Measurement of certain plasma and serum enzymes in the horse

The study of the use of serum or plasma enzymes in the horse is reviewed.

Analyses of such enzymes in the horse have been performed mainly for the detection and monitoring of abnormalities which affect liver tissue and muscle fibres. Examples of muscle disorders are post-anaesthetic forelimb lameness and the clinical myopathy syndrome which varies from a mild “tying-up” to a severe paralytic myoglobinuria (EPM). Measurements have also been made during training periods in an endeavour to assess the effects of exercise on muscle tissue. One of the benefits of such a study could be the prediction of the period of optimum performance.

The two enzymes most frequently used for. muscle studies have been glutamic oxaloacetic transaminase (GOT) (aspartate aminotransferase) and creatine Phosphokinase (CPK). The former, while not muscle specific and less sensitive than CPK to small amounts of muscle tissue damage, has a slower clearance rate from blood than CPK. Determination of both enzymes together has some advantages in determining the prognosis in cases with severe muscle damage. Later studies have included aldolase, which is a sensitive skeletal muscle specific enzyme and lactic dehydrogenase (LDH), which is widely distributed by various tissues at high concentrations. Most of the work on serum LDH has centred on its separation into 5 isoenzymes, and on relating the isoenzyme pattern to the various tissues. More studies on this, and on the isoenzymes of CPK, are required.

Apart from cost, one of the major problems in enzymology has been lack of a standardisation of laboratory methods which has led to a wide range of published normal values. Reliance on such values may lead to difficulties in interpretation, particularly when serum changes are small.