Effects of Exercise on Plasma and Tissue Levels of Lactate Dehydrogenase and Isoenzymes in Rats

Elevated and variable serum levels of LDH in control rats were found to result from the commonly used method of collecting the blood by cardiac puncture and from the preparation of serum for analysis. Evidence is presented that LDH from heart, red blood cells, and platelets are contributing factors to this discrepancy. When blood was collected from the inferior vena cava and plasma was immediately prepared in plastic tubes for analysis instead of serum, the extraneous factors were largely eliminated. These modifications were employed for the determination of LDH and isoenzymes in untrained rats subjected to 4 hours of swimming, and in untrained controls. The data indicated a 3-fold increase of LDH activity in the plasma of exercised rats. LDH-isoenzyme determination and histological examination indicated that probable sources of the increased LDH activity were the heart, liver, and skeletal muscle.