Electrophysiological effects

Additionally, the electrophysiological effects are often obtained from normal myocardial preparations and the abnormalities of cellular electrophysiology which cause arrhythmias in a diseased myocardium may be uniquely related to the disease process (10). Nevertheless, antiarrhythmic agent classifications have been useful as a mnemonic device. 

The Class I agents decrease excitability, slow conduction velocity, inhibit diastoHc depolarization (decrease automaticity), and prolong the refractory period of cardiac tissues (1,2). These agents have anticholinergic effects that may contribute to the observed electrophysiologic effects. Heart rates may become faster by increasing phase 4 diastoHc depolarization in SA and AV nodal cells. This results from inhibition of the action of vagaHy released acetylcholine [S1-84-3] which, allows sympathetically released norepinephrine [51-41-2] (NE) to act on these stmctures (1,2). 

Glass lA Antiarrhythmic Agents. Class lA antiarrhythmic agents decrease automaticity, ie, depress pacemaker rates, especially ectopic foci rates produce moderate depression of phase 0 depolarization and thus slow conduction in atria, A-V node, His-Purkinje system, and ventricles prolong repolarization, ie, lengthen action potential duration increase refractoriness and depress excitabiHty. These electrophysiological effects are manifested in the ECG by increases in the PR, QRS, and QT intervals. 

Elestolol sulfate is a nonselective, ultrashort acting P-adrenoceptor blocker. It has no ISA and produces weak inhibition of the fast sodium channel. The dmg is under clinical investigation for supraventricular tachyarrhythmias, unstable angina, and acute MI. In humans, flestolol has hemodynamics and electrophysiologic effects similar to those of other P-adrenoceptor blockers. The pharmacokinetics of flestolol are similar to those of esmolol. It is 50 times more potent than esmolol and the elimination half-life is 7.2 min. Recovery from P-adrenoceptor blockade is 30—45 min after stopping iv infusions. The dmg is hydrolyzed by tissue esterases and no active metabohtes of flestolol have been identified (41). 

The electrophysiological effects of amiodarone may be a composite of several properties. In addition to prolonging action potential duration and refractory period in ad tissues of the heart, the compound is an effective sodium channel blocker (49), calcium channel blocker (50), and a weak noncompetitive -adrenoceptor blocking agent (51). Amiodarone slows the sinus rate, markedly prolongs the QT interval, and slightly prolongs the QRS duration (1,2). 

Since alterations of thyroid fimction by amiodarone are related to the iodine substitution of the drug, the iodine-free derivative dronedarone has been developed with similar electrophysiological effects as amiodarone. It seems to act also as a T3-anatgonist, but does not provoke hyperthyreoidism [1]. 

Rea TM, Nash JF, Zabik JE, et al Effects of toluene inhalation on brain biogenic amines in the rat. Toxicology 31 143-1450, 1984 Rebert CS, Matteucci MJ, Pryor GT Acute electrophysiologic effects of inhaled toluene on adult male Long-Evans rats. Pharmacol Biochem Behav 33 157—165, 1989 Reynolds JEF Martindale The Extra Pharmacopoeia, 28th Edition. London, Pharmaceutical Press, 1982, pp 745-746... 

An intermediate-duration oral MRL of 0.0007 mg/kg/day was derived for methyl parathion based on the observation of electrophysiological effects in the central and peripheral nervous systems of male rats exposed to methyl parathion through gavage administration of 0.22 mg/kg/day to the dams on days 5-15 of gestation and days 2-28 of lactation, followed by direct administration of the same dose to the male pups for 8 weeks. More marked effects occurred at the two higher doses, 0.44 and 0.88 mg/kg/day. The effects were dose-related, and were statistically significant at all three dose levels. The MRL was derived by dividing the LOAEL from this study (0.22 mg/kg/day) by an uncertainty factor of 300 (3 for a minimal LOAEL, 10 for extrapolation from animals to humans, and 10 for human variability). 

ATSDR has derived an intermediate-duration oral MRL of. 0007 mg/kg/day for methyl parathion based on a minimal LOAEL of 0.22 mg/kg/day for electrophysiological effects in the central and peripheral nervous systems in rats (Desi et al. 1998). 

Concentration and end point used for MRL derivation 0.22 mg/kg/day electrophysiological effects in the central and peripheral nervous systems... 

Greenhoff, J and Johnson, SW (1997) Electrophysiological effects of dopamine receptor stimulation. In The Dopamine Receptors (Eds Neve, KA and Neve, RL), Humana Press, Totowa, NJ, pp. 267-304. 

If some of the electrophysiological effects of oxidant stress occur secondary to an elevation in intracellular calcium, it is important to consider the possible factors that may underlie the initial elevation of calcium. In the simplest analysis, elevation of cytosolic calcium may be due to (1) redistribution of intracellular calcium stores (2) increased calcium influx or (3) decreased calcium efflux. 

Bruce, M., Scott, N., Lader, M. and Marks, V., The psychopharmacological and electrophysiological effects of a single dose of caffeine in healthy human subjects. British Journal of Clinical Pharmacology 22, 81-87, 1986. 

Martin, R.J. (1982) Electrophysiological effects of piperazine and diethylcarba-mazine on Ascaris suum somatic muscle. British Journal of Pharmacology 77, 255-265. 

Dopamine receptor blocking agents. Many of the neuroleptics used in the treatment of schizophrenia frequently produce parkinsonian symptoms as unwanted effects. Neuroleptics block dopamine receptors and their therapeutic effect seems to be related to this action. Although these drugs act on DA systems without distinction, some are more selective. Thioridazine, clozapine and molindone, for example, have electrophysiological effects in the limbic region of the brain but little action in the nigro-striatal area. This selectivity may be related to receptor subtype specificity (see Chs 12 and 54). 

Grosser, B. I., Monti-Bloch, L., Jennings-White, C. and Berliner, D. L. (2000) Behavioral and electrophysiological effects of androstadienone, a human pheromone. Psychoneuroendocrinol. 25, 289-299. 

Schmidt SH, Anniko M, Hellstrom S. 1990. Electrophysiological effects of the clinically used local anesthetics lidocaine, lidocaine-prilocaine and phenol on the rat s inner ear. Eur Arch Otorhinolaryngol 248 87-94. 

Electrophysiology Studies of the electrophysiological effects of lobelia are scant. In one study, increases were seen in low-frequency activity in the hippocampus but in higher-frequency activity in the amygdala (Sopranzi et al. 1991). 

Electrophysiological effects Extracts of hypericum were examined for their electrophysiological effects in animals. The onset of effects occurred 3-4 hours after administration. Frequencies affected first were in the alpha range and were maximal in the frontal cortex (Dimpfel and Hofmann 1995). Another study examined the EEG effects for two hypericum extracts in rats one extract high in hyperforin and lacking naphthodi-anthrones (C02), and another extract (LI 160) low in hyperforin. Both extracts showed similar early alpha effects, but only LI 160 had a late effect of increased delta frequencies. The alpha effects are comparable to... 

Cannabis has electrophysiological effects on human sleep as well. Daily doses (70 to 210 mg) of THC reduced REM sleep and increased... 

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