Isoenzymes in Laboratory Animals

Isoenzyme studies are useful in resolving the specific organ of origin when certain enzymes common to multiple organs are elevated in a disease process. In order to discriminate the specific organ effects of some toxins we determined the isoenzyme distribution patterns of lactate dehydrogenase LD and creatine kinase CK in monkeys, guinea pigs, rats, and mice. Serum and tissue extracts from normal animals were separated by electrophoresis. An immunochemical method of isoenzyme determination was used to mouse heart extracts. Five distinct bands of LD were demonstrated in all the species studied. As in man, LD1 fraction was the dominant fraction in heart and kidney tissues whereas LD5 was the preponderant fraction in skeletal muscle and liver. The serum of rhesus monkeys like man, showed the LD2 fraction to be greater than the LD1 fraction. All the other species tested showed no significant difference between LD1 and LD2 fractions. In man and in the rhesus monkey but not later species when LD1 greater than or equal to LD2 myocardial injury could be suggested. No CK-MB fraction was seen in the sera in any of the species tested, although many organs other than the heart contained high values of the CK-MB fraction. Isoenzyme electrophoresis may be a useful tool for evaluating single organ pathology in animals but diagnostic concepts in human diagnosis may not be applicable to laboratory animals.