The effects of N-G-monomethyl-L-arginine (L-NMMA) on total finger and forearm, and dorsal finger and forearm skin, blood flows were studied in the basal state and during reflex sympathetic vasoconstriction in normal subjects. Total flows were measured by venous occlusion plethysmography and skin flows by laser-Doppler flowmetry (LDF). L-NMMA in doses of 2, 4, and 8 mu M/min given by constant infusion via a brachial artery catheter significantly decreased finger blood flow, forearm blood flow, and vascular conductances. At 8 mu M/min, total finger blood flow decreased 38.4% and forearm blood flow decreased 24.8%. Dorsal finger and forearm skin LDF were also significantly decreased (25 and 37% at 8 mu M/min). Body cooling significantly decreased finger blood flow (73.6%), vascular conductance, and finger LDF (59.7%). L-NMMA had no effect on total finger blood flow or dorsal finger LDF during body cooling. Nitric oxide or related compounds contribute to the basal dilator tone of the dorsal finger and forearm skin but not during reflex sympathetic vasoconstriction.
