Heat stress produces an early phase of protection against oxidative damagein human muscle

Background: It has been rarely reported that heat stress induces an early p hase of protection against oxidative damage, whereas a delayed phase of pro tection is shown in heat stress. To explore the early effect of heat stress against oxidative damage, we evaluated the changes in contractility, lipid peroxidation, and ultrastructure induced by hydrogen peroxide (H2O2) With or without heat stress (MS) in human skeleton muscle Methods: Thirty-two muscle samples were obtained from the vastus lateralis muscle of 7 subjects. These specimens were divided into three groups based on form of treatment: HS (n=13), non HS (n=14), and control group (n=5). Th e control group was performed under identical conditions without H2O2 Speci mens in the MS group were incubated at 42 degrees C for 20 min, while those in the non-HS and control groups were maintained at 37 degrees C. Results: The control group showed no significant change in contractile forc e. Although contractile force significantly decreased 30 min after H2O2 adm inistration in both the HS and non-HS groups, only the MS group showed appa rent recovery of contractile force 60 min after H2O2 administration. Lipid peroxidation was lower in the HS group than in the non-HS group. Ultrastruc tural examination revealed less mitochondrial damage in the HS group compar ed with the non-HS group. Conclusion: We found that human skeleton muscle escaped cellular damage ind uced by H2O2 in the early phase after heat stress. These data suggest evide nce for an early effect of heat stress against ischemia/reperfusion injury in human muscle.