AJP - Cell Physiology, Vol 252, Issue 3 C335-C341, Copyright © 1987 by American Physiological Society
Peripheral nerve as an osmometer: role of endoneurial capillaries in frog sciatic nerve
S. Odman, H. Levitan, P. J. Robinson, M. E. Michel, P. Ask and S. I. Rapoport
The sciatic nerve of the frog was perfused in vivo with isotonic Ringer
solution followed by Ringer made hypertonic by addition of sucrose or of
NaCl. Nerve diameter and endoneurial hydrostatic pressure fell during
hypertonic Ringer perfusion. Using a model that describes the elastic and
osmotic properties of the nerve, sigma sLp, the product of the osmotic
reflection coefficient at endoneurial capillaries for s equals sucrose or
NaCl (which approximates 1), and of capillary hydraulic conductivity, was
found to equal 73 X 10(-13) cm3 X s-1 X dyn-1. The nerve is elastic. It has
a compliance K of 3.7 X 10(-5) cm2 X mmHg-1, corresponding to a modulus of
elasticity E of the perineurium equal to 1.2 X 10(6) dyn X cm-2. The
results indicate that the nerve behaves as an osmometer during vascular
perfusion, due to the low permeability of endoneurial capillaries to small
solutes such as NaCl and sucrose. A low capillary hydraulic conductivity
limits bulk water flow between blood and nerve, and a low compliance limits
nerve swelling and edema.
