Guanethidine chemical sympathectomy: spinal cord and sciatic nerve blood flow

The spinal cord vasculature is innervated by noradrenergic nerve fibers, the role of which in the regulation of regional spinal cord blood flow (RSCBF) is presently unclear. We used the distribution of [14C]butanol to simultaneously measure RSCBF at seven cord levels and the regional blood flow in sciatic nerve (NBF), truncal skin, and biceps femoris muscle. The subjects were control rats and rats that had been given parenteral guanethidine sulfate for 5 wk to induce selective postganglionic "chemical sympathectomy." Flows were measured under basal conditions (group I) and immediately after an arterial hemorrhage (group II). The results indicate that RSCBF was unchanged from control after guanethidine administration in both groups; however, NBF was elevated after guanethidine by 47% in group I and by 41% in group II. We conclude that in the spinal cord as in the brain, sympathetic inflow does not appear to have an important role in the regulation of regional blood flow. Sympathetic inflow appears to partly regulate NBF, however, probably by varying vascular tone.