Tissue storage of vitamins A and E in rats drinking or infused with total parenteral nutrition solutions

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Abstract
The total parenteral nutrition (TPN) rat and its sham-operated control were used as a model to compare the metabolism and storage of vitamins A and E when they are administered intravenously or orally. Male Fisher rats were depleted of both vitamins for several months with a diet free of vitamins A or E, but containing retinoic acid for growth. TPN solutions containing aqueous dispersions of retinol, retinyl palmitate and dl-α-tocopheryl acetate were infused at 2.3 ml/h into the jugular veins of 10 TPN rats. Eight sham-operated control rats drank similar volumes from food cups. TPN rats received 115.3 ± 4.5 (mean ± SEM) µg of retinol equivalents and 2.2 ± 0.2 mg of α-tocopherol equivalents per day; controls received 146.4 ± 16.5 µg and 2.1 ± 0.3 mg, respectively. After 7 days the animals were fasted overnight and killed. Plasma levels of retinol were 27.8 ± 1.5 µg/dl for TPN rats, and 27.4 ± 1.2 for controls. Plasma α-tocopherol was 1909 ± 183 µg/dl for TPN rats and 1063 ± 77 for controls. The only forms of the vitamins found in plasma after overnight fasting were unesterified retinol and unesterified α-tocopherol. Sham-operated control rats stored amounts of vitamins A and E similar to values reported in the literature for fed animals. TPN rats stored more of both vitamins than controls in liver, heart, and spleen, but not in testes. The enhanced liver vitamin storage by TPN rats did not appear to be due to a slight increase in lipid content. The results indicate that both vitamins A and E infused in TPN solutions maintain blood levels and are stored in tissues.