NERVE BLOOD FLOW IN NORMAL AND ISCHEMIC PERIPHERAL NERVE

神经微血管系统在生理上是独特的，是一个很差的

Nerve microvasculature is physiologically unique, being a poorly autoregulating, nutritive-capacitance system of large capillaries that is relatively resistant to ischemia. Yet angiopathic neuropathies occur, are relatively common and are difficult to treat. Nerve ischemia may also occur in disorders such as diabetic , edematous and entrapment neuropathies. The broad aim of this continuation proposal is an intensified focus on the physiology of nerve ischemia. The specific aims, rationale, and methods proposed are: First, a 3-dimensional reconstruction of nerve blood flow (NBF) in ischemic models of neuropathy and in response to sympathetic stimulation and denervation. Studies to date on the physiology of nerve ischemia have been unidimensional, focusing on nerve trunk and neglecting the much more metabolically active cell body and at-risk distal axon. By using combined microelectrode-H2-polarography and 14C- iodoantipyrine autoradiography, it should be possible to determine flow simultaneously at the cell body (dorsal root and sympathetic ganglia) and the nerve fiber levels. Second, an evaluation of the molecular mechanisms of nerve ischemic and reperfusion injury on which information is totally lacking. The hypothesis that nerve is damaged during ischemia and reperfusion due to an interplay of oxygen free radicals (OFR) and eicosanoids will be tested. NBF, computerized videoangiology, blood-nerve barrier (BNB; to 14C- sucrose) and nerve electrophysiologic indices will be supplemented by estimations of nerve cholesterol, arachidonic acid, fatty acid profile, malondialdehyde (MDA) and superoxide dismutase (SOD) as indices of OFR damage and the biosynthesis by nerve in situ and in vitro of thromboxane B2 and 6-keto-PFG1 alpha will be used as indices of nerve eiscosanoids and nerve catecholamines will be measured. These studies will be done during ischemia and following reperfusion. Third, an evaluation of mechanisms to ameliorate the effects of ischemia and reperfusion. Calcium channel blockers, vasodilator eiscosanoids, corticosteroids, pentoxifylline and ketanserin may ameliorate microvascular ischemia in other tissues, but their mechanisms and effectiveness in peripheral nerve is unknown. Since the time-course of ischemic fiber damage is very slow, occurring over many hours, nerve comprises a system particularly suited for intervention therapy should it become available. Finally, nerve catecholamines, eicosanoids, MDA and SOD will be measured in sural nerve biopsied for reasons unrelated to this proposal to apply some of these techniques and strategies to humans.