Post-Effects of Nandrolone Decanoate Treatment on Contractile Responses of Rat Skeletal Muscles

Abstract

steroids have been a subject of great interest in recent years. However, animal studies have given contradictory results, ranging from an insignificant effect [1] to improvement in physical working capacity [2], strength [3][4][5], protein synthesis [6], lysosomal and mitochondrial activities [7], and functioning of the sarcotubular system [8]. In general, many factors make it difficult to compare results, such as the species used, the gender and age of animals, the type of muscle studied [3,[9][10][11], experimental conditions, the specific anabolic androgenic steroids used [12], the doses, the mode and period of administration [6,[13][14][15], and the diet [5].In skeletal muscle, contraction is generated when action potentials invade the interior of individual fibers along the membrane of the transverse tubule system (T-tubule). The passage of the action potential is followed by an increase in free myoplasmic calcium concentration that activates troponin and allows crossbridge cycling and contraction. Changes in Ca 2ϩ concentration depend on an interaction between different processes: T-tubule action potential, voltage-sensor response, putative excitation-contraction coupling mechanism, the properties of the Ca 2ϩ release channel, Ca 2ϩ diffusion to and through myofibrils, Ca Japanese Journal of Physiology, 52, 479-487, 2002 Key words: anabolic androgenic steroid, contraction. Abstract:The post-effects of nandrolone decanoate treatment (15 mg · kg Ϫ1 · week Ϫ1) were studied on contractile responses of isolated small bundles of intact slow-(soleus) and fast-(extensor digitorum longus, edl) twitch fibers in rat. Five weeks of treatment induced, in edl, an increase in the amplitude of twitch (55%) and K ϩ contracture (32%) without significant change in the time constant of relaxation and caffeine contracture. In soleus, an increase in the amplitude of twitch (35%) and caffeine contracture (0.2 mM: 218%, 0.5 mM: 88%, 5 mM: 28%, and 10 mM: 25%) was observed without change in K ϩ contracture characteristics. In addition to these effects, 10 weeks of drug treatment increased the amplitude of soleus K ϩ contracture (29%) and edl caffeine contracture (0.2 mM: 247%, 0.5 mM: 170%, 5 mM: 29%, and 10 mM: 45%), and reduced the 50% recovery time for K ϩ contracture (EC 50 ) (soleus: 37%, edl: 12%). After 5-week treatment followed by 5-week arrest, as compared to the control group, no change in the amplitude of twitch, K ϩ or caffeine contractures was found in edl. In soleus, although no significant difference was observed in the amplitude of twitch, the amplitude of K ϩ (35%) and caffeine contractures (0.2 mM: 227%, 0.5 mM: 128%) remained greater than the control group. Moreover, the EC 50 values were prolonged (46%) in soleus, whereas no significant difference was observed in edl. The present work suggests that nandrolone decanoate treatment induced differential post-effects on contractile responses developed in slowand fast-twitch skeletal muscles by acting differently on the different steps of the excitation-contractio...

Androgen replacement therapy improves function in male rat muscles independently of hypertrophy and activation of the Akt/mTOR pathway

“…2000). Alternatively, it could improve the excitation–contraction coupling mechanism (Joumaa et al. 2002), another process that could be altered by fatigue.…”