Cardiac arrhythmias produced by bretylium in cats anesthetized with halothane

Digitalis glycosides: a discussion of the similarities and differences in actions and existing controversies

The writing of this review was initiated to answer the question of whether differences in the actions of the various digitalis glycosides exist and to discuss current controversies in the research area of the digitalis glycosides. Data obtained in our laboratory indicated that the effect of digoxin on postganglionic cardiac sympathetic neural discharge in the minute prior to the occurrence of arrhythmia differed from that of ouabain. This raised the question of whether data published in other laboratories would support the contention that differences in glycosides do exist. To answer this question, a review of the literature was begun. Our survey of these studies are cited in the tables of this review. These tables summarize the actions of glycosides in vivo and in vitro in different animal models. The reader should bear in mind that the data included within the tables do not represent an inclusive summary of all studies in the literature. For detailed review articles, the reader is referred to the following references: Gillis et al; Gillis and Quest; Roberts et al; Lathers and Roberts; Farah and Alousi; Benthe; Levitt et al; Smith and Haber; Somberg; Lee and Klaus; Mason; Schwartz. Furthermore the summary of the results for each particular study cited in the table may not, in all cases, include each finding of the published data. Nevertheless, the tables do provide a summary of data obtained in various species with different glycosides in several different areas of research, and as such, represent an abridged compendium for the research working in the field of digitalis glycosides. This review has been organized firstly to consider glycoside-induced alterations in the autonomic nervous system and, secondly, to examine their direct actions on the heart.

Succinylcholine, cholinoceptors and catecholamines: proposed mechanism of early adverse haemodynamic reactions

An hypothesis is proposed to account for the occurrence of adverse haemodynamic reactions to succinylcholine. Interaction of succinylcholine with cholinergic receptors is postulated to result in release of endogenous catecholamines (predominantly norepinephrine). The occurrence and the clinical manifestations of the adverse reactions would be dependent on the extent of the release. Based on literature reports of findings in experimental animals with nicotinic and muscarinic agents, a mechanism for the release of norepinephrine is outlined. Interaction of succinylcholine with muscarinic and nicotinic receptors is proposed to result in an initial activation which is followed by a phase of chemical insensitivity. Activation of the presynaptic nicotinic receptors on the postganglionic sympathetic terminals leads to a short-lasting release of norepinephrine. Activation of the presynaptic muscarinic receptors produces attenuation of the norepinephrine release. In the majority of patients these opposing actions are balanced and the net result is small, variable, and of little clinical importance. An unbalanced response leading to clinical manifestations can be expected if the two types of the presynaptic cholinoceptors are differentially activated.

Cardiac arrhythmias induced by guanethidine in cats anesthetized with halothane

Rapid i.v. administration of guanethidine provokes severe and sustained ventricular arrhythmias in cats anesthetized with halothane. The arrhythmias include premature ventricular excitations, multifocal ventricular rhythm, bigeminy, trigeminy and ventricular tachycardia. They begin in about 20 sec and last from 4 to 100 min. By comparison, a standard dose of noradrenaline (10 micrograms/kg) induces ventricular arrhythmias which develop in about 12 sec and continue for 1-2.5 min. Pretreatment with beta-adrenoceptor blocking drugs prevents arrhythmias from both drugs, and pretreatment with imipramine or reserpine prevents arrhythmias for guanethidine but not noradrenaline. The adrenergic neuron blocking action of guanethidine does not alter the arrhythmogenic action of guanethidine since arrhythmias can still be produced after adrenergic neuron blockade. These results indicate that guanethidine causes arrhythmias by releasing noradrenaline from cardiac adrenergic neuron storage sites and, therefore, point out the vulnerability of the heart to arrhythmias when noradrenaline-releasing drugs interact with halogenated hydrocarbon anesthetics.