Barriers and transport properties of the perineurium. An ultrastructural study with 125I-labeled albuminin and horseradish peroxidase in normal and protein-deprived rats.

The permeability properties of the perineurium in sciatic nerves of 12-week-old rats were studied. The penetration of 125I-labeled albumin and horseradish peroxidase into the perineurium was investigated electronmicroscopically 10, 30, and 120 min after the local extraneural application of the tracers. The autoradiographic study included age-matched protein-deprived rats. It was concluded that the perineurium acted as a diffusion barrier but also permitted a slow passage of the macromolecules into the endoneurium. The result indicates that this penetration to some extent is due to vesicular transport across the perineurial cells. The significance of these barrier and transport properties of the perineurium is discussed. No obvious differences in perineurial permeability between normal and protein-deprived rats were obtained.