Exercise-induced changes in lipoprotein lipase activity (LPLA) in skeletal muscles of the dog

Abstract

The aim of this work was to study the effect of physical exercise on muscle lipoprotein lipase activity (LPL) in dogs. Existence of two forms of LPL: heparin releasable and unreleasable was demonstrated in skeletal muscles, and the changes in the activity of both forms were followed during 3 h treadmill running, using biopsy samples taken from m. biceps femoris. During the first two hours of exercise the heparin releasable form of LPL was progressively increasing, whereas the heparin unreleasable form of the enzyme was decreasing. Thus, a significant negative correlation between activities of the two forms was ascertained (r = 0.72, P less than 0.01). In the final period of exercise, activity of the heparin releasable form of LPL tended to stabilize on the enhanced level, and activity of the heparin unreleasable form increased. In the further series of experiments a relationship between exercise intensity and activity of the heparin releasable form of LPL was studied during 1 h exercise bouts. A significant positive correlation (r = 0.84, P less than 0.001) was ascertained between LPL activity and intensity of work. A comparison between LPL activity in the muscle engaged in exercise (m. biceps femoris) and nonactive muscle (m. coccygeus) revealed that the enhancement of the enzyme activity during physical work does not occur in the latter.

In conclusion: it was found that physical exercise induces a marked intensity-dependent increase of LPL activity in working muscles, which is probably caused by an elevated transport of the enzyme molecules from the muscle cells to the intravascular space. The latter suggestion is based on the reciprocal changes of the heparin releasable and unreleasable (probably intracellular) forms of LPL.