Bradycardia induces angiogenesis, increases coronary reserve, and preserves function of the postinfarcted heart.
BACKGROUND
We tested the hypothesis that induction of chronic bradycardia would trigger an upregulation of key growth factors and receptors, which would then lead to angiogenesis and improve coronary reserve in the left ventricle after myocardial infarction.


RESULTS
Bradycardia was induced in rats by administering alinidine via osmotic pumps beginning 1 day after coronary artery ligation. Echocardiographic analysis was conducted before and after treatment. Morphometric analysis was used in perfusion-fixed hearts to document arteriolar and capillary growth. Western blots were used to evaluate growth factor and receptor changes. During the first week of treatment, vascular endothelial growth factor (VEGF), VEGF receptor 1 (Flt-1), and basic fibroblast growth factor proteins were higher in the treated group, whereas VEGF receptor 2 (Flk-1), angiopoietin-1, and angiopoietin-2 were not affected by treatment. After 3 weeks, VEGF protein remained elevated, and bradycardia was associated with a higher capillary length density in the border (40%) and remote (14%) regions and a higher arteriolar length density in the septum (62%), despite a greater increase in left ventricular mass. Although arteriolar length density increased in all size classes, the greatest increase occurred in the smallest (terminal) arterioles. This vascular growth was associated with a 23% greater coronary reserve. Echocardiography revealed a smaller increase in ventricular volume and a greater preservation of ejection fraction in rats treated with bradycardia.


CONCLUSIONS
Pharmacologic induction of bradycardia enhances vascularity and coronary reserve, preserves function of surviving myocardium, and therefore, is a noninvasive, therapeutic avenue that provides an alternative to gene therapy.
Lei
Li
L
Department of Anatomy and Cell Biology, University of Iowa Carver College of Medicine, Iowa City, IA 52242, USA.
Zhou
Ruifeng
R
Zheng
Wei
W
Christensen
Lance P
LP
Weiss
Robert M
RM
Tomanek
Robert J
RJ
D042683:Angiopoietin-1 / Q000031:analogs & derivatives* / Q000097:blood; D042702:Angiopoietin-2 / Q000097:blood; D000818:Animals; D001919:Bradycardia / Q000139:chemically induced / Q000503:physiopathology*; D002317:Cardiovascular Agents / Q000494:pharmacology / Q000627:therapeutic use*; D003000:Clonidine / Q000031:analogs & derivatives* / Q000494:pharmacology / Q000627:therapeutic use*; D003331:Coronary Vessels; D004353:Drug Evaluation, Preclinical; D016326:Extracellular Matrix Proteins / Q000097:blood; D016222:Fibroblast Growth Factor 2 / Q000097:blood; D006352:Heart Ventricles / Q000000981:diagnostic imaging; D017379:Hypertrophy, Left Ventricular / Q000139:chemically induced / Q000503:physiopathology; D008026:Ligation; D008297:Male; D023421:Models, Animal; D009203:Myocardial Infarction / Q000503:physiopathology*; D032383:Myocytes, Cardiac / Q000473:pathology; D018919:Neovascularization, Physiologic / Q000187:drug effects*; D051381:Rats; D017207:Rats, Sprague-Dawley; D013318:Stroke Volume; D014463:Ultrasonography; D042461:Vascular Endothelial Growth Factor A / Q000097:blood; D040281:Vascular Endothelial Growth Factor Receptor-1; D040301:Vascular Endothelial Growth Factor Receptor-2 / Q000097:blood
D042683:Angiopoietin-1; D042702:Angiopoietin-2; C467629:Angpt1 protein, rat; D002317:Cardiovascular Agents; D016326:Extracellular Matrix Proteins; D042461:Vascular Endothelial Growth Factor A; D016222:Fibroblast Growth Factor 2; C022192:alinidine; C501164:Flt1 protein, rat; D040281:Vascular Endothelial Growth Factor Receptor-1; D040301:Vascular Endothelial Growth Factor Receptor-2; D003000:Clonidine