Received March 4, 2004
Revised March 25, 2004
Accepted after revision July 8, 2004
L-thyroxine increases susceptibility of young rats to low K+-induced ventricular fibrillation while facilitates sinus rhythm restoration in old ones
Narcis Tribulova 1*,
Vladimir Knezl 1,
Ludmila Okruhlicova 1,
Jan Drimal 1,
Dalma Lamosova 1,
Jan Slezak 1,
Jan Styk 1
1 Slovak Academy of Sciences
* To whom correspondence should be addressed. E-mail: narcisa.tribulova{at}savba.sk.
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Abstract |
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Summary.
Hypokalaemia increases the risk for life threatening arrhythmias, however data about interaction with thyroid status are missing. The aim of the study was to investigate vulnerability of L-thyroxine (T4)-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 T4 50ìg/100g/day during two 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 and coronary flow were continuously monitored. The results showed that compared to untreated rats, the onset of low K+-induced ventricular premature beats was delayed and their number was significantly decreased in both T4-treated groups. Nevertheless, VF occurred earlier in T4-treated than in non-treated adult rats (6.78+0.28 vs 9.59+0.55 min, P<0.05), while the difference was not significant in aged animals. Furthermore, sinus rhythm appeared earlier in old T4-treated rats compared to non-treated ones (7.18+0.57 vs 8.94+0.64, P<0.05 min), while in adult hearts it set in at practically the same time regardless of treatment. In conclusion, our results indicate that administration of pharmacological dosage of T4 can increase the risk of low K+-induced VF in young adult but not in old animals, in which it even facilitated restoration of sinus rhythm. Moreover, enhanced mechanical function was observed in both adult and old T4-treated hearts.
Key Words:
Arrhythmia, Heart, Thyroid hormone
