REGIONAL SPINAL-CORD BLOOD-FLOW DURING LOCAL COOLING

We used the tissue distribution of [14C]butanol to quantitate regional blood flow in the spinal cord (RSCBF) of pentobarbital-anesthetized, normothermic rats in which segmental local cooling of the spinal cord (to 25-28°C) at vertebral levels C4-C6 (n = 6) or T13-L1 (n = 6) was induced. Thirty minutes later, blood flow measurements were made at seven levels of the spinal cord and in the sciatic nerve trunks and biceps femoris muscles. Sham-cooled rats served as controls (n = 12). In control rats, RSCBF varied between 41.5 ± 2.4 and 65.1 ± 3.2 ml · min-1 · 100 g-1. Local cooling of the C4-C6 cord segment reduced RSCBF by 32%, from 65.1 ± 3.2 to 44.4 ± 3.5 ml · min-1 · 100 g-1 (P < 0.01). Tissue vascular resistance (R) in the cooled C4-C6 segment was elevated versus control. There were no other changes in RSCBF at the other cord levels or in the cauda equina. Similarly, local cooling of the T13-L1 segment resulted in a 40% fall in RSCBF in that segment, from 57.1 ± 2.4 to 34.1 ± 4.3 ml · min-1 · 100 g-1 (P < 0.001). R in the cooled T13-L1 segment was elevated versus control. RSCBF was reduced by 30% in the adjacent proximal T12 segment (P < 0.001) and by 21% in the adjacent distal L2-L3 segment (P < 0.05). R was increased in both of these adjacent segments. RSCBF was not altered elsewhere in the cord. There were no differences among test and control rats in mean arterial blood pressure, arterial blood gases, or anesthetic duration. We conclude that local cooling of the spinal cord in pentobarbital-anesthetized rats reduces RSCBF in the cooled (and adjacent) segments, but not at other levels of the spinal cord.