The effects of denervation, tenotomy, or tenotomy with simultaneous denervation on the activity of heparin-releasable and intracellular, residual lipoprotein lipase (LPL) and triacylglycerol (TG) content were examined in rat skeletal muscles. An influence of muscle electrostimulation on denervated and tenotomized muscles was also evaluated. Activity of both LPL fractions was decreased in denervated and/or tenotomized soleus and red portion of gastrocnemius muscles. It was accompanied by a slight elevation of the intracellular TG content. Electrostimulation increased activities of both fractions of LPL in red muscles from intact hindlimbs. In stimulated denervated muscles without or with simultaneous tenotomy, activity of two LPL fractions was also enhanced, but control values were reached only in denervated soleus muscle. Electrical stimulation had no pronounced effect on LPL activity in tenotomized muscles. In conclusion, denervation and/or tenotomy decreases LPL activity in red muscles, indicating reduction of the muscle potential to utilize circulating TG. Electrostimulation only partly restores the diminished LPL activity in denervated muscles, without any effect in tenotomized ones. Thus, to maintain LPL activity in resting muscle, intact innervation and tension are needed.

Ż ernicka, E., E. Smol, J. Langfort, and M. Gó recka. Time course of changes in lipoprotein lipase activity in rat skeletal muscles during denervation-reinnervation. J Appl Physiol 92: 535-540, 2002; 10.1152/japplphysiol.00820. 2001.-The effects of denervation-reinnervation after sciatic nerve crush on the activity of extracellular and intracellular lipoprotein lipase (LPL) were examined in the soleus and red portion of gastrocnemius muscles. The activity of both LPL fractions was decreased in the two muscles within 24 h after the nerve crush and remained reduced for up to 2 wk. During the reinnervation period, LPL activity was still reduced in the soleus and started to increase only on the 40th day. In the red gastrocnemius, LPL activity increased progressively with reinnervation, exceeding control values on the 30th day postcrush. The LPL activity in the soleus from the contralateral to denervated hindlimb was also affected, being increased on the postoperation day and then gradually decreased during the following days. In conclusion, the time course of changes in muscle LPL activity after nerve crush confirmed the predominant role of nerve conduction in controlling muscle potential to take up free fatty acids derived from the plasma triacylglycerols. However, other factors, such as muscle fiber composition and the fiber transformation, should also be considered in this aspect of the denervation-reinnervation process. Moreover, it was found that denervation of muscles from one hindlimb may influence LPL activity in muscles from the contralateral leg. skeletal muscle; denervation; reinnervation PERIPHERAL NERVE CRUSH leads to functional denervation of muscles with a variety of degenerative changes in muscle morphology and biochemistry that subsist until the regeneration of injured nerve takes place. The changes include an immediate loss of muscle activity followed by atrophy and degeneration of muscle fibers, a decrease in mitochondrial oxidative enzyme activities, and a fall in high-energy phosphate contents (6,8,21,38). Reinnervation and regeneration of skeletal muscles result in restoration, to some degree, of the original muscle fiber structure and contractile activity accompanied by a reversal of some previous biochemical alterations (8,12,24,25). The rate of recovery of metabolic alterations induced by denervation is different for enzymes of various metabolic pathways, and so it depends on the muscle fiber type (33, 38).Lipoprotein lipase (LPL) is a major enzyme responsible for hydrolysis of triacylglycerols (TG) derived from circulating TG-rich lipoproteins, making fatty acids available for cellular uptake. LPL in skeletal muscles, as in other tissues, is under a complex control by dietary and hormonal factors that modulate the enzyme activity at the cellular and molecular levels. In addition, LPL exhibits muscle fiber type-specific regulation that is closely related not only to the oxidative capacity of the muscle but also to its capability of replenishing the intramuscular TG stores (3,20). LPL activi...