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 V, isoform, compos ed of two alpha -MHC, to V, isoform, composed of two beta -MHC. In rat, bes ides ageing, cardiac hypertrophy as adaptive response to a superimposed pre ssure load (such as hypertension) is characterized by predominance of V, my osin isoform. The aim of our study was to evaluate the expression of R-MHC in right (RV) and left (LV) ventricles of spontaneously hypertensive rats ( SHRs), a well defined animal model of hypertension, in relation to aping. W e 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 f ound that B-MHC is already present in both RV and LV of 8-week old SHRs, an d is markedly predominant in RV and LV of 15-week old SHRs, when compared w ith age-matched control rats. Our study showed that the shift to V, myosin isoform in SHRs is an early event, resembling accelerated senescence. We ha ve also demonstrated that B-MHC is actively synthesized also in young (15-w eek old) normal rats.