AJP - Heart and Circulatory Physiology, Vol 252, Issue 6 1175-H1182, Copyright © 1987 by American Physiological Society
Transfer of nonelectrolytes from blood into peripheral nerve endoneurium
E. Rechthand, Q. R. Smith and S. I. Rapoport
Permeability-surface area (PA) products were determined for the transfer of
seven nonelectrolytes across the blood-nerve barrier (BNB) of rat tibial
nerve using a quantitative in vivo injection technique. PA values at the
BNB for slowly penetrating nonelectrolytes such as urea, mannitol,
L-glucose, and sucrose differed by less than threefold from values at the
blood-brain barrier in the same animals. Permeability coefficients for
transfer across the BNB were calculated assuming both endoneurial
capillaries and perineurium contribute to solute flux into endoneurium.
Total BNB surface area was determined as 175 cm2/g with morphometric
techniques. Calculated permeability coefficients for slowly penetrating
nonelectrolytes ranged from 7 X 10(-8) cm/s for sucrose to 4 X 10(-7) cm/s
for urea and were directly proportional to solute lipid solubility as
measured by the octanol-water partition coefficient. BNB permeability
coefficients for sucrose, mannitol, L-glucose, and urea were within 60% of
values at cerebral capillaries, of the same order of magnitude as values at
aporous lipid membranes, and 100-1,000 times less than values at most
nonneural capillaries, such as in skeletal muscle. These results
demonstrate that the BNB markedly restricts the transfer of hydrophilic
nonelectrolytes between plasma and endoneurium and that diffusion
restriction of the BNB is comparable to that of the blood-brain barrier.
