of inhibiting the activity of Na+/K(+)-ATPase and, to some extent, Ca(2+)-ATPase in endoplasmic reticulum.

[Tolerance to cardiotoxic effect of strophanthane K in experimental total heart block and electrocardiostimulation]

Tolerance to the cardiotoxic effect of strophanthin K was studied in narcotized dogs with experimental complete heart block (CHB) and ventricular electrostimulation. A threshold to the toxic arrhythmogenic effect of strophanthin K was significantly reduced as compared to that in the control group. As the electrocardiostimulation (ECS) frequency increased, the minimum arrhythmogenic dose of strophanthin K showed a growth, while not reaching a level for the sinus rhythm. It is concluded that the basic mechanisms of the arrhythmogenic effect of strophanthin K under the conditions studied are the trigger activity in dogs with ECS and the increased peacemaker's activity in dogs with CHB.

[Effect of strophanthin on the electrophoretic mobility of blood erythrocytes in adults and children]

As assessed by changes in the erythrograms asymmetry coefficient, selectivity of the strophantin effect on cell populations with different mobility and age specifics of reciprocal responses, was revealed in adult subjects and in children. The data obtained suggest existence of difference in quality of functional condition of the erythrocytes with normal as well as reduced mobility in children and in adults.

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

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

The inhibitory effect of strophanthidin on secretion by the isolated gastric mucosa

The unidirectional fluxes of Na⁺ and Cl^- were measured across the isolated gastric mucosa of the bullfrog (R. catesbiana). The addition of strophanthidin, a cardiac aglycone, resulted in marked reductions of the spontaneous potential and short-circuit current. Associated with these changes, the isolated gastric mucosa ceased secreting chloride and hydrogen ion. Although the active component of chloride transfer was inhibited, the exchange diffusion component seemed to increase. No significant changes in membrane conductance or sodium flux were noted. Possible mechanisms of strophanthidin inhibition were discussed in view of its effect on chloride transport across the gastric mucosa and on sodium and potassium transfer in other tissues. It was concluded that the cardiac glycosides may not be specific inhibitors of sodium and potassium transport. This non-specific inhibition suggests that active chloride transport is affected by strophanthidin directly and/or anion secretion is dependent upon normal functioning of cation transport systems in the tissue.

Effect of strophanthin G on peroxidase oxidation kinetics of slowly oxidizable peroxidase substrates

Steady-state kinetics of thioproperazine, triftazine, aminazine, and o-dianisidine oxidation with hydrogen peroxide catalyzed by horseradish peroxidase were studied in the presence of strophanthin G. Values of the inhibition and activation constants (Ki, Ka) were determined in the pH range 5.0-7.5. At acidic pH, strophanthin G activated peroxidase during the oxidation of thioproperazine by the uncompetitive mechanism, and when triftazine was oxidized, the inhibition was noncompetitive. At pH > 6.0, the patterns of activation and inhibition changed to mixed-type during the peroxidase oxidation of thioproperazine and triftazine and to competitive inhibition of peroxidase with strophanthin G during the oxidation of aminazine. These effects are suggested to be due to an ionizable enzyme group of pK approximately 6.0. Strophanthin G inhibited free-radical oxidation of o-dianisidine via binding to the enzyme-substrate complex, preventing the generation of a stable semi-oxidized product of o-dianisidine, and thus inhibiting the enzyme by the anticompetitive mechanism. Mechanisms of oxidation of slowly and rapidly oxidizable substrates of peroxidase in the presence of strophanthin G are suggested.

[Effect of strophanthin on the absorption of sodium and short chain fatty acids from the sheep rumen]

In vivo, intraruminal strophantin administration suppressed the sodium absorption by up to 50% in the sheep reticulo-rumen. Absorption of the shortchain fatty acids was not affected. The findings suggest absence of a combined transport of sodium and short-chain fatty acids' anions in basic and lateral membranes of the reticulo-rumen apithelium in sheep.

Homeopathic effect on heart rate variability

We record ECGs from healthy human subjects during 24-h long intervals, using ambulatory equipment. We calculate from the data various parameters, searching for those that change in a clear and systematic way under a homeopathic stimulus, (Strophantus hispidus 30c). The energy fraction at high frequencies in the power spectrum of heart rate variability fulfills this condition, and we are able to interpret our results in a way consistent with the information on this medicine in the homeopathic Materia Medica.

Effect of ouabain on potassium exchange in heart muscle mitochondria

Potassium in the working frog ventricle exists in two physiological compartments and the more slowly exchanging compartment is influenced by the amount of work performed, ventricular failure and ouabain. In the present study, the exchange of potassium in mitochondria is investigated both in the control state and after exposure to ouabain, in order to determine whether mitochondria potassium represents the slowly exchanging compartment. Mitochondria potassium represents only 15% of the total ventricular potassium, while the slowly exchanging phase contains about 50%. Ouabain perfusion is associated with inhibition of entrance of potassium into the slowly exchanging ventricular phase, but no isolated specific effect on the mitochondria potassium is found. Alterations in mitochondria potassium directly reflect changes within the total ventricle. A fraction of mitochondria potassium is found to be inexchangeable under the conditions of the experiment. The results indicate that mitochondria potassium does not represent the major part of the slowly exchanging compartment.

Ouabain-induced ventricular tachycardia and its effect on the performance and metabolism of the dog heart

At constant pressure work there was an increase in the oxygen consumption of the dog heartlung preparation after tachycardia due to auricular stimulation and a far greater increase in consumption after ouabain-induced ventricular tachycardia, as compared with control hearts beating at their own sinus rhythm. In neither condition was the increase in coronary flow greater than the spontaneous increase in the controls. It is suggested that an increase in oxygen demand, under certain circumstances, may be met primarily by an increased desaturation of coronary blood. "Therapeutic" doses of ouabain did not improve the mechanical efficiency of the preparation. "Toxic" doses of ouabain which gave rise to ventricular tachycardia did not decrease the phosphocreatine or labile nucleotide phosphorus content of the heart provided there was no hypoxia of the heart muscle.

[The effect of kavinton and korglycon on the central and cerebral hemodynamics of patients with an ischemic stroke in stenoses and occlusions of the major cerebral arteries]

Of the 40 patients, stenoses of major brain arteries were identified in 34, occlusions in 6, affection of two arteries in eleven patients, that of three arteries in 3 patients. The following disturbances in central hemodynamics were detected: arterial pressure getting higher, this referring also to the peripheral vascular resistance, hematocrit value, with the bloodflow in the arm-ear portion slowing down, hemodynamics being predominantly of hyperkinetic type. Treatment with cavinton, cavinton plus corglucone resulted in improvement of bloodflow in the affected major brain arteries at the expense of a compensating redistribution of bloodflow from intact collectors to the stenosed arteries basin. Changes in central hemodynamics were manifested by increase in the number of cases presenting with eukinetic-type circulation at the expense of decrease in those of hyperkinetic type. Under hypokinetic type hemodynamics, it is advisable that cavinton be prescribed in combination with cardiac glycosides.

[The effect of the glycoside strophanthin K on the ultrastructure of the cardiomyocytes in the pro-oxidant zone of the myocardium in rats with experimental heart failure]

The effect of the cardiotonic strophanthin K on the ultrastructure of cardiomyocytes in the "pro-oxidant zone" in hypercatecholemia was studied in Wistar rats with experimental cardiac insufficiency (ECI). In ECI two differently directed processes, compensatory and degenerative, develop in the "pro-oxidant zone". After administration of strophanthin K the degenerative processes in the "pro-oxidant zone" increased: the number of degenerated cardiomyocytes was 41.9 +/- 1.4% in ECI and 85.35 +/- 3.4% after strophanthin administration (p > 0.99).

[Effect of a sodium transmembrane gradient on efflux of creatinine from the myocardium]

Heart maintains a gradient for creatine under physiological conditions, so that creatine release is relatively small. Calcium depletion, addition of strophanthin or decrease of sodium concentration (till 80 mM) provoke release of creatine. Elevation of transmembrane sodium gradient by raising of extracellular sodium concentration prevented loss of creatine. The effect of elevated concentration of sodium ions was blocked by strophanthin but depended on osmolarity, because solutions with the same osmolarity that hypersodium media had no protective effect on release of creatine. A sarcolemmal mechanism of Na creatine cotransports is proposed.