ARE THERE OXYGEN-DEFICIENT REGIONS IN RESTING SKELETAL-MUSCLE

The purpose of this study was to determine whether there are local reg ions in resting skeletal muscle in which the oxygen delivery is insuff icient to support oxidative metabolism. This hypothesis was tested by stopping the blood supply to the exteriorized cat sartorius muscle for 5 min while monitoring NADH fluorescence in localized tissue areas 15 -25 mu m in diameter. A rise in fluorescence was taken to indicate a s hift to anaerobic metabolism. Tissue sites in the arteriolar and venul ar regions of the capillary network were selected for study. After flo w stoppage, fluorescence did not change for an average of 48 +/- 22 (S D) s and then rose over a period of 61 +/- 27 s to an average value 55 +/- 19% above control for arteriolar and venular sites combined. Fluo rescence began to rise within 5 s of flow stasis in only 1 of 61 sites and within 10 s in 2 sites. There was no difference in the time cours e or magnitude of fluorescence changes at arteriolar and venular sites . The data indicate that in resting skeletal muscle, oxygen supply app ears sufficient to support oxidative metabolism in over 95% of the tis sue.