Lactate dehydrogenase and its isoenzyme activities in different parts of the normal human heart.

Activity and distribution of lactate dehydrogenase (LD) and its isoenzymes (LD1-5) were determined and both the heart (H) and muscle (M) subunit activities were calculated in myocardial samples from six brain dead human organ donors with normal hearts. Ten parts of each heart were analysed. LD1-3 were found to be the main LD isoenzymes. The LD1 activity predominated in all parts analysed. The activities of total LD, H subunit and LD1 increased from atria and auricular appendages via the right ventricle to the left ventricle. The H subunit activity varied more than twofold and the M subunit activity by only 20% between different locations of the heart. The left ventricular papillary muscle was found to have higher activities than other locations of both H and M subunits. It is concluded that the isoenzyme profile could be a metabolic adaptation to divergent work demand on the different heart chambers.