1677 We investigated, using the microdialysis ethanol technique, the response of nutritive flow within skeletal muscle to vasoactive substances that affect nitric oxide release and/or action. Four microdialysis probes were placed in the resting vastus lateralis of the quadriceps femoris muscle group in 9 male subjects (31±6 yrs.) and perfused with a Ringer solution containing 10 mM ethanol and three successively higher doses of sodium nitroprusside (SN), acetylcholine (AC), NG-monomethyl-L-arginine (LN), norepinephrine (NE), or no additional substance (control). Data obtained with the ethanol technique are expressed as the ethanol outflow/inflow ratio (o/i ratio), which is inversely related to changes in local nutritive flow. The ethanol o/i ratio was decreased as compared to control (indicating increased nutritive flow) in response to SN and AC. The ethanol o/i ratio was increased as compared to control (indicating reduced blood flow) in response to NE and LN (Table 1: data expressed as % difference from control and are mean ± SE). These data indicate that microdialysis can be used in vivo in humans to investigate the effects of nitric oxide on the microvasculature of skeletal muscle. Furthermore, since microdialysis can also be used to monitor metabolism, this methodology allows for a unique opportunity to simultaneously investigate the effects of nitric oxide on skeletal muscle nutritive flow and metabolism.TableThis study was supported by a Faculty Research Grant from East Carolina University