The Effect of Noradrenaline and of Increased Sympathetic Activity on the Hyperemia following Short and Prolonged Forearm Work

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Abstract
Forearm blood flow was measured plethysmographically after 5- and 55-min forearm work. While the post-exercise peak flow was essentially the same in both situations, venous PCO2, H+, lactate, K+, and osmolality were lower during and after prolonged work. It was concluded that they could not have acted as major flow-increasing factors unless the sensitivity to vasoactive stimulation was changed. The sensitivity to adrenergic stimuli was then tested by noradrenaline infusion and lower body low pressure, which evoked almost the same flow reduction after long and short term work. The infusion after prolonged work was, however, followed by a marked flow increase which could be blocked by propranolol, indicating a qualitative change in sensitivity. However, the change in adrenergic sensitivity seems not to be great enough to be the factor maintaining flow during prolonged work.