Plasma lactate dehydrogenase

Assay of plasma enzymes aids diagnosis and prognosis. For example, a myocardial infarction elevates serum levels of lactate dehydrogenase isozyme I,. 

An important point to note is that this the above reaction produces lactate, not lactic acid. Nonetheless, protons are produced in glycolysis but in another reaction (Appendix 6.5). Consequently, the two end-products are lactate plus protons, which can be described as lactic acid. Despite this discussion, it can be argued that lactate dehydrogenase is not the terminal reaction of glycolysis, since the lactate plus protons have to be transported out of the cell into the interstitial space. This requires a transporter protein, which transports both lactate and protons across the plasma membrane and out of the cell. 

Plasma hormones and enzymes of testicular origin were used as markers for evaluation of acute testicular toxicity in rats treated with 1,3-DNB. Lactate dehydrogenase isozyme C4 (LDH-C4) and ABP were both elevated after treatment with doses between 10 and 25 mg/kg of 1,3-DNB (Reader et al. 1991). Testosterone levels were reduced after treatment with 10 and 32 mg/kg of 1,3-DNB (Reader etal. 1991 Rehnberg et al. 1988). 

The involvement of testosterone in the testicular atrophy caused by di(2-ethyl-hexyl) phthalate was examined by co-administration of testosterone (1 mg/kg bw) subcutaneously with 2000 mg/kg bw di(2-ethylhexyl) phthalate [purity not specified] in groundnut oil to adult male Wistar rats for 15 days (Parmar et al., 1987). Administration of di(2-ethylhexyl) phthalate reduced the sperm count and also significantly increased the activity of y-GT, lactate dehydrogenase and P-glucuronidase and decreased the activity of sorbitol dehydrogenase and acid phosphatase. Co-adminis-tration of testosterone seemed to normalize the sperm count and the activity of testicular enz5mies. The role of testosterone in the testicular toxicity of di(2-ethylhexyl) phthalate has not been fully elucidated. Several reports refer to increased or decreased testosterone levels in plasma and testicular tissue. 

Timbrell et al. (1996) reported that much higher hydrazine concentrations were required in rat hepatocyte cultures in comparison to plasma concentrations in male Sprague-Dawley rats to elicit the following hepatic/hepatocellular effects lactate dehydrogenase leakage, ATP and GST depletion, increase in citrulline level, protein synthesis inhibition, taurine leakage and triglyceride accumulation. 

Reasons for the presence of enzymes in the plasma Enzymes can normally be found in the plasma either because they were specifically secreted to fulfill a function in the blood, or because they were released by dead or damaged cells. Many diseases that cause tissue damage result in an increased release of intracellular enzymes into the plasma. The activities of many of these enzymes (for example, creatine kinase, lactate dehydrogenase, and alanine aminotransferase) are routinely determined for diagnostic purposes in diseases of the heart, liver, skeletal muscle, and other tissues. 

Both aspartate aminotransferase and alanine aminotransferase are released into the blood after damage to tissues or after cell death. Consequently, they are used as diagnostic tools when heart or liver damage has occurred, such as after a heart attack or in hepatitis, respectively. Other enzymes are also released into the blood at such times. For example, damage to heart muscle is further characterized by the presence of isoenzymes of creatine kinase or lactate dehydrogenase in the plasma. 

Propylene glycol causes acute hemolysis with raised lactate dehydrogenase activity, and raised bilirubin and plasma hemoglobin concentrations after use of a stock solution during intravenous administration of glyceryl trinitrate (11). 

The cell membrane serves as a protective barrier in renal cells. It is the initial site which p-lactams encounter in their journey to the cellular environment from the blood or tubular fluid, p-lactams may disrupt the functional organization of the membrane through peroxidation of membrane lipids, which, in turn, leads to the inability of membrane to serve as an osmotic barrier and causes the cytosol contents to leak. As a result of the cephalosporins disruptive effect on cell membrane, increased leakage of the cytosolic enzyme lactate dehydrogenase (LDH) occurs. The increased LDH concentration was from the cytosol of the renal cortex [49,71] or from isolated proximal and distal tubular cells [39] or in the urine of experimental animals [39]. The results of these studies indicate that plasma membrane became permeable to large molecules such as LDH. After cephalosporin treatment, cephaloridine caused the greatest decrease of LDH concentration in cytosol [49]. Whereas, cephaloridine induced a greater release of LDH from proximal tubular cells than cepha-lothin and cephalexin, distal cells were not affected by any of these cephalosporins [38,39]. 

Lactate dehydrogenase, serum Luteinizing hormone, serum/plasma... 

E202 Greenberg, N. and Byrne, D. (1985). Plasma lactate dehydrogenase activity assayed with the Kodak Ektachem 7(X) Analyzer is unaffected by platelet contamination. Clin. Chem. 31, 1022, Abstr. 623. 

Potassium oxalate and NaF (2000/2 500 mg/1) lead to markedly reduced lactate dehydrogenase values and are therefore unsuitable for plasma separation. 

Combined ammonium and/or potassium oxalate does not cause shrinkage of erythrocytes. However, other oxalates can cause shrinkage by drawing water into the plasma. Reduction in hematocrit may be as much as 10%, causing a reduction in the concentration of plasma constituents of 5%. As fluid is lost from the cells, an exchange of electrolytes and other constituents across the cell membrane occurs. Oxalate inhibits several enzymes, including acid and alkaline phosphatases, amylase, and lactate dehydrogenase, and may cause precipitation of calcium as the oxalate salt. 

Hemolysis is defined as the disruption of the red cell membrane and results in the release of hemoglobin. Serum shows visual evidence of hemolysis when the hemoglobin concentration exceeds 200 ing/L. Slight hemolysis has little effect on most test values. Severe hemolysis causes a slight dilutional effect on those constituents present at a lower concentration in the erythrocytes than in plasma. However, a notable effect may be observed on those constituents that are present at a higher concentration in erythrocytes other than in plasma. Thus plasma activities or concentrations of aldolase, total acid phosphatase, lactate dehydrogenase, isocitrate dehydro-... 

Although transport of specimens from the patient to the clinical laboratory is often done by messenger, pneumatic tube systems have been used to move the specimens more rapidly over long distances within the hospital. Hemolysis may occur in these systems unless the tubes are completely filled and movement of the blood tubes inside the specimen carrier is prevented. The pneumatic tube system should be designed to eliminate sharp curves and sudden stops of the specimen carriers, because these factors are responsible for much of the hemolysis that may occur. With many systems, however, the plasma hemoglobin concentration may be increased, and the serum activity of red cell enzymes, such as lactate dehydrogenase, may also be increased. Nonethe-... 

Bais R, Edwards JB. Plasma lactate dehydrogenase activity will be increased if detergent and platelets are present. Clin Chem 1977 23 1056-8. 

There are five enzymes that are commonly used in diagnosis of liver disease Aspartate aminotransferase (AST EC 2.6.1.1), alanine aminotransferase (ALT EC 2.6.1.2), alkaline phosphatase (ALP 3.1.3.1), and y-glutamyl transferase (GGT EC 2.3.2.2), are commonly used to detect liver injury, and lactate dehydrogenase (LD EC 1.1.1.27) is occasionaEy used. ALT and GGT are present in several tissues, but plasma activities primarily reflect liver injury. AST is found in liver, muscle (cardiac and skeletal), and to a liipited extent iti fed cells. LD has wide tissue distribution, and is thus relatively nonspecific. ALP is found in a number of tissues, but in normal individuals primarEy reflects bone and liver sources. Thus based on tissue distribution, ALT and GGT would seem to be the most specific markers for liver injury. 

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