Depletion of adipose tissue and peripheral nerve alpha-tocopherol in adult dogs.

To assess the relationship between tissue alpha-tocopherol depletion and histopathologic or functional changes in nervous tissue, a longitudinal study of male 1-year-old beagle dogs, two fed a vitamin E-deficient diet (0.05 +/- 0.02 mg alpha-tocopherol/kg;--E dogs) and two fed a vitamin E-supplemented diet (114 +/- 14 mg alpha-tocopherol/kg; +E dogs), was carried out. Plasma and adipose tissue alpha-tocopherol concentrations, neurological examinations, and sensory and motor nerve conduction velocities were determined at approximately 8-wk intervals over 109 wk. Tibial nerve alpha-tocopherol concentrations were measured at 65 and 109 wk; adjacent sections were examined for histologic changes. In the two -E dogs, plasma alpha-tocopherols declined linearly on a semilog plot to < 0.1 microgram/mL by 109 wk. Plasma alpha-tocopherol concentrations were depleted to half of the initial concentrations in approximately 87 d. Adipose tissue alpha-tocopherol concentrations (based on wet weight, cholesterol or triglyceride) also declined linearly on semilog plots, and were depleted to half of the initial concentrations in approximately 120 d. Tibial nerve alpha-tocopherols (ng/microgram cholesterol) in -E dogs decreased to 16% of average +E at 65 wk, and to 2% at 109 wk. Neurologic examinations, histologies and nerve conduction velocities were normal in all dogs throughout the study. Our results demonstrate in dogs that depletion of plasma, adipose tissue and nerve alpha-tocopherol precedes histologic and functional changes in peripheral nerves during vitamin E deficiency.