Distribution of enzymes in dog heart and liver; significance for assessment of tissue damage from data on plasma enzyme activities.

When organ damage is assessed from activities of tissue enzymes in plasma, it is assumed that variations in tissue enzyme content, both among individuals and between different sites within an organ, are small. We checked these assumptions, using canine heart and liver. We determined creatine kinase (CK; EC 2.7.3.2), lactate dehydrogenase (LD; EC 1.1.1.27), aspartate aminotransferase (AST; EC 2.6.1.1), and glucosephosphate isomerase (GPI; EC 5.3.1.9) in different sites of different hearts; the results showed CVs of 9.3, 9.1, 13.5, and 8.2%, respectively. A small transmural gradient in CK is found in the left ventricle. Determination of AST, GPI, and alanine aminotransferase (ALT; EC 2.6.1.2) in different sites of different livers gave CVs of 12.5, 17.0, and 11.6%, respectively. Most of the total variation is interindividual. The unreliability of early data and conflicting reports on transmural myocardial enzyme gradients are discussed. We conclude that by use of proper enzymes, such as LD for the heart and ALT for the liver, organ damage can be estimated, although there are inherent problems in relating enzyme release to loss of tissue mass.