title: Peripheral nerve as an osmometer: role of the perineurium in frog sciatic nerve.
abstract: Measurements of volume and hydrostatic pressure in the frog sciatic nerve in vitro demonstrate that the nerve acts as an osmometer, in large part because the perineurium is a semipermeable membrane for water flow. Endoneurial hydrostatic pressure in nerves in isotonic Ringer exceeds bath pressure by about 7 mmHg. In Ringer made hypertonic by addition of sucrose, nerve volume and endoneurial pressure fall linearly in relation to 1/osmolality. The slope of the plot of pressure against volume provides a value for nerve compliance equal to 0.006 mm2/mmHg. Calculations based on the model of the nerve as an osmometer indicate that the nerve has an osmotically "inactive" volume equal to 0.19 mm3/mm, which is about 75% of the total volume of a nerve segment of unit length in normal Ringer. Perineurial hydraulic conductivity (Lp) equals 7.5 x 10(-13) cm3.s-1.dyn-1, a value characteristic of nonleaky epithelia. The perineurium is an elastic tissue with a constant modulus of elasticity equal to 3 x 10(6) dyn/cm2 when not markedly stretched and may limit nerve swelling under pathological conditions of nerve edema.
mesh_terms: D000818:Animals; D002463:Cell Membrane Permeability; D005260:Female; D006874:Hydrostatic Pressure; D006982:Hypertonic Solutions; D066298:In Vitro Techniques; D007700:Kinetics; D009994:Osmolar Concentration; D011894:Rana pipiens; D012584:Sciatic Nerve / Q000033:anatomy & histology / Q000502:physiology*; D014882:Water-Electrolyte Balance
chemical_list: D006982:Hypertonic Solutions