Effect of aging and hypertension on beta-myosin heavy chain in heart of spontaneously hypertensive rats.

During aging rat myocardium undergoes structural changes characterized by a shift in the synthesis of myosin heavy chain (MHC) from V1 isoform, composed of two alpha-MHC, to V3 isoform, composed of two beta-MHC. In rat, besides ageing, cardiac hypertrophy as adaptive response to a superimposed pressure load (such as hypertension) is characterized by predominance of V3 myosin isoform. The aim of our study was to evaluate the expression of beta-MHC in right (RV) and left (LV) ventricles of spontaneously hypertensive rats (SHRs), a well defined animal model of hypertension, in relation to aging. We used very young (8-week old) and young (15-week old) SHRs and age-matched normotensive Harlan Sprague-Dawley control rats. By Western analysis, we found that beta-MHC is already present in both RV and LV of 8-week old SHRs, and is markedly predominant in RV and LV of 15-week old SHRs, when compared with age-matched control rats. Our study showed that the shift to V3 myosin isoform in SHRs is an early event, resembling accelerated senescence. We have also demonstrated that beta-MHC is actively synthesized also in young (15-week old) normal rats.