Document Detail

L-thyroxine increases susceptibility of adult rats to low K+-induced ventricular fibrillation, and sinus rhythm restoration in old rats.
MedLine Citation:
PMID:  15258117     Owner:  NLM     Status:  MEDLINE    
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 microg (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.
Narcis Tribulova; Vladimir Knezl; Ludmila Okruhlicova; Jan Drimal; Dalma Lamosova; Jan Slezak; Jan Styk
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Publication Detail:
Type:  Comparative Study; In Vitro; Journal Article; Research Support, Non-U.S. Gov't     Date:  2004-07-15
Journal Detail:
Title:  Experimental physiology     Volume:  89     ISSN:  0958-0670     ISO Abbreviation:  Exp. Physiol.     Publication Date:  2004 Sep 
Date Detail:
Created Date:  2004-09-22     Completed Date:  2005-02-15     Revised Date:  2006-11-15    
Medline Journal Info:
Nlm Unique ID:  9002940     Medline TA:  Exp Physiol     Country:  England    
Other Details:
Languages:  eng     Pagination:  629-36     Citation Subset:  IM    
Institute for Heart Research, Slovak Academy of Sciences, Dubravska cesta 9, 840 05 Bratislava 45, PO Box 104, Slovak Republic.
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MeSH Terms
Aging / drug effects*,  physiology
Disease Susceptibility / metabolism,  physiopathology
Heart / drug effects,  physiology
Hypokalemia / chemically induced,  physiopathology
Potassium / pharmacology*
Rats, Wistar
Thyroxine / pharmacology*
Ventricular Fibrillation / chemically induced*,  physiopathology*
Reg. No./Substance:
7440-09-7/Potassium; 7488-70-2/Thyroxine

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