Water content, vasoactive intestinal polypeptide and substance P in intact and crushed sciatic nerves of normal and streptozotocin-diabetic rats

Observations on streptozotocin-diabetic rats have confirmed overhydration of peripheral nerve. As in previous studies, the sorbitol and fructose content, when expressed in terms of wet weight of nerve was found to be increased and myo-inositol decreased. The reduction in myo-inositol content was less, although still significant, when expressed in terms of protein content. Nerve water content increased during Wallerian degeneration following a crush injury in both normal and diabetic animals, but was relatively less in the latter. Vasoactive intestinal polypeptide (VIP) concentrations were significantly increased in diabetic nerve, those for substance P being normal. Both became severely reduced during Wallerian degeneration following nerve crush and ligature. The significance of these findings is discussed. The accumulation of water in the endoneurial compartment may be related to impaired extraction by the perineurium, to which the increased VIP content may contribute. These changes are unlikely to be responsible for nerve fibre damage.