Effects of angiotensin II blockade on cardiomyocyte regeneration after myocardial infarction in rats.

Introduction: We studied the effects of angiotensin type 1 receptor blockade (ARB) on formation of new cardiomyocytes, neovascularization and ventricular remodelling after myocardial infarction (MI).

Methods: Male Wistar rats with MI or sham-operated controls were treated with either losartan or vehicle. Bromodeoxyuridine (BrdU) was given to identify newly formed cardiac cells. Immunohistochemical analysis was used to quantify proliferative and apoptotic cardiomyocytes, vascular structures and c-Kit+ stem/progenitor cells, western blotting to evaluate gene expression, and planimetry and echocardiography to assess cardiac structure and function.

Results: The number of BrdU+ cardiomyocytes increased similarly in the vehicle and losartan treated MI groups. The number of apoptotic or proliferating cardiomyocytes did not differ between losartan and vehicle treated rats. Losartan induced an increase in capillary and BrdU+ vascular densities in the infarct border zone. Losartan treatment completely prevented post-MI cardiac hypertrophy. In the non-infarcted myocardium the amount of all BrdU+ cells (including non-cardiomyocyte cells) was highest in the vehicle treated MI rats at week 4.

Conclusions: The number of newly formed cardiomyocytes increased after MI. Angiotensin II blockade neither stimulated nor prevented cardiomyocyte regeneration. ARB treatment increased vascular densities in the infarct border zone and modulated remodelling of the non-infarcted myocardium preventing effectively post-MI cardiac hypertrophy.