Effect of norepinephrine on regional sciatic nerve blood flow

The purpose of this study was to explore further adrenergic regulation of peripheral nerve blood flow (NBF) before and after surgical stress. We applied norepinephrine (NE) to one sciatic nerve of rats either immediately after the nerve had been exposed or 2 hr later. Regional NBF was then measured using [14C]butanol distribution. Biceps femoris muscle flow (MBF) was measured simultaneously. The effect of NE on endoneurial NBF was also measured. Contralateral limbs were controls. Control NBF was 11.9 +/- 1.9 total, 9.1 +/- 1.5 endoneurial (units: ml min-1 100 g-1). If 10(-5) M NE was applied immediately postexposure, neither total nor endoneurial NBF was affected. If 10(-5) M NE was applied 2 hr postexposure, however, total NBF on the control side was 21 +/- 2.3 vs 8.3 +/- 1.2 on the NE side (P < 0.001). In all surgically exposed limbs, MBF was elevated and fell sharply in response to 10(-5) M NE. We conclude that under basal conditions, neither total nor endoneurial NBF is affected by topical NE. When NBF is already elevated from surgical trauma, however, NE reduces it.