Different vasodilator responses of human arms and legs

• Published in: The Journal of physiology 2004-05, Vol.556 (3), p.1001-1011
• Main Authors: Newcomer, Sean C., Leuenberger, Urs A., Hogeman, Cynthia S., Handly, Brian D., Proctor, David N.
• Format: Article
• Language: English
• Subjects: Acetylcholine - administration & dosage; Acetylcholine - pharmacology; Adult; Algorithms; Arm - physiology; Blood Flow Velocity - drug effects; Blood Flow Velocity - physiology; Blood Pressure - drug effects; Blood Pressure - physiology; Brachial Artery - drug effects; Brachial Artery - physiology; Femoral Artery - drug effects; Femoral Artery - physiology; Heart Rate - drug effects; Heart Rate - physiology; Humans; Hyperemia - physiopathology; Infusions, Intra-Arterial; Leg - physiology; Male; Nitroprusside - administration & dosage; Nitroprusside - pharmacology; Research Papers; Substance P - administration & dosage; Substance P - pharmacology; Vasodilation - drug effects; Vasodilation - physiology
• ISSN: 0022-3751; 1469-7793
• DOI: 10.1113/jphysiol.2003.059717

Forearm vascular responses to intra-arterial infusions of endothelium-dependent and -independent vasodilators have been thoroughly characterized in humans. While the forearm is a well-established experimental model for studying human vascular function, it is of limited consequence to systemic cardiovascular control owing to its small muscle mass and blood flow requirements. In the present study we determined whether these responses could be generalized to the leg. Based upon blood pressure differences between the leg and arm during upright posture, we hypothesized that the responsiveness to endothelium-dependent vasodilators would be greater in the forearm than the leg. Brachial and femoral artery blood flow ( Q , ultrasound Doppler) at rest and during intra-arterial infusions of endothelium-dependent (acetylcholine and substance P) and -independent (sodium nitroprusside) vasodilators were measured in eight healthy men (22–27 years old). Resting blood flows in the forearm before infusion of acetylcholine, substance P or sodium nitroprusside were 25 ± 4, 30 ± 7 and 29 ± 5 ml min −1 , respectively, and in the leg were 370 ± 32, 409 ± 62 and 330 ± 30 ml min −1 , respectively. At the highest infusion rate of acetylcholine (16 μg (100 ml tissue) −1 min −1 ) there was a greater ( P < 0.05) increase in Q to the forearm (1864 ± 476%) than to the leg (569 ± 86%). Similarly, at the highest infusion rate of substance P (125 pg (100 ml tissue) −1 min −1 ) there was a greater ( P < 0.05) increase in Q to the forearm (911 ± 286%) than to the leg (243 ± 58%). The responses to sodium nitroprusside (1 μg (100 ml tissue) −1 min −1 ) were also greater ( P < 0.05) in the forearm (925 ± 164%) than in the leg (326 ± 65%). These data indicate that vascular responses to both endothelium-dependent and -independent vasodilator agents are blunted in the leg compared to the forearm.