The effect of sympathetic innervation on canine muscle and skin blood flow

Two microsphere techniques were used to measure skin and muscle capillary blood flow, plus blood flow through arteriovenous anastomoses (AVAs), before and after unilateral lumbar sympathectomy in 12 anesthetized dogs. Sympathectomy did not alter capillary flow to tibial muscle, thigh, or lower leg skin, whereas paw skin capillary flow decreased, from 28 to 13 mL/min/100 g. However, total extremity blood flow increased after sympathectomy, because of the rate of AVA flow, which increased from 7 to 30 mL/min. Transient nerve stimulation of the cut distal end of the lumbar sympathetic chain immediately and reversibly decreased the AVA flow rate, from 30 to 10 mL/min. The rate of total hind-limb capillary flow also decreased during nerve stimulation, from 86 to 46 mL/min. The only significant effect of sympathectomy in anesthetized dogs was to redistribute distal hind-limb capillary blood flow to AVAs, which are anatomically located in this region. In contrast to capillaries, AVAs have little intrinsic myogenic tone and are highly dependent on adrenergic innervation.