title: Sympathetic control of the forearm blood flow in man during brief isometric contractions.
abstract: 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 X min(-1) X 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 X min(-1) X 100 ml(-1). Venous catecholamines, principally norepinephrine, increased throughout exercise, reaching peak values of 983 +/- 258 pg X 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 alpha-adrenergic constriction to the vascular beds in active muscles in the human forearm during isometric exercise, that is only partially counteracted by vasoactive metabolites.
mesh_terms: D000328:Adult; D004837:Epinephrine / Q000097:blood; D005260:Female; D005542:Forearm / Q000098:blood supply*; D006801:Humans; D008297:Male; D009119:Muscle Contraction; D009638:Norepinephrine / Q000097:blood; D010646:Phentolamine / Q000494:pharmacology; D012039:Regional Blood Flow / Q000187:drug effects; D013564:Sympathetic Nervous System / Q000502:physiology*
chemical_list: D009638:Norepinephrine; D004837:Epinephrine; D010646:Phentolamine