Role of nitric oxide in exercise-induced vasodilation of the forearm.
BACKGROUND
We wished to determine the role of NO in exercise-induced metabolic forearm vasodilation.


RESULTS
Young healthy volunteers (n = 11) underwent static handgrip exercise (4 to 5 kg, 3 minutes). Forearm blood flow (FBF) measured by strain plethysmography increased from 4.1 +/- 0.7 mL.min-1.100 mL-1 at rest to 9.8 +/- 1.2 mL.min-1.100 mL-1 immediately after exercise and gradually decreased thereafter. Exercise was repeated after intrabrachial artery infusion of NG-monomethyl-L-arginine (L-NMMA) at 4.0 mumol/min for 5 minutes. L-NMMA did not alter blood pressure and heart rate. L-NMMA decreased FBF at rest to 2.9 +/- 0.4 mL.min-1.100 mL-1 (P < .01), peak FBF immediately after exercise to 7.2 +/- 0.7 mL.min-1.100 mL-1 (P < .01), and FBF during the mid to late phase of metabolic vasodilation (P < .01). Calculated oxygen consumption during peak exercise was comparable before and after L-NMMA. Intra-arterially infused L-arginine (10 mg/min, 5 minutes) reversed the inhibitory effect of L-NMMA. To determine the effect of the decrease in resting FBF on exercise-induced hyperemia, we normalized FBF after exercise by resting FBF. The percent increases in FBF after exercise from resting FBF were similar before and after L-NMMA. Furthermore, we examined the effect of intra-arterially infused angiotensin II on FBF at rest and after exercise (n = 7). Angiotensin II decreased FBF at rest from 3.1 +/- 0.3 to 1.8 +/- 0.3 mL.min-1.100 mL-1 (P < .01), peak FBF after exercise from 8.1 +/- 0.5 to 5.6 +/- 0.5 mL.min-1.100 mL-1 (P < .01), and FBF during the mid to late phase of metabolic vasodilation. The effects of L-NMMA and angiotensin II on FBF at rest and exercise were similar.


CONCLUSIONS
Our results suggest that L-NMMA decreased FBF after exercise largely by decreasing resting FBF. These results suggest that NO may not play a significant role in exercise-induced metabolic arteriolar vasodilation in the forearm of healthy humans.
Endo
T
T
Research Institute of Angiocardiology, Faculty of Medicine, Kyushu University, Fukuoka, Japan.
Imaizumi
T
T
Tagawa
T
T
Shiramoto
M
M
Ando
S
S
Takeshita
A
A
D000328:Adult; D000804:Angiotensin II / Q000494:pharmacology; D001120:Arginine / Q000031:analogs & derivatives / Q000494:pharmacology; D005542:Forearm / Q000098:blood supply*; D006801:Humans; D007269:Injections, Intra-Arterial; D008297:Male; D009569:Nitric Oxide / Q000037:antagonists & inhibitors / Q000502:physiology*; D005082:Physical Exertion; D012039:Regional Blood Flow / Q000187:drug effects; D014664:Vasodilation / Q000502:physiology*; D019323:omega-N-Methylarginine
D000804:Angiotensin II; D019323:omega-N-Methylarginine; D009569:Nitric Oxide; D001120:Arginine