The behavior of some enzymes of the hypertrophied and postnatally developing myocardium of the rat.

The present study was undertaken in order to investigate the behavior of lactate dehydrogenase (LDH) and hexokinase (HK) in the mechanically overloaded and the postnatally developing left ventricle of the rat. In Goldblatt rats (GBR) 2 to 4 months after operation total LDH activity was decreased by 7%, accompanied by an isoenzyme shift towards a higher M proportion. Swimming rats (SR) showed an 11% increase in LDH activity. HK activity was increased by 14% in GBR and unaltered in SR. Histochemical investigations revealed no indication of heterogeneous alterations in various areas of the myocardium. During postnatal development, a gradual increase of activity and H subunit proportion of LDH were observed. HK activity was increased after one week, but underwent a slow decreased thereafter. These changes are interpreted as processes of adaptation to the conditions of extrauterine life.