Telomere length and adrenergic-induced left ventricular dilatation and systolic chamber dysfunction in rats.
OBJECTIVE
The mechanisms responsible for telomere shortening in heart failure are uncertain. We evaluated whether left ventricular (LV) dilatation and systolic chamber dysfunction produced by chronic β-adrenergic receptor (β-AR) activation is associated with leukocyte or cardiac telomere shortening.


METHODS
Following 6 months of daily injections of the β-AR agonist, isoproterenol (0.02 mg/kg/day) or the saline vehicle to rats, the extent of LV dilatation and LV systolic chamber dysfunction were determined using echocardiography and isolated perfused heart procedures, and relative telomere length of leukocyte (LTL) and cardiac (CTL) deoxyribonucleic acid were determined using a quantitative real-time polymerase chain reaction assay.


RESULTS
β-AR activation resulted in LV dilatation as indexed by increased LV diastolic diameters (9.2 ± 0.6 vs. 8.4 ± 0.9 mm, P = 0.01) and increased diastolic volume intercepts at zero pressure of the LV diastolic pressure-volume relationship (isolated, perfused heart preparation) (0.40 ± 0.06 vs. 0.37 ± 0.08 ml, P = 0.03). Moreover, β-AR activation resulted in LV systolic chamber dysfunction as indexed by reductions in LV endocardial fractional shortening (0.40 ± 0.05 vs. 0.45 ± 0.06, P = 0.01) and the slope of the LV systolic pressure-volume relation (609 ± 176 vs. 901 ± 230, P = 0.01). Although LTL decreased with age in rats receiving either the β-AR agonist or the saline vehicle (P < 0.05), neither CTL (-0.10 ± 0.14 vs. -0.15 ± 0.12, P = 0.3) nor LTL (-0.11 ± 0.19 vs. -0.15 ± 0.18, P = 0.5) were modified by β-AR activation.


CONCLUSIONS
In conclusion, chronic β-AR activation sufficient to produce LV dilatation and systolic chamber dysfunction is not associated with alterations in leukocyte or cardiac telomere length. Telomere shortening in chronic heart failure is unlikely to be attributed to chronic β-AR activation.
Cardiovascular Pathophysiology and Genomics Research Unit, School of Physiology, University of the Witwatersrand Medical School, 7 York Road, Parktown, Johannesburg, 2193, South Africa.
Andrew R
AR
Raymond
Bryan
B
Hodson
Angela J
AJ
Woodiwiss
Gavin R
GR
Norton
Richard L
RL
Brooksbank
D000318:Adrenergic beta-Agonists / Q000633:toxicity*; D000818:Animals; D002311:Cardiomyopathy, Dilated / Q000139:chemically induced / Q000378:metabolism* / Q000503:physiopathology; D006352:Heart Ventricles / Q000378:metabolism / Q000473:pathology / Q000503:physiopathology; D007545:Isoproterenol / Q000633:toxicity*; D008297:Male; D051381:Rats; D017207:Rats, Sprague-Dawley; D013599:Systole; D016615:Telomere / Q000235:genetics / Q000378:metabolism*; D059506:Telomere Shortening; D018487:Ventricular Dysfunction, Left / Q000139:chemically induced / Q000378:metabolism* / Q000503:physiopathology
D000318:Adrenergic beta-Agonists; D007545:Isoproterenol