Mechanisms of increased susceptibility to angiotensin II-induced apoptosisin ventricular cardiomyocytes of spontaneously hypertensive rats

Previous findings have shown that hypotensive doses of losartan prevent the excess of apoptosis present in the hypertrophied left ventricle of adult s pontaneously hypertensive rats (SHR). This study was designed to determine whether angiotensin II facilitates apoptosis in cardiomyocytes of adult SHR . Primary cultures of ventricular cardiomyocytes from 30-week-old normotens ive Wistar-Kyoto rats (WKY) and SHR with left ventricular hypertrophy were exposed to 10(-9) mol/L angiotensin II for 24 hours. Apoptotic cells were a ssessed by terminal deoxynucleotidyl transferase assay and confirmed by Ann exin V detection. The expression of Bar-alpha, Bcl-2, p53, and caspase-3 pr oteins was assessed by Western blot assays. The expression of BAX gene was assessed by Northern blot. Angiotensin II increased (P<0.01) cardiomyocyte apoptosis, and this effect was higher (P<0.001) in SHR cells than in WKY ce lls. Whereas losartan (10(-7) mol/L) blocked the apoptotic effect of the oc tapeptide in cells from the two strains of rats, PD123319 (10(-7) mol/L) in hibited angiotensin II-mediated apoptosis only in SHR cells. Angiotensin II stimulated (P<0.01) Bax-<alpha> protein, and this effect was higher (P<0.0 1) in SHR cells than in WKY cells. Angiotensin II did not modify Bcl-2, p53 , and BAX mRNA in cells from the two strains of rats. Angiotensin II indude d a similar increase (P<0.05) in the ratio caspase-3/procaspase-3 tan index of caspase-3 activation) in cardiomyocytes from the two strains of rats. T he present in vitro results indicate that SHR cardiomyocytes exhibit enhanc ed susceptibility to angiotensin II-induced apoptosis. Ligand binding to an giotensin II type I and type 2 receptors leading to changes in posttranscri ptional processing of Bax-alpha and accumulation of this proapoptotic prote in may be involved in the abnormal response of SHR cardiomyocytes. These da ta support a role for angiotensin II in apoptosis observed in the left vent ricle of these rats.