The effect of oxytocin and adrenaline on blood flow in the hind limb of the dog following chronic lumbar sympathectomy.

1. In a number of dogs the last two lumbar ganglia were removed unilaterally. At various dates up to the 56th day after operation the dogs were anaesthetized and the effect of oxytocin and adrenaline on hind-leg blood flow studied. Oxytocin alone reduced leg flow in all dogs after operation.2. Until approximately day 11 after operation oxytocin given during an infusion of adrenaline increased leg blood flow, as it does in normal dogs not given adrenaline infusion. After that date it reduced the flow even during adrenaline infusion. The timing of this change suggests that the normal response to adrenaline depends on the presence of undegenerated nerve fibres.3. In one animal the sympathetic nerves were crushed between the last two lumbar ganglia and beyond the last, and hind-leg blood flow frequently measured by means of venous occlusion plethysmography until day 204, when the animal was anaesthetized and acute observations made. Electrical stimulation of the sympathetic chain above the site of crushing caused a reduction in leg flow, indicating that at least some of the nerve supply had regenerated. However, oxytocin reduced leg flow when used alone and exerted no apparent effect in the presence of adrenaline.4. It is suggested that sympathetic nerves to vascular smooth muscle have a function or functions other than transmitter release and that when crushed nerves regenerate the functions do not recover at the same rate.