Role of local contractile activity and muscle fiber type on LPL regulationduring exercise

The purpose of this study was to determine the influence of local contracti le activity on lipoprotein lipase (LPL) regulation in skeletal muscle. Shor t-term voluntary run training increased LPL mRNA concentration and LPL immu noreactive mass about threefold in white skeletal muscles of the rat hindli mb tall P < 0.01). Training also increased total and heparin-releasable LPL enzyme activity in white hindlimb muscles and in postheparin plasma (P < 0 .05). Training did not enhance LPL regulation in a white muscle that was no t recruited during running (masseter). LPL levels were already high in red skeletal muscles of control rats, and training did not result in a further rise. In resting rats, local electrical stimulation of a motor nerve to a p redominantly white muscle caused a significant rise in LPL mRNA, immunoreac tive mass, and enzyme activity relative to the contralateral control muscle of the same animals tall P < 0.01). Finally, LPL expression was several ti mes greater in a red muscle (soleus) of rats with normal postural activity than rats with immobilized hindlimbs (P < 0.01). In summary, these studies support the hypothesis that local contractile activity is required for incr easing LPL expression during exercise training and for maintaining a high l evel of LPL expression in postural muscles.