Disposition of vitamin E in the eye

To study the effect of exogenous vitamin E on its plasma and eye tissue levels, we administered 100 mg/kg of dl-alpha-tocopherol either by intravenous, intramuscular, or oral routes in 3-day-old newborn kittens. Controls did not receive the drug. alpha-Tocopherol levels in the plasma, retina, choroid, and vitreous were analyzed by high-performance liquid chromatography at selected intervals following drug administration. Our results showed that after intravenous administration of vitamin E, the retinal alpha-tocopherol levels increased 300 and 500% the baseline value at 2 and 4 h, respectively. By contrast, comparable retinal levels were achieved at 24 h following intramuscular administration and 72 h following oral administration. In the intravenous group high retinal levels were maintained up to 168 h, while in the intramuscular and oral groups retinal levels continued to increase up to 192 h. Irrespective of route of administration, the retinal concentration of alpha-tocopherol remained high even when the plasma levels were declining; plasma levels did not reflect retinal levels at any time. Following exogenous vitamin E administration, alpha-tocopherol levels increased both in the choroid (4 to 6 times the control) and in the vitreous (1.5 to 4 times the control). Significant differences in tocopherol levels were also seen between the eyes in the same animal in all groups. Our studies suggest a single dose of vitamin E by intravenous, intramuscular, or oral routes increases retinal levels from 3 to 5 times the control levels. However, peak retinal levels are achieved earlier by parenteral than by the oral route.(ABSTRACT TRUNCATED AT 250 WORDS)