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Results for “Hexamethonium Compounds”

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At least 19 recordsLinked to original sources
PubMed1977

Reexamination of carbodiimide as a possible affinity label for the acetylcholine receptor at the frog neuromuscular junction.

The effects of water-soluble carbodiimide were examined at the frog neuromuscular junction. Acetylcholine sensitivity was measured using a fluid electrode technique and intracellular recording of miniature end-plate potentials. The carbodiimide blocked synaptic sensitivity by a reversible, curare-like action. Irreversible blockade was also observed, probably due to covalent binding. The conditions of reaction and irreversibility suggest that several different residues may be attacked. The inability of cholinergic antagonists to protect the receptor from attack indicates that nonspecific sites, and not the acetylcholine binding site, are involved.

Acetylcholine↗
PubMed1991

Effect of an anticholinesterase compound on the ultrastructure and function of the rat blood-brain barrier: a review and experiment.

Soman, an organophosphorous irreversible inhibitor of acetylcholinesterase, was studied for its effect on the rat blood-brain barrier (BBB) during the first 24 h of intoxication. Young adult male Sprague-Dawley rats, injected with Evans blue-dye and surviving a subsequent single convulsive dose of soman (114 micrograms/kg, 0.9LD50), presented focal and diffuse penetration of dye in areas of brain normally considered protected by the BBB. Invasion was widest during the first hour when signs of excitation, respiratory distress and convulsions peaked and was absent at 24 h. During this time period, cholinesterase inhibition, as measured by enzyme assay, persisted in brain and blood at 10% and 6% of control values respectively. Brains of nonconvulsing animals and animals pretreated with nembutal (45 mg/kg, I.P.) or with diazepam (10 mg/kg, I.P.) were free of extravasated dye. A ranking of dye-breached brain areas suggested that cerebellar and cerebral cortex were most frequently involved while brain stem was rarely stained. Ultrastructural analysis of breached areas with horseradish peroxidase as a tracer molecule, revealed that the probable subcellular mechanism of the induced breach was enhanced vesicular transport, a mechanism similarly described for seizure. Consequences of the breach were emphasized with the detection of significantly elevated levels of an exogenously administered quaternary compound, 3H-hexamethonium. These findings present additional evidence that an anticholinesterase-induced breach of the rat blood-brain barrier is convulsive dependent, demonstrates BBB mechanisms similar to that of seizure, and can allow CNS penetration of blood-borne drugs and circulatory proteins that normally would be slowed or excluded by an intact BBB.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1979

Toluene di-isocyanate-induced asthma. I. Reactions to TDI, MDI, HDI and histamine.

A group of twenty four workers handling di-isocyanates and with respiratory disease were investigated by occupational-type bronchial provocation tests for sensitivity to toluene di-isocyanate (TDI), to which all were exposed, and to diphenylmethane di-isocyanate (MDI) and hexamethylene di-isocyanate (HDI). Sixteen gave asthmatic reactions to TDI and eight of these also reacted to MDI. Four of the eight TDI and MDI reactors had histories of exposure only to TDI, and of them two reacted also to HDI. Of nine subjects tested with HDI, three gave asthmatic reactions, and all three also reacted to TDI and MDI. Thus reactions to MDI and HDI were elicited only in the TDI reactors. The possibility of specific sensitivity to these and other di-isocyanates requires tests in subjects exposed to them and not to TDI.

Asthma↗
PubMed1977

Binding of alpha-bungarotoxin and cholinergic ligands to acetylcholine receptors in the membrane of skeletal muscle.

A membrane fraction enriched in acetylcholine receptors was prepared from denervated cat leg muscles. 97% of the alpha-bungarotoxin-binding sites in the dispersed membranes are sensitive to nicotinic cholinergic ligands. In intact msucle, 90% are. A filtration assay of the binding to the membranes of tritiated alpha-bungarotoxin, as retarded by these ligands, provides a convenient system for the determination of affinities of ligands for the muscle receptor in its membrane-bound state. Affinities were found thus for 6 nicotinic ligands. An allosteric system, rather than desensitisation, may explain the high affinities observed for certain ligands.

Acetylcholine↗
PubMed1989

Effect of acute complete obstruction on the rabbit urinary bladder.

Studies on the effect of partial bladder outlet obstruction demonstrate that significant alterations in urinary bladder structure and function occur within 24 hours of the creation of the obstruction. These studies suggest that many of the functional and structural alterations following partial outlet obstruction may result from the initial overdistension which occurs within the first 24 hours. In these present studies, we investigated the time course of the effect of complete obstruction of the rabbit urinary bladder on the contractile response to bethanechol and field stimulation and on the muscarinic receptor density. Male White New Zealand rabbits were divided into five groups: controls, four, eight, 20, and 24 hours of complete obstruction. The results demonstrated that there was a significant decrease in both the contractile response to muscarinic stimulation and muscarinic receptor density at four hours following outlet obstruction (at a time when there was no bladder overdistension). The receptor density and contractile response to stimulation further decreased over the 24 hour period. These studies indicate that the initial decrease in muscarinic receptor density and contractile response to muscarinic stimulation may be mediated in part by the high level of spontaneous contractile activity induced by ligation of the urethra.

Animals↗
PubMed1975

Synthesis and biological activity of spin-labeled analogs of biotin, hexamethonium, decamethonium, dichlorisoproterenol, and propranolol.

Spin-labeled analogs of biotin (vitamin H), hexamethonium, decamethonium, dichlorisoproterenol, propranolol, and primaquine containing the nitroxide free radical have been synthesized and tested for biological activity. The four spin-labeled analogs of biotin, 4-biotinamido-2,2,6,6-tetramethyl-1-piperidinyloxy (IV), 3-biotinamido-2,2,5,5-tetramethyl-1-pyrrolidinyloxy (V), 3-biotinamidomethyl-2,2,5,5-tetramethyl-1-pyrrolidinyloxy (VI), and 4-(biotinylglycyl)amino-2,2,6,6-tetramethyl-1-piperidinyloxy (VII), all interacted with avidin, a specific biotin binding protein found in raw egg white, at the same sites as did biotin itself. An unsymmetrical decamethonium spin label (XVIII) in which one of the quaternary methyl groups had been replaced by the 4-(2,2,6,6-tetramethyl-1-piperidinyloxy) moiety was 13 times more potent as an inhibitor of Torpedo californica acetylcholinesterase than the parent drug. The symmetrical decamethonium (XVI) and hexamethonium (XIV) spin labels were 18 and 1.8 times as active as decamethonium in the same assay system. The substitution of the 4-(2,2,6,6-tetramethyl-1-piperidinyloxy) group for the isopropyl groups of beta-adrenergic blocking drugs dichlorisoproterenol and propranolol, to give spin labels XXI and XXII, caused a 45 and 54% reduction, respectively, in the ability of these compounds to inhibit the isoproterenol-stimulated activity of rat fat cell membranes. Finally, modification of primaquine by the introduction of the 4-(2,2,6,6-tetramethyl-1-piperidinyloxy) substituent into the amino group of the butyl side chain completely abolished the ability of the drug to bind to nuclei acids. These results suggest that the incorporation of the nitroxide group into drug molecules may be a useful approach to the synthesis of more specific spin labels for biological systems, such as egg white avidin, acetylcholinesterase, and the beta-adrenergic receptor.

Adenylyl Cyclase Inhibitors↗
PubMed1989

Evidence for a respiration-modulated cholinergic action on the activity of medullary respiration-related neurons in the rabbit. An iontophoretic study.

Effects of the iontophoretically administered cholinergic agonists acetylcholine, bethanechol and DMPP on the activity of medullary respiration-related neurons were examined in urethane-anaesthetized rabbits. Inhibitory effects prevailed over excitatory effects. Analysis of cholinergic effects by cycle-triggered averaging revealed three major types of neuronal responses: (i) constant alterations of spike-density throughout the whole period of activity ("constant effects"), (ii) effects increasing during the progression of the burst of discharge or effects restricted to a particular fraction of the burst ("phasic effects") and (iii) effects which were characterized by an excitation during one respiratory phase and an inhibition during the other phase ("bi-phasic effects"). The latter type of effects was observed in phase-spanning respiration-related neurons. Phasic effects were mainly observed in inspiration-related neurons which were predominantly inhibited by stimulation of muscarinic receptors. Inspiratory R beta-neurons in no case were phasically affected by cholinergic agents. The mean muscarinic inhibition of inspiration-related neurons increased with the progression of inspiration. The mean nicotinic inhibition of expiration-related neurons decreased with the progression of expiration. Results suggest that the efficacy of (i) a central inspiration terminating mechanism and (ii) the onset of discharge of expiratory neurons is modulated by acetylcholine.

Acetylcholine↗
PubMed1989

[Ionic mechanisms evoked by acetylcholine-, nicotine-, and muscarine-induced depolarization of Helix lucorum RPa4 neurons].

Three cholinomimetics: acetylcholine, nicotine and muscarine were applied locally on soma of Helix lucorum RPa4 neuron to study ionic nature of its depolarization. Substances that inhibit Na-, K-, Ca- and Cl-conductances were used. Acetylcholine increased Na-, Ca- and Cl-conductances. As the chlorine response part was small due to the proximity of the resting membrane potential and chlorine equilibrium potential, it may be concluded that the dominating response to acetylcholine is connected with the chemocontrolled input of Na+ and Ca2+ ions into a cell. Nicotine induced mainly Na-conductance and muscarine induced Ca-conductance.

Acetylcholine↗
PubMed1979

Muscarinic receptor regulation of NG108-15 adenylate cyclase: requirement for Na+ and GTP.

Cholinergic agonists inhibit the basal and PGE1-activated adenylate cyclase activity in membranes isolated from the mouse neuroblastoma x glioma hybrid cell NG108-15. Inhibition is observed with acetylcholine, acetyl-beta-methylcholine and carbachol and is blocked by two specific muscarinic antagonists, atropine and quinuclydinylbenzilate. Inhibition of basal and PGE1-activated activity is only partial. Carbachol-directed inhibition has an apparent Km of 6 microM in the presence or absence of PGE1. Both the guanine nucleotide GTP and the monovalent cation Na+ are required for this muscarinic inhibition of basal and PGE1-activated NG108-15 adenylate cyclase. The selectivity observed for monovalent cations (all chloride salts) in this process is Na+ congruent to Li+ greater than K+ greater than Choline+ with the ED50 for Na+ congruent 40 microM. Of the nucleotides tested, only IT (and not ATP, UTP or CTP) replaces GTP in this process. GTP at 10 microM represents a saturating nucleotide concentration. Opiate-directed inhibition of NG108-15 adenylate cyclase has recently been shown to exhibit a similar requirement for GTP and Na+ [Blume, A. J., Lichtshtein, D. and Boone, G. (1979) Proc. National Academy of Sciences, USA, in press]. The data presented here therefore support the hypothesis that the general transfer of inhibitory information from membrane receptors to adenylate cyclase involves both a Na+ and GTP-sensitive process.

4-(3-Butoxy-4-methoxybenzyl)-2-imidazolidinone↗
PubMed1985

The action of cholinomimetic and cholinolytic agents, hemicholinium-3 and alpha- and beta-bungarotoxin on the body wall muscle of the earthworm, Lumbricus terrestris.

Strips of muscle, approximately 12 segments in length, were prepared from the body wall of the earthworm, Lumbricus terrestris, from which the nerve cord and viscera had been removed. Contractions to electrical stimulation and acetylcholine agonists were recorded using an isometric transducer. A range of nicotinic and muscarinic agonists and antagonists were tested on this preparation and the results indicate that the acetylcholine receptor on this muscle cannot be classified as either nicotinic or muscarinic. Hemicholinium-3 abolished electrically induced muscle twitches at concentrations which had no effect on the acetylcholine response. Alpha-Bungarotoxin blocked the responses to both electrical stimulation and acetylcholine while beta-bungarotoxin blocked the contractions induced by electrical stimulation but potentiated the acetylcholine contraction.

Acetylcholine↗