Sympathomimetic effects of pancuronium bromide on the cardiovascular system of the pithed rat: a comparison with the effects of drugs blocking the neuronal uptake of noradrenaline

Bromide impairs the circadian clock and glycolytic homeostasis via disruption of autophagy in rat H9C2 cardiomyocytes

Background

Trace elements function as essential cofactors that are involved in various biochemical processes in mammals. Autophagy is vital for nutrient supplement, which is an important Zeitegber for the circadian homeostasis in heart. Here, we considered the possibility that autophagy, as well as the cardiomyocyte clock and glycolysis are interlinked. Detrimental effects were observed when cardiac system is exposed to bromine containing drugs. This study investigated the effects and mechanisms of bromide on the circadian clock and glycolytic metabolism of H9C2 cardiomyocytes.

Results

In the present study, bromide does not affect cell viability and apoptosis of H9C2 cardiomyocytes. Bromide dampens the clock and glycolytic (Hk2 and Pkm2) gene expression rhythmicity in a dose-dependent manner. Additionally, bromide inhibits autophagic process in H9C2 cardiomyocytes. In contrast, rapamycin (an autophagy inducer) dramatically restores the inhibitory effect of NaBr on the mRNA expression levels of clock genes (Bmal1, Cry1 and Rorα) and glycolytic genes (Hk2 and Pkm2).

Conclusions

Our results reveal that bromide represses the clock and glycolytic gene expression patterns, partially through inhibition of autophagy.

Haemodynamic differences between pancuronium and vecuronium in an experimental pig model

OBJECTIVE

To compare baseline cardiovascular function in anesthetised pigs using either pancuronium or vecuronium as a neuromuscular blocker.

STUDY DESIGN

Retrospective, non-randomized comparison.

ANIMALS

Norwegian Land Race pigs (Sus scrofa domesticus) weighing mean 42 ± SD 3 kg.

METHODS

One hundred and sixteen animals from four different research protocols premedicated with identical doses of ketamine, diazepam, atropine and isoflurane, and anaesthetised with pentobarbital, fentanyl, midazolam and N(2)O were arranged into three uniform groups with respect to neuromuscular blocking agent: pancuronium bolus of 0.063 mg kg(-1) followed by 0.14 mg kg(-1) hour(-1) (n = 54), low-dose vecuronium 0.4 mg kg(-1) /0.2 mg kg(-1) hour(-1) (n = 29) and high-dose vecuronium 0.6 mg kg(-1) /0.3 mg kg(-1) hour(-1) (n = 33).

RESULTS

The majority of cardiovascular parameters demonstrated no significant differences between groups. For heart rate, there was an overall group difference, p = 0.036. Dromotropy was low in the pancuronium group, with an increased normalised PR-interval compared to the high-dose vecuronium group, median 0.200 interquartile range (0.190, 0.215) versus 0.182 (0.166, 0.199), p < 0.05. Left ventricular compliance was increased in pancuronium-treated animals, demonstrated as a reduction in the nonlinear end-diastolic pressure volume relationship β compared to both vecuronium groups, 0.021 (0.016, 0.025) versus 0.031 (0.025, 0.046) and 0.031 (0.022, 0.048), p < 0.05. The linear end-diastolic pressure volume relationship EDPVR(lin) was reduced as well in the pancuronium group, compared to the low-dose vecuronium group, 0.131 (0.116, 0.169) versus 0.181 (0.148, 0.247), p < 0.05.

CONCLUSIONS

There are only minor haemodynamic differences when using pancuronium compared to vecuronium in the fentanyl-pentobarbital-midazolam-N(2)O anesthetised domestic pigs. Furthermore, increasing doses of vecuronium have minimal haemodynamic effects.

CLINICAL RELEVANCE

Experimental studies in pigs using either pancuronium or vecuronium as a neuromuscular blocking agent are comparable with regard to cardiac and haemodynamic performance.

Investigation of the cardiac effects of pancuronium, rocuronium, vecuronium, and mivacurium on the isolated rat atrium

BACKGROUND

Pancuronium, vecuronium, rocuronium, and mivacurium are nondepolarizing neuromuscular blocking agents that affect the cardiovascular system with different potencies. Their cardiovascular effects are clinically significant in the anesthetic management of patients, particularly those undergoing cardiac surgery.

OBJECTIVE

We aimed to compare the cardiac effects of these compounds, such as heart rate and developed force, in one species under identical experimental conditions in isolated rat atria.

METHODS

The left or right atria of rats were removed and suspended in organ baths. Pancuronium, vecuronium, rocuronium, or mivacurium were added cumulatively (10(-9)-10(-5) M) in the presence and absence of the nonselective β-blocker propranolol (10(-8) M) and the noradrenaline reuptake inhibitor desipramine (10(-7) M), and heart rate changes were recorded in spontaneously beating right atria. Left atrial preparations were stimulated by electrical field stimulation using a bipolar platinum electrode, and the effects of cumulative concentrations of these nondepolarizing neuromuscular blocking agents on the developed force in the presence and absence of propranolol (10(-8) M) and desipramine (10(-7) M) were recorded.

RESULTS

Pancuronium increased heart rate in a dose-dependent manner compared with the control group (P < 0.027). Vecuronium, rocuronium, and mivacurium also increased heart rate in a dose-dependent manner, but the changes were not statistically significant. Although propranolol decreased the pancuronium heart rate effect (P < 0.05), it did not change the heart rate effects with vecuronium, rocuronium, or mivacurium. Desipramine did not change the heart rate effects of vecuronium, rocuronium, mivacurium, or pancuronium. All 4 drugs increased developed force in a dose-dependent manner; the increases were significant at 10(-5) M concentration for pancuronium and at 10(-6) and 10(-5) M concentrations for vecuronium, rocuronium, and mivacurium (P < 0.038). These increases in developed force were abolished with the addition of propranolol. Desipramine did not change the developed force effects of any of the 4 drugs.

CONCLUSIONS

The heart rate effect of pancuronium and developed force effects of pancuronium, vecuronium, rocuronium, and mivacurium may occur via direct stimulation of β receptors. Although our investigation was an in vitro study, the effects found may be important especially under pathologic conditions, such as hypertension, in which patients usually use β-blocking agents, which cause β receptor upregulation.

Recruitment of functionally active heart beta2-adrenoceptors in the initial phase of endotoxic shock in pithed rats

A supersensitivity of the beta-adrenoceptor-mediated chronotropic response has been demonstrated in atria isolated from rats subjected to septic shock. Our study was undertaken to investigate whether bacterial endotoxin/LPS affects the increase in heart rate induced by beta-adrenoceptor agonists in the rat also in vivo. In pithed and vagotomized rats, the nonselective beta-adrenoceptor agonist isoprenaline (0.05-0.15 nmol/kg) and agonists at the high- and low-affinity state of beta1-adrenoceptors, that is, prenalterol (0.3-3 nmol/kg) and (+/-)-4-[3-[(1,1-dimethylethyl)amino]-2-hydroxypropoxy]-1,3-dihydro-2H-benzimidazole-2-one (CGP 12177; 3-6 nmol/kg), respectively, and at beta2-adrenoceptors, that is, fenoterol (1-5 nmol/kg), increased heart rate by 50 to 60 beats/min. Administration of LPS (0.4, 1, and 1.5 mg/kg), under continuous infusion of vasopressin, dose-dependently amplified the chronotropic response to isoprenaline, prenalterol, and fenoterol (by 80%, 50%, and 100%, respectively) but not to CGP 12177. The beta2-adrenoceptor antagonist erythro-(+/-)-1-(7-methylindan-4-yloxy)-3-isopropylaminobutan-2-ol (ICI 118551 0.1 mumol/kg) did not affect the chronotropic responses of isoprenaline, fenoterol, and prenalterol under non-endotoxic conditions, but abolished the potentiation of tachycardia produced by LPS (1.5 mg/kg). The beta1-adrenoceptor antagonist (+/-)-2-hydroxy-5-[2-[[2-hydroxy-3-[4-[1-methyl-4-(trifluoromethyl)-1H-imidazol-2-yl]-phenoxy]propyl]-amino]ethoxy]-benzamide CGP 20712A; 0.1 mumol/kg almost completely reduced the chronotropic effects of isoprenaline, fenoterol, and prenalterol both in control rats and in animals exposed to LPS (1.5 mg/kg). We conclude that LPS sensitizes cardiac beta-adrenoceptors by recruiting functionally active beta2-adrenoceptors, but the amplification of tachycardia occurs only when both beta1- and beta2-adrenoceptors are concomitantly activated. The pithed rat may serve as a model to examine the beta-adrenoceptor supersensitivity in vivo.

Fluorescent ligands, antibodies, and proteins for the study of receptors

Fluorescent molecules bound to receptors can show their location and, if binding is reversible, can provide pharmacological information such as affinity and proximity between interacting molecules. The spatial precision offered by visualisation transcends the diverse localisation and low molecular concentration of receptor molecules. Consequently, the relationships between receptor location and function and life cycles of receptors have become better understood as a result of fluorescent labeling. Each of these aspects contributes new insights to drug action and potential new targets. The relationships between spatial distribution of receptor and function are largely unknown. This is particularly apparent for native receptors expressed in their normal host tissues where communication between heterogeneous cell types influences receptor distribution and function. In cultured cell systems, particularly for G-protein-coupled receptors (GPCR), fluorescence-based methods have enabled the visualisation of the cycle of agonist-stimulated receptor clustering, endocytic internalisation to the perinuclear region, degradation of the receptor-ligand complex, and recycling back to the surface membrane. Using variant forms of green fluorescent protein (GFP), antibodies, or fluorescent ligands, it is possible to detect or visualise the formation of oligomeric receptor complexes. Careful selection of fluorescent molecules based on their spectral properties enables resonance energy transfer and multilabel visualisation with colocalisation studies. Fluorescent agonist and antagonist ligands are now being used in parallel with GFP to study receptor cycling in live cells. This review covers how labeling and visualisation technologies have been applied to the study of major pharmacologically important receptors and illustrates this by giving examples of recent techniques that have relied on GFP, antibodies, or fluorescent ligands alone or in combination for the purpose of studying GPCR.

Effects of methylenedioxymethamphetamine on noradrenaline-evoked contractions of rat right ventricle and small mesenteric artery

We have compared the effects of methylenedioxymethamphetamine (MDMA) and cocaine on contractions to noradrenaline in 1 Hz paced rat right ventricular strips, and in rat small mesenteric artery and aorta. Noradrenaline increased the force of contraction of 1 Hz paced ventricular strips with a pD(2) (-log EC(50)) of 5.64+/-0.07. Both cocaine (10 microM) and MDMA (10 microM) significantly increased the potency of noradrenaline to 6.31+/-0.11 and 6.42+/-0.13, respectively. However, in the presence of cocaine (10 microM) which increased the potency of noradrenaline to 6.78+/-0.15, MDMA (10 microM) no longer increased the potency of noradrenaline (pD(2) of 6.78+/-0.32). Likewise, following chemical sympathectomy, MDMA failed to increase the potency of noradrenaline. The potency of the agonist isoprenaline, which is not a substrate for the noradrenaline transporter, was not increased by either cocaine or MDMA. In rat small mesenteric artery, but not aorta, MDMA and cocaine significantly increased the potency of noradrenaline, but in the presence of cocaine, MDMA had no further effect. Hence, MDMA shares with cocaine an ability to potentiate the actions of noradrenaline, an action in the case of MDMA which may involve competitive blockade of the noradrenaline transporter, rather than simply displacement of noradrenaline. Since cocaine is linked to an increased incidence of myocardial infarction, these results may have implications in terms of cardiac morbidity of MDMA.

Sequential V(A)/Q distributions in the normal rabbit by micropore membrane inlet mass spectrometry

We developed micropore membrane inlet mass spectrometer (MMIMS) probes to rapidly measure inert-gas partial pressures in small blood samples. The mass spectrometer output was linearly related to inert-gas partial pressure (r(2) of 0.996-1.000) and was nearly independent of large variations in inert-gas solubility in liquid samples. We infused six inert gases into five pentobarbital-anesthetized New Zealand rabbits and used the MMIMS system to measure inert-gas partial pressures in systemic and pulmonary arterial blood and in mixed expired gas samples. The retention and excretion data were transformed into distributions of ventilation-to-perfusion ratios (V(A)/Q) with the use of linear regression techniques. Distributions of V(A)/Q were unimodal and broad, consistent with prior reports in the normal rabbit. Total blood sample volume for each VA/Q distribution was 4 ml, and analysis time was 8 min. MMIMS provides a convenient method to perform the multiple inert-gas elimination technique rapidly and with small blood sample volumes.

Investigation of the prejunctional alpha2-adrenoceptor mediated actions of MDMA in rat atrium and vas deferens

1. We have investigated the effects of methylenedioxymethamphetamine (MDMA, 'ecstasy') on peripheral noradrenergic neurotransmission in the rat. 2. In rat atrial slices pre-incubated with [3H]-noradrenaline and in the presence of desipramine (1 micronM) to prevent effects of MDMA on basal outflow of tritium, MDMA (10 micronM) significantly inhibited the release of tritium evoked by short trains of six pulses at 100 Hz every 10 s for 3 min. This effect did not occur in the presence of the alpha2-adrenoceptor antagonist yohimbine (1 micronM). 3. In epididymal portions of rat vas deferens in the presence of nifedipine (10 micronM), MDMA produced a concentration-dependent inhibition of single pulse nerve stimulation-evoked contractions with a pD2 of 5.88+/-0.16 (n=4). Inhibitory effects of MDMA were antagonized by the alpha2-adrenoceptor antagonist yohimbine (0.3 micronM), but not by the 5-hydroxytryptamine receptor antagonist cyanopindolol in a concentration (1 micronM) which markedly antagonized the inhibitory actions of the 5-HT-1 receptor agonist 5-carboxamidotryptamine. 4. In prostatic portions of rat vas deferens in the presence of cocaine (3 micronM), MDMA produced a concentration-dependent inhibition of single pulse nerve stimulation-evoked contractions with a pD2 of 5. 12+/-0.21 (n=4). In the absence of cocaine, only the highest concentration of MDMA (30 micronM) produced an inhibition, but the alpha2-adrenoceptor antagonist yohimbine (0.3 micronM) converted the response to MDMA from inhibition to potentiation of the stimulation-evoked contraction. 5. In radioligand binding studies, MDMA showed similar affinities for alpha2B, alpha2C and alpha2D-adrenoceptor sites, with pKi values of 5.14+/-0.16, 5.11+/-0. 05 and 5.31+/-0.14, respectively. 6 It is concluded that MDMA has significant alpha2-adrenoceptor agonist actions.

Side effects of nondepolarizing muscle relaxants: relationship to their antinicotinic and antimuscarinic actions

Since acetylcholine (ACh) is the 'master key' to different subtypes of nicotinic and muscarinic receptors, and muscle relaxants (MRs) available in clinical practice are structurally related to it, MRs may exert their unwanted effects through inhibition of these receptors. Since the subunit composition of nicotinic ACh receptors (nAChRs) of pre- and/or postsynaptic location and the binding potency of MRs to these and muscarinic receptors are different, a search for selective muscle nAChR antagonists without or with less side effects seems to be promising and important for clinical practice.

Left ventricular regional wall motion and haemodynamic changes following bolus administration of pipecuronium or pancuronium to adult patients undergoing coronary artery bypass grafting

The objective of this study was to compare the haemodynamic and myocardial effects of pipecuronium and pancuronium in patients undergoing coronary artery bypass grafting (CABG) during benzodiazepine/sufentanil anaesthesia. Twenty-seven ASA III-IV patients received lorazepam (1-3 mg) po and midazolam ( < 0.1 mg.kg-1) i.v. before induction of anaesthesia with sufentanil (3-8 micrograms.kg-1) was administered to facilitate tracheal intubation. According to random allocation, each patient received either pipecuronium (150 micrograms.kg-1) or pancuronium (120 micrograms.kg-1) after sternotomy but before heparinization. Mean arterial pressure, central venous pressure (CVP), pulmonary artery pressure (PAP), ST segment position and ECG (leads III, V5, AVF) were monitored continuously throughout the procedure. Thermodilution determinations of CO in triplicate were made immediately before, and at two and five minutes after muscle relaxant administration. Multiplane transoesophageal echocardiography (TEE, midpapillary short axis views of the left ventricle) images were continuously recorded from ten minutes before until ten minutes after muscle relaxant administration and graded by two experienced echocardiographic readers. Heart rate, MAP and CO increased after administration of pancuronium (by 13.6 beats.min-1, 10.8 mmHg and 1.0 L.min-1 respectively) but not after pipecuronium (P < 0.05). Evidence of myocardial ischaemia was not detected in any patients using ECG ST segment analysis or TEE assessment of left ventricular wall motion. We conclude that pancuronium caused increases in HR, MAP and CO but that neither pancuronium nor pipecuronium caused myocardial ischaemia.

Contribution of brain injury to hypertension following intravenously-administered pancuronium in rats

Abnormal hypertension sometimes occurs following intravenous administration (i.v.) of pancuronium in patients with brain injury. The present experiment was designed to determine whether brain injury contributes to the hypertensive response of i.v. pancuronium. Forty-six Wister strain rats were studied, of which 39 had induced brain injury at (a) upper pons (b) midbrain (c) thalamus region (excluding hypothalamus) and (d) cerebellum or a combination of these sites. The injury was made by single insertion of a 22 Gauge needle through the skull surface. The quantity of pancuronium solution administered i.v. in each case was 1.0 ml containing either 0.8 mg/kg or 8 mg/kg of pancuronium. Group A (n = 7) had no brain injury and the mean arterial pressure (MAP) did not change following i.v. administration of pancuronium. In Group B (n = 9) (a+b+c, 8.0 mg/kg) MAP rose from 90.9 +/- 15.4 to 102 +/- 22.0 mmHg and in Group C (n = 7) (a+b+c, 0.8 mg/kg) MAP rose from 148.4 +/- 13.3 to 160 +/- 14.4 mmHg. In Group D (n = 5) (b+c, 8.0 mg/kg) MAP remained unchanged. In Group E (n = 5) (a, 8.0 mg/kg) MAP rose from 130.3 +/- 18.7 to 146 +/- 27.6 mmHg and in Group F (n = 6) (a, 0.8 mg/kg) MAP rose from 129.7 +/- 15.6 to 135.8 +/- 13.8 mmHg. In Group G (n = 7) (d, 8.0 mg/kg) MAP remained unchanged. Since the MAP was elevated in only those groups that received injury in the upper pons, we concluded that injury in the upper pons can lead to hypertension following i.v. administration of pancuronium.

A comparison of pipecuronium with pancuronium on haemodynamic variables and plasma catecholamines in coronary artery bypass patients

Pipecuronium bromide, a new neuromuscular relaxant with steroidal structure, is devoid of effects on the autonomic nervous system and may be useful in patients where haemodynamic stability is mandatory. However, tracheal intubation may alter this haemodynamic profile. Therefore, we carried out a prospective double-blind study in 30 patients undergoing coronary artery bypass surgery with the purpose (1) of determining if intubation influenced the haemodynamic stability in patients paralyzed with pipecuronium and (2) of comparing plasma catecholamine concentrations after pipecuronium with those after pancuronium. Thirty patients were randomized into two groups receiving either pipecuronium 100 micrograms.kg-1 or pancuronium 150 micrograms.kg-1 after induction of anaesthesia with midazolam and fentanyl. Haemodynamic variables and plasma catecholamines were measured before and after induction, after the muscle relaxant three times and twice after intubation. After anaesthesia induction decreases in heart rate (HR), mean arterial pressure (MAP) and cardiac index (CI) were observed in both groups. These haemodynamic variables were unchanged after pipecuronium whereas after pancuronium HR increased from 53 +/- 11 b.min-1 to 64 +/- 9 b.min-1 after induction (P < 0.05) and CI from 2.5 +/- 0.5 L.min-1 to 3.0 +/- 0.8 L.min-1 (P < 0.05). Furthermore ECG signs of myocardial ischaemia appeared in four patients after pancuronium and the decay of plasma norepinephrine concentration was slower than with pipecuronium. We conclude that pipecuronium given after induction of anaesthesia is free of sympathomimetic or vagolytic activity and does not influence haemodynamic variables for up to ten minutes after tracheal intubation.

Cervico-thoracic epidural anaesthesia blunts pancuronium-induced increase in heart rate in humans

This study was conducted to evaluate the effects of cervico-thoracic epidural anaesthesia upon pancuronium-induced tachycardia in surgical patients. In the control (no blockade) group (n = 8) and the lumbar epidural group (n = 8), pancuronium produced significant increases in heart rate (P < 0.01 and P < 0.01, respectively) and no significant changes in mean arterial pressure. In the cervico-thoracic epidural group (n = 8), no increase in heart rate and a significant decrease in mean arterial pressure were seen following pancuronium. The lack of an increase in heart rate following pancuronium with cervico-thoracic epidural anaesthesia might be due to cardiac sympathetic denervation. The authors concluded that tachycardia after pancuronium administration was attenuated by cervico-thoracic epidural anaesthesia in humans and that the pancuronium-induced tachycardia seemed to be a cardiac sympathomimetic effect.

Cerebrovascular carbon dioxide reactivity and failure of autoregulation in preterm infants

Changes in cerebral blood flow velocity (CBFV) in response to a rise in arterial carbon dioxide tension (PaCO2) in 94 ventilated preterm infants were determined using Doppler ultrasound to assess whether the nature of this change might predict subsequent neurological injury. Concomitant changes in mean arterial pressure (MAP) were recorded. Both CBFV and MAP rose significantly in response to the rise in PaCO2, the response being significantly less in the first 24 hours. Analysis indicated that the change in CBFV in the first day of life in infants less than or equal to 30 weeks' gestation was dependent to a great extent on the concomitant change in MAP. Similar dependence also occurred after administration of pancuronium to infants whose CBFV response was previously independent of changes in MAP. This dependency lasted for the duration of paralysis. Changes in CBFV after a rise in PaCO2 did not predict subsequent neurological injury. The influence of pancuronium on cerebrovascular regulation warrants further study.

Comparison of the haemodynamic effects of pipecuronium and pancuronium during fentanyl anaesthesia

Haemodynamic variables were measured following administration of pipecuronium 70 micrograms.kg-1 and pancuronium 90 micrograms.kg-1 (approximately equivalent to 1.5 x ED95) in patients anaesthetised with fentanyl 50 micrograms.kg-1 and scheduled to undergo coronary artery bypass grafting. There were significant increases in heart rate (22%), mean arterial pressure (10%), cardiac index (16%), and the rate pressure product (35%) following administration of pancuronium. The absolute values of these parameters were, however, within acceptable clinical limits. Administration of pipecuronium produced minimal and insignificant changes in these parameters. Other measured or derived indices showed only small changes with both agents and these were generally insignificant. There were no incidences of significant bradycardia following pipecuronium administration. The results from the present study suggest that pipecuronium would have advantages for use in patients with significant cardiovascular disease.

Hemodynamic responses to pancuronium and vecuronium during high-dose fentanyl anesthesia for coronary artery bypass grafting

The hemodynamic and electrocardiographic (ECG) effects of pancuronium and vecuronium were compared during high-dose fentanyl anesthesia for coronary artery bypass grafting (CABG) surgery. Forty-eight morphine-scopolamine premedicated patients scheduled for elective CABG were anesthetized with fentanyl (100 micrograms/kg) in divided doses, and either of two muscle relaxants, pancuronium (n = 26; 0.10 mg/kg) or vecuronium (n = 22; 0.09 mg/kg). Hemodynamic data, blood gas samples, and ECG tracings were obtained at the following intervals: (1) control; (2) prior to intubation; (3) 1 minute after intubation; (4) prior to sternotomy; and (5) 1 minute after sternotomy. In the pancuronium group, heart rate (HR), cardiac index (CI), and rate-pressure product (RPP) were increased after induction of anesthesia and following intubation. Eleven patients (42.3%) displayed ischemic ST segment changes. Four patients in this group developed tachycardia and hypertension to an extent requiring pharmacological intervention. Vecuronium-treated patients displayed no increases in HR, MAP, and RPP, and a decrease in CI. Only one patient (5.6%) developed evidence of ischemic ECG changes. Four patients in the vecuronium group, all receiving preoperative beta-blocker therapy, became hypotensive and bradycardic after the induction of anesthesia. The present investigation confirms the increased incidence of myocardial ischemia during high-dose fentanyl-pancuronium anesthesia. Although vecuronium was associated with fewer myocardial ischemic changes, the occurrence of bradycardia and hypotension in some patients receiving preoperative beta-adrenergic blocking drugs remains a concern.

The effects of ageing on neuronal uptake of noradrenaline in the rat

We have examined the effects of ageing on the physiological function of the neuronal noradrenaline uptake system by comparing responses to cocaine in young adult (5 month) and aged (22 month) male Sprague-Dawley rats. In rat atria pre-incubated with [3H]-noradrenaline, cocaine (3-30 mumol/l) significantly augmented the 2 Hz stimulation-evoked release of noradrenaline in tissues from young but not from old rats. Cocaine (1 mg/kg) produced a greater increase of the pressor response to noradrenaline in young than in old pithed rats. Cocaine significantly increased the tachycardia to noradrenaline only in young pithed rats, but in old pithed rats the duration of the response to noradrenaline was significantly increased. It is concluded that ageing in the rat is associated with a decreased function of the neuronal noradrenaline uptake system, at least in the cardiovascular system.

QT interval of the ECG, heart rate and arterial pressure using five non-depolarizing muscle relaxants for intubation

The QT interval, heart rate and arterial pressure were measured during anaesthetic induction in 186 patients without cardiovascular diseases or any preoperative drugs. The study was randomized and double-blind. The patients were premedicated with either pethidine 1 mg/kg + atropine 0.01 mg/kg or with only pethidine 1 mg/kg i.m. Anaesthesia was induced with thiopental. After both types of premedication, either d-tubocurarine 0.5 mg/kg, alcuronium 0.3 mg/kg, pancuronium 0.1 mg/kg, vecuronium 0.1 mg/kg or atracurium 0.5 mg/kg was injected after thiopental. Laryngoscopy was performed 4 min after the relaxant. The control values of the QT intervals (mean value 433 ms, range of the mean values 422-453 ms), were comparable. After thiopental, the mean values in the groups were no longer in the normal range (less than 440 ms). After atropine, the values at 3 min were statistically significantly prolonged in the pancuronium, atracurium and alcuronium groups, but not in the other groups, when compared with the values after thiopental. In the absence of atropine, no statistically significant prolongation of the QT interval occurred. After intubation in the absence of atropine, the values were statistically significantly prolonged in the alcuronium, pancuronium, vecuronium and atracurium groups and in the presence of atropine in the atracurium group when compared with the preceding values. The QT intervals were prolonged only in relation to the increased heart rate. At 6.5 min, the values in all groups were decreased to about the same level as before intubation. The mean control values of the heart rate were between 80 and 90 b.p.m. in the atropine-treated groups and between 70 and 80 b.p.m. in the other groups.(ABSTRACT TRUNCATED AT 250 WORDS)

Positive inotropic and chronotropic effects of pancuronium and vecuronium in the canine blood-pefused papillary muscle and sinoatrial node preparations

The positive inotropic and chronotropic potencies of pancuronium (Pc) and vecuronium (Vc) were compared with developed tension of the isolated papillary muscle (DT) and sinoatrial rate of the sinoatrial node preparation (SAR). Both Pc and Vc caused dose-dependent positive inotropic and chronotropic effects. Pc showed much more potent effect than Vc on DT (0.1, 0.3 mg; P << 0.05) or SAR (0.03, 0.1, 0.3 mg; P << 0.05). DT and SAR were increased by Pc and Vc, and the increase in DT was inhibited by propranolol or tetrodotoxin. These results suggest that the cardiac effects of Pc or Vc may be mediated by release of norepinephrine from the synpathetic nerve endings.

Direct evidence that pancuronium and gallamine enhance the release of norepinephrine from the atrial sympathetic nerve by inhibiting prejunctional muscarinic receptors

The effect of different non-depolarizing muscle relaxants (gallamine, pancuronium, vecuronium, D-tubocurarine) on [3H]norepinephrine release in response to electrical stimulation was studied in isolated guinea-pig atrium. High pressure liquid chromatography combined with electrochemical and radiochemical detection revealed that the released radioactivity was mainly in the form of [3H]norepinephrine release. Oxotremorine, a pure muscarinic agonist, reduced the release of tritium. Gallamine and pancuronium, like atropine, prevented the inhibitory effect of oxotremorine. D-Tubocurarine and vecuronium had no such effect. These findings indicate that gallamine and pancuronium exert a presynaptic antimuscarinic, atropine-like effect, by inhibiting muscarinic receptors located on the axon terminals of sympathetic neurons thereby enhancing norepinephrine release. It is suggested that this phenomenon might play some role in tachycardia observed during surgical anaesthesia when gallamine or pancuronium have been administered.

Analysis of the alpha-adrenoceptor-mediated, and other, components in the sympathetic vasopressor responses of the pithed rat

The vascular receptors activated following sympatho-adrenal stimulation were determined by analysing the effects of 'selective' antagonists on the vasopressor response to spinal sympathetic nerve activation in the pithed rat. The net vascular response to adrenal stimulation was a balance between alpha-adrenoceptor-mediated vasoconstriction and beta-adrenoceptor-mediated vasodepression. Part of the alpha-adrenoceptor-mediated response was 'prazosin-sensitive' (alpha 1) and the remainder was abolished by rauwolscine (alpha 2). As with adrenal stimulation, direct sympathetic nerve stimulation of the vasculature evoked pressor responses which were partly resistant to prazosin. Rauwolscine only partly blocked the prazosin-sensitive component. Reserpine pretreatment led to smaller responses than prazosin plus rauwolscine. Thus, the response resistant to alpha-adrenoceptor antagonists could be mediated, in part, by adrenoceptors distinct from alpha-adrenoceptors, as currently defined. alpha, beta-Methylene ATP reduced the nerve-mediated pressor response after alpha-adrenoceptor blockade or reserpine pretreatment but not in drug-free controls. The results suggest that stimulation of the adrenal medulla can produce a vasopressor response which consists of summating alpha 1- and alpha 2-adrenoceptor-mediated components, and is identical to the effect of injected adrenaline. In contrast, the response to vasopressor nerve stimulation appears to be essentially mediated by alpha 1-adrenoceptors, with a facilitatory influence from alpha 2-adrenoceptors. A further response obtained after alpha-adrenoceptor blockade may contain a purinergic component and another which is adrenergic but not mediated by stimulation of alpha-adrenoceptors.

Circulatory effects of pancuronium and alcuronium in patients with coronary artery stenosis

Heart rate and systemic arterial blood pressure were recorded during induction of anaesthesia up to 9 min after endotracheal intubation in 92 patients scheduled for coronary artery bypass surgery, in order to study to what degree the circulatory response to induction of anaesthesia and intubation was modified by different relaxants. Pancuronium (pancuronium bromide) 0.1 mg X kg b.w.-1 and alcuronium (diallyl-nortoxiferine) 0.25 mg X kg b.w.-1 were randomly studied in 36 patients during induction with high-dose fentanyl and in 36 patients induced with thiopentone, diazepam, fentanyl and nitrous oxide. In patients given high-dose fentanyl anaesthesia, systolic blood pressure before, during and after intubation was significantly lower with alcuronium (P less than 0.01). The same difference between alcuronium and pancuronium was observed in balanced anaesthesia before endotracheal intubation. Induction of anaesthesia and intubation were followed by a moderate increase in heart rate, irrespective of the type of anaesthesia and relaxant. Subsequently, 20 patients (10 with high-dose fentanyl and 10 with balanced anaesthesia) were studied. They received pancuronium 0.05 mg X kg b.w.-1 + alcuronium 0.125 mg X kg b.w.-1. This mixture of relaxants produced an intermediate blood pressure response.

Experimental and clinical evaluation of neuromuscular blocking agents

Neuromuscular blocking agents can be evaluated in anesthetized cats, dogs, or rhesus monkeys using dose-response relationships to assess the degree of separation between neuromuscular blocking activity and effects on cardiovascular and autonomic systems. Histamine release can be studied in anesthetized dogs by establishing whether any induced hypotension is reduced by pretreatment with H1 and H2 receptor antagonists. In anesthetized cats, the role of the liver in metabolism is investigated after administration of the drug by the hepatic portal vein and determining whether this "first pass" effect through the liver reduces potency. The involvement of the kidneys in the elimination of the drug can be assessed by ascertaining whether or not the potency and duration of action are enhanced after bilateral renal ligation. In anesthetized man, the simultaneous measurement of the tetanic (50 Hz) and single twitch contractions of the adductor pollicis muscle of the hand has proved a valuable technique for the quantitative assessment of skeletal muscle relaxants. Furthermore, the tetanic response overcomes the relative insensitivity of the single twitch, and tetanic fade provides a measure of the effects of these drugs at presynaptic sites. Cumulative effects may be evident as a prolonged recovery after repeated dosage or after an infusion. The effectiveness of neostigmine as an antagonist should be investigated both from partial and complete block, and recovery of respiration should be compared with that of peripheral neuromuscular blockade.

Barrier pressure and muscle relaxants. Comparison of the effects of pancuronium and vecuronium on the lower oesophageal sphincter

The effects of pancuronium and vecuronium on the lower oesophageal sphincter pressure were studied in 24 healthy patients anaesthetised with 0.5% halothane in nitrous oxide and oxygen. Following pancuronium 0.1 mg/kg intravenously, there was a significant increase in barrier pressure from a control value of 2.0 (SEM 0.14) kPa to 3.0 (SEM 0.27) kPa 1 minute after injection (p less than 0.05). This increase was sustained throughout the 15 minute period of recording and was accompanied by a significant increase in heart rate (p less than 0.001). Following administration of vecuronium 0.1 mg/kg intravenously there was an initial modest, though not significant increase in barrier pressure. This increase was significant (p less than 0.05) at 15 minutes. There were no cardiovascular changes following vecuronium.

Muscarinic receptor inhibition and other effects of pancuronium in the rabbit ear artery preparation

The effect of pancuronium in the rabbit ear artery was investigated in order to measure the inhibition it produces at the prejunctional muscarinic receptor on sympathetic nerve endings in this tissue. Pancuronium (0.1-0.2 mmol/l) produced an enhancement of responses to transmural electrical stimulation but this effect was absent in experiments conducted in the presence of cocaine (10 mumol/l) suggesting that an inhibition of the uptake1 mechanism occurs with pancuronium in this tissue. Pancuronium (10 mumol/l) in the presence of cocaine (10 mumol/l) and yohimbine (1 mumol/l) caused a small transient increase in resting output of tritium from arteries preincubated with 3H-noradrenaline but did not affect stimulated output of tritium nor the perfusion pressure in perfused preparations. Pancuronium in the presence of cocaine or cocaine plus yohimbine caused a parallel shift of the concentration-response curve for the inhibitory effect of carbachol (CCh) on the increase in perfusion pressure induced by nervous stimulation. An Arunlakshana-Schild plot of the data was linear but the slopes of 0.92 and 0.95 respectively, were significantly different from unity (P less than 0.05). The calculated pKB value suggests that pancuronium has a different affinity for prejunctional muscarinic receptors on sympathetic nerve endings in this tissue compared to that previously reported in cardiac or ileal smooth muscle.

A comparison of the muscarinic antagonist actions of pancuronium and alcuronium

1 In the pithed rat, muscarine (2.5-10 microgram/kg i.v.) normally produced bradycardias, but tachycardias were seen in the presence of pancuronium (0.1-1.0 mg/kg i.v.) and alcuronium (0.1-5.0 mg/kg i.v.). 2 The tachycardia was probably a result of muscarinic receptor stimulation, because it was antagonized by atropine (10 microgram/kg i.v.) and pirenzepine (10-30 microgram/kg i.v.). The location of these muscarinic receptors is probably within the sympathetic ganglia since the tachycardias were inhibited by pretreatment with propranolol (1 mg/kg i.v.) or reserpine (5 mg/kg i.p. 24 h prior to study). 3 In the rat isolated atria preparation, pancuronium was 86 times more potent as an antagonist of the effects of muscarine than in the rat isolated superior cervical ganglion. The mechanism of action in both tissues may be non-competitive. 4 Pancuronium selectivity antagonized atrial inhibitory muscarinic responses compared to excitatory muscarinic responses in sympathetic ganglia in the rat.

A new non-depolarizing myorelaxant with high activity and specificity

The curare-like activity and mode of action of tercuronium (p,p"-bistriethylammonium-p-terphenyl dibenzen-sulphonate) have been investigated in experiments with cats, rabbits, mice and pigeons as well as with rat phrenic diaphragm preparations. The curare-like activity of tercuronium was higher than that of tubocurarine and was close to that of pancuronium bromide. The curare-like activity of tercuronium was higher than that of tubocurarine and was close to that of pancuronium bromide. The neuromuscular blocking doses (ED95) of tercuronium, (+)-tubocurarine and pancuronium in cats, for example, were 0.08 microM/kg, 0.4 microM/kg and 0.04 microM/kg respectively. The time of development and duration of action were similar to those of (+)-tubocurarine and pancuronium. Tercuronium is a nondepolarizing myorelaxant. In experiments with cats the antagonism of neostigmine (0.1 mg/kg) to tercuronium was more pronounced than in the case of (+)-tubocurarine, pancuronium or gallamine. Tercuronium affected neither the arterial pressure nor the heart rate when given in neuromuscular blocking doses. Tercuronium did not block transmission through autonomic ganglia and had no atropine-like action. Only a 10-fold increase in the dose of tercuronium produced the ganglion blocking effect in cats. Under artificial respiration, cats and rabbits tolerated tercuronium in a dose 200 times exceeding its myoparalytic dose. It is concluded that tercuronium is distinguishable from (+)-tubocurarine by its high neuromuscular blocking activity as well as by its specificity and more pronounced neostigmine antagonism.

The interaction of pancuronium with cardiac and ileal muscarinic receptors

The activity of pancuronium as a muscarinic antagonist was compared in atria from several species and in guinea-pig ileal longitudinal muscle. Pancuronium had a 20-fold greater affinity for muscarinic receptors mediating the negative inotropic response to carbachol (CCh) in the guinea-pig left atrium (pKB = 6.96) than for muscarinic receptors in guinea-pig ileal longitudinal muscle (pKB = 5.65). The greater affinity of pancuronium in the atria was not due to an interaction with noradrenergic neurones as pretreatment of atria with propranolol (3 microM) or of guinea-pigs with 6-hydroxydopamine (400 mg/kg total dose) failed to modify the degree of inhibition exhibited in atria. The affinities of pancuronium for muscarinic receptors mediating negative inotropic responses in the kitten left atrium or negative chronotropic responses in guinea-pig or rabbit right atria were not significantly different from that in the guinea-pig left atrium (P greater than 0.05) but the affinity of pancuronium for muscarinic receptors in ileal longitudinal muscle was significantly different (P less than 0.05) from all values obtained in the cardiac preparations suggesting differences in the binding of the antagonist in smooth and cardiac muscle. The A-S plot for pancuronium (0.27 microM-0.20 mM) as an antagonist of negative inotropic responses to CCH was non-linear, showing a flattening at the higher concentrations of pancuronium. This was not apparent in the A-S plot for the inhibition of tonic responses to CCh in ileal longitudinal muscle.

An examination of factors influencing adrenergic transmission in the pithed rat, with special reference to noradrenaline uptake mechanisms and post-junctional alpha-adrenoceptors

Adrenergic mechanisms were analysed in the pithed rat to determine to what extent the actions of drugs observed in vitro are relevant in situ. The drugs examined were those which are known to block the neuronal or extraneuronal uptake of noradrenaline (cocaine, desipramine and corticosterone) or to be antagonists at post and/or pre-junctional alpha-adrenoceptors (prazosin and yohimbine) together with the antidepressant, mianserin, which has been implicated in several of these actions. These drugs were tested against the arterial diastolic pressor, cardiac chronotropic and vas deferens responses to sympathetic nerve stimulation, to indirect sympathomimetics or to direct sympathomimetics, which were chosen according to whether they were substrates for noradrenaline uptake processes or selective between adrenoceptors. Pressor and cardiac responses to sympathetic nerve stimulation or to intravenous noradrenaline were potentiated by blockade of neuronal uptake but only the pressor effect of noradrenaline was potentiated by blockade of extraneuronal uptake. The effects of the antagonists suggested that the pressor effects of noradrenaline and of sympathetic nerve stimulation result from a combination of activation of alpha 1- and alpha 2-adrenoceptors, but that the effect of noradrenaline had a relatively greater contribution from the alpha 2-adrenoceptors. Mianserin was found to potentiate adrenergic responses at low doses, to produce limited antagonism at post-junctional alpha 1-adrenoceptors in high doses but to have no detectable effect at post-junctional alpha 2-adrenoceptors.

The factors influencing the time course of drug action at alpha-adrenoceptors: an investigation of the effects of clonidine in the pithed rat

1 The time courses of the pre- and post-junctional effects of clonidine were examined on heart rate and blood pressure and on the isometric tension responses of the vas deferens and anococcygeus in situ in the pithed rat. Plasma levels of clonidine were also monitored. 2 The time courses of the pre-junctional inhibition of sympathetic nerve mediated responses in all tissues monitored were related to the plasma levels of clonidine, but the degree of inhibition which was observed varied with the tissue and with the test stimulus employed. 3 The post-junctional agonist effects of clonidine, expecially at low doses, exhibited an initial 'peak' followed by a decline to a lower plateau. This decline of the response was not due to receptor desensitization but was related to a decline in the plasma clonidine level from an initially high value caused by injection of a bolus. 4 The factors determining the time course of drugs' effects in the preparation are discussed and it is concluded that pre- and post-junctional responses should be compared at a point in time after injection of the-drug, at which equilibration has occurred.

A comparison of the effects of pancuronium bromide and its monoquaternary analogue, ORG NC 45, on autonomic and somatic neurotransmission in the rat

1 Potentiation by pancuronium of the effects of adrenergic nerve stimulation, previously shown in cardiovascular tissues, was also found in rat anococcygeus and vas deferens, in vitro or in vivo. 2 In the pithed rat, in the presence of pancuronium, pre-junctional alpha-adrenoceptor-mediated feedback inhibition of cardiac sympathetic transmission was uncovered at relatively low stimulation frequencies by phentolamine or yohimbine. 3 The effects of pancuronium and its mono-quaternary analogue Org NC 45 on autonomic and somatic neuromuscular transmission were compared, in the pithed rat. Org NC 45 was less potent than pancuronium at blocking somatic neuromuscular transmission by a factor of 2.1, at blocking cardiac, parasympathetic transmission by a factor of 538 and at potentiating sympathetic transmission by a factor of 33.

The effects of dihydrochandonium and other chandonium analogues on neuromuscular and autonomic transmission

The muscle relaxant chandonium and four of its analogues have been assessed for neuromuscular, ganglion blocking and vagolytic activity in the chloralose-anaesthetized cat, for neuromuscular blocking activity in the chick isolated biventer cervicis and rat phrenic nerve-hemidiaphragm preparations, for muscarinic and histamine blocking activity in the guinea-pig isolated ileum preparation and for effects on adrenergic responses in the rat isolated vas deferens preparation. All five compounds produced neuromuscular block of rapid onset and short duration when given to cats in doses of 5–500 μg kg−1 and produced non-depolarizing competitive neuromuscular blockade in the isolated skeletal muscle preparations. Saturation of the 5–6 androstene bond to produce dihydrochandonium (HS692) resulted in a loss of potency by a factor of 0·5. The NN-diethyl analogue of dihydrochandonium (HS693) was about half as potent as HS692. The triethyl (HS704) and NN-diethyl (HS705) analogues of chandonium possessed one-tenth and one-fifth respectively of the muscle relaxant activity of chandonium. In cats, all compounds inhibited the bradycardia produced by vagal stimulation and by methacholine, the vagolytic effect of HS693 being particularly powerful and long-lasting. Although the compounds did not block the depressor response to methacholine in vivo, all the compounds inhibited responses to carbachol in the guinea-pig isolated ileum. However, from pA2 values the compounds were found to be 10–100 times more active at nicotinic than at muscarinic receptors. None of the compounds had histamine-blocking activity, ganglion-blocking activity, or actions on adrenergic responses.

An analysis of some factors influencing alpha-adrenoceptor feed-back at the sympathetic junction in the rat heart

1 The effects of the selective prejunctional alpha-adrenoceptor antagonist, yohimbine, on the cardioacceleration responses to sympathetic stimulation were examined in the pithed rat. 2 Yohimbine reversed the inhibitory effects of the alpha-adrenoceptor agonist, clonidine, on the stimulation-induced tachycardia. 3 Yohimbine failed to potentiate significantly responses to stimulation in the absence of clonidine when stimulation was applied at the optimal level for cardiac responses (C6-T1). 4 When the pithing rod electrode was moved to T2-T6, cardioaccelerator responses were smaller and yohimbine produced potentiation at frequencies of greater than or equal to 1 Hz. This potentiation was prejunctional since responses to exogenous noradrenaline (NA) were not increased by yohimbine. 5 In the presence of cocaine, potentiation by yohimbine could be shown at the lower frequency of 0.1 Hz. 6 The possible physiological significance of a negative feed-back effect of noradrenaline on cardiac sympathetic nerves is discussed.