Eur J Appl Physiol (1996) 73:516-520 © Springer-Verlag 1996 Kei Sakamoto • Kazunori Nosaka • Satoshi Shimegi Hajime Ohmori • Shigeru Katsuta Creatine kinase release from regenerated muscles after eccentric contractions in rats Accepted: 12 January 1996 Abstract The purpose of this study was to test the hy- pothesis that an increase in plasma creatine kinase (CK) activity after eccentric contractions (ECC) would be attenuated in regenerated muscle fibres. Adult male Wistar rats (aged 12-14 weeks) were randomly as- signed to a treatment group (n = 14) or a control group (n = 10). In the treatment group, 1.2% barium chloride solution (BaCI2) was injected into the tibialis anterior (TA) and extensor digitorum longus (EDL) muscles to induce degeneration and subsequent regeneration. The same amount of isotonic saline solution was injected into TA and EDL for the control group. Histological observation showed that approximately 50% of the fi- bres in the transverse sections of both muscles under- went necrosis 2 days after BaC12 injection. The CK ac- tivity increased about tenfold at 2-4 h after BaC12 injec- tion. At 4 weeks after BaCI2 injection, when the regen- eration process was almost complete, the TA and EDL of anaesthetized rats from both groups were subjected to ECC in which maximal dorsiflexion was caused by nerve electrical stimulation and the flexed foot was for- cibly extended by a lever arm connected to a motor. This action was performed in 2 sets of 30 repetitions. Maximal isometric torque of the dorsiflexors decreased to about 15% (P < 0.01) of the pre-ECC value immedi- ately after the exercise. Blood samples were collected before and 2, 4, 12, 24, 48 h after ECC. The CK activity increased significantly (P<0.01) and peaked at 2-4 h K. Sakamoto ([]) - K. Nosaka Laboratory of Exercise and Sports Science, Department of EnvironmentalScience, Yokohama City University, 22-2, Seto, Kanazawa-ku,Yokohama, 236 Japan S. Shimegi Exercise Physiology Laboratory, Faculty of Health and Sports Sciences, Osaka University, Toyonaka, Osaka 560, Japan H. Ohmori - S. Katsuta Institute of Health and Sport Sciences, University of Tsukuba, Tsukuba, Ibaraki 305, Japan after ECC, and there was no significant difference in the amount of CK increase between the treatment [1007 (SEM 120) IU.I-1] and the control [1064 (SEM 120) IU-I-1] group. Contrary to the hypothesis, CK re- lease after ECC was not attenuated in muscle regener- ated from BaC12-induced myonecrosis. Key words Myonecrosis • Regeneration • Creatine kinase • Barium chloride • Eccentric contraction Introduction Increased levels of muscle protein, especially creatine kinase (CK), in the blood have been used as markers of skeletal muscle disease (Jones and Witkowski 1983; Rowland 1980), myocardial infarction (Ebbeling and Clarkson 1989; Warhol et al. 1985), or exercise-induced muscle damage (Ebbeling and Clarkson 1989; Noakes 1987). Because CK is found almost exclusively in mus- cle cells, increased blood levels of CK are considered to be due to leakage from damaged muscle fibres. Previous studies have demonstrated that repeating a single bout of eccentric contractions (ECC) results in a smaller or no increase in plasma CK activity after the second bout of contractions (Clarkson et al. 1992; No- saka et al. 1991; Schwane and Armstrong 1983). The lower CK response has been suggested to be due to less muscle damage because of changes in the structure of muscle fibres, i.e. cytoskeletal proteins such as desmin (Helliwell 1988; Thornell et al. 1983) or surrounding connective tissue, i.e. collagen, proteoglycans (Fritz and Stauber 1988; Stauber 1989) that have occurred during the regeneration process. These changes in muscle tis- sue may reduce the susceptibility of muscle fibres such that they can better withstand a subsequent stimulus of muscle damage. If this were to be the case, it is hypo- thesized that regenerated muscle would result in less CK leakage after ECC compared to the muscle that has not undergone degeneration and subsequent regenera- tion.