Differentiation of neurogenic vasoconstrictor responses in skin and skeletal muscle of dog hindlimb.

Femoral blood flow was measured electromagnetically in chloralose-anaesthetised dogs pretreated with atropine and pancuronium, during preganglionic stimulation of the ipsilateral lumbar sympathetic chain. Circulation to the paw pads was occluded with a ligature. Trains of 10 stimuli at frequencies of 4 or 40 Hz elicited vasoconstrictor responses, the recovery phases of which were prolonged during temporary occlusion of the circulation to the leg below the knee, and shortened in the presence of low doses of the ganglion blocking drug hexamethonium (0.5-3 mg/kg i.v.). Numerical summation of the responses persisting after 2 mg/kg hexamethonium and those obtained during lower limb occlusion produced curves that closely matched control responses in timecourse and amplitude. It is suggested that skin and muscle resistance vessels in the hindlimb receive their primary vasoconstrictor nerve supply via peripheral pathways that can be distinguished by the sensitivity to hexamethonium of their ganglionic synapses, and that the timecourse of constrictor responses in skeletal muscle is longer than that in skin.