Preconditioning with short cycles improves ischemic tolerance in rat fast-and slow-twitch skeletal muscle

Aim: The aim of this study was to investigate whether the efficacy of ische mic preconditioning (IP) in rat skeletal muscle depends on the duration of the preconditioning cycles. Methods: Rats were divided into four groups (n = 10 each). The right hindlimb of rats in group A were subjected to 2.5 h o f tourniquet ischemia followed by 2 h of reperfusion (I-R). Thereafter, mus cular function was analyzed in vitro and high-energy phosphates (HEP) were determined by HPLC. Before I-R, right hindlimbs of rats in groups B-D subje cted to IP with three cycles each consisting of 2.5, 5 or 10 min of ischemi a followed by reperfusion for the same duration. Results: Postischemic func tion of the extensor muscle was significantly improved with all three preco nditioning protocols. Postischemic function of the soleus muscle was only i mproved by IP with three cycles of 5 min of ischemia and 5 min of reperfusi on. Postischemic HEP tissue levels were not influenced by IF. Conclusion: T his study shows for the first time that IP increases ischemic tolerance not only of fast-twitch but also of slow-twitch skeletal muscle. The efficacy of IP seems to be less dependent on the duration of the single precondition ing cycle than on the number of cycles performed. Three cycles each of 2.5, 5 or 10 min ischemia and reperfusion significantly improved postischemic s keletal muscle function. Tissue levels of HEPs, however, were not influence d by IP indicating that preservation of HEPs does not play a major role in the effects of IP on rodent skeletal muscle. Copyright (C) 2000 S. Karger A G, Basel.