title: The training-induced changes on automatism, conduction and myocardial refractoriness are not mediated by parasympathetic postganglionic neurons activity.
abstract: The purpose of this study is to test the role that parasympathetic postganglionic neurons could play on the adaptive electrophysiological changes produced by physical training on intrinsic myocardial automatism, conduction and refractoriness. Trained rabbits were submitted to a physical training protocol on treadmill during 6 weeks. The electrophysiological study was performed in an isolated heart preparation. The investigated myocardial properties were: (a) sinus automatism, (b) atrioventricular and ventriculoatrial conduction, (c) atrial, conduction system and ventricular refractoriness. The parameters to study the refractoriness were obtained by means of extrastimulus test at four different pacing cycle lengths (10% shorter than spontaneous sinus cycle length, 250, 200 and 150 ms) and (d) mean dominant frequency (DF) of the induced ventricular fibrillation (VF), using a spectral method. The electrophysiological protocol was performed before and during continuous atropine administration (1 μM), in order to block cholinergic receptors. Cholinergic receptor blockade did not modify either the increase in sinus cycle length, atrioventricular conduction and refractoriness (left ventricular and atrioventricular conduction system functional refractory periods) or the decrease of DF of VF. These findings reveal that the myocardial electrophysiological modifications produced by physical training are not mediated by intrinsic cardiac parasympathetic activity.
authors.affiliation: Department of Physiology, School of Medicine and Dentistry, University of Valencia, Blasco Ibañez 15, 46010 Valencia, Spain.
authors.forename: M
authors.initials: M
authors.lastname: Zarzoso
authors.forename: L
authors.initials: L
authors.lastname: Such-Miquel
authors.forename: G
authors.initials: G
authors.lastname: Parra
authors.forename: L
authors.initials: L
authors.lastname: Brines-Ferrando
authors.forename: L
authors.initials: L
authors.lastname: Such
authors.forename: F J
authors.initials: FJ
authors.lastname: Chorro
authors.forename: J
authors.initials: J
authors.lastname: Guerrero
authors.forename: A
authors.initials: A
authors.lastname: Guill
authors.forename: J E
authors.initials: JE
authors.lastname: O'Connor
authors.forename: A
authors.initials: A
authors.lastname: Alberola
mesh_terms: D000818:Animals; D016275:Atrial Function / Q000502:physiology; D054537:Atrioventricular Block; D001332:Automatism; D017776:Autonomic Pathways / Q000502:physiology; D018680:Cholinergic Antagonists / Q000494:pharmacology; D006321:Heart / Q000502:physiology*; D006329:Heart Conduction System / Q000502:physiology; D008297:Male; D009206:Myocardium / Q000201:enzymology; D009474:Neurons / Q000502:physiology*; D017777:Parasympathetic Fibers, Postganglionic / Q000502:physiology*; D010275:Parasympathetic Nervous System / Q000502:physiology*; D010805:Physical Conditioning, Animal / Q000502:physiology*; D011817:Rabbits; D011950:Receptors, Cholinergic / Q000378:metabolism; D012032:Refractory Period, Electrophysiological / Q000502:physiology*; D014693:Ventricular Fibrillation / Q000503:physiopathology; D016276:Ventricular Function / Q000502:physiology
chemical_list: D018680:Cholinergic Antagonists; D011950:Receptors, Cholinergic