Metabolic and contractile responses of fast and slow twitch rat skeletal muscles to ischemia and reperfusion.

The purpose of this study was to investigate the significance of fiber type and the effects of the duration of ischemia on metabolic and contractile function of skeletal muscle. Under anesthesia, the distal tendons of the fast twitch extensor digitorum longus (EDL) and slow twitch soleus (SOL) muscles of the right hindlimb of female Wistar rats (250 to 300 gm) were connected to force transducers. Rats were assigned to group 1, 1 hour of ischemia; group 2, 2 hours of ischemia; or group 3, 3 hours of ischemia (n = 10 for each group). After ischemia, muscles were assessed for 2 hours of reperfusion. In both muscles, isometric twitch (Pt) and tetanus (Po) and 11 metabolic parameters were measured and compared with controls. After 1, 2, or 3 hours of ischemia Pt and Po were significantly (p < 0.05) lower than preischemic values. After 2 hours of reperfusion, forces and metabolic parameters of group 1 recovered to preischemic levels. However, contractile function of either muscle failed to recover fully after 2 hours of ischemia and 2 hours of reperfusion (SOL: Pt = 43.7 +/- 12 percent of initial; EDL: Pt = 32.2 +/- 9.2 percent) or after 3 hours of ischemia and 2 hours of reperfusion (SOL: Pt = 26.8 +/- 11 percent of initial; EDL: Pt = 19.3 +/- 6.8 percent). Although ADP and AMP recovered to preischemic levels in both muscles after 2 hours of ischemia and 2 hours of reperfusion, ATP recovered to just 70 percent in the soleus muscles (13.4 +/- 1.7 mmol/kg dry weight) and 60 percent in the extensor digitorum longus muscles (17.93 +/- 4.1 mmol/kg dry weight). After 3 hours of ischemia and 2 hours of reperfusion, ATP was further significantly (p < 0.05) decreased in the soleus muscles (48 percent initial) but not in the extensor digitorum longus muscles. Significant partial correlation coefficients (p < 0.005) were obtained between ATP levels and Pt (SOL: r = 0.757; EDL: r = 0.619) or Po (SOL: r = 0.810; EDL: r = 0.759). For this rat hindlimb model, we conclude that both fiber type and the duration of ischemia significantly affect metabolic and contractile function.