The hypertrophied myocardium accumulates the MB-creatine kinase isozyme.

Myocardial hypertrophy was produced in the dog by volume overload, secondary to hypertension, and pressure overload to left or right ventricles and in the rat by pressure overload to the left or right ventricles, by elevating thyroxine-levels and secondary to spontaneous hypertension in order to test whether there are changes in the creatine kinase system in hypertrophied heart. Although there was little or no change in total creatine kinase activity, there were changes in the distribution of the creatine kinase isozymes. In the dog, a 4-10-fold increase in the tissue content of MB-creatine kinase was observed for heart chambers with a 40-90% increase in the ratio of ventricular weight to body weight. In the rat, MB-creatine kinase also accumulated in hypertrophied ventricles. For the spontaneously hypertensive rat, the correlation between increased fetal creatine kinase isozymes and increased ratio of ventricular weight to body weight was excellent (r approximately 0.92). During the transition from compensated hypertrophy to failure in the spontaneously hypertensive rat, there is a 50% decrease in mitochondrial creatine kinase activity. P-31 NMR magnetization transfer experiments suggest that flux through the creatine kinase reaction is 3-fold lower than normal in these failing hearts. These results show that there are changes in the distribution of the creatine kinase isozymes in hypertrophied heart and suggest that one of these changes characterizes compensated hypertrophy (increased fetal-type creatine kinase isozymes) while another characterizes the transition to failure (decreased mitochondrial creatine kinase).