Mechanisms Of Acute Prolonged Eccentric Exercise Induced TNF-α Expression In Rat Skeletal Muscle

The main purpose of the present study is to investigate the mechanisms of TNF-a expression in rat skeletal muscle in response to an acute bout of prolonged eccentric exercise.A secondary purpose of this study is to investigate the relationship between serum TNF-a response and skeletal muscle mechanical and oxidative damage.Methods:Thirty three-month old female Sprague-Dawley rats were randomly divided into the following five groups(N=6):ran at 25 m/min,-10%grade on the treadmill for 1h(Ex1h) or 2h(Ex2h) and were killed immediately;ran on the treadmill for 2h and were killed at 6 h(Ex2+6h) or 24h(Ex2+24h) after exercise;or killed at rest as controls(REST).After anaesthesia by injection of 10%chloral hydrate,the serum,deep portion of vastus lateralis(DVL) and gastrocnemius(GAS) muscles of the rats were collected and frozen at -80℃.Results:1) TNF-a mRNA levels showed progressive increases after exercise in GAS of Ex1h,Ex2h,Ex2+6h and Ex2+24h rats,and in DVL of Ex2h,Ex2+6h and Ex2+24h rats.2) Both GAS and DVL TNF-a protein levels showed progressive increases in Ex1h,Ex2h,Ex2+6h and Ex2+24h.3) P65 protein levels in the GAS and DVL nuclear extraction were significantly higher in Ex1h,Ex2h and Ex2h+24h rats compared to Rest rats.4) Mitochondrial aconitase activity showed progressive decline in GAS and DVL of Ex1h and Ex2h compared with Rest,but was elevated in Ex2+6h and returned to REST levels at Ex2+24h.5) GAS and DVL H₂O₂ concentrations and MPO activities were significantly higher in Ex2+24h rats vs.REST rats.6) During and after exercise,there were no significant changes in Mn-SOD activity in GAS or DVL.7) During and after exercise,the magnitude of blood vessels hyperemia, connective tissue hyperplasia,muscle fiber necrosis and inflammation cell infiltration showed progressive aggravation.8) Serum concentrations of TNF-a and MDA,and CK activity were significantly higher in Ex2,Ex2+6h and Ex2+24h rats,compared with REST rats.9) In the testing range of this study,serum concentrations of TNF-a showed significant positive correlations with CK activity and MDA level.Conclusions:1) Acute prolonged eccentric exercise can induce TNF-a mRNA and protein expression in rat skeletal muscle.2) The increased TNF-a expression is probably triggered by NFkB activation by elevated ROS production in a biphasic manner.Increased mitochondrial 0₂ during exercise can explain the first phase, whereas the increased de novo expression of TNF-a and elevated H₂O₂ during respiratory burst can explain the second phase.3) The observed upregulation of TNF-a may play an important role in the inflammatory response of skeletal muscle to mechanical and oxidative damage and for the maintenance of oxidant-antioxidant homeostasis.