Abstract
Lactate dehydrogenase (LDH) is widely distributed enzyme in cells of various living systems where it is involved in carbohydrate metabolism catalyzing interconversion of lactate and pyruvate with NAD+/NADH coenzyme system. Cells of tissues are direct source of lactate dehydrogenase isoenzymes that are naturally distributed in blood plasma/serum of animals and humans producing characteristic profile. This profile depends on intracellular isoenzyme concentration in all tissues that contribute to the common pool of lactate dehydrogenases in plasma/serum as a consequence of natural cell degradation. LDH is widely distributed in the body, high activities are found in the heart, liver, skeletal muscle, kidney, and erytrocytes, whereas lesser amounts are found in the lung, smooth muscle, and brain. Because of its widespread activities in numerous body tissues, LDH is elevated in a variety of disorders. There are many conditions that contribute to increased activity of LDH. An elevated total LDH value is a rather nonspecific finding. Therefore, LDH assays assume a more clinical significance when separated into isoenzyme fractions. The activity of LDH and its serum and tissue patterns and composition show great variations between the species. These differences do not allow using catalytic activities of LDH isoenzymes from one species to another. Instead, the pattern of serum LDH isoenzymes should be interpreted in respect to its species origin that is important in particular in veterinary medicine. Determination of total LDH activity and its isoenzyme pattern in serum of mammals had become one of the biochemical indicators in the assessment of organ disorders. When the content of cells is released from tissue to plasma, as on cell injury, the LDH isoenzyme pattern of the serum changes in favour of the profile of the affected organ (tissue) that can be used in the diagnostic practice.
Highlights
Lactate dehydrogenase (LDH) is widely distributed enzyme in cells of various living systems where it is involved in carbohydrate metabolism catalyzing interconversion of lactate and pyruvate with NAD+/NADH coenzyme system
An elevated total LDH value is a rather nonspecific finding. erefore, LDH assays assume a more clinical significance when separated into isoenzyme fractions. e activity of LDH and its serum and tissue patterns and composition show great variations between the species. ese differences do not allow using catalytic activities of LDH isoenzymes from one species to another
The mean activity of LDH was higher in milk from udders affected with Subclinical mastitis (SCM) than in milk from healthy udders. ere were no significant differences in blood serum LDH of healthy and SCM cows. e higher level of LDH in mastitic milk than blood serum shows that blood serum was not the sole source of this enzyme in mastitic milk and it was probably liberated from disintegrated leukocytes and the parenchymal cells of the udder. e increment in LDH in milk of udders shows the presence of tissue damage provoked by SCM. e origin of LDH in mastitic milk is attributed to leukocytes and epithelial cells from the udder [15, 46]
Summary
Keller [20] described the behaviour of serum LDH isoenzymes during experimentally induced liver and muscle damage in bovine. Total LDH showed fairly high serum levels, but in view of its normal variation in serum, the changes appeared less significant than that of its isoenzymes. Sanda [30] evaluated the serum enzymes in experimental hepatic lesions and clinical cases with hepatic and muscular lesions in dairy cattle including total LDH activity and its isoenzymes. Total serum LDH activity increased with the occurrence of skeletal muscular and hepatic lesions. E author concludes that when the activity of total serum LDH is high, LDH isoenzymes should be assessed He recommended this enzyme as an aid in differential diagnosis of hepatic and/or skeletal muscular lesions in dairy cattle. In most birds, increased plasma LDH activity with normal CK activity is suggestive of hepatocellular disease. e plasma LDH activity is considered to have a wide tissue distribution in reptiles. erefore increases in the plasma LDH activity may be associated with damage to the liver, skeletal muscle, or cardiac muscle [36]
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