REGRESSION SPEED OF CARDIAC MYOSIN HEAVY-CHAIN ISOZYME V3 IN LOADED RIGHT OR LEFT-VENTRICLE AFTER RELIEF OF THE LOAD

The authors examined whether there is any correlation between the regr ession speed of cardiac beta (V3)-myosin heavy-chain (MHC) isozyme and duration of overload. The results showed that in the right ventricle of a 1-week overloaded group, the loaded ventricular MHC isozyme V3 (2 9.0 +/- 5 0%, P < 0.05) returned to the control level within 1 week af ter relief of overload (20.4 +/- 4.2%, P=NS), whereas in a 3 week over loaded group (32.8 +/- 5.3%, P < 0.05) it took 10 weeks (36.6 +/- 8.6% , P=NS). The left ventricle showed the same tendency as the right vent ricle. In sham-operated rats, however, the changes in MHC isozyme V3 i n the left ventricle were greater than those in the right ventricle. T hese results suggest that regression speed of the cardiac MHC isoform, changed by pressure overload, is accompanied by the duration of overl oad. Furthermore, the right and left ventricles may have different res ponsiveness to MHC isoform transitions in heart stresses.