Sympathetic control of the forearm blood flow in man during brief isometric contractions |
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Authors: | Carole A Williams J G Mudd Alexander R Lind |
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Institution: | (1) Department of Physiology, St. Louis University School of Medicine, 1402 South Grand Boulevard, 63104 St. Louis, Missouri, USA;(2) Department of Physiology, East Tennessee State University, Quillen-Dishner College of Medicine, P. O. Box 19780A, 37614 Johnson City, Tennessee, USA |
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Abstract: | Summary Experiments were performed to assess the possible neurally mediated constriction in active skeletal muscle during isometric
hand-grip contractions. Forearm blood flow was measured by venous occlusion plethysmography on 5 volunteers who exerted a
series of repeated contractions of 4 s duration every 12 s at 60% of their maximum strength of fatigue. The blood flows increased
initially, but then remained constant at 20–24 ml·min−1·100 ml−1 throughout the exercise even though mean arterial blood pressure reached 21–23 kPa (160–170 mm Hg). When the same exercise
was performed after arterial infusion of phentolamine, forearm blood flow increased steadily to near maximal levels of 38.7±1.4
ml·min−1·100 ml−1.
Venous catecholamines, principally norepinephrine, increased throughout exercise, reaching peak values of 983±258 pg·ml−1 at fatigue. Of the vasoactive substances measured, the concentration of K+ and osmolarity in venous plasma also increased initially and reached a steady-state during the exercise but ATP increased
steadily throughout the exercise. These data indicate a continually increasing α-adrenergic constriction to the vascular beds
in active muscles in the human forearm during isometric exercise, that is only partially counteracted by vasoactive metabolites. |
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Keywords: | Muscular exercise Forearm blood flow Sympathetics Vasodilators |
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