Premium
L‐thyroxine increases susceptibility of adult rats to low K + ‐induced ventricular fibrillation, and sinus rhythm restoration in old rats
Author(s) -
Tribulova Narcis,
Knezl Vladimir,
Okruhlicova Ludmila,
Drimal Jan,
Lamosova Dalma,
Slezak Jan,
Styk Jan
Publication year - 2004
Publication title -
experimental physiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.925
H-Index - 101
eISSN - 1469-445X
pISSN - 0958-0670
DOI - 10.1113/expphysiol.2004.027607
Subject(s) - sinus rhythm , medicine , perfusion , ventricular fibrillation , heart rate , endocrinology , cardiology , normal sinus rhythm , rhythm , atrial fibrillation , blood pressure
Hypokalaemia increases the risk for life‐threatening arrhythmias; however, data about interaction with thyroid status are lacking. The aim of this study was to investigate vulnerability of l ‐thyroxine (T 4 )‐treated adult and old rats to low K + ‐induced ventricular fibrillation (VF) as well as the ability of the heart to recover sinus rhythm. The experiments were performed on isolated heart preparations using the heart of 4‐ and 20‐month‐old female Wistar rats without and with feeding with T 4 50 μg (100 g day) −1 over a period of 2 weeks. Perfusion of the isolated heart with oxygenated Krebs–Henseleit solution at constant pressure was followed by perfusion with K + ‐deficient solution until occurrence of VF (< 10 min). After 2 min of sustained VF, the heart was perfused with normal solution for 10 min, during which sinus rhythm was restored. ECG, left ventricular pressure (LVP) and coronary flow were continuously monitored. The results showed that compared with untreated rats, the onset of low K + ‐induced ventricular premature beats was delayed and their number was significantly decreased in both T 4 ‐treated groups. Nevertheless, VF occurred earlier in T 4 ‐treated than in non‐treated adult rats (6.78 ± 0.28 vs. 9.59 ± 0.55 min, P < 0.05), whereas the difference was not significant in aged animals. Furthermore, sinus rhythm appeared earlier in old T 4 ‐treated rats compared with non‐treated rats (7.18 ± 0.57 vs. 8.94 ± 0.64 min, P < 0.05), whereas in adult hearts it set in at practically the same time regardless of treatment. In conclusion, our results indicate that administration of a pharmacological dose of T 4 can increase the risk of low K + ‐induced VF in adult but not in old animals; in the latter it even facilitated restoration of sinus rhythm. Moreover, enhanced mechanical function was observed in both adult and old T 4 ‐treated hearts.