Fibroblast apoptosis precedes cardiomyocyte mass reduction during left ventricular remodeling in hypertensive rats treated with amlodipine

Background A transient induction of apoptosis accompanies the normalization of left ventricular mass index in spontaneously hypertensive rats (SHR) treated with dihydropyridine calcium-channel blockers. However, the cell type undergoing apoptosis in this model and the temporal correlation with onset cardiac remodeling remain undefined. Methods and results SHR were treated either with vehicle or amlodipine (20 mg/kg per day) for 4, 7,10,14 or 28 days. Amlodipine stably reduced systolic blood pressure by day 2 (-26 ± 2%) and stably reduced the left ventricular concentration of atrial natriuretic peptide (ANP) mRNA by ∼50% as early as day 4, suggesting the early reduction of cardiomyocyte stress. Left ventricular mass index was significantly reduced by day 7 (-4.6 ± 1.5%), in coordination with reduced DNA content (-23 ± 2%) and non-cardiomyocyte number (-17±4%). However, the cardiomyocyte cross-sectional area was reduced only starting from day 14. Caspase-3 cleavage was significantly increased at day 7 only. Ultimately, amlodipine for 28 days induced a slight increase in capillary density without affecting total cardiomyocyte number, while reducing the total number of non-cardiomyocytes down to levels seen in untreated normotensive Wistar-Kyoto rats. Bax to Bcl-2 protein ratios were increased from day 7 to day 28. In situ double labeling by the terminal deoxynucleotidyl transferase biotin-dUTP nick end labeling (TUNEL) method (apoptosis) combined with rhodamine-labeled lectin binding (endothelial cell marker) revealed a significant increase (>3-fold) in TUNEL-positive, lectin-negative non-cardiomyocytes in the interstitium between days 7 and 14. Conclusions Left ventricular remodeling induced by amlodipine in SHR involves selective deletion of excess fibroblasts via apoptosis prior to cardiomyocyte mass reduction, but after attenuation of ANP gene expression.