Effect of alpha-tocopherol supplementation on the ultrastructural abnormalities of peripheral nerves in experimental diabetes.

Ultrastructural observations were made on myelinated fibers in the tibial nerves in order to investigate the beneficial effects of alpha-tocopherol administration in streptozotocin-diabetic rats. Male Wistar rats, aged 12 weeks and weighing between 250 g to 300 g were studied. Six onset control rats were used to obtain the baseline parameters for this strain and age. Further 3 groups--untreated diabetic animals, diabetic animals treated with alpha-tocopherol, and age-matched controls--were studied over a 3-month period. In the diabetic animal, administration of alpha-tocopherol resulted in a significant increase (p < 0.05) in total plasma vitamin E levels when compared with other groups. Myelinated fiber cross-sectional area (p < 0.05), axonal area (p < 0.01) and myelin sheath area (p < 0.05) were significantly less in the tibial nerve of diabetic animals than in age-matched controls, but not different from those of onset controls. In the alpha-tocopherol treated diabetic animals, the values for these parameters were intermediate without showing significant difference when compared with age-matched controls and untreated diabetics. The "g" ratio (axon to fiber area) did not differ between any experimental groups. The number of large myelinated fibers were less in the untreated diabetic animals, but in the alpha-tocopherol-treated diabetics, the values were significantly higher (p < 0.05) than with untreated diabetics and were similar to those of age-matched controls. In conclusion, this ultrastructural study reiterated the fact that structural abnormalities of myelinated fibers occur in experimental diabetes and that alpha-tocopherol administration may be useful in preventing the development of these abnormalities.