Liver and Plasma Malic Dehydrogenase Activities in the Exercised Rat. ∗

Abstract

Nikkila et al(1) have reported increased activity of serum malic dehydrogenase (MDH), and of other enzymes, as a consequence of exercise in untrained subjects and, to a lesser extent, in trained athletes Gardner et al (2) have reported similar observations with human subjects, noting a relationship of degree and duration of exercise (treadmill) with serum enzyme levels; training per se did not alter basal enzyme activities. More recently, we have reported (3) that liver and plasma MDH activities were increased in rats made to swim for 2 hours. Repeated daily exercise (training) caused an increased basal MDH activity in liver but not plasma; in the trained rat, a 2-hour swimming exercise did not elicit a further elevation of MDH activity in liver nor did it elicit an elevation in plasma. Neither acute nor repeated exercise caused any alteration in liver or plasma glutamic-pyruvate transaminase activities.

The lack of unanimity in observations from several laboratories on effects of exercise on enzyme activities indicates that several factors are involved in enzyme response. Critz(4) and Gardner et al(2) have provided evidence that the degree and duration of exercise are important in determining enzyme responie. Another possible factor is the nature of the exercise; whereas some workers have used swimming, others have used treadnil running. A difficulty with swimniing exercise is that it is not possible to quantitate. Further, at least on removal from the water, swimming could induce some degree of cold exposure which might alter enzyme activities. The present experiments were undertaken to investigate liver and plasma MDH in rats exercised on a treadmill to compare observations with those made using the swimming exercise (3)

Materials and methods.In these experiments, young male rats of the n' istar strain weiqhing 240-270 g were used. Prior to experimentation, the rats were housed in individual wire cages at an environmental temjwrature of 24 ± 1°C with laboratory chow and drinking water provided ad libitunz. Kxercise consisted of making the rats run on a circular trcatlmill at a ipecd of 1044 meters per hour; the exercise period consisted of 2 hours' continuous running and a total running distance of 2088 meters.