Diagnostic value of serum creatine kinase and lactate dehydrogenase isoenzyme determinations for monitoring early cardiac damage in rats.

Serum activities of creatine kinase (CK, EC 2.7.3.2) and CK isoenzymes, lactate dehydrogenase (LDH, EC 1.1.1.27) and LDH isoenzymes, alpha-hydroxybutyrate dehydrogenase (alpha-HBDH, no EC) and the LDH/alpha-HBDH ratio were studied following a single s.c. application of 5-250 mg isoproterenol/kg body weight (b.w.) in rats. Measurements of the serum enzymes and histological and enzyme-histochemical examinations of hearts were performed 2, 4, 6, 8 and 24 h after treatment. A drastic increase in serum levels of the isoenzymes CK-MB, LDH1, LDH2 and alpha-HBDH and decrease in the ratio LDH/alpha-HBDH were observed from 2 h onwards after isoproterenol application in all dose groups, the maximum effect being after 4-8 h. Focal cellular injury in the myocardium could also be observed from 2 h onwards after isoproterenol application by an enzyme-histochemical method using nitro blue tetrazolium (NBT) whereas the earliest histological alterations using haematoxylin and eosin (HE) stain could be detected 6 h after treatment. A dose-dependent effect as to enzyme values as well as to myocardial necrosis was observed 24 h after isoproterenol application. No kidney damage could be detected on the basis of serum urea nitrogen and histological examinations. Thus, measurement of serum activities of CK-MB isoenzyme alone or LDH1-2 isoenzymes in combination with other tests to exclude kidney damage are valuable indicators of cardiac lesions in rats.