The effect of beta-adrenoceptor blocking agents, with differing ancillary properties, on the arrhythmias resulting from acute coronary artery ligation in anaesthetized rats

Comprehensive phytochemical profiling of American ginseng in Jilin province of China based on ultrahigh-performance liquid chromatography quadrupole time-of-flight mass spectrometry

American ginseng (AG), the underground part of Panax quinquefolium L., is composed of four morphological regions, including main root (MR), lateral root (LR), fibrous root (FR), and rhizome (RH). In the clinical, MR is the main medicinal region, other regions are rarely attention. Aiming at revealing the chemical composition of AG and making better use of AG, screening analysis and metabolomic analysis were both performed to profile MR, LR, FR, and RH. First, in the systematical screening analysis, a total of 134 compounds (including 122 shared components) with various structural patterns were identified and tentatively characterized. The results indicated that the phytochemicals with various structural types were rich in MR, LR, FR, and RH. Second, 6, 4, 8, and 11 chemical markers were identified from MR, LR, FR, and RH, respectively. Seven triterpene saponins (protopanaxatriol, quinquenoside R1 , ginsenoside Rc, Rk1 , Rg1 , Re, and vinaginsenoside R1 ) might be used for rapid differentiation of four morphological regions. This comprehensive profile study of metabolites illustrated the similarities and differences of phytochemicals in four morphological regions of AG. The results could be used for the quality control of AG and furnish a basis for the further development and utilization of AG sources.

Rat Models of Ventricular Fibrillation Following Acute Myocardial Infarction

A number of animal models have been designed in order to unravel the underlying mechanisms of acute ischemia-induced arrhythmias and to test compounds and interventions for antiarrhythmic therapy. This is important as acute myocardial infarction (AMI) continues to be the major cause of sudden cardiac death, and we are yet to discover safe and effective treatments of the lethal arrhythmias occurring in the acute setting. Animal models therefore continue to be relevant for our understanding and treatment of acute ischemic arrhythmias. This review discusses the applicability of the rat as a model for ventricular arrhythmias occurring during the acute phase of AMI. It provides a description of models developed, advantages and disadvantages of rats, as well as an overview of the most important interventions investigated and the relevance for human pathophysiology.

Participation of central and peripheral kappa 1 and kappa 2 opioid receptors in arrhythmogenesis

1. The kappa 1 and kappa 2 opioid receptor agonists U-62066 (8 mg/kg, i.p.) and (-)-bremazocine (0.7 mg/kg, i.v.), respectively, both exhibit anti-arrhythmic properties against adrenaline-induced dysrhythmias in rats. 2. In contrast, (+)-bremazocine has no effect on adrenaline-induced dysrhythmias. 3. The kappa 1 opioid receptor agonists U-50488 (110 nmol) and [D-Ala2]-dynorphin A (20 nmol) and the kappa 2 opioid receptor agonist (-)-bremazocine (30 nmol) exhibit pro-arrhythmic properties following intracerebroventricular administration. 4. Prior administration of the kappa opioid receptor antagonist nor-binaltorphimine doses i.c.v. (14 nmol), i.p. (10 mg/kg), completely abolishes the pro-arrhythmic (BNI, i.c.v., 14 nmol) as well as anti-arrhythmic (BNI, 10 mg/kg, i.p.) effects of the kappa opioid receptor agonists. 5. Neither hexamethonium (10 mg/kg, i.v.) nor atropine (1 mg/kg, i.v.) have any effect on the anti-arrhythmic actions of the kappa 1 opioid receptor agonist U-62066 following systemic administration. 6. It is suggested that the anti-arrhythmic effects of U-62066 and (-)-bremazocine are associated with the activation of peripheral kappa opioid receptors and do not depend on the activation of kappa opioid receptors in the autonomic nervous system.

Change in opioid peptide level in the heart and blood plasma during acute myocardial ischaemia complicated by ventricular fibrillation

1. The influence of acute myocardial ischaemia (AMI) complicated by ventricular fibrillation (VF) on opioid peptide level in myocardium and blood plasma of rats has been studied. 2. Leu-enkephalin level in myocardium of rats with AMI and VF has been found to be significantly lower than in animals with AMI but without VF. 3. Met-enkephalin level has been found to be significantly increased in both animals with VF and without it. We have not found a significant difference in met-enkephalin level in myocardium of animals with VF and without it. 4. AMI was induced to increase the enkephalin and beta-endorphin level in blood plasma of all the animals, whether VF had occurred or not. 5. Preliminary administration of D-Ala2,Leu5,Arg6-enkephalin, a synthetic analogue of leu-enkephalin, has prevented a decrease of ventricular fibrillation threshold in experimental coronary occlusion. 6. The obtained results allow us to conclude that enkephalins of myocardium but not opioid peptides of blood plasma play an important role in VF occurrence.

Mechanisms underlying the antiarrhythmic properties of beta-adrenoceptor blockade against ischaemia-induced arrhythmias in acutely prepared rats

1. The mechanism underlying the limited antiarrhythmic effects of beta-adrenoceptor blocking agents against occlusion-induced arrhythmias in acutely prepared, pentobarbitone-anaesthetized rats has been investigated. 2. Atenolol, ICI 111,581 and propranolol were given at low, medium and high doses calculated to shift dose-response curves to exogenous agonists by factors of 10-30, 100-300 and 1000-3000, respectively. 3. Arrhythmias, blood pressure, heart rate, ECG changes and serum K+ were measured. 4. Antiarrhythmic activity was seen with beta-blocker treatment. This was minimal with atenolol (0.1, 1 and 10 mg kg-1) and only statistically significant with the highest dose of ICI 111,581 (5 mg kg-1), and propranolol (10 mg kg-1). 5. Treatment with beta-adrenoceptor blockers elevated serum potassium concentrations, as compared with saline controls, especially when measured at 30 min post-occlusion. 6. Only ICI 111,581 (5 mg kg-1) and propranolol (1 and 10 mg kg-1) prolonged P-R interval. 7. In order to evaluate possible mechanisms of antiarrhythmic action, attempts were made to correlate antiarrhythmic activity with beta-blockade, serum potassium concentrations, and/or with changes in the P-R interval of the ECG. 8. Reductions in arrhythmias did not correlate well with presumed beta-blockade. Better correlation was obtained with elevations of serum potassium concentration, and with prolongation of P-R interval (a presumed Class I antiarrhythmic action). 9. These results suggested that antiarrhythmic effects of adrenoceptor blocking agents in acutely-prepared anaesthetized rats, subjected to occlusion of a coronary artery, are unrelated to cardiac beta-blockade. The limited antiarrhythmic effects which were observed could be attributed to elevations in serum potassium concentration (due to peripheral beta-blockade) and/or possible Class I antiarrhythmic actions.

Effects of morphine on catecholamine release and arrhythmias evoked by myocardial ischaemia in rats

The effects of morphine (10 mg kg-1 i.p.) on haemodynamics, arrhythmias and plasma and myocardial catecholamines (CA) were studied after coronary artery occlusion in anaesthetized rats. Myocardial intraneuronal CA were assessed histofluorimetrically and CA concentrations measured by high performance liquid chromatography. Morphine increased blood pressure, presumably due to higher plasma noradrenaline (NA) concentrations found in morphine-treated rats. Morphine increased the area of catecholamine-containing fluorescing neurones in the myocardium (as a percentage of total field area) 60 min after sham-operation (0.87 +/- 0.07%) or occlusion (0.57 +/- 0.05%) compared to untreated animals (0.67 +/- 0.06 and 0.38 +/- 0.03% respectively). Tissue NA content was not significantly affected by coronary occlusion and/or morphine within the first 60 min. Morphine had no effect on ischaemia-induced arrhythmias. Whether the higher intraneuronal NA content following morphine resulted from reduced central sympathetic outflow to the heart, presynaptic inhibition of NA release, or increased uptake due to higher plasma concentrations is unclear. Ischaemia-induced local NA release appears independent of these mechanisms, as it was unaffected by morphine.

Pharmacokinetics and antiarrhythmic activity of ajmaline in rats subjected to coronary artery occlusion

The pharmacokinetics and the antiarrhythmic action of intravenous ajmaline were investigated in anaesthetized rats subjected to coronary artery occlusion. Ajmaline (0.125-2 mg kg-1, i.v. given just after occlusion) suppressed arrhythmias in a dose-dependent manner, judged by the reduction of premature ventricular complexes. The incidence of malignant arrhythmias (ventricular tachycardia and fibrillation) was preferentially suppressed at the higher doses of ajmaline (1 and 2 mg kg-1). Coronary occlusion induced a change in pharmacokinetics of ajmaline (2 mg kg-1) and its total body blood clearance was significantly decreased from 56.6 ml min-1 kg-1 in sham-operated rats to 43.1 ml min-1 kg-1 in rats after coronary occlusion. Ajmaline exhibited a significantly increased negative dromotropic action (increased PQ interval) in rats after coronary occlusion compared with that in sham-operated rats. The difference seems to be due to the pharmacokinetic change since the concentration-effect relationship was similar in the two groups of rats. We suggest that the measurement of drug levels is important in the assessment of antiarrhythmic agents.

Effects of sotalol, (-)-propranolol and prazosin on reperfusion-induced arrhythmias and increased cardiac norepinephrine release

The pharmacological actions of sotalol, (-)-propranolol and prazosin on norepinephrine (NE) concentration and creatine kinase (CK) activity in the coronary sinus blood of the ischemic heart were studied in open-chest dogs. A 60 min occlusion of the left anterior descending coronary artery was followed by a reperfusion period of 30 min. In saline-treated dogs, a significant increase in coronary sinus NE concentration occurring 30 s after the onset of reperfusion was followed by a rapid decrease to the initial value within 15 min. CK activity increased gradually and continuously starting 5 min after the beginning of reperfusion. A good correlation (r = 0.9, n = 8, P less than 0.05) was obtained in saline-treated dogs when the calculated slope of the time-activity curves for CK release was plotted against the corresponding peak concentration of NE. The increase in coronary sinus NE concentration upon reperfusion was accompanied by an increased arrhythmic ratio. Sotalol (5 mg/kg i.v.) diminished the increase in coronary sinus NE concentration along with a significant decrease in the arrhythmic ratio. The administration of either (-)-propranolol (0.1 mg/kg i.v.) or prazosin (1 mg/kg i.v.) did not significantly affect the increase in coronary sinus NE concentration. The arrhythmic ratio was significantly reduced by prazosin but not by (-)-propranolol. The rise in coronary sinus CK activity was significantly diminished in the presence of either sotalol, (-)-propranolol or prazosin. These results suggest that the occurrence of severe ventricular arrhythmias upon reperfusion may be related to the action of the increased myocardial NE on the cardiac alpha-adrenoceptors. The increased coronary sinus CK activity suggests that increased cardiac sympathetic activation may accelerate or aggravate the myocardial damage. We conclude that the antiarrythmic effect of sotalol may be due at least in part to its inhibitory action on the release of cardiac NE upon reperfusion.

The effects of ablations in the central nervous system on arrhythmias induced by coronary occlusion in the rat

The role of the central nervous system (CNS) in arrhythmogenesis in the 4 h period following occlusion of a coronary artery was investigated in rats by use of CNS ablations and other procedures. Ablations in the CNS included pithing, spinalization and decerebration combined with acute and chronic surgical preparation and noradrenaline/adrenaline infusions. All procedures involving acute surgery reduced the incidence and severity of the arrhythmias induced by occlusion. Such reductions were most marked in the second (0.5-4 h post-occlusion) arrhythmic period. The observed reductions in arrhythmias could not be explained in terms of involvement of the CNS or adrenoceptor activation. When circulating leucocytes, platelets and serum potassium were measured in a group of pithed rats before and after occlusion, reduced levels (20-50%) of both leucocytes and platelets occurred while serum potassium levels rose by 50-100%. Arrhythmias following coronary occlusion may depend in part on factors in the blood such as leucocytes, platelets and serum potassium and these factors may be altered by acute surgery.

The effects of metoprolol and dazmegrel, alone and in combination, on arrhythmias induced by coronary artery occlusion in conscious rats

The effects of metoprolol and the thromboxane synthetase inhibitor dazmegrel, alone and in combination, were examined in a model of coronary artery occlusion in conscious rats. In a dose (2 mg kg-1), intravenously, that resulted in a marked bradycardia (of 50-80 beats min -1) metoprolol did not influence the incidence or severity of the ventricular arrhythmias that occur in the first 20 min following occlusion, nor did it improve survival (assessed at both 20 min and 16 h). In a dose (5 mg kg-1), intravenously, that in another conscious rat model involving tissue hypoperfusion inhibited thromboxane production, dazmegrel also did not modify ischaemic arrhythmias or survival. In contrast, metoprolol and dazmegrel (2 mg kg-1 and 5 mg kg-1 i.v.) when given together prior to coronary artery occlusion, produced a significant reduction in mortality both at 20 min and 16 h (e.g. from 60-75% in the control, metoprolol alone and dazmegrel alone groups and only 25% in the combined-treatment group). This was due to a decrease in the incidence of terminal ventricular fibrillation. The results suggest that a combination of beta-adrenoceptor blocking drug with a drug that inhibits thromboxane synthesis may offer more protection against ischaemia-induced ventricular fibrillation than either drug used alone. They suggest a role for both catecholamines and thromboxane in the genesis of ischaemia-induced ventricular fibrillation.

The effects of the combined administration of beta-adrenoceptor antagonists and non-steroidal anti-inflammatory drugs on ligation-induced arrhythmias in rats

Pretreatment of anaesthetized rats with intravenously administered beta-adrenoceptor antagonists or non-steroidal anti-inflammatory drugs (NSAIDs) reduced the incidence and severity of ventricular arrhythmia which resulted from acute coronary artery ligation. The beta-adrenoceptor antagonists preferentially suppressed the immediate (Phase 1A) arrhythmia while the NSAIDs suppressed the delayed (Phase 1B) arrhythmias. Combined administration of beta-adrenoceptor antagonists and the NSAIDs produced a more pronounced antiarrhythmic effect than either of the drugs alone.

Antifibrillatory properties of alinidine after coronary artery occlusion in rats

Ligation of the left anterior descending coronary artery was performed in open-chest anaesthetized rats and mortality as well as changes in ECG were evaluated for 30 min thereafter. Saline or drugs were administered 15 min prior to ligation. In the control group, following a 4 min lag period ventricular arrhythmias as single ectopic beats, ventricular tachycardia and ventricular fibrillation (VF) appeared, reaching a maximum between 10 and 20 min and disappearing after 30 min. Mortality (40% in the control group) coincided with the period of maximal arrhythmias, with VF more common in animals that died than in those surviving. Alinidine, a drug which reduces sino-atrial rate specifically but has no conventional antiarrhythmic properties, reduced mortality and VF. By means of order statistics the quantity 'risk of death' was used for evaluation of drug effects, considering incidence of death and VF as well as duration of VF. This quantity was reduced in correlation with the dose of alinidine (1-6 mg/kg i.v.) and in correlation with the reduction of heart rate. Mexiletine, an antiarrhythmic drug with membrane-depressant properties, also reduced the 'risk of death' dose dependently (1-10 mg/kg i.v.), but there was no correlation with a decrease in heart rate. It is suggested that alinidine reduced 'risk of death' by means of a reduced oxygen demand due to a decrease in heart rate.

The effects of timolol on arrhythmias and prostanoid release during canine myocardial ischaemia and reperfusion

Timolol (50 micrograms kg-1), administered intravenously to chloralose-anaesthetized open-chest greyhounds 30 min prior to occlusion of the left anterior descending coronary artery, reduced heart rate and mean arterial blood pressure. This dose caused a 20 fold increase in the dose of isoprenaline required to increase heart rate by 25 beats min-1. During the first 30 min of myocardial ischaemia the number of extrasystoles in the timolol-treated dogs (327 +/- 179) was less than in the control group (888 +/- 168) and none of the dogs that received timolol fibrillated. The haemodynamic changes induced by coronary artery occlusion (decreased cardiac output and stroke volume, increased peripheral vascular resistance) were similar in both control and timolol-treated dogs as were the increases in PCO2 and decreases in PO2 and pH in blood draining from the ischaemic myocardium. Timolol did not alter the release during myocardial ischaemia, of either thromboxane B2 or prostacyclin (measured as 6-keto PGF1 alpha). Reperfusion-induced ventricular fibrillation occurred in 7 out of 8 control dogs and in 5 out of 10 timolol-treated dogs. The overall survival following occlusion and reperfusion was improved by 10% to 50% by timolol.