Myocyte loss in early left ventricular hypertrophy of experimental renovascular hypertension

Left ventricular hypertrophy (LVH) develops very early in experimental renovascular hypertension after clipping of one renal artery and is accompanied by a remodeling of cardiac structure which has not yet been investigated in detail. It was the aim of the present study to analyze changes in cardiomyocyte number and volume in LVH after 2 weeks of renovascular hypertension. Sprague-Dawley rats were subjected to clipping of the left renal artery (2K1C) or sham operation (sham). One group of 2K1C rats received antihypertensive treatment with dihydralazine. The experiment was terminated after 2 weeks. Hearts were investigated using stereological methods, electron microscopy, immunohistology for the proliferation marker proliferating cell nuclear antigen, the pro- and anti-apoptotic proteins Bax and Bcl-2 as well as the TUNEL technique. After 2 weeks, systolic blood pressure and relative left ventricular weight were significantly higher in untreated 2K1C animals than in sham and dihydralazine-treated 2K1C rats. Volume fraction of interstitial tissue and capillary length density were not different, whereas wall thickness of intramyocardial arteries was significantly higher in untreated 2K1C (5.12+/-0.7 micro m) than in sham (3.92+/-0.6 micro m) and in dihydralazine-treated 2K1C (3.91+/-0.7 micro m) rats. Cardiomyocyte diameter and volume were significantly higher in untreated 2K1C than in sham animals. The number of cardiomyocytes per left ventricle was significantly lower in untreated 2K1C rats (5.5+/-1.6 vs 3.9+/-6.9 x10(7)). Using immunohistochemistry, no direct evidence of apoptosis was found, but a relative higher expression of the anti-apoptotic protein bcl-2 expression was seen in untreated 2K1C than in sham animals. This may reflect a protective mechanism as a consequence of earlier occurring apoptosis. These observations document that experimental renovascular hypertension induces a rapidly developing LVH characterized by marked cardiac remodeling and substantial loss of cadiomyocytes.