[Creatine phosphokinase activity and its isoenzymatic ratio in the myocardium in adaptation of the heart to prolonged loading].

Three isoenzymes of creatine phosphokinase (CPK) were detected in rat heart myocardium after electrophoretic separation of the enzyme in agarose gel: MM-isozyme, MB-isozyme and BB-isozyme. The ratios of their activities were 60 : 30 : 5. Total activity of CPK per unit mass of myocardium was increased as well as transformation of its isoenzyme spectrum occurred at the early step of heart adaptation to the increased loading caused by aorta contraction. Within the third day of the heart hyperfunction the BB-isozyme activity was as high as 15% in the heart, the hybrid MB-isozyme activity was increased up to 40% and relative activity of the main muscle MM-isozyme was decreased down to 45%. The relative increase in the activity of BB-isozyme appears to reflect the preferable accumulation of the most functionally effective short-living isoenzymes, which play the key role in adaptation of tissues and systems to long-term loading.