ROLE OF NITRIC-OXIDE IN SKELETAL-MUSCLE BLOOD-FLOW AT REST AND DURINGDYNAMIC EXERCISE IN HUMANS

The role of nitric oxide at rest and in the active hyperemic response within skeletal muscle was investigated in eight physically active men . Three microdialysis probes were inserted into the vastus lateralis o f the quadriceps femoris muscle group in each subject. Microdialysis p robes were perfused, with a Ringer solution containing 5.0 mM ethanol, 2.5 mM glucose, and either 10 mg/ml of the nitric oxide synthase inhi bitor N-G-monomethyl-L-arginine (L-NMMA) monoacetate salt, 30 mg/ml of the nitric oxide precursor L-arginine, or no additional substance (co ntrol probe). Subjects performed one-legged cycling exercise at work r ates ranging from 25 to 100 W. Dialysate and perfusate ethanol concent rations were presented as the ratio of [ethanol](dialystate)to [ethano l](perfusate) (ethanol outflow-to-inflow ratio), an indicator that is inversely related to blood flow. The ethanol outflow-to-inflow ratios at rest were 0.614 +/- 0.032, 0.523 +/- 0.023, and 0.578 +/- 0.039 in the L-NMMA, L-arginine, and control probes, respectively. Calculated r esting blood flows were therefore 8.7 +/- 4.1, 20.5 +/- 4.6, and 14.0 +/- 4.7 ml.min(-1).100 g(-1) around the L-NMMA, L-arginine, and contro l probes, respectively. The ethanol outflow-to-inflow ratios were sign ificantly higher at all exercise intensities in the L-NMMA probe than in the control and L-arginine probes, resulting in calculated blood fl ows of 195 +/- 55, 407 +/- 47, and 352 +/- 60 ml.min(-1).100 g(-1) at 25 W and 268 +/- 65, 602 +/- 129, and 519 +/- 113 ml.min(-1).100 g(-1) at 100 W around the L-NMMA, L-arginine, and control probes, respectiv ely. Skeletal muscle blood flow was therefore reduced both at rest and during continuous, dynamic exercise by the action of L-NMMA, whereas blood flow was increased only at rest by L-arginine.