Endoneurial fluid is hypertonic. Results of microanalysis and its significance in neuropathy

A new technique has been developed for the microanalysis of interstitial fluid from peripheral nerve. Energy dispersive spectrometry (EDS) was employed to measure X-ray fluorescence secondary to electron excitation of endoneurial fluid in order to determine the concentration of sodium, chloride, and potassium from 100 picoliter samples collected in situ. Normal Long-Evans (L-E) rats had endoneurial fluid electrolyte values which were higher than serum values and which explained the positive fluid pressure in peripheral nerve interstitium. Ten weeks after starting a diet containing 6% lead carbonate in powdered laboratory chow, endoneurial fluid electrolytes in LE rats were significantly reduced and approached serum electrolyte concentrations. This change occurred subsequent to angiopathy and increased permeability of the blood-nerve barrier. This sensitive new technique should provide previously unattainable data to assess the pathological role and the dynamics of the nerve fiber environment in relationship to early changes in nerve function.