Adrenergic control of nerve blood flow.

The factors that regulate blood flow within peripheral nerve (NBF) are largely unexplored. The presence of norepinephrine (NE)-containing terminals on vasa nervorum suggests that adrenergic regulation may be important. In this study we investigated the adrenergic responsiveness of NBF to agonist and antagonist agents using three separate techniques: (i) laser doppler flowmetry (LDV) using an epineurial probe, (ii) hydrogen clearance (HC) using an endoneurial microelectrode, and (iii) direct video recording (VA) of epineurial microvessels. Selective intraarterial NE delivery induced a phentolamine-reversible fall in NBF. Phentolamine alone increased NBF and lowered microvascular resistance (MR) as measured by HC. Epineurial microvessels had segmental vasoconstriction to bathing solutions of NE as observed by VA. Our findings suggest that NBF responds to adrenergic manipulation, possibly due to a heterogenous distribution of alpha receptors on epineurial vessels that supply the endoneurium.