AJP - Heart and Circulatory Physiology, Vol 272, Issue 1 76-H82, Copyright © 1997 by American Physiological Society

ARTICLES

Exogenous opioids influence the microcirculation of injured peripheral nerves

L. Schaafsma, H. Sun and D. Zochodne
Department of Clinical Neurosciences, University of Calgary, Alberta, Canada.

Local microvessels of peripheral nerve trunks (vasa nervorum) dilate following capsaicin-induced inflammation or local nerve trunk injury. In previous work, we observed that morphine blocked capsaicin-induced dilation of vasa nervorum presumably through the action of local opioid receptors. In the present work, we studied injury-related hyperemia of the rat sciatic vasa nervorum using laser Doppler and hydrogen clearance microelectrode measurements of local perfusion. Systemic morphine reversed hyperemia by vasoconstricting both extrinsic and intrinsic microvessels supplying 48-h-old "neuroma" preparations or crush zones of peripheral nerve trunks. Morphine did not constrict microvessels of contralateral uninjured or sham exposed but uninjured sciatic nerves. In contrast to the injured nerves, contralateral uninjured nerves exposed to morphine frequently had a rise in local perfusion, indicating vasodilation. The vasoconstrictive actions of morphine were blocked by pretreatment with naloxone and were not mimicked by saline injections alone. Systemic doses of selective opioid agonists to mu-, kappa-, and delta-receptors also selectively constricted microvessels of injured nerves. Local blood flow in older experimental neuromas at 7 days had partial sensitivity to morphine, whereas at 14 days perfusion flow was not influenced by morphine. Exogenous opioids dampen early but not later inflammatory microvasodilation and could have important influences on the nerve regenerative milieu.

This article has been cited by other articles:

				M.-C. Ko, E. R. Butelman, and J. H. Woods The Role of Peripheral Mu Opioid Receptors in the Modulation of Capsaicin-Induced Thermal Nociception in Rhesus Monkeys J. Pharmacol. Exp. Ther., July 1, 1998; 286(1): 150 - 156. [Abstract] [Full Text]