Skeletal Muscle Form and Function after 4 hr Ischemia-Hypothermia

The purpose of this study was to examine the use of hypothermia to protect skeletal muscle from the effects of 4 hr of tourniquet ischemia. Muscle recovery was investigated at 6 weeks. Four hours of tourniquet ischemia was induced in two groups ( n = 8 per group) of male, Wistar rats (344 ± 15 g). In the ischemia-only group (IO), the ischemic leg was exposed to room temperature. In the ischemic-hypothermic group (IH), the ischemic leg was cooled to 5-8°C throughout the ischemic period. The contralateral leg served as control. After 6 weeks, the isometric contractile function of the gastrocnemii of both the ischemic and nonischemic legs was determined. Following the functional assessment, the soleus and plantaris muscles were removed and weighed, and biopsies were taken for muscle fiber composition, mean fiber area, and myosin heavy chains (MHC) analysis. Differences between groups ( P < 0.05) were determined using ANOVA. Muscle wet weight, tetanic forces, fiber area, fiber type, and MHC composition of IH group were the same as the control group. Yet, twitch tension and relaxation time were lower and longer in the IH group than control group. The tetanic force at 100 Hz of the IH group (12.62 ± 0.73 N/g) was significantly greater than that of the IO group (2.12 ± 0.84 N/g). The type 1 muscle fiber areas of plantaris in the IH (1.84 ± 0.04 × 1000 μm 2) were significantly greater than those of the IO group (1.56 ± 0.42 × 1000 μm 2). Myosin heavy chain composition reflected the fiber count data of the soleus with an increase in Type IIa fibers associated with a decrease in Type I fibers in the IO group compared to IH and controls. In this study, hypothermia during 4 hr of ischemia reduced the extent of muscle injury compared with ischemia at ambient temperature; this was demonstrated by better contractile function and fewer changes in muscle fiber size and composition at 6 weeks after ischemia.