AJP - Regulatory, Integrative and Comparative Physiology, Vol 255, Issue 2 317-R325, Copyright © 1988 by American Physiological Society
A compartmental analysis of solute transfer and exchange across blood-nerve barrier
E. Rechthand, Q. R. Smith and S. I. Rapoport
Laboratory of Neurosciences, National Institute on Aging, Bethesda, Maryland 20892.
A three-compartment model was derived to analyze solute exchange among
plasma, peripheral nerve epineurium, and endoneurium. The model was fit to
measured tibial-nerve epineurial and endoneurial contents of [14C]sucrose
after intravenous bolus injection of tracer in pentobarbital
sodium-anesthetized rats. The transfer constant (K) for tracer at
epineurial vessels approximated 1.1 X 10(-3) ml.s-1.g whole-nerve-1. K at
the blood-nerve barrier (BNB) equaled 1.36-1.51 X 10(-5) ml.s-1.g
endoneurium-1. The endoneurial uptake data were analyzed also by a
simplified two-compartment model incorporating solute exchange between
plasma and endoneurium. K at the BNB (1.46 X 10(-5) ml.s-1.g
endoneurium-1), determined by multiple uptake time graphic analysis, was
only threefold greater than K at the blood-brain barrier. The transfer
constant at the perineurium alone was determined in situ and equaled (1 X
10(-6) ml.s-1.g endoneurium-1. Calculated permeability coefficients (X
10(-8) cm/s) equaled 3.2 at the perineurium, 23 at the endoneurial
capillaries, and 3.2 at the brain vasculature. The results demonstrate that
for hydrophilic nonelectrolytes 1) flux across the perineurium contributes
significantly to solute uptake from plasma into the endoneurium; 2)
although nerve capillaries are more permeable than brain capillaries, the
tissues of the BNB function as a unit to markedly restrict solute diffusion
into the endoneurium; and 3) a two-compartment analysis accurately
describes hydrophilic solute transfer from plasma into peripheral nerve.
