The effects of lumbar sympathectomy on regional spinal cord blood flow in rats during acute hemorrhagic hypotension.

It has not previously been determined whether the sympathetic nervous system has a role in the regulation of regional blood flow in the spinal cord. The authors used 14C-butanol distribution to measure regional spinal cord blood flow at seven cord levels, in the sciatic nerve, and in the biceps femoris muscle in 36 rats, 18 of which had undergone excision of both lumbar sympathetic chains at least 6 days previously. Blood flows were measured during pentobarbital anesthesia. Mean arterial blood pressure (MABP) was monitored and arterial pO2, pCO2, and pH were determined prior to flow measurement. Anesthetic dose and duration were controlled. Measurements were made in normotensive rats and in rats with MABP maintained at either 69 +/- 3 mm Hg or 48 +/- 3 mm Hg for 1 hour by the withdrawal of arterial blood. One-half of the rats in each group had undergone sympathectomy. The resting cord blood flow was lower than control values following sympathectomy only at the S1-4 cord level (p less than 0.01) and cauda equina (p less than 0.01), and was marginally lower at the L1-2 and L3-6 levels (p less than 0.1). Cord blood flow was unaffected by sympathectomy during moderate hypotension. During severe hypotension, cord blood flow was less than control at the C3-5 level (p less than 0.05), but did not differ from control at the other six levels. Flows in nerve and muscle were consistent with known effects of sympathectomy on peripheral tissues. It is concluded that, at most, sympathectomy may moderately decrease resting blood flow in the cord levels caudal to L-1. Sympathectomy has no major effect on regional spinal cord blood flow in rats stressed by either moderate or severe arterial hemorrhage.