H. Nagashima

Heterogeneity of presynaptic muscarinic receptors involved in modulation of transmitter release

In order to extend the characterization of muscarinic receptors at presynaptic sites their inhibitory effect on the stimulation-evoked release of [3H]noradrenaline and [3H]acetylcholine from different axon terminals was studied and the dissociation constants and potencies of different antagonists were estimated, in guinea-pig and rat. While oxotremorine reduced the release of [3H]acetylcholine and [3H]-noradrenaline in a concentration-dependent manner from different release sites (Auerbach plexus, noradrenergic neurons in the right atrium, cerebral cortex), McN-A 343, an M1 receptor agonist, enhanced their release evoked by field stimulation. When the inhibitory effect of oxotremorine on transmitter release was studied, pancuronium, pirenzepine and atropine were competitive antagonists of presynaptic muscarinic receptors located on the noradrenergic axon terminals of the atrium. While atropine and pirenzepine inhibited the muscarinic receptors of cholinergic axon terminals in the Auerbach plexus, pancuronium and gallamine had a very low affinity. Significant differences were found in the affinity constants of antagonists for muscarinic receptors located in the cholinergic axon terminals of Auerbach plexus and cerebral cortex, and noradrenergic axon terminals of the atrium. While atropine and pirenzepine exerted similar effects on these presynaptic sites, pancuronium, gallamine and (11-(2-[diethylamino)-methyl)-1-piperidinyl)acetyl)-5, 11-dihydro-6(1-pyrido(2,3-b)(1,4)-benzodiazepin-6-on) were much more effective on muscarinic receptors controlling acetylcholine release from the cerebral cortex and noradrenaline release from the heart. There was more than 100-fold (2.0 pA2 units) difference in affinities of these antagonists.(ABSTRACT TRUNCATED AT 250 WORDS)

Respiratory and circulatory effects of intravenous butorphanol and morphine

The respiratory and circulatory effects and other side effect liability of intravenous doses of 30 and 60 μg/kg butorphanol, 150 to 300 μg/kg norphine, and a placebo were investigated in a crossover double‐blind study.

Modulation of norepinephrine release by ATP-dependent K+-channel activators and inhibitors in guinea-pig and human isolated right atrium

OBJECTIVEnThe aim of this study was to show, whether ATP sensitive K+ channels (KATP channels), are involved in the modulation of norepinephrine (NE) release from the sympathetic nerves innervating the guinea-pig and human right atrium.nnnMETHODSnThe resting and stimulation-evoked release of [3H]norepinephrine ([3H]NE) was measured from the isolated guinea-pig and human right atrium and the effect of activators and inhibitors of ATP sensitive K+ channels was studied.nnnRESULTSnCromakalim (30-300 microM), a KATP channel-agonist decreased concentration-dependently the stimulation-evoked release of NE from the guinea-pig atrium, an effect, antagonized by glibenclamide, a KATP channel-antagonist (30 microM). Diazoxide (30-300 microM), another activator of the KATP channels reduced the resting release of NE, and also attenuated the evoked release at a single concentration (100 microM), and this latter action was also counteracted by glibenclamide (30 microM). Pinacidil, increased dose-dependently the resting and stimulation-evoked release of NE in a glibenclamide-sensitive manner and reversed the inhibitory effect of cromakalim (100 microM), suggesting that it acts as an antagonist. Glibenclamide (30-300 microM), by itself enhanced the stimulation-evoked release of [3H]NE, and also increased the resting release of NE. On the other hand, 5-hydroxydecanoate, an ischemia-selective inhibitor of cardiac KATP channels did not change NE release. Adenosine, (30-300 microM), an A1-receptor agonist, clonidine (3 microM), an alpha 2-adrenoceptor agonist and oxotremorine, a muscarinic receptor agonist (30 microM) all reduced the evoked release of [3H]NE, but these effects were not modified by glibenclamide (300 microM), indicating that neuronal adenosine (A1), adrenergic (alpha 2) and muscarinic (M3) receptors do not act on KATP channels. In the human right atrium, cromakalim, and diazoxide did not affect significantly the release of [3H]NE. However, glibenclamide (30-300 microM) and pinacidil (30-300 microM) enhanced dose-dependently the evoked-release of NE, and pinacidil also augmented the resting release.nnnCONCLUSIONSnOur results indicate that sympathetic nerve endings of the human and guinea-pig atrium are endowed with ATP-sensitive K+ channels. These channels responded to agonists and antagonists under the experimental conditions applied and they could modulate the release of NE thereby affecting the autonomic control of cardiac function under various physiological and pathophysiological conditions.

Modulation of stimulation-evoked release of newly formed acetylcholine from mouse hemidiaphragm preparation

SummaryA radioisotope method has been developed for measuring the stimulation-evoked release of acetylcholine without the use of cholinesterase inhibitors from the mouse hemidiaphragm preparation which had been loaded with 3H-choline. Evidence has been obtained that 3H-choline was taken up by and released from both innervated and non-innervated mouse hemidiaphragm preparations. However, it was released in the form of 3H-acetylcholine in response to electrical field stimulation only from the innervated preparations. Long lasting (51 min) S1 stimulation of the preparations exhausted the radioactive acetylcholine stores to the extent that S2 did not evoke any release of 3H. These data suggest that when the labelled acetylcholine stores become exhausted, the labelled choline, still present in the tissue, cannot be released by electrical stimulation. Tetrodotoxin (1 μmol/1) administration and Ca withdrawal inhibited, 20–100 μmol/l 4-aminopyridine enhanced the release of 3H-acetylcholine in response to electrical stimulation. Activation of the presynaptic muscarinic receptors by the agonist oxotremorine (50 μmol/l) decreased the liberation of 3H-acetylcholine. The muscarinic antagonist atropine (1 μmol/l) abolished the inhibitory effect of oxotremorine and by itself increased the evoked release of the newly formed 3H-acetylcholine. Adenosine (50 μgmol/l) reduced the evoked release of radioactivity. Theophylline (30 μmol/l) prevented the inhibitory effect of adenosine and itself enhanced the release. Xylazine (1 μmol/l), an alpha2-adrenoceptor agonist did not affect the release. It is concluded that the stimulation-evoked release of 3H-acetylcholine from the mouse phrenic nerve hemidiaphragm preparation preloaded with 3H-choline is derived from the motor nerves. The release of acetylcholine is modulated by activation of presynaptic muscarinic and adenosine receptors.

α2A subtype of presynaptic α2-adrenoceptors modulates the release of [3H]-noradrenaline from rat spinal cord

The modulation of noradrenaline (NA) release from rat spinal cord slices was investigated and the subtype of presynaptic alpha 2-adrenoceptors involved in the negative feedback modulation was characterized using in vitro perfusion experiments. Rat spinal cord slices were loaded with [3H]NA and the release of radioactivity at rest and in response to field stimulation was determined. The alpha 2-adrenoceptor agonists, clonidine and dexmedetomidine inhibited the stimulation-evoked release of NA from spinal cord slices, whereas alpha 2-adrenoceptor antagonists yohimbine and CH-38083 (7,8-(methylenedioxy)-14-alpha-hydroxyalloberbane HCI), enhanced it. ARC 239, a selective alpha 2B-antagonist, had no effect on the release. In contrast, BRL 44408 a selective alpha 2A-antagonist increased the release of NA. Our results indicate that the negative feedback modulation of NA release from noradrenergic fibres in the spinal cord is mediated via alpha 2A subtype of alpha 2-adrenoceptors.

Neuromuscular and cardiovascular effects of pipecuronium

Pipecuronium bromide (Arduan) is a bisquaternary, steroid-type neuromuscular blocking agent in clinical use in Eastern Europe. Before its introduction into clinical practice in the USA, in the first phase of this study the neuromuscular potency of pipecuronium was determined under “balanced” and enflurane anaesthesia by the cumulative log dose-response method in 30 patients each. In the second phase the intubation and onset times, clinical duration of the first and repeated doses, spontaneous recovery index, reversibility of its residual neuromuscular effect by an anticholinesterase and its effect on heart rate and blood pressure was compared with the same variables observed in patients, anaesthetized with identical techniques but who had received vecuronium or pancuronium. The neuromuscular potency of pipécuronium was greater under enflurane [ED95 = 23.6 ± 1.1 μg · kg−1 (mean ± SEM)] than under balanced (ED95 = 35.1 ± 17 μg · kg−1) anaesthesia. Pipecuronium was more potent than vecuronium under both balanced (ED95 = 45.8 μg · kg−1) and enflurane anaesthesia (ED95 = 27 A μg · kg−1). Following the administration of 2 × ED95 doses there were no clinically significant differences in the intubation or onset times of pipecuronium, vecuronium and pancuronium. Under balanced anaesthesia the clinical duration of 2 × ED95 dose of pipécuronium (110.5 ± 0.3 min) or pancuronium (115.8 ± 8.1 min) were similar and about three times longer than that of vecuronium (36.3 ± 2.1 min). The recovery indices of pipécuronium (44.5 ± 8.2 min) and pancuronium (41.3 ± 4.2 min) were also similar and about three times longer than that of vecuronium (14.3 ± 1.4 min). Residual neuromuscular block of the three muscle relaxants could be equally well reversed by anticholinesterases at the end of anaesthesia. The 2 × ED95 doses of pipécuronium or vecuronium had no significant effect on heart rate or blood pressure. Pancuronium increased heart rate by about 20 per cent. Pipecuronium is preferable to pancuronium for the production of muscular relaxation for relatively long operations, when it is desirable to avoid acceleration of heart rate.RésuméLe bromure de pipécuronium (Arduan) est un curare biquaternaire de type stéroïdien employé en Europe de l’Est. Nous avons mesuré quelques unes de ses propriétés avant d’en recommander l’usage clinique aux Etats-Unis. Dans un premier temps, nous avons déterminé sa puissance en comparant la réponse neuromusculaire au logarythme de la dose cumulative chez deux groupes de 30 patients. Nous avons établi que sa DE95 était de 23,6 ± 1,1 μg · kg−1 (moyenne ± erreur-type) sous anesthésie á l’enflurane, et de 35,l ± 17 μg kg−1 sous neurolepanesthésie tandis que ces deux valeurs étaient respectivement de: 27,4 μ-kg−1 et 45,8 μg · kg−1 pour le vécuronium. Dans un deuxième temps, nous avons établi quen présence de conditions anesthésiques identiques, l’injection d’une dose égale 2 × DE95 s’accompagnait de temps de latence avant le debut d’action et l’instauration de conditions propices à l’intubation virtuellement semblables pour le pipécuronium, le pancuronium et le vécuronium tandis que sa durée d’action s’etablissait dans l’ordre à 110,5 ± 0,3 min, 115,8± 8,1 min et 36,3 ± 2,1 min et son index de récupération à 44,5 ± 8,2 min, 41,3 ± 4,2 min et 14,3 ± 1,4 min pour ces mémes produits. A la fin de l’intervention, le bloc neuromusculaire residuel était aussi facile à contrer avec un inhibiteur de la cholinestérase quelque soit le myorelaxant employé. Le pipécuronium et le vécuronium à raison d’une dose égale à 2 × DE95 ne modifièrent ni la pression artérielle ni la fréquence cardiaque tandis que cette dernìere augmentait de 20 pour cent avec le pancuronium. Il semble done que si on veut utiliser un myorelaxant de longue durée sans accélérer le pouls, on doive préférer le pipécuronium au pancuronium.

Evaluation of Neuromuscular and Cardiovascular Effects of Two Doses of Rapacuronium (ORG 9487) versus Mivacurium and Succinylcholine

BACKGROUNDnThis study compares the neuromuscular blocking and cardiovascular effects of rapacuronium (ORG 9487), a new aminosteroid nondepolarizing muscle relaxant, to recommended intubating doses of succinylcholine and mivacurium.nnnMETHODSnAdult patients were randomized in an open-label fashion to receive 1-5 microg/kg fentanyl before 1.5 mg/kg propofol induction followed by 1.5 or 2.5 mg/kg rapacuronium, 1.0 mg/kg succinylcholine, or 0.25 mg/kg mivacurium (i.e., 0.15 mg/kg followed by 0.1 mg/kg 30 s later).nnnRESULTSnPatient neuromuscular blockade status was monitored by measuring the train-of-four response to a supramaximal stimulus at the ulnar nerve every 12 s. Percentage of the first twitch of the train-of-four (T1) at 60 s was similar in patients receiving 1.5 mg/kg rapacuronium, 2.5 mg/kg rapacuronium, and succinylcholine and was significantly less than in patients in the mivacurium group (26, 16, and 18%, respectively, vs. 48%; P < 0.01). Times to 80% T1 depression were also similar among patients in the 1.5 mg/kg rapacuronium, 2.5 mg/kg rapacuronium, and succinylcholine groups and significantly longer in the mivacurium group (62, 54, and 54 s, respectively, vs. 112 s; P < 0.01). Clinical duration was longer in all groups compared with the succinylcholine group; however, clinical duration in the 1.5 mg/kg rapacuronium group was shorter compared with the mivacurium group (15 vs. 21 min, respectively; P < 0.01). Heart rate changes were mild in the 1.5 mg/kg rapacuronium, succinylcholine, and mivacurium groups. The patients in the 2.5 mg/kg rapacuronium group had significantly higher heart rates compared with patients in the mivacurium group. No differences were found in blood pressure changes among patients in the four groups.nnnCONCLUSIONSnRapacuronium, 1.5 and 2.5 mg/kg, produced neuromuscular blockade as rapidly as succinylcholine and significantly faster than mivacurium. Although succinylcholine continued to show the shortest duration, 1.5 mg/kg rapacuronium used a rapid onset and a relatively short duration and may be considered an alternative to succinylcholine.

Effects of adenosine on norepinephrine and acetylcholine release from guinea pig right atrium: Role of A1-receptors

The effect of adenosine or its stable analogues (2-chloroadenosine, CADO: 5-N-ethyl-carboxamidoadenosine, NECA; and N6-cyclopentyladenosine, CPA) and a non-selective A1 and A2-receptor antagonist, 8-phenyltheophylline (8-PT), or an A1-receptor antagonist, 8-cyclopentyl-1,3-dipropylxanthine (DPCPX), on the stimulation-evoked release of [3H]norepinephrine ([3H]NE) and [3H]acetylcholine ([3H]ACh) from the isolated guinea pig right atrium was investigated. Adenosine and its stable analogues (CADO, NECA and CPA) inhibited the stimulation-evoked release of [3H]NE in a concentration-dependent manner. The order of potencies was CPA > NECA > CADO > adenosine. CGS 21680 (30 nM), an A2a receptor agonist, failed to affect the release. The inhibitory effect of adenosine and CADO on [3H]NE release was competitively antagonized by 8-PT. DPCPX also prevented the effect of adenosine (Kd = 5.2 nM) and CADO (Kd = 3.3 nM). The Kd value of 8-PT was 0.40 microM for the antagonism of CADO and 0.51 microM for the antagonism of adenosine. When the negative feedback modulation of NE release was inhibited by idazoxan, the inhibitory effect of adenosine and CADO on [3H]NE release was more pronounced. Under this condition DPCPX (10 nM) prevented the inhibitory effect of CADO, indicating that A1-purinoceptors are involved in this action. The release of [3H]NE is tonically modulated by ACh release from the vagal nerve endings, as evidenced by the finding that 4-diphenylacetoxy-N-methyl-piperidine methiodide (4-DAMP), a M3-subtype selective muscarinic receptor antagonist, and atropine significantly enhanced the release of NE. Adenosine, its stable analogues (CADO and NECA), and 8-PT inhibition was eliminated by atropine, adenosine and CADO did not have any effect on [3H]ACh release. Quinpirole, a selective D2-receptor agonist, and neuropeptide Y (NPY) failed to affect the release of ACh. However, atropine and 4-DAMP, a selective M3-receptor antagonist, significantly enhanced the stimulation-evoked release of [3H]ACh. These findings indicate that there are no presynaptic heteroceptors (adenosine, D2, and NPY) on the vagal nerve endings of the guinea pig right atrium. It is concluded that the sympathetic nerve endings of the guinea pig right atrium are equipped with A1-, subclass of purinoceptors and alpha 2B-, and muscarinic (M3)-receptors. Cholinergic vagal nerve endings in the heart are only equipped with muscarinic autoreceptors. Therefore, adenosine liberated during hypoxia inhibits NE release from the cardiac sympathetic nerve and thereby protects against tachyarrhythmia caused by myocardial hypoxia. In contrast, adenosine does not inhibit the vagal innervation of the right atrium.

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.

Electrochemical determination of histamine derivatized with o-phthalaldehyde and 2-mercaptoethanol

High-performance liquid chromatography coupled with electrochemical detection was used to determine histamine following precolumn derivatization with o-phthalaldehyde (OPA) and 2-mercaptoethanol. The isoindole derivative which is obtained as reaction product was electrochemically active at a moderate potential (peak potential +0.4 V). Direct oxidation of histamine required a much higher potential (peak potential +1.05 V) and was of no practical use. No electrochemical signal was observed for the reaction product of histamine with OPA. Changing the pH of the mobile phase had little effect on the electrochemical response of the isoindole derivative of histamine, which was well separated from analogous derivatives of methylated histamines, mono- and polyamines and amino acids by isocratic elution from a reversed-phase column. An example of a practical application of the method to the estimation of histamine in rat brain is presented.