Age-related difference in cardiac adaptation to chronic hypertension in rats, with and without nifedipine treatment

Three myosin isozymes, V1 (alpha alpha MHC = Myosin Heavy Chain gene), V2 ( alpha beta MHC) and V3 (beta beta MHC) that are identified in the cardiac v entricles of most mammals have been shown to shift to a V3 predominance pat tern during cardiac growth and in response to left ventricular pressure ove rload, and to V1 predominance following anti hypertensive treatment. This s tudy examined whether long-term hypertension impairs the ability of the adu lt heart to restructure myosin isozyme proportions. Using pyrophosphate gel electrophoresis, we studied proportions of cardiac myosin isozymes (V1 and V3) in young (16 weeks) and adult (36 weeks) spontaneously hypertensive ra ts (SHR), and following 12 weeks of nifedipine (N) treatment in age-matched SHR rats (SHR-N). The values of V1 and V3 myosin isozymes were derived by adding half of the value of V2 to each isozyme proportion. The V3 proportio n in the young SHR control (SHR-C) group (49%) was 34% higher (p < 0.05) th an in the young Wistar Kyoto control (WKY-C) group (37%). However, the prop ortion was similarly high, though not statistically significant, in both th e adult SHRC (73%) and WKY-C (71%) groups. The proportion in the young SHR- N group (29%) was 41% lower (p < 0.05) than in the young SHR-C group (49%), and the proportion in the adult SHR-N group (47%) was 34% lower (p < 0.05) than in the adult SHR-C group (73%). The ratio of left ventricular weight to body weight (LVW/BW), which determines left ventricular hypertrophy (LVH ), was higher in both young and adult SHR-C (26%, p < 0.05, and 42%, p < 0. 05, respectively) than in WKY-C groups. The mean LVW/BW was 27% (p < 0.05) greater in adult than in young SHR-C rats. The LVW/BW in both age groups of treated SHR-N was similar to that in age matched WKY-C rats. Conclusion: O ur study showed that a rise in the V3 level occurs in young hypertensive ra ts, but no rise occurs in the V3 level in adult hypertensive rats. High blo od pressure seems to contribute to the high V3 level in young hypertensive rats, but in adult hypertensive rats, high blood pressure does not accentua te the V3 rise already acquired due to the aging process. Nifedipine treatm ent in both young and adult hypertensive rats prevented the V3 rise due to hypertension and to the aging process. This effect of nifedipine seems to b e through its antihypertensive action.