title: Intravenous amiodarone modifies autonomic balance and increases baroreflex sensitivity in conscious rats.
abstract: Amiodarone is an antiarrhythmic agent commonly used to treat cardiac arrhythmias. This study was designed to investigate the effects of intravenous amiodarone on the neural control of heart rate and arterial pressure and spontaneous baroreflex sensitivity (BRS). Experiments were carried out on conscious freely moving normotensive Wistar (WR) and spontaneously hypertensive rats (SHR). Arterial pressure was continuously monitored before and after amiodarone (50 mg/kg i.v.) or vehicle for 30 min. Heart rate (expressed as the pulse interval, PI) and systolic arterial pressure (SAP) variabilities were assessed using autoregressive spectral analysis. BRS was calculated as the alpha-index (the square root of the ratio between the PI and SAP powers). Amiodarone induced bradycardia and hypotension in both strains, with these effects being more intense in SHR. The variability profile of PI was characterized by a significant reduction of normalized low frequency (LF) and LF/HF ratio, while the high frequency (HF) component both in absolute and normalized units (nu) was increased in both WR and SHR strains. A significant decrease in SAP variance and its LF oscillation was observed. In addition, BRS was also increased in both groups, being more intense in SHR. In both WR and SHR, intravenous amiodarone had a considerable effect on heart rate variabilities (HRV), shifting cardiac sympathovagal balance toward a sympathetic inhibition and/or vagal activation, which were associated with an increase in spontaneous BRS. Decreases of SAP variance and LF(SAP) suggest sympatholytic effects on peripheral vessels. Besides the direct ion channel effects, these changes in the autonomic balance could contribute to the antiarrhythmic action of the intravenous amiodarone.
authors.affiliation: Department of Biological Sciences, School of Medicine of Triangulo Mineiro, Uberaba (MG), Brazil.
authors.forename: José
authors.initials: J
authors.lastname: Dias da Silva Valdo
authors.forename: Cesar Cavalcante
authors.initials: CC
authors.lastname: Viana Públio
authors.forename: Rodrigo
authors.initials: R
authors.lastname: de Melo Alves
authors.forename: Rubens
authors.initials: R
authors.lastname: Fazan
authors.forename: Tomaso Gnecchi
authors.initials: TG
authors.lastname: Ruscone
authors.forename: Alberto
authors.initials: A
authors.lastname: Porta
authors.forename: Alberto
authors.initials: A
authors.lastname: Malliani
authors.forename: Helio Cesar
authors.initials: HC
authors.lastname: Salgado
authors.forename: Nicola
authors.initials: N
authors.lastname: Montano
mesh_terms: D000638:Amiodarone / Q000494:pharmacology*; D000818:Animals; D000889:Anti-Arrhythmia Agents / Q000494:pharmacology*; D001145:Arrhythmias, Cardiac / Q000188:drug therapy* / Q000503:physiopathology; D017704:Baroreflex / Q000187:drug effects* / Q000502:physiology; D001794:Blood Pressure / Q000187:drug effects / Q000502:physiology; D003243:Consciousness / Q000502:physiology; D006321:Heart / Q000187:drug effects* / Q000294:innervation; D006339:Heart Rate / Q000187:drug effects / Q000502:physiology; D006706:Homeostasis / Q000187:drug effects / Q000502:physiology; D006973:Hypertension / Q000503:physiopathology; D007275:Injections, Intravenous; D008297:Male; D051381:Rats; D011918:Rats, Inbred SHR; D017208:Rats, Wistar; D013564:Sympathetic Nervous System / Q000187:drug effects* / Q000502:physiology; D014630:Vagus Nerve / Q000187:drug effects* / Q000502:physiology
chemical_list: D000889:Anti-Arrhythmia Agents; D000638:Amiodarone