Nicardipine dose dependently reduces the effect of equinatoxin II on coronary flow in isolated rat heart.

Equinatoxin II (EqT II) decreases coronary flow in guinea-pig and rat heart. It increases cytosolic Ca2+ activity and is supposed to form cation selective membrane pores. In the present study we tried to evaluate the influence of the L-type Ca2+ channel antagonist nicardipine upon the vasoconstrictory effect of EqT II on coronary vessels in isolated heart of the rat. Coronary flow was measured during the experiment. Ten min after bolus injection of EqT II the coronary flow decreased to 17.2 +/- 4.3% in experiments without nicardipine, and to 39.4 +/- 4.5% in the group with 0.1 microM nicardipine (p < 0.05). Our results indicate the possibility that L-type Ca2+ channels could be involved in the effects of EqT II on coronary flow in the rat heart.

Lacidipine decreases the honeybee venom-induced vasoconstriction of the isolated porcine coronary artery.

The venom of the honeybee Apis mellifera induces cardiovascular dysfunction. As its effects on coronary arteries have not yet been described, we studied the effects of the whole honeybee venom (non-volatile part) in the isolated porcine left anterior descending coronary artery (LAD) and the influence of L-type Ca2+ channel blocker, lacidipine, upon the venom effects in LAD. The venom produced concentration dependent contractions (7-70 microg/ml) of the porcine LAD; maximal effect of the venom was approximately the same as the effect of 30 mM KCl. Lacidipine concentration dependently (0.1-10 microM) and significantly (P < or = 0.05) decreased the venom-induced vasoconstriction. The results indicate the involvement of L-type Ca2+ channels in coronary contraction, induced by bee venom.

Effects of mibefradil and verapamil on ischemic-reperfusion in the hearts of guinea pigs with acute renal failure.

Two parameters indicating the ischemic-reperfusion myocardial injury, coronary flow and lactate dehydrogenase (LDH) release rate, were evaluated in guinea pigs with gentamicine-induced acute renal failure (ARF) and compared with those of healthy animals. Isolated Langendorffs hearts were exposed to 50 min of zero-flow global ischemia and 60 min of reperfusion. The influences of calcium channel antagonists (of T- and L-type antagonist mibefradil and of L-type antagonist verapamil) in reperfusion solution were evaluated. Our results showed coronary dilatation and higher LDH release rate in ARF than in control hearts before ischemia. Recovery of coronary flow during reperfusion was better and LDH release rate lower in ARF vs. control hearts. Perfusion with mibefradil and verapamil did not additionally increase coronary flow, however 0.1 microM mibefradil and verapamil decreased LDH release rate during reperfusion in ARF hearts in comparison to control hearts. Our results showed some protective effects of 0.1 microM mibefradil and verapamil on LDH release rate during reperfusion, but not on coronary flow in guinea pigs hearts with ARF.

Thermal conductivity of the porcine heart tissue.

The porcine heart was used as a model for studying the thermal changes in myocardium at cooling and re-warming during open heart surgery. A section of the heart septum was excised and tissue was cut into two similar square slices. The same shape of the tissue, cut from the surface from the upper lateral wall of the left ventricle, covered with epicardium and fat, was taken for another measurement. A thin (<0.5 mm) square thermal source of the same length of the side as the tissue samples was put between the two slices of tissue. This set was placed in the middle of two identical copper cylinders (2r=50 mm, height=55 mm) used to keep the outer side of the specimen at controlled room temperature. Thermal conductivity of the heart tissue was determined at controlled thermal power, and known difference of the temperature at the edge of the tissue and at the middle of the heater, when steady state was reached. Thermal conductivity calculated from the temperature difference and the geometry of heater and samples was 0.75 W/m.K for septal heart tissue, and 0.60 W/m.K for the lateral wall ventricle tissue with epicardium and fat.

Nicardipine dose-dependently reduces the effect of equinatoxin II on coronary flow in isolated porcine heart.

Death after i.v. administration of equinatoxin II (EqT II) has been attributed to the circulatory failure resulting from cardiotoxic effects. The mechanism of action is unknown. The aim of the present work was to study the effects of the toxin on vascular tone in the isolated porcine coronary artery and on coronary flow in the isolated pig heart. EqT II caused concentration-dependent contractions of rings of the isolated epicardial porcine coronary artery with an EC50 value of 89+/-5 nM (n=5-6) and maximal effect of about 140% of the contraction induced by 20 nM KCl. On Langendorffs porcine heart preparation EqT II caused a dose-dependent decrease of coronary flow. At EqT II doses lower than 0.05 micromol/100 g of heart weight there were no measurable effects of the toxin. At dose 0.5 micromol/100 g the toxin decreased coronary flow to less than 9.8+/-2.5% of the control value. The constrictory effect of the toxin on isolated porcine coronary arteries was diminished by the L-type calcium channel antagonist nicardipine (NC). NC in 1 microM concentration almost completely abolished the effect of EqT II on coronary flow. Our results confirmed involvement of L-type calcium channels in the vasoconstrictory effects of EqT II on epicardial coronary arteries.

Action of mibefradil and lacidipine on the isolated human anterior tibial artery.

In isolated human anterior tibial artery the effects of two different types of calcium channel antagonists, mibefradil (a selective T-type Ca2+ channel antagonist) and lacidipine (a 1,4 dihydropyridine Ca2+ channel antagonist, acting at L- and T-type, but binds preferentially at L-type Ca2+ channels) were compared. Both drugs reduced the contractions of isolated arteries induced by 60 mM KCl. The potency (IC50) of mibefradil was 6.5 microM and of lacidipine 82.4 nM. The potencies of both Ca2+ channel antagonists differed significantly (p<0.001 at 0.1 and 1 microM; p<0.01 at 10 microM). Lacidipine was 79-times more effective than mibefradil in reducing the vasoconstriction in isolated human anterior tibial artery. One of the reasons for higher potency of lacidipine could be a higher density of L-type than of T-type Ca2+ channels in tissue of the human anterior tibial artery.

Comparison of effects of nitrendipine, lacidipine and mibefradil on postischaemic myocardial damage in isolated rat hearts.

During ischaemia and reperfusion increased cytosolic Ca2+ is one of the important causes for ischaemic-reperfusion myocardial injury. In the present study we compared effects of preferentially L-type Ca2+ antagonists nitrendipine (NT) and lacidipine (LP), and of mibefradil (MB) a Ca2+ antagonist with higher affinity to T- than to L-type channels on myocardial function during reperfusion. Coronary flow (CF), heart rate (HR), left ventricular pressure (LVP), lactate dehydrogenase (LDH) release rate and ECG were registered during 40 min of reperfusion following 30 min of global zero flow ischaemia in Langendorff's isolated rat hearts. Either NT (100 nmol/L) or LP (10 nmol/L) or MB (100 nmol/L) was added to Krebs-Henseleit solution 10 min before ischaemia till the end of experiments. All three drugs influenced CF, HR and LVP. All of them decreased LDH release rate (P < 0.05, in microkat/g x min) when compared with control hearts (53.2 +/- 5.1): MB (19.4 +/- 4.3) > LP (30.7 +/- 6.6) > NT (43.3 +/- 2.8). NT reduced the duration of continuous arrhythmias at the beginning of reperfusion (to 59.1 +/- 6.1% of ischaemic controls) as well as the number of single arrhythmic events arising during the whole period of reperfusion (to 26.1 +/- 6.0% of ischaemic controls). MB diminished only single arrhythmic events during reperfusion to 39.1 +/- 17.3% of ischaemic controls. LP did not affect the onset of arrhythmias. Results of our experiments indicate a relatively greater importance of T-type than of L-type Ca2+ channels in the arising of postischaemic myocardial damage.

Lowering of the coronary flow in isolated rat heart by equinatoxin II depends upon extracellular Ca2+ concentration.

Equinatoxin II (EqT II) is a basic polypeptide toxin from the sea anemone Actinia equina (L.). Its LD50 in mice is 33 g/kg. The cause of death after intravenous application has been attributed to the circulatory failure resulting in the cardiotoxic effects. In Langendorff's rat and guinea-pig heart preparations EqT II caused dose dependent decrease in the coronary flow (CF). Morphologic changes of different cell cultures incubated with EqT II are the result of Ca2+ entry through the newly formed discrete pores. Pores in the cell membranes are composed of the toxin oligomeres. In the present study we tried to evaluate the dependence of vasoconstrictor effects of EqT II on isolated rat hearts upon the Ca2+ concentration in the perfusion solution. EqT II did not affect the CF in the group without Ca2+. The strongest effect was observed in the group with 1.5 mM Ca2+ where the CF decreased to 7.7+/-7%. The results of our experiments indicate that the effects of EqT II on CF depend on Ca2+ concentration in the extracellular solution.

Stereoselective and endothelium-independent action of nicardipine on the isolated porcine coronary artery.

The qualitative and quantitative effects of the (+)-S and (-)-R enantiomers and of the racemic mixture of the Ca2+ channel antagonist, nicardipine, were compared on the isolated porcine coronary artery with intact and removed endothelium. All three forms of nicardipine inhibited the contractions induced by KCl (5-90 mM) in both vessel preparations. The potency (IC50) of the (+)-S and (-)-R enantiomers and of the racemic mixture was 6.6, 31.8 and 10.9 nM in the vessel with endothelium and 6.4, 41.9 and 9.8 nM in the vessel without endothelium. The parameters of the concentration-response curves for each form of nicardipine at a submaximal KCl (60 mM) concentration and the potency ratios between the two enantiomers ((+)-S/(-)-R) were not statistically significantly different (P>0.05) in the two vessel preparations. In conclusion, qualitatively, all three forms of nicardipine showed only Ca2+ channel antagonistic effects in both vessel preparations. Quantitatively, the inhibition of contraction was stereoselective, the (+)-S enantiomer being the most potent, and was endothelium-independent.

Computer support for experiments on isolated hearts.

The left ventricular pressure (LVP) and ECG signals that appear during and after ischaemia tend to be very irregular (fibrillation, arrhythmia). Computer based data acquisition system, that we developed to support experiments on isolated Langendorff's rat heart, enabled the usage of methods derived from non-linear dynamics. To classify the irregularity of heart action, ECG and LVP time series have been used to calculate correlation dimension (D2) and largest Lyapunov exponent. We compared the results of signals derived from isolated heart at standard conditions and hearts rendered ischaemic for 60 minutes. Our results show that the level of irregularity can be classified efficiently using the quoted approach.

Pharmacological studies with two new ergoline derivatives, the potential antipsychotics LEK-8829 and LEK-8841.

The pharmacological properties of 9,10-didehydro-N-methyl-N-(2-propynyl)-6-methyl-8 beta-aminomethylergoline (LEK-8829) and 9,10-didehydro-N-methyl-N-(2-propynyl)-2-bromo-6-methylergoline -8-beta-carboxamide (LEK-8841), new ergoline derivatives, were compared with those of haloperidol and clozapine by in vitro radioligand displacement assays, various behavioral tests and blood pressure measurements. Both ergolines displayed low affinity for rat striatal 3H-SCH23390 (7-chloro-8-hydroxy-3-methyl-1-phenyl-2,3,4,5-tetrahydro-1H-3-benzaze pin e)- labeled dopamine (D)1 binding sites and high affinity for striatal 3H-spiperone-labeled D2 and cortical 3H-ketanserin-labeled serotonin-2 (5-HT2) sites. The ratio of pKi values 5-HT2/D2 was 1.11 for LEK-8829 (close to that of clozapine, 1.13) and 0.98 for LEK-8841 (close to that of haloperidol, 0.95). All compounds inhibited apomorphine-induced locomotor activity in rats, apomorphine-induced climbing behavior in mice and 5-hydroxytryptophan-induced head twitches in mice and induced catalepsy in rats and in mice. LEK-8829 and clozapine, but not LEK-8841 and haloperidol, showed a certain degree of mesolimbic selectivity, i.e., they caused more potent inhibition of apomorphine-induced locomotion compared with the induction of catalepsy in rats. In the case of LEK-8829, nonspecific effects that presumably predict a side effect profile, such as potentiation of pentobarbital-induced anesthesia in mice (sedation), antagonism of oxotremorine-induced tremors in mice (anticholinergic activity), spontaneous locomotor activity in mice and norepinephrine-induced lethality in rats (sedation and hypotension), were relatively weak compared with the activities described earlier. In contrast, LEK-8841 showed nonspecific effects at the similar dose levels as dopamine and 5-HT antagonistic effects. The results of direct measurements of the influences of both compounds on blood pressure agreed with the previously mentioned findings, i.e., LEK-8829 was relatively less hypotensive than LEK-8841 was. It is suggested that LEK-8829 might be an efficient antipsychotic with a reduced propensity to cause sedative, anticholinergic and hypotensive side effects. A certain degree of mesolimbic selectivity also points toward the possibility of a reduced propensity to cause extrapyramidal symptoms. In contrast, in regard to side effects (including extrapyramidal symptoms), the profile of LEK-8841 is less promising.

Ca2+ channel antagonists inhibit the intestinal absorption of digoxin in the guinea-pig.

Simultaneous administration of digoxin and Ca2+ channel antagonists results in an increased plasma level of digoxin. A possible mechanism underlying this interaction might be the influence of Ca2+ channel antagonists on the enteral absorption of digoxin. To study this interaction, two groups of experiments were performed with guinea-pigs. In the first group, the influence of Ca2+ channel antagonists on the rate of enteral absorption of digoxin in vivo was studied. In the second group, the influence of Ca2+ channel antagonists on the transfer of digoxin through the wall of the isolated everted small intestine in vitro was investigated. The intravenously determined minimal lethal dose of digoxin 30 min after its intraduodenal administration was increased in animals pretreated with either verapamil, diltiazem, nifedipine or nicardipine. Addition of either verapamil or diltiazem to the solution on the mucosal side of isolated everted small intestine sacs decreased the transfer of digoxin through the intestinal wall. Similar results obtained in both groups indicate that, under our experimental conditions, Ca2+ channel antagonists inhibit the enteral absorption of digoxin in the guinea-pig.

Structure-activity study of some newly synthesized ergoline derivatives on 5-HT2 receptors and alpha-adrenoceptors in rabbit isolated aorta.

In a structure-activity study, carried out in rabbit isolated aorta, the effect of different structural modifications in the ergoline nucleus upon the activity at 5-HT2 receptors and alpha-adrenoceptors was determined. 9,10-didehydro-N-methyl-N-(2-propynyl)-6-methylergoline-8 beta-carboxamide (LEK 8842) was chosen as the basic backbone of this study. The parent compound LEK 8842 showed strong alpha-adrenoceptor agonistic activity and partial 5-HT2 receptor agonistic activity, and its potency (pD2 = 6.41) was comparable with that of 5-hydroxytryptamine (5-HT, pD2 = 6.84) and noradrenaline (pD2 = 6.82). Hydrogenation of the double bond in the position 9,10 (LEK 8822) attenuated the potency (pD2 = 5.35) as well as the intrinsic activity on alpha-adrenoceptors and eliminated 5-HT2 receptor agonistic activity. LEK 8822 acted on the alpha-adrenoceptors not only as a partial agonist but also as a competitive antagonist of responses elicited by noradrenaline. When tested against 5-HT, LEK 8822 acted as an antagonist. Bromination in position 2 yielded the derivative LEK 8841 with no agonistic activity at concentrations up to 3 mumol/l, yet the affinity for 5-HT2 receptors and alpha-adrenoceptors was preserved. LEK 8841 was the only one that acted as pure simple competitive antagonist of responses elicited by 5-HT (pA2 = 7.93) and noradrenaline (pA2 = 6.45). Its activity was qualitatively similar to that observed with the 5-HT2/alpha-adrenoceptor antagonist ketanserin which was tested for comparison. Concerning selectivity for 5-HT2 receptors versus alpha-adrenoceptors, LEK 8841 proved to be more selective for 5-HT2 receptors than ketanserin. pA2 values for ketanserin antagonistic activity to 5-HT and to noradrenaline were 8.22 and 7.48, respectively. Finally, quaternization in the N(6) position (LEK 8827) almost completely eliminated affinity for 5-HT2 receptors and for alpha-adrenoceptors. This study has shown that relatively small modifications in the structure of the ergoline system led to pronounced changes in the affinity as well as intrinsic activity at both receptors studied.