Heterogeneous responses of human limbs to infused adrenergic agonists: a gravitational effect?

• Published in: Journal of applied physiology (1985) Vol. 92; no. 5; pp. 2105 - 2113
• Main Authors: Pawelczyk, James A, Levine, Benjamin D
• Format: Journal Article
• Language: English
• Published: Legacy CDMS Am Physiological Soc 01.05.2002; American Physiological Society
• Subjects: Adaptation, Physiological - physiology; Adolescent; Adrenergic Agonists - administration & dosage; Adult; Arms; Biological and medical sciences; Blood Flow Velocity - drug effects; Brachial Artery - physiology; Dose-Response Relationship, Drug; Female; Femoral Artery - physiology; Forearm - blood supply; Forearm - physiology; Fundamental and applied biological sciences. Psychology; Gravitation; Gravity; Hemodynamics. Rheology; Humans; Infusions, Intra-Arterial; Isoproterenol - administration & dosage; Leg - blood supply; Leg - physiology; Legs; Life Sciences (General); Male; Nervous system; Phenylephrine - administration & dosage; Reference Values; Regional Blood Flow - drug effects; Regional Blood Flow - physiology; Space life sciences; Vascular Resistance - drug effects; Vascular Resistance - physiology; Vertebrates: cardiovascular system; Clinical Trial; Non-Nasa Center; Nasa Discipline Cardiopulmonary; Human; Agonist; Vasoconstriction; Lower limb; α1-Adrenergic receptor; Posture; β-Adrenergic receptor; Heterogeneity; Vasomotricity; Upper limb; Blood pressure; Hemodynamics; Gravity; NASA Discipline Cardiopulmonary; Non-NASA Center
• ISSN: 8750-7587; 1522-1601
• DOI: 10.1152/japplphysiol.00979.2001

1  Noll Physiological Research Center and Department of Kinesiology, The Pennsylvania State University, University Park, Pennsylvania 16802; and 2  Institute for Exercise and Environmental Medicine, University of Texas Southwestern Medical Center and Presbyterian Hospital of Dallas, Dallas, Texas 75231 Unlike quadrupeds, the legs of humans are regularly exposed to elevated pressures relative to the arms. We hypothesized that this "dependent hypertension" would be associated with altered adrenergic responsiveness. Isoproterenol (0.75-24 ng · 100 ml limb volume 1 · min 1 ) and phenylephrine (0.025-0.8 µg · 100 ml limb volume 1 · min 1 ) were infused incrementally in the brachial and femoral arteries of 12 normal volunteers; changes in limb blood flow were quantified by using strain-gauge plethysmography. Compared with the forearm, baseline calf vascular resistance was greater (38.8 ± 2.5 vs. 26.9 ± 2.0 mmHg · 100 ml · min · ml 1 ; P  < 0.001) and maximal conductance was lower (46.1 ± 11.9 vs. 59.4 ± 13.4 ml · ml 1 · min 1 · mmHg 1 ; P  < 0.03). Vascular conductance did not differ between the two limbs during isoproterenol infusions, whereas decreases in vascular conductance were greater in the calf than the forearm during phenylephrine infusions ( P  < 0.001). With responses normalized to maximal conductance, the half-maximal response for phenylephrine was significantly less for the calf than the forearm ( P  < 0.001), whereas the half-maximal response for isoproterenol did not differ between limbs. We conclude that 1 - but not -adrenergic-receptor responsiveness in human limbs is nonuniform. The relatively greater response to 1 -adrenergic-receptor stimulation in the calf may represent an adaptive mechanism that limits blood pooling and capillary filtration in the legs during standing. vasoconstriction; -adrenergic receptor; -adrenergic receptor