Diabetes induces the formation of large diameter collagen fibrils in the sciatic nerves of BB rats.

Diabetes mellitus (DM) is known to be associated with widespread connective tissue changes. However, the connective tissue of peripheral nerves in diabetes has gained little attention. Thickening of the basement membranes of Schwann, perineurial and endothelial cells suggests a perturbation in the metabolism of type IV collagen. We studied the ultrastructure of endoneurial collagen fibrils in the sciatic nerves of spontaneously diabetic BB rats and found that the fibrils in the diabetic rats were significantly thicker than in the age and sex matched non-diabetic BB rats, both in the proximal (52.6 vs. 46.1 nm) and the distal part (52.4 vs. 45.5 nm) of the nerve, respectively. The mechanism for the thickening of endoneurial collagen fibrils remains unknown, but conceivably involves changes in the biochemical composition of the nerve connective tissue matrix: e.g. altered metabolism of type I and/or type III collagen, increased glycosylation of the collagen molecules, or changes in the glycosaminoglycan content of the ground substance.